1. Executive Summary

This white paper examines scan-based eye shape measurement technology for scleral lens design, with particular focus on the Gaudi Profilometer—a multi-modal profilometry system designed to support the complete scleral lens fitting workflow from initial measurement through long-term follow-up care.

Scleral lens fitting is increasingly data-driven. Because scleral lenses vault the cornea and limbus and land on conjunctival tissue overlying the sclera, clinical success depends primarily on how the lens landing zone aligns with ocular surface shape beyond the cornea. Published studies show that the sclera is commonly rotationally asymmetric and that asymmetry increases at larger chord diameters where scleral lens landing zones bear. [1] When landing zone geometry does not match underlying anatomy, clinicians commonly see conjunctival compression or edge lift, lens decentration, unstable optics, and difficult troubleshooting.

Corneal topography alone is insufficient for scleral lens fitting because it typically characterizes only the central 10-11 mm of the eye. Objective wide-field eye shape measurement that captures peripheral scleral geometry at diameters where lenses land (approximately 15-18+ mm) improves first-lens selection, accelerates identification of asymmetry-driven fit problems, and supports rational design of toric, quadrant-specific, or freeform landing zones.

1.1 Gaudi Profilometer: what it measures and why it matters

The Gaudi Profilometer is a multi-modal corneo-scleral profilometry platform built around a digital light processing (DLP) engine. Its core output is the sagittal height (surface elevation) of the anterior ocular surface across corneal and scleral regions - the fundamental measurement required for scleral lens design.

1.2 Measurement modes (summary)

Fluorescein line scan (0.2 s): primary method for most scleral lens fitting; robust signal across cornea and sclera; approximately 50 microns accuracy.

Non-fluorescein line scan (0.3 s): dye-free alternative for severe dry eye, fluorescein sensitivity, or repeated scans.

Fluorescent Fourier profilometry (0.15 s): high-precision corneal measurement (~5 microns) for specialized GP/ortho-k applications; lower scleral precision.

Multi-gaze dual-band Fourier profilometry (~30-60 s protocol): extended coverage beyond 20 mm with high precision across cornea and sclera for large-diameter and complex cases.

1.3 Clinical and business differentiation (summary)

Gaudi differentiates from single-function profilometers by combining measurement flexibility with integrated design and follow-up tools. Key differentiators include integrated lens design software (supporting same-visit measurement-to-order), an open XML data format (supporting manufacturer-independent ordering), and follow-up evaluation tools including fluorescein imaging, lens centration analysis, and blood vessel blanching detection. The system also includes infrared meibography, with additional modules in testing (Placido topography and non-invasive TBUT, expected 2026).

1.4 Workflow and appropriate use (summary)

In routine cases, single-gaze acquisition and design can be completed within minutes and can be used either in a practitioner-designed workflow or in a lab-consulted workflow. Profilometry provides maximum incremental value in complex cases (irregular corneas, significant scleral asymmetry, post-surgical anatomy, previous fitting failures) and in large-diameter designs (>18 mm) where peripheral data is critical.

Profilometry complements - and does not replace - anterior segment OCT (for precise vault quantification and edge cross-sections), corneal tomography (for ectasia screening and posterior corneal analysis), comprehensive dry eye diagnostics, and practitioner clinical judgment. Measurement challenges can arise in severe dry eye, significant corneal opacity, extreme fixation instability, and certain post-surgical complications. Full proficiency typically requires a learning investment and consistent clinical use.

2. The Clinical Need: Why Eye Shape Matters in Scleral Lens Design

Scleral lenses are an essential modality for managing irregular corneas and ocular surface disease because they provide a stable rigid optical surface while maintaining a fluid reservoir over the cornea. Unlike corneal GP lenses, scleral lenses are designed to vault the cornea and limbus and land on conjunctival tissue overlying the sclera with minimal movement.

That fitting principle has a direct implication: successful scleral lens wear depends on ocular surface shape beyond the cornea. Corneal measurements alone can be insufficient because the landing zone interacts with bulbar conjunctiva and sclera, where geometry is often non-spherical, toric, and frequently irregular. In practice, predictable scleral fitting is less about selecting a corneal base curve and more about achieving appropriate sagittal height and peripheral alignment for the individual ocular surface.

2.1 Scleral lens performance is governed by how the lens lands on the eye

Clinically, practitioners evaluate a scleral lens in three interacting zones:

Corneal vault (central clearance): sufficient to avoid corneal touch while controlling reservoir thickness over time.

Limbal clearance: adequate clearance to avoid limbal bearing and adverse responses.

Landing zone alignment: an even, physiologically acceptable resting relationship between the lens and the conjunctiva/sclera.

Among these, landing zone alignment is most directly dependent on eye shape and often differentiates a successful from a poor scleral lens fit. The practical goal is even bearing without compression, impingement, or edge lift. Compression/impingement is commonly associated with blood vessel blanching, while edge lift reflects mismatch between landing zone design and scleral contour and can present as an edge shadow, a visible bubble, or fluorescein uptake beneath the edge.

In scleral lens wear, fit is not only an optical issue - it is a tissue-interface engineering problem. Ocular surface shape influences pressure distribution, seal characteristics, and lens stability throughout the day.

2.2 The sclera is not rotationally symmetric and asymmetry increases farther from the cornea

A key reason eye shape matters is that the sclera commonly deviates from rotational symmetry. Consejo et al. reported that the human sclera is rotationally asymmetric, varies considerably between individuals, and shows measurable nasal-temporal differences. [2] Importantly, asymmetry increases with radial distance from the corneal apex - the region where larger-diameter scleral lens landing zones bear.

Complementary evidence from anterior segment OCT-based profiling supports clinically relevant regional differences in sagittal height and corneoscleral transition angles. Ritzmann et al. found statistically significant differences between opposing segments at a 15.0 mm chord, including nasal regions with flatter scleral angles than temporal regions - findings directly relevant to lenses that rest beyond the limbus. [3]

Clinically, these anatomical findings imply that:

Two eyes can share similar corneal keratometry yet have meaningfully different scleral landing geometries.

A spherical landing zone may align acceptably in some quadrants while compressing or lifting in others.

Larger diameters (landing farther from the limbus) often encounter greater asymmetry, increasing the need for toric, quadrant-specific, and freeform landing designs.

2.3 Common problems when the lens does not match eye shape

When the landing zone does not match underlying ocular surface shape, practitioners commonly observe:

Localized compression and blanching: excessive bearing in a meridian or quadrant can compress conjunctival vessels, contribute to discomfort, and increase suction and removal difficulty.

Impingement versus edge lift: a digging edge (impingement) or lifting edge (edge lift) reflects landing zone mismatch. Edge lift can introduce bubbles and unwanted tear exchange patterns; impingement can create focal tissue insult.

