Scan-Based Freeform Scleral Lenses: a Review

Do you struggle with multiple fits? Did you know that only 6% of scleras are spherical?¹ Maximizing available technology, such as profilometry, could save you quite a bit of headache, provided you know why and when to use it.

When fitting conventional scleral lenses, practitioners examine a trial lens on the patient’s eye and make any necessary adjustments to the curves of the lens so that it fits the eye properly and provides good vision. Freeform scleral lenses are an exciting innovation in the world of specialty contact lenses.

There are several freeform lens designs available from different manufacturers (Table). These lenses were created based on scleral profilometry, and each has its own unique characteristics and fitting method. This article highlights some of the scan-based freeform scleral lenses available, along with their customization options—but first, let’s talk about profilometry.

PROFILOMETRY

Profilometry is the imaging of both the cornea and sclera to generate maps or models that can be used in scleral lens design.² The images obtained from profilometers are stitched together at the mapped limbus, and a 3D image is generated for virtual corneal-scleral design.¹ Profilometers have the most integration with the available scan-based scleral designs.

The two most commonly used profilometers are the Eye Surface Profiler (ESP) scleral topographer (Eaglet-Eye) and the Oculus Pentacam corneal tomographer (Oculus) with added Cornea Scleral Profile (CSP) scan. The ESP uses fluorescein and a lubricant to help image the sclera-to-chord measurements of up to 20 mm and uses a rasterized grid of multiple points to generate its image with Placido disk technology.³ The Pentacam uses 250 Scheimpflug images obtained as several images in primary gaze, which are then merged into a single 3D image.² The Pentacam images are not dependent on the tear film and therefore do not require ocular lubricant or fluorescein.

Both machines extrapolate missing data using algorithms to provide an estimated curvature. As a result, the data closely match the true shape of the cornea and sclera, but with some weaknesses, especially in the areas where images are stitched to create a 3D image or when scans have poor quality.

The lens designs discussed below are compatible with both the ESP and the Pentacam.

LENS DESIGNS

ScanFitPro

One of the first scan-based freeform scleral lens designs was the ScanFitPro (EyePrint Prosthetics), which was developed in October 2019.⁴ In January 2022, the company announced a partnership with specialty contact lens company SynergEyes to increase accessibility of the lens.

Instead of a spline or linear format lens design, ScanFitPro (Figure 1) uses a point cloud system, which allows the customization of a more succinct area of the lens. Lens diameter can be customized by 0.1 mm and multiple parameters, including the optic zone, transition zone, landing zone, and edge lift zone, can be adjusted with the software. An option to add a freeform “bump” on the lens further increases clearance in a specific zone (Figure 2). The ScanFitPro also incorporates multifocal optics. Additional software licensing is required, which allows scans and designs to be directly uploaded to consultation for order.

Smart360

The Smart360 (BostonSight) is a freeform scleral lens that was introduced in November 2019.⁵ An account with BostonSight’s FitConnect is required to fit the lens, and orders can be placed by uploading profilometry scans to BostonSight’s FitConnect website via the Smart360 section (Figure 3).

Lenses range from 16 mm to 19 mm in diameter and the base curve, corneal clearance, horizontal iris diameter, and vertical iris diameter can each be adjusted on the website. Once the lens arrives, it can be further adjusted using the FitConnect website in a similar method to other BostonSight lenses, where modifications are made along four quadrants. A SmartChannel can then be added as needed to vault over conjunctival elevations, promote tear exchange, or relieve suction.

Gaudi

Valley Contax has two scan-based freeform lens options: the base model Gaudi QS and the more customizable Gaudi Legend. The company offers two different options for ordering its lenses: With the first option, the Valley consulting team designs the lens based on profilometry data. The second option involves the practitioner downloading the lens design software and designing the lens themselves.⁶

Both Gaudi options employ a point-based cloud design, enabling more concise customization options over spline-based systems. The Gaudi QS allows 45˚ adjustments along the edges and haptics. The diameter is adjustable and multifocal optics can be added. The Gaudi Legend offers a plethora of customization options, including the ability to make changes in 1˚ increments; add prism; decenter the optic zone; adjust for back and front surface tilt; add fenestrations, notches, vaults; and more.

Maxim 3D

Released in July 2021, the Maxim 3D (AccuLens) boasts a simplified fitting process for reduced chair time.⁷ First, scleral profilometry is taken. Secondly, a specific AccuLens trial lens is placed on the eye to determine proper lens diameter based on laser etching on the trial lens, and an overrefraction is performed. These data are then sent to an AccuLens consultant, and an initial lens is designed and dispensed. No extra software is required for this lens. The lens may be designed at 90˚ intervals at any angle on the haptic. Additional features include multifocal optics along with an AccuVault for conjunctival elevations.

Wave ScleraLens

The Wave ScleraLens (Wave Contact Lens System) is a software-based scleral lens.⁸ Data from the profilometer scan is directly imported into the software, and initial lens desired parameters, including lens diameter and central clearance, can be entered. A freeform lens is then simulated on screen, where it can be further customized (Figure 4). Any changes to the edge of the haptic, limbal clearance, or central clearance can be modified in 45˚ intervals. Additional modifications, such as adjusting optic zone diameter, prism inclusion, and multifocal optics, can also be incorporated.

The company’s rigid gas permeable lens design technology has also been expanded to extrapolate an expected scleral profilometry, so practitioners who do not have a profilometer can still order an empirical lens using corneal topography alone, although additional adjustments will be needed. Wave Contact Lens System offers a loyalty program to practitioners, with reduced pricing and additional benefits based on the number of lenses sold in a year.

GROWING OPTIONS IMPROVE CHAIR TIME AND PATIENT EXPERIENCE

The increasing availability and popularity of scan-based scleral lens designs improve patient access to quality, customizable specialty lenses and can help resolve historically challenging fittings. The chair time involved in initial fitting visits has been a barrier to providing specialty lens care in many offices, but with technician-based testing and empirical lens design, that time can be significantly reduced. Each manufacturer’s unique fitting philosophy provides ample options for any optometrist to choose what fits best for their practice.