Decentration and optical consequences: decentration affects clearance distribution, limbal relationships, and optical performance. Kowalski et al. reported average temporal and inferior decentration in healthy eyes and associated nasal-temporal scleral elevation asymmetry with horizontal decentration magnitude. [4]

Flexure, rotation, and stability: stability matters for astigmatic correction and any design sensitive to orientation. Alexander et al. found that toric landing zones reduced lens flexure and rotation compared with spherical landing zones. [5]

Post-lens reservoir debris and midday fogging: patients may experience progressive clouding from particulate accumulation in the tear reservoir. Midday fogging is multifactorial; in practice it is often evaluated alongside landing zone alignment and tightness.[6]

2.4 Why measuring eye shape improves predictability and patient experience

Traditional scleral fitting often relies on diagnostic lens sets and iterative refinement. While effective, this approach can be time-consuming and variable when ocular shape information beyond the cornea is unavailable. Learning-curve work by Macedo-de-Araújo et al. shows that as practitioners gain experience, the mean number of trial lenses and reorders decreases, reflecting both the iterative nature of fitting and the value of improved predictability.[7]

When high-quality corneo-scleral shape data is available, it can support:

More accurate first-lens selection (sagittal depth and landing geometry).

Earlier identification of asymmetry-driven issues (for example, repeated edge lift in one quadrant).

Rational selection of toric or quadrant-specific landing zones.

Improved stability for advanced optics by reducing rotation and flexure drivers.

Reduced patient burden from repeated visits, discomfort troubleshooting, and interrupted wear.

2.5 Summary

Because scleral lenses are scleral-supported devices, conjunctival and scleral geometry is central to comfort, physiology, and visual outcomes. The evidence consistently shows patient-specific asymmetry that increases with chord diameter, creating the rationale for scan-based eye shape measurement in modern scleral lens practice.

3. Overview of Eye Shape Measurement Technologies

Modern scleral lens fitting increasingly relies on objective measurement because the fitting problem extends beyond the cornea. In practice, clinicians use a combination of technologies that measure different aspects of anterior segment shape:

Curvature-focused systems (for example, Placido-based corneal topography).

3D structural systems (corneal tomography, typically including posterior corneal surface and pachymetry).

Cross-sectional imaging (anterior segment OCT) for vault, settling, and edge relationships.

Surface elevation mapping (corneo-scleral profilometry) that directly describes sagittal height where scleral lenses land.

A practical distinction is the primary output: curvature, 3D structure, cross-sectional geometry, or surface elevation. Scleral lens design and troubleshooting are driven by sagittal height and peripheral alignment[8], which are not always recoverable from corneal-only curvature data - especially at larger chord diameters.

3.1 Corneal topography (Placido-based surface shape)

What it measures: Placido-disc corneal topography quantifies anterior corneal curvature patterns and remains central for characterizing irregular corneas and monitoring anterior corneal changes.

Why it matters for scleral lenses:

Characterization of corneal irregularity (ectasia patterns, post-surgical irregularity).

Baseline documentation for longitudinal monitoring.

Supporting initial parameter estimates when vaulting the cornea.

Key limitations for scleral lens design:

Cornea-centric: does not directly measure conjunctival/scleral geometry where scleral lenses land.

Sagittal height is typically calculated indirectly by integrating curvature along meridians; this can propagate error compared with methods that directly measure elevation and sagittal height.

3.2 Corneal tomography (Scheimpflug, scanning slit, OCT-based tomography)

What it measures: Tomography provides a three-dimensional reconstruction of the cornea, commonly including anterior and posterior surfaces and pachymetry, using approaches such as scanning slit, Scheimpflug imaging, or OCT-based tomography.

Why it matters for scleral lenses:

Posterior corneal analysis and pachymetry patterns relevant to ectasia assessment and co-management.

Baseline corneal structure documentation prior to scleral wear.

Clinical decision support for refractive surgery screening and corneal disease monitoring.

Key limitations for peripheral corneo-scleral measurement:

Large differences in reflective properties between cornea and sclera can require merging steps that introduce artifacts near the limbus.

Many systems rely on mechanical rotation and multi-meridian acquisition; longer scan durations increase motion artifact risk and can reduce peripheral accuracy.

3.3 Anterior segment OCT (AS-OCT) for fit evaluation and ocular response

What it measures: AS-OCT provides high-resolution cross-sectional imaging of anterior segment structures and is widely used for scleral lens fit assessment.

Why it matters clinically:

Objective vault measurement and quantification of settling over time (for example, Rathi et al. reported vault commonly decreases during scleral lens trials).[9]

Improved accuracy versus subjective estimation (for example, Yeung et al. reported systematic clinician estimation bias for clearance[10]).

Cross-sectional differentiation of impingement versus edge lift and monitoring of tissue response.

Key limitation:

Most commercial AS-OCT workflows are slice-based (2D). OCT excels at answering "What does the lens-eye relationship look like here?" but typically does not provide a full 360-degree wide-field surface elevation map unless paired with specialized scan protocols.

3.4 Corneo-scleral profilometry (wide-field surface elevation mapping)

What it measures: Corneo-scleral profilometry captures the 3D surface elevation (sagittal height) of the anterior ocular surface across the cornea, limbus, and sclera, enabling direct estimation of sagittal height at diameters relevant to scleral lens landing.

Why it matters for scleral lenses:

Direct measurement of the geometry that governs landing zone alignment.

Objective characterization of asymmetry that drives toric, quadrant-specific, and freeform landing designs.

Improved first-lens predictability and more rational modifications when troubleshooting.

Profilometry systems use different measurement principles, including line-scan triangulation, structured-light projection, and Fourier transform profilometry. Performance is influenced by coverage, data density, peripheral accuracy, and integration into design workflows.

3.5 Impression-based methods (physical capture of ocular surface shape)

Impression-based workflows physically capture ocular surface geometry and digitize it for lens design. These methods share the same clinical goal as profilometry: capturing the shape the lens must align to, particularly in eyes with significant asymmetry or complex anatomy.

4. Gaudi Profilometer: System Architecture and Operating Principles

The Gaudi Profilometer is a multifunctional optometric device purpose-designed to provide measurements relevant to specialty contact lens fitting, particularly scleral lenses. The instrument is built around a digital light processing (DLP) engine that enables multiple imaging modes. This multi-modal architecture allows practitioners to select measurement protocols matched to patient-specific conditions (tear film stability, iris color, fluorescein tolerance) and case requirements (lens diameter, anatomical complexity, and desired peripheral coverage).

4.1 System architecture (hardware and illumination)

The optical architecture follows standard profilometry design principles and includes a front-facing camera, an angled DLP projector (to the right of the camera when facing the instrument), and concentric rings of white and infrared LEDs around the camera for illumination and fixation control.

Current Gaudi functions span three categories:

Profilometry: ocular surface elevation mapping for lens design.

Lens fit evaluation: post-fitting assessment tools (fluorescein and color imaging, centration analysis, vessel blanching assessment).

Infrared meibography: meibomian gland imaging for dry eye assessment.

EYEXY is also testing a Placido topography module and a non-invasive tear break-up time (TBUT) attachment, both expected to be available in 2026.

Across all profilometry modes, the raw output is sagittal height (surface elevation) of the anterior ocular surface across corneal and scleral regions. Sagittal height is the primary geometric variable required to design scleral lenses that align with conjunctival and scleral shape.

4.2 Single-gaze fluorescein line scan imaging

Operating principle

Fluorescein dye is applied to create a uniform fluorescent tear layer. Blue illumination excites fluorescein, and imaging through a green filter isolates the fluorescent signal. The DLP projector scans parallel blue lines across the field of view. Line displacement is captured by the camera and converted to surface height through triangulation using the known projector-camera geometry.

A key advantage is signal uniformity: the fluorescent tear layer provides consistent contrast across both corneal and scleral regions, simplifying reconstruction across the full measurement zone.

Clinical advantages

Fast acquisition (0.2 s) to minimize motion artifact and fixation challenges.

Robust imaging across a wide range of ocular surface conditions due to fluorescein signal uniformity.

Clinically appropriate precision (~50 microns) for landing zone evaluation and troubleshooting.

Familiar workflow: uses standard diagnostic fluorescein strips and aligns with slit lamp evaluation habits.

Clinical considerations

Requires a reasonably stable tear film and adequate fluorescein coverage; severe dry eye or rapid drainage can reduce quality.

Single-gaze capture covers a 16 mm diameter zone centered on the limbus, supporting most scleral designs up to approximately 17-18 mm. Beyond 16 mm, the system applies controlled extrapolation based on measured peripheral slope.

For large-diameter lenses or cases requiring extended peripheral data, multi-gaze acquisition provides expanded coverage (see Section 4.5).

When to use

First-choice modality for most initial scleral fittings.

Routine follow-up measurements.

Cases with stable tear film and no contraindications to fluorescein.

Technical specifications

4.3 Single-gaze non-fluorescein line scan profilometry

Operating principle

This dye-free mode uses green illumination to capture natural surface reflectance. The projector scans parallel green lines at two intensities: a lower intensity optimized for scleral mapping and a higher intensity optimized for corneal mapping. The system identifies the limbus and applies different processing for cornea versus sclera. In the corneal zone, additional processing distinguishes corneal surface reflections from underlying iris reflections before triangulation is applied.

This approach is conceptually similar to the operating principle of scanning-slit systems that must separate corneal surface signal from deeper reflections.

Clinical advantages

No dye requirement: avoids fluorescein-related concerns and reduces preparation steps.

Often performs better than fluorescein modes in extremely dry eye where fluorescein wetting is inadequate.

Supports rapid repeat scans without re-instilling dye; useful when multiple acquisitions are needed.

Fast acquisition (0.3 s) with comparable point density to fluorescein line scan.

Clinical considerations

May be less reliable with significant corneal scarring or opacity that alters reflection patterns.

Very light iris colors (pale blue or light gray) can reduce cornea-iris contrast and increase error risk.

Single-gaze capture covers a 16 mm diameter zone (similar to fluorescein line scan).

When to use

Severe dry eye where tear film instability limits fluorescein imaging quality.

Rapid fluorescein drainage that complicates repeat imaging.

Fluorescein sensitivity or strong patient preference to avoid dye.

Situations requiring multiple scans in quick succession (including multi-gaze protocols).

Avoid this mode when iris color is extremely light or when corneal scarring is severe; use fluorescein-based imaging instead.

Technical specifications

4.4 Single-gaze fluorescent Fourier profilometry

Operating principle

Fluorescein dye is applied and captured using blue excitation and green-filtered imaging. Instead of scanning discrete lines, the system projects multiple phases of continuous sinusoidal patterns. Fourier transform analysis is applied at the pixel level to compute surface height based on phase shifts, producing dense, high-resolution maps.

Because every pixel contributes to the height calculation, Fourier methods generate substantially higher spatial resolution than line-scan methods.

Clinical advantages

High corneal precision (~5 microns) for detailed corneal surface characterization.

Very high data density (>1,000,000 points) enabling detection of subtle corneal irregularities.

Fast capture (0.15 s), minimizing motion artifact.

Useful for specialty GP lens fitting, orthokeratology, and research requiring fine corneal detail.

Clinical considerations

Highly dependent on image quality, tear film stability, and fluorescein distribution; uneven fluorescein coverage can degrade results.

Corneal accuracy is high, but scleral accuracy is lower (approximately 100 microns), because Fourier signal quality is optimized for smoother corneal surfaces.

Not recommended as the primary mode for routine scleral lens landing-zone design when line-scan modes provide better scleral performance.

When to use

When maximum corneal precision is clinically necessary (complex corneal GP fitting, orthokeratology design).

Research protocols requiring high density and detection of subtle corneal changes.

Longitudinal monitoring where small corneal surface changes are important.

Technical specifications

4.5 Multi-gaze dual-band Fourier profilometry

Operating principle

This advanced mode combines Fourier profilometry with multi-gaze acquisition and dual-wavelength imaging to extend coverage and improve scleral accuracy. Fluorescein is applied. During each gaze capture, the system simultaneously acquires a fluorescent channel optimized for corneal reconstruction and a non-fluorescent channel optimized for scleral reconstruction. Multiple gaze directions (typically center plus four to eight peripheral gazes) are then merged to create a comprehensive wide-field surface map.

Clinical advantages

Extended measurement coverage beyond 20 mm (dependent on gaze count and positioning).

Supports large-diameter scleral lens designs (>18 mm), including full-scleral designs.

High precision across cornea and sclera (~5 microns).

Captures quadrant-specific and regional asymmetry critical for freeform landing zone design.

High data density (>1,000,000 points per gaze).

Clinical considerations

Requires patient cooperation for multiple gaze directions and stable corneal tear film during the protocol.

Total protocol time typically 30-60 seconds including gaze changes; this introduces sensitivity to tear film changes and alignment consistency.

Generates larger datasets and requires point cloud registration and merging (handled by software but with longer processing time than single-gaze modes).

When to use

Large-diameter scleral lenses (>18 mm) requiring extended peripheral coverage.

Complex cases with significant asymmetry or previous fitting challenges.

Post-surgical eyes (for example, post-radial keratotomy or penetrating keratoplasty) with irregular peripheral shape.

Quadrant-specific or freeform landing zone designs requiring detailed peripheral asymmetry characterization.

For routine fittings at standard diameters (18 mm or smaller) with typical anatomy, single-gaze modes are usually more time-efficient.

Technical specifications

5. Contextual Comparison of Ocular Surface Measurement Technologies

Ocular surface measurement technologies support scleral lens fitting along a spectrum - from comprehensive anterior segment diagnostic platforms to dedicated corneo-scleral profilometers. Key comparison factors include measurement principle, coverage at scleral landing diameters, peripheral accuracy, acquisition speed (motion artifact risk), data accessibility, and integration into clinical and laboratory workflows.

5.1 Gaudi Profilometer (EYEXY Inc., San Pedro, CA)

Gaudi is purpose-built for scleral lens workflows. Its defining characteristic is measurement flexibility: fluorescein and non-fluorescein line-scan triangulation plus Fourier-based modes including a multi-gaze dual-band protocol for extended coverage. Unlike single-function profilometers, Gaudi integrates measurement, lens design, and follow-up evaluation tools in one platform.

Key clinical differentiators:

Multiple measurement modes to optimize performance across diverse patient presentations (dry eye, light iris colors, extended diameters).

Integrated lens design software for same-visit measurement-to-order workflows.

Open XML data format enabling manufacturer-independent ordering (avoids vendor lock-in).

Follow-up evaluation tools: fluorescein imaging, centration analysis, and blood vessel blanching detection.

Infrared meibography included; Placido topography and non-invasive TBUT modules in testing (expected 2026).

5.2 Pentacam (Oculus Optikgerate GmbH, Wetzlar, Germany)

Pentacam is a rotating Scheimpflug anterior segment tomography system widely used for corneal assessment. Its strengths are posterior corneal analysis, pachymetry, and keratoconus screening indices rather than scleral profilometry specialization.

Considerations for scleral lens fitting:

Typical acquisition duration is approximately 2 seconds; longer acquisition increases motion artifact risk compared with rapid profilometry captures.

Differences in corneal versus scleral reflectivity can require merging steps near the limbus that may introduce peripheral artifacts.

Data is typically stored in proprietary formats (with export options) and integrates with multiple specialty lens platforms.

5.3 Eye Surface Profiler (Eaglet Eye B.V., Houten, Netherlands)

The Eye Surface Profiler (ESP) is a dedicated Fourier transform profilometer designed for wide-field corneo-scleral elevation mapping. Its main strengths are single-capture coverage (22 mm), rapid acquisition (<0.1 s), and high data density.

Practical considerations:

Strong for large-diameter designs because 22 mm coverage is achieved in a single acquisition.

Primarily a measurement system (limited follow-up/diagnostic tools compared with multi-function platforms).

DirectConnect integration supports workflows with multiple third-party lens laboratories.

5.4 sMap3D/iContour (Precision Ocular Metrology LLC / Visionary Optics LLC)

sMap3D/iContour uses multi-gaze fluorescein line-scan triangulation to extend coverage beyond 20 mm. It is integrated into a proprietary design and manufacturing ecosystem.

Key consideration:

Encrypted proprietary data format restricts lens ordering to a single manufacturer, creating manufacturer lock-in and limiting scan portability across laboratories. Practitioners cannot compare designs from multiple manufacturers using the same scan data, cannot switch manufacturers if service issues arise, and cannot maintain competitive pricing leverage through multi-source bidding.

5.5 Medmont Vantage (Medmont International Pty Ltd, Australia)

Medmont Vantage is a multi-function anterior segment imaging platform combining profilometry with Placido topography and additional dry eye and fit evaluation tools. Its profilometry approach uses simultaneous line projection with very rapid single-shot acquisition (approximately 0.5 s).

Considerations:

Single-shot acquisition minimizes motion artifacts.

Because surface data exists primarily along projected lines, reconstruction relies on interpolation between lines; measured point density is lower than scanning or Fourier approaches.

Appealing for practices prioritizing equipment consolidation and multi-function capability.

Commonly cited additional functions include:

Infrared meibography for meibomian gland assessment.

Anterior segment color imaging for documentation.

Lens centration analysis.

Placido corneal topography.

Non-invasive tear break-up time (NIBUT) assessment.

5.6 Comparative summary and selection considerations

No single technology optimally serves all clinical contexts. The table below summarizes practical trade-offs relevant to scleral lens fitting.

A practical decision framework:

If your priority is measurement flexibility, integrated lens design software, follow-up evaluation tools, and manufacturer independence: Gaudi is designed for the complete scleral lens lifecycle.

If you want maximum single-gaze coverage with strong lab-connected workflows and a measurement-only focus: ESP is a leading option.

If you prioritize comprehensive corneal diagnostics (posterior cornea, ectasia indices) beyond contact lenses: a tomography platform such as Pentacam adds value, but is not a dedicated scleral profilometer.

If you value equipment consolidation (topography + dry eye tools + fit evaluation in one platform): Medmont Vantage is designed for multi-function use, with trade-offs in profilometry sampling density.

If you accept exclusive reliance on a single manufacturer ecosystem: sMap3D can be effective, but scan portability is restricted.

6. Practical Integration into Clinical and Lab Workflows

The clinical value of ocular surface measurement depends on workflow integration. A profilometry system must convert measurement data into actionable lens parameters without adding excessive appointment time or operational complexity. Gaudi is designed to integrate measurement, design, and follow-up evaluation into a single workflow.

6.1 Initial evaluation and measurement

Pre-measurement preparation

For fluorescein-based modes, standard fluorescein instillation (the same strips used for slit lamp evaluation) is typically sufficient. For severe dry eye or unstable tear film where fluorescein imaging is challenging, the non-fluorescein line-scan mode provides a dye-free alternative.

Measurement acquisition (typical steps)

Patient positioning at chin rest and forehead support (similar to other anterior segment imaging devices).

Alignment and centration on the limbus with real-time feedback.

Single-button capture (0.2-0.3 s for single-gaze modes).

Immediate quality review; repeat capture if blink or tear film artifacts are present.

For standard single-gaze acquisition (typical designs up to 17-18 mm), total measurement time including positioning is commonly 1-3 minutes. Multi-gaze protocols for extended diameters typically require 3-5 minutes including gaze changes.

Integration with the clinical exam

A common sequence is: corneal evaluation (topography/tomography) to characterize irregularity and rule out progressive ectasia; Gaudi profilometry to capture corneo-scleral elevation and asymmetry; then lens design and patient consultation. Some practices also use diagnostic lenses for power refinement and to validate comfort and handling.

6.2 Integrated lens design: from measurement to order

Gaudi includes integrated lens design software within the measurement environment. After scan validation, practitioners can design the lens without exporting files or switching applications.

Design workflow capabilities include:

Automated first-lens parameter suggestions based on measured sagittal height, diameter, and detected asymmetry.

Interactive refinement of sagittal depth, diameter, limbal clearance, and landing zone geometry (spherical, toric, quadrant-specific).

Visualization of predicted lens-eye relationship to support decision-making and patient communication.

Practices using the integrated workflow often complete scan-to-order steps within approximately 5-15 minutes, depending on case complexity and patient counseling needs.

6.3 Laboratory integration and manufacturing workflows

Gaudi exports measurement data in open XML format. This supports two common workflow models:

Model 1: Practitioner-designed lenses

The practitioner designs the full lens specification in the Gaudi software and transmits the finalized design for manufacturing.

Best fit for experienced scleral lens practices seeking full design control and immediate patient communication.

Model 2: Laboratory-consulted design

The practitioner transmits raw measurement data and clinical requirements; the laboratory proposes a design for approval.

Best fit for practices that prefer consultant-supported design or for unusually complex cases.

Because data is not locked to a single manufacturer, practices can select laboratories based on case type, service quality, pricing, and continuity needs.

6.4 Follow-up visits and data-informed modifications

Gaudi includes tools to document and quantify fit characteristics during follow-up. Common applications include:

Fluorescein imaging for vault and landing zone assessment (pooling patterns, edge behavior, settling comparisons).

Blood vessel blanching detection to identify conjunctival compression patterns.

Lens centration analysis to quantify positioning and evaluate stability.

Side-by-side comparison of baseline profilometry with follow-up images to identify geometric mismatch drivers.

When modification is needed, practitioners can adjust design parameters in software, visualize predicted changes, and transmit updated specifications to the laboratory.

6.5 Training and learning curve

Multi-modal measurement and integrated design provide flexibility but require training and repetition to develop proficiency. Typical adoption trajectory:

Weeks 1-2: focus on reliable measurement acquisition and scan quality assessment; use automated suggestions conservatively.

Weeks 3-8: develop confidence in mode selection and begin refining suggested designs based on clinical judgment.

Months 3-6: routine case proficiency; begin using advanced features such as multi-gaze protocols and more complex landing zone designs.

Beyond 6 months: full workflow proficiency for complex cases and efficient troubleshooting using comparative tools.

6.6 Data management and long-term care

The Gaudi software environment supports longitudinal patient records, including measurement history, design history, and follow-up imaging. This enables efficient reorders for replacement lenses and objective monitoring of anatomical change over time.

6.7 Summary: workflow value in practice

Workflow benefits most commonly reported with profilometry-integrated fitting include:

Improved first-lens parameter selection by measuring sagittal height and scleral asymmetry directly.

Reduced trial-and-error and fewer reorders in complex cases.

Faster troubleshooting when fit problems arise (objective localization of mismatch).

Enhanced patient confidence through visualization and explanation of customized lens design.

Manufacturer independence through open data architecture.

7. Limitations, Considerations, and Appropriate Use

Transparent assessment of limitations is essential for appropriate technology deployment. Profilometry can substantially improve scleral lens fitting efficiency and predictability, but it measures a dynamic biological system under constrained conditions and should be interpreted in context.

7.1 Fundamental limitations of profilometry technology

Peripheral accuracy generally decreases with distance from the cornea due to eyelid obstruction, tear film variability, and signal challenges on conjunctival tissue.

Tear film instability can introduce noise in any surface-imaging system; dry eye can reduce repeatability unless protocols are adapted.

Measurements represent a snapshot. Scleral lenses settle over time, and conjunctival tissues deform under load; a static map does not fully predict dynamic tissue response.

Registration and merging steps (especially in multi-gaze protocols) can introduce alignment error if gaze consistency is poor.

7.2 Gaudi-specific technical considerations

Mode selection matters: fluorescein line scan is typically the most robust scleral fitting mode; non-fluorescein is preferred when dye performance is compromised; Fourier modes are best reserved for high-precision corneal applications or extended-diameter protocols.

Very light iris colors can reduce contrast for non-fluorescein processing and may require fluorescein-based acquisition for best reliability.

Severe corneal scarring or opacity can disrupt signal interpretation in non-fluorescein modes; fluorescein imaging is usually more tolerant.

Extended diameters (>18 mm) often benefit from multi-gaze acquisition; this increases protocol time and patient cooperation requirements.

7.3 Clinical scenarios with measurement challenges

Profilometry may be more difficult or less reliable in:

Severe dry eye with rapid tear film breakup (requires mode selection and potential repeated capture).

Significant fixation instability (nystagmus, poor visual fixation) where multi-gaze protocols may be impractical.

Dense corneal opacity that limits optical signal quality for dye-free modes.

Some post-surgical cases with unusual scarring patterns that reduce reconstruction quality.

7.4 Appropriate use: when profilometry adds maximum value

Profilometry tends to provide the highest incremental value for:

Complex scleral lens cases: significant corneal irregularity, marked scleral asymmetry, post-surgical anatomy, or repeated fitting failures.

Large-diameter scleral lenses (>18 mm) where peripheral landing data strongly influences outcomes.

Practices fitting scleral lenses at sufficient volume to maintain proficiency (often >5-10 scleral patients per month).

Practices adopting toric, quadrant-specific, or freeform landing zone designs where asymmetry data is actionable.

7.5 Complementary technologies: what profilometry does not replace

Profilometry should be viewed as a complementary tool within a comprehensive specialty lens practice. It does not replace:

Anterior segment OCT: for high-resolution vault quantification, edge cross-sections, and dynamic settling assessment.

Corneal tomography: for ectasia screening, posterior corneal surface assessment, and pachymetry patterns.

Slit lamp examination: for tissue response evaluation, staining, inflammation, and overall ocular health.

Dry eye assessment tools: to evaluate tear film and ocular surface disease that can influence lens tolerance and measurement stability.

7.6 Economic and practical limitations

As with any specialty technology, return on investment depends on patient volume, case mix, and fee structure.

Training time and workflow adjustment are real costs; practices benefit most when they commit to consistent use rather than occasional scanning.

Laboratory relationships and service capabilities remain important - measurement is only valuable when designs can be manufactured and iterated efficiently.

7.7 Ongoing research needs and future development

Key research and development themes in corneo-scleral measurement include:

Better prediction of lens settling and tissue response using baseline shape plus material and design parameters.

Improved modeling of conjunctival compliance and suction effects to predict compression patterns.

Enhanced peripheral reconstruction algorithms and quality metrics to reduce error at extreme diameters.

Integration of measurement with outcomes datasets (comfort, physiology, vision) and machine-learning approaches to refine first-lens selection.

7.8 Summary

Profilometry provides objective corneo-scleral shape data that can reduce trial-and-error in scleral lens fitting, especially in asymmetrical or large-diameter cases. Realistic expectations, appropriate mode selection, and integration with OCT, tomography, and clinical judgment are essential to realize its benefits.

8. Conclusion

Scan-based eye shape measurement has shifted scleral lens fitting from an empirical process toward a more predictable, data-informed workflow. Because scleral lenses land on conjunctival tissue overlying the sclera, wide-field corneo-scleral geometry - particularly sagittal height and regional asymmetry - is often the limiting variable in comfort, stability, and physiological response.

The Gaudi Profilometer supports this modern approach by combining multi-modal corneo-scleral measurement with integrated lens design, follow-up evaluation tools, and an open XML data format that supports manufacturer-independent ordering. Used appropriately, profilometry can improve first-lens selection, shorten troubleshooting cycles in difficult fits, and strengthen patient communication through objective visualization.

As with any measurement technology, clinical outcomes depend on correct interpretation and integration with complementary diagnostics such as anterior segment OCT, corneal tomography, and slit lamp examination. The future of scleral lens fitting lies in combining objective measurement with informed clinical judgment and efficient manufacturing workflows.

9. References

[1] Macedo-de-Araújo RJ, Fadel D, Barnett M. How Can We Best Measure the Performance of Scleral Lenses? Current Insights. Clin Optom (Auckl). 2022;14:47–65. doi:10.2147/OPTO.S284632. PMCID: PMC9000539. PMID: 35418790.

[2] Consejo A, Llorens-Quintana C, Bartuzel MM, Iskander DR, Rozema JJ. Rotation asymmetry of the human sclera. Acta Ophthalmol. 2019;97(2):e266–e270. doi:10.1111/aos.13901. PMID: 30146759.

[3] Ritzmann M, Caroline PJ, Börret R, Korszen E. An analysis of anterior scleral shape and its role in the design and fitting of scleral contact lenses. Contact Lens Anterior Eye. 2018;41(2):205–213. doi:10.1016/j.clae.2017.10.010.

[4] Kowalski LP, Collins MJ, Vincent SJ. Scleral lens centration: The influence of centre thickness, scleral topography, and apical clearance. Contact Lens Anterior Eye. 2020;43(6):562–567. doi:10.1016/j.clae.2019.11.013. PMID: 31836202.

[5] Alexander J, Aweke YB, Bhebhe Z, et al. The effect of landing zone toricity on scleral lens fitting characteristics and optics. Ophthalmic Physiol Opt. 2024;44(5):867–875. doi:10.1111/opo.13324. PMID: 38699941.

[6] Fogt JS, et al. Midday Fogging of Scleral Contact Lenses: Current Perspectives. Clin Optom (Auckl). 2021. PMCID: PMC8311169.

[7] Macedo-de-Araújo RJ, van der Worp E, González-Méijome JM. Practitioner Learning Curve in Fitting Scleral Lenses in Irregular and Regular Corneas Using a Fitting Trial. Biomed Res Int. 2019;2019:5737124. doi:10.1155/2019/5737124. PMCID: PMC6369499. PMID: 30834269.

[8] Fadel D. The influence of limbal and scleral shape on scleral lens design. Contact Lens Anterior Eye. 2018;41(4):321–328. doi:10.1016/j.clae.2018.02.003. PMID: 29496327.

[9] Rathi VM, Mandathara PS, Dumpati S, Sangwan VS. Change in vault during scleral lens trials assessed with anterior segment optical coherence tomography. Cont Lens Anterior Eye. 2017;40(3):157–161.

[10] Yeung D, et al. Scleral Lens Clearance Assessment with Biomicroscopy and Anterior Segment Optical Coherence Tomography.

Appendix A: Scleral Measurement Terminology Glossary

Appendix A provides standardized terminology used in scan-based eye shape measurement, corneo-scleral profilometry, and freeform scleral lens design to support consistent clinical communication and interpretation of scan data.

This glossary defines common terminology used in scan-based ocular surface measurement (corneo-scleral profilometry) and in designing freeform or custom scleral lenses. Terminology and parameter names can vary by manufacturer and laboratory; definitions below reflect common clinical and engineering usage in profilometry-driven workflows.

Terms are listed alphabetically. When units are stated, microns (µm) are commonly used for height and clearance values in scleral lens design and evaluation.

A

Accuracy: Closeness of a measurement to the true value. In ocular surface scanning, accuracy is typically expressed in microns (µm) across a defined diameter.

Acquisition time: Time required to capture a scan. Short acquisition reduces motion artifacts from blinks, microsaccades, and fixation drift.

Alignment (instrument): The patient and device positioning step that centers the measurement zone on the limbus and sets proper working distance and focus.

Anterior segment OCT (AS-OCT): Optical coherence tomography imaging of the cornea, limbus, and sclera used to quantify scleral lens vault, settling, and edge relationships in cross-section.

Apical clearance: Central clearance over the highest point of the cornea (apex) under a scleral lens; a subset of central vault assessment.

Artifact: A non-anatomical feature in scan data caused by blinking, tear film breakup, eyelid shadowing, or motion during acquisition.

Asphericity: Departure of a surface from a best-fit sphere. Ocular surfaces and scleral lens designs may be aspheric, especially outside the central cornea.

Axis: Angular orientation (0–180 degrees) used to describe toric geometry on a scleral lens (e.g., toric haptic axis) or ocular shape asymmetry.

B

Back surface: The posterior surface of a scleral lens that interfaces with the tear reservoir and aligns to the ocular surface (cornea, limbus, sclera).

Back-surface toric: Toric geometry on the posterior surface used to align the lens to scleral toricity and improve stability and comfort.

Base curve: A traditional contact lens parameter describing central posterior curvature. In scan-based scleral fitting, sagittal height often replaces base curve as the primary design variable.

Best-fit sphere (BFS): A reference sphere used to describe elevation differences across the cornea or corneo-scleral surface maps.

Blanching: Whitening of conjunctival blood vessels caused by localized compression from the scleral lens landing zone (haptic).

Bleb (filtering bleb): Elevated conjunctival tissue created by glaucoma surgery. Blebs can require notch or localized vault features in scleral lens designs.

Bulbar conjunctiva: The conjunctival tissue covering the anterior sclera; primary tissue contact area for scleral lens landing zones.

C

CAD/CAM: Computer-aided design and manufacturing used to convert scan data and design parameters into a lathe-cut or milled scleral lens.

Calibration: Procedure that ensures the scanner's geometric model and optics produce accurate height measurements over time.

Capture diameter (measurement diameter): The diameter of ocular surface area captured by a scan (e.g., 16 mm or >20 mm), which should cover the intended scleral lens landing zone.

Center thickness: Thickness at the lens center. Higher thickness can reduce flexure but may reduce oxygen transmissibility (Dk/t).

Central clearance: Clearance between the central cornea and the posterior surface of a scleral lens, typically evaluated at application and after settling.

Centration: How well the lens optical zone aligns with the visual axis or corneal apex; influenced by scleral shape and haptic design.

Chord diameter: A specified diameter across the eye used to reference sagittal height or elevation; commonly aligned to the intended lens diameter.

Clearance: The separation between the scleral lens and the ocular surface (corneal or limbal) filled by the tear reservoir; distinct from landing zone alignment on the sclera.

Compression: Excess bearing by the landing zone that can cause blanching, discomfort, suction, and conjunctival indentation.

Conjunctival prolapse: Conjunctival tissue drawn into the space under the lens near the limbus, sometimes associated with large vault or certain limbal geometries.

Corneal vault: The intended space between a scleral lens and the cornea, maintained by sagittal depth; evaluated clinically via fluorescein or OCT.

Corneo-scleral junction (CSJ): Transition zone from cornea to sclera near the limbus. Shape and angle variation at the CSJ influences limbal clearance and lens alignment.

Cylinder: Astigmatic optical power component. Can be placed on the front surface (requires stable orientation) or managed via back-surface design and alignment.

D

Data density: Number of measured points captured by a scan (e.g., >100,000 to >1,000,000). Higher density can improve representation of local asymmetry.

Data portability: Ability to export and use scan data across labs/software (e.g., open formats such as XML) without vendor lock-in.

Decentration: Offset of the lens center from the visual axis or corneal apex (often temporal and/or inferior). Decentration influences optics and clearance distribution.

Design diameter: The planned overall lens diameter. Scan coverage should extend beyond the intended landing zone region for reliable design.

Diameter: Overall lens size. Larger diameters move the landing zone farther onto the sclera where asymmetry is often greater.

Digital light processing (DLP): Projection technology that rapidly displays structured patterns (lines or sinusoidal fringes) used in structured-light ocular surface measurement.

Dk (oxygen permeability): Material property describing oxygen diffusion through the lens material.

Dk/t (oxygen transmissibility): Oxygen transmissibility accounting for material permeability (Dk) and lens thickness (t); relevant to hypoxia risk in scleral lenses.

E

Edge clearance: Local relationship of the lens edge to conjunctiva; includes edge lift and impingement assessment.

Edge lift: Separation between the lens edge and conjunctiva, often seen as an edge shadow, bubble, or localized fluorescein entry.

Edge profile: The geometry of the lens periphery (edge). Edge design affects comfort, seal, tear exchange, and risk of impingement.

Elevation map: A surface map describing height relative to a reference surface (often BFS) across cornea and sclera; used to characterize asymmetry.

Extrapolation: Mathematical extension of measured data beyond the captured zone. Extrapolation is less reliable than directly measured data for large diameters.

Eyelid interference: Loss of scan data or lens interaction caused by eyelids covering peripheral regions, especially superiorly and inferiorly.

F

Fenestration: A small hole in a scleral lens to reduce suction or improve tear exchange; used selectively in certain clinical scenarios.

Fit evaluation imaging: Objective imaging (fluorescein photography, OCT, or surface imaging) used to document vault, limbal clearance, and landing zone effects.

Fixation instability: Inability to maintain steady gaze during scanning; increases motion artifacts and reduces scan repeatability.

Fixation target: A visual target used to stabilize gaze during scanning; fixation stability reduces artifacts and improves repeatability.

Fluorescein: A dye used to enhance visualization of the tear layer. In scan-based systems, fluorescein can improve signal consistency across cornea and sclera.

Fluorescein excitation: Illumination (often blue) that causes fluorescein to emit green light, enabling high-contrast imaging through a green filter.

Fourier transform profilometry: Structured-light method using sinusoidal fringe patterns and phase analysis to reconstruct surface height, often with high point density.

Freeform design: A scleral lens surface (often the back surface or haptic) that is not limited to simple spherical/toric curves and can be customized point-by-point to match measured ocular shape.

Freeform haptic: A haptic surface generated from scan data that allows localized, non-symmetric alignment beyond toric or quadrant-specific designs.

Front surface: The anterior lens surface. Front-surface design may include sphere/cylinder, multifocal optics, or wavefront-guided corrections.

Front-surface toric: A cylinder correction placed on the front surface of the lens; requires rotational stability to maintain axis alignment.

G

Gaze (multi-gaze acquisition): A scanning approach that captures multiple fixation positions to extend coverage beyond a single-gaze capture diameter; scans are later stitched/merged.

H

Haptic (landing zone): The scleral landing zone region of the lens that rests on conjunctiva over sclera. Haptic alignment is a primary determinant of comfort and physiology.

Higher-order aberrations (HOAs): Optical aberrations beyond sphere and cylinder. Some scleral designs incorporate HOA control; stability and centration affect performance.

Hybrid design workflow: A fitting approach that combines scan-based design with diagnostic lens evaluation and over-refraction to refine parameters.

I

Impingement: A steep or tight lens edge that 'digs in' to conjunctiva near the periphery, potentially causing staining, discomfort, and vascular changes.

Impression-based fitting: Workflow that physically captures ocular surface shape (impression), then digitizes it for lens design; an alternative to optical scanning.

Interpolation: Estimation of surface between measured points. Systems with sparse sampling rely more heavily on interpolation than high-density scanning.

Iris reflectance / iris color effect: In non-fluorescein methods, light iris colors can reduce contrast between corneal reflection and iris signal, affecting reconstruction quality.

L

Landing zone alignment: How evenly the haptic rests on conjunctiva/sclera without compression, impingement, or edge lift.

Landing zone toricity: Toric geometry in the haptic to match scleral toricity; can improve alignment and reduce rotation and flexure.

Landing zone width: The radial width of the haptic zone contacting conjunctiva. Width influences pressure distribution and comfort.

Lathe-cut manufacturing: Common scleral lens manufacturing method using CNC lathes to cut lens surfaces based on design parameters or freeform surfaces.

Lens flexure: Bending of the lens on-eye, which can induce residual astigmatism or alter optics; influenced by thickness and landing zone alignment.

Lens settling: Decrease in vault over time as the lens compresses conjunctiva and redistributes the tear reservoir; measured clinically via OCT or serial evaluation.

Limbal bearing: Unwanted contact or pressure at the limbus; associated with discomfort and potential adverse tissue response.

Limbal clearance: Clearance over the limbus under a scleral lens; evaluated to avoid limbal bearing and support physiological wear.

Limbal vault: Clearance over the limbus and corneo-scleral junction; part of the overall vault design and evaluation.

Limbus: The transition region between cornea and sclera. Adequate limbal clearance helps protect limbal tissues.

Line-scan triangulation: Structured-light method that projects lines and reconstructs 3D height from projector-camera geometry; often robust for scleral landing zone measurement.

Local vault (microvault): A localized elevation or cutout feature to vault an obstacle (e.g., pinguecula) or protect tissue without changing overall sagittal height.

M

Manufacturer lock-in: A limitation where scan data can only be used with one lab or ecosystem (e.g., encrypted formats), reducing portability and competitive sourcing.

Measurement repeatability: How consistent the same device is when measuring the same eye under similar conditions.

Measurement reproducibility: How consistent results are across different operators, sessions, or devices.

Meibography: Infrared imaging of meibomian glands; relevant because ocular surface disease can influence scleral lens tolerance and fogging.

Meibomian gland dysfunction (MGD): A common cause of evaporative dry eye that can affect tear film stability and scleral lens wearing performance.

Mesh / surface mesh: A triangulated surface representation derived from a point cloud; used for visualization and freeform surface fitting.

Microsaccade: Small involuntary eye movement that can introduce motion artifacts during longer acquisition times.

Midday fogging: Accumulation of debris in the tear reservoir causing vision clouding during wear; often evaluated alongside landing zone alignment and inflammation.

Mini-scleral lens: A smaller scleral lens (commonly ~14.5–16.5 mm) that still lands on sclera; coverage requirements differ from full scleral designs.

Multi-modal measurement: Availability of more than one scanning modality (e.g., fluorescein line scan, non-fluorescein scan, Fourier) to optimize scanning for varied patient conditions.

N

NIBUT (non-invasive break-up time): Tear film stability metric measured without fluorescein; relevant to scan quality and ocular surface management.

Notch: A lens edge cutout used to avoid contacting an obstacle (e.g., pinguecula, bleb). Often paired with scan-based design for precise placement.

NURBS: Non-Uniform Rational B-Splines, a common mathematical representation for smooth freeform surfaces used in CAD/CAM manufacturing.

O

O-SAG (ocular sagittal height): Sagittal height of the ocular surface at a specified chord diameter; a key parameter for selecting initial scleral lens sagittal depth.

Ocular surface disease (OSD): A broad category including dry eye and inflammatory conditions that can reduce scan quality and affect scleral lens tolerance.

Open data format: A scan file structure that can be read and used by multiple labs and software tools (e.g., XML) to support portability.

Optic zone: Central optical area of the lens. Optic zone size and centration influence visual quality, especially in irregular corneas.

Optimization (surface fitting): A computational step that fits a smooth mathematical surface to measured points (point cloud) to generate a manufacturable freeform lens surface.

Over-refraction: Refraction performed over a lens on-eye to refine final power; common in scleral fitting workflows.

P

Pachymetry: Corneal thickness measurement; important for disease monitoring and evaluating edema risk, typically via tomography or OCT.

Phase shifting: A Fourier profilometry technique using multiple pattern phases to compute surface height with high precision.

Plasma treatment: Surface treatment used to improve wettability of gas permeable materials; may reduce deposits and improve comfort.

Point cloud: A set of 3D points representing the measured ocular surface. Point clouds are the raw input for surface fitting and freeform design.

Power map: A map of refractive power distribution across a surface; used in analysis of corneal shape or lens optics.

Precision: Repeatability of measurements (how tightly repeated measurements cluster), distinct from accuracy.

Profilometry: Measurement of surface elevation (height) across the cornea, limbus, and sclera for scleral lens design and analysis.

Q

Quadrant-specific haptic: A landing zone design with different geometry in each quadrant to match asymmetric scleral shape more precisely than simple toric haptics.

Quality metric (scan): Software-reported indicators of scan completeness and reliability (e.g., coverage, noise, missing regions, or stitching confidence).

R

Registration (stitching): Alignment and merging of multiple scans (e.g., multi-gaze point clouds) into a single extended surface map.

Residual astigmatism: Astigmatism remaining with the lens on-eye, caused by optics, flexure, rotation, or decentration; addressed via design changes or front-surface cylinder.

Rotational stability: Ability of the lens to maintain a consistent orientation on-eye; essential for front-surface toric, prism, or wavefront-guided designs.

S

Sag profile: The overall sagittal contour of the lens from center to periphery, including optic, transition, and haptic zones.

Sagittal depth (sag): The depth of the lens required to vault the cornea at a given diameter; often used as the primary fitting parameter in scleral lenses.

Sagittal height (surface sag): Height of the ocular surface at a given chord diameter; scan-based systems directly measure sagittal height to inform lens design.

Sampling resolution: Spacing between measured points in the scan. Higher resolution captures finer features but may increase data size and processing needs.

Scheimpflug imaging: Tomography technique using a rotating camera and slit illumination to reconstruct corneal structure; may include limited corneo-scleral mapping.

Scleral asymmetry: Non-rotational symmetry of scleral shape that may require toric, quadrant-specific, or freeform haptic designs.

Scleral lens: A rigid gas permeable lens designed to vault the cornea and land on the sclera, creating a tear reservoir over the cornea.

Scleral toricity: Difference in scleral shape between meridians; commonly increases with larger chord diameters.

Seal (seal-off): A tight landing zone that limits tear exchange, potentially contributing to suction, fogging, or removal difficulty.

Settling curve: Change in central and limbal clearance over time after application; influenced by tissue compliance and lens design.

Spherical haptic: A landing zone with rotational symmetry; may be insufficient in eyes with significant scleral toricity or quadrant asymmetry.

Spline surface: A smooth mathematical surface fit to measured data points; often used to generate manufacturable freeform haptic geometry.

Structured light: 3D measurement approach projecting known patterns onto a surface and reconstructing shape from observed distortion.

Suction: Negative pressure under a scleral lens associated with tight alignment, seal-off, or removal difficulty.

Surface elevation: Height of the ocular surface relative to a reference surface; the core output of corneo-scleral profilometry.

T

TBUT (tear break-up time): Tear film stability metric, often measured with fluorescein; unstable tear film can affect both scan quality and comfort.

Tear exchange: Movement of tears under the lens during wear. Scleral lenses generally have limited exchange; excessive or insufficient exchange can be problematic.

Tear film: Thin fluid layer covering the ocular surface. Tear film stability affects scanning signal quality and wearing comfort.

Tear reservoir: Fluid reservoir between the cornea and the posterior lens surface. Reservoir thickness changes with settling.

Tissue compliance: How easily conjunctiva/sclera deform under load. Compliance influences settling and compression patterns.

Toric haptic: A landing zone with two principal meridians of different sagittal height to match scleral toricity.

Toric periphery: A peripheral lens design element with toricity to match scleral shape; commonly used to reduce edge lift and improve stability.

Transition zone: Lens region between optic zone and haptic; may influence mid-peripheral clearance and overall sagittal profile.

V

Vault: The clearance created by the lens over the cornea and limbus; includes central and limbal clearance and changes with settling.

Visual axis: Line connecting the fixation target to the fovea. Lens centration relative to the visual axis can affect subjective visual quality.

W

Wavefront aberrometry: Measurement of optical aberrations of the eye; can inform advanced scleral optics (e.g., wavefront-guided designs).

Wavefront-guided scleral optics: Customized optics designed to reduce measured aberrations. Performance depends on centration and rotational stability.

Wettability: How easily tears spread on the lens surface; affects comfort, vision stability, and deposits.

X

XYZ coordinate system: The 3D coordinate reference used to represent scan data and lens surfaces, enabling surface fitting and point cloud registration.

Z

Zernike polynomials: Mathematical functions often used to describe corneal shape and optical aberrations; sometimes used in advanced design and analysis.

Zone-based design: Lens design approach that divides the lens into functional zones (optic, transition, haptic) with separate parameters.