How to fit lenses with simple devices and when to expand your armature.
Ten years ago, I was midway through a cornea and contact lens residency at Pacific University and wondering whether scleral lenses (SLs) would be here to stay or if they were a passing trend. In 2023, it seems SLs are being reached for more than ever. Along with the continued excitement about using SLs, we have seen impressive advancements in the technology to fit and manage them.
During my evolution as a scleral practitioner, I have encountered a range of approaches to fitting, using equipment as ubiquitous a slit lamp as well as some of the most advanced fitting technology in the world. Most recently, I took the plunge to add 1 advanced tool that was missing from my toolbox, the EyePrintPro (EyePrint Prosthetics). This custom, 3D-printed, impression-based lens is among the most sophisticated tools available for fitting SLs. But I didn’t reach for this technology right out the gate; I grew into it and my patient base evolved to include patients who need advanced levels of SL wear.My experience with SL technology has helped me understand how different technologies can be used at different levels of SL management.
Every optometrist has the tools to fit scleral lenses; the only necessary add-on is a diagnostic fitting set. A trial lens can be selected using the anterior chamber (AC) depth (Figure 1) and width to select an appropriate sagittal height (SAG) and diameter, respectively, for the starting lens.
The width of the AC is estimated by measuring the horizontal visible iris diameter and then selecting a SL that is at least 3 mm greater, ie, allowing at least 1.5-mm overlap on each side. From the best estimated first diagnostic lens, make an assessment and move up and down in SAG and diameter until there is appropriate clearance (100 to 500 μm works well), landing outside the limbus, allowing for an overrefraction and lens assessment. Consult fitting guides, take videos, call consultants, document everything, and you have all you need to be successful.
Moving beyond the first several SLs, a developing practitioner can begin to invest in equipment to monitor underlying diseases and investigate complications proactively and to design more sophisticated SLs if desired. The precise technology that fits into a practice is unique, considering the SL and ocular features that are a priority in the practice and what combinations of instruments can accomplish these goals. There are essentially 3 features you want to be able to assess with technology: the corneal shape, the scleral shape, and the optics, and there are various technologies that can assess them.
Corneal shape is important to understand so that disease can be diagnosed and monitored, particularly in irregular corneas, ie, in most SL wearers. SLs alter the corneal curvature,1-3 thickness,4-9 and aberrations,10 and although these changes are not often clinically significant, they cannot be fully understood without corneal topography or tomography. Some options for evaluating corneal shape are as follows:
1. Corneal topographers:These measure the anterior corneal surface. There are several commercially available options, including E300 Corneal Topographer (Medmont), Keratograph 5M, (Oculus), and IOLMaster 700 (Zeiss). A nice feature of topography is that it allows assessment of tear film quality (eg, in a dry eye patient), which may be a priority for some scleral practitioners. A drawback is that they do not measure the posterior cornea.
2. Corneal tomographers: These measure the anterior and posterior corneal surfaces, allowing for global pachymetry and posterior curvature measurements. Available options include Pentacam (Oculus) and Galilei (Ziemer Ophthalmic Systems). Although there is usually minimal corneal edema with SL,7,11,12 there are several populations (eg, postsurgical and postinfectious corneas13-15) in which there appears to be a heightened risk for edema. Furthermore, posterior curvatures may be of interest to a scleral practitioner who is working with irregular corneas (eg, keratoconus) and advanced optical designs.
3. Optical coherence tomography (OCT): This instrument is widely used for many ocular applications and can be useful in SL management.16-19 An OCT with anterior segment capabilities—eg, Optovue Avanti OCT (Visionix) and Cirrus OCT (Zeiss)—is a good method to measure global pachymetry and can also be used to measure corneal vault,19 the peripheral SL fit,18 and even scleral shape.20
Advancements in the understanding and technology available to measure scleral shape have brought SL fitting to a new echelon. As SLs become a bigger part of a practice, it’s time to invest in a scleral topographer (Figure 2).
A scleral topographer allows specific, data-based decisions about lens shape, which can be quite variable and unpredictable,21-25 even in normal eyes.22,23 Focal elevations (eg, pinguecula, AC surgeries) are particularly difficult to estimate as they exist on a micron scale. In the US, there are 2 available stand-alone scleral topographers—the sMap3D (Precision Ocular Metrology) and the Eye Surface Profiler (Eaglet Eye)—as well as an add-on to some models of the Pentacam. I cannot recommend these advanced technologies enough in the context of SL management, but I do concede that aside from the Pentacam, they do not have additional utility beyond scleral topography.
Scleral lenses are all about providing superior optics so technology that allows precise measurement and correction of advanced optics or higher order aberrations (HOAs) is useful as a practice grows. An aberrometer is necessary to detect and correct HOAs in SL and while there are several available—eg, iTrace visual function analyzer (Tracey Technologies) and xwave System (Ovitz)—most are not currently able to collaborate with manufacturing labs on lens designs, although Ovitz has started to partner with manufacturers in the US. Correcting HOAs is a complicated and advanced process but at last, these advancements are available to a deeply invested scleral practitioner.
One of the most advanced methods of SL practice is to use a molded scleral lens design such as the EyePrintPro (EPP) (Figure 3), and/or incorporating HOA correction and other advanced features to SLs. At our community-based urban practice at the University of Houston College of Optometry, we see many train wrecks, and my colleague and friend Karen Lee (OD, assistant professor, University of Houston College of Optometry) and I have been collecting patients who have been kicking the can down the road, so to speak, making it work with the best that we had but being limited on wear time, comfort, and dodging from 1 complication to another. We finally decided that we needed to bring the EPP to our practice.
My first patient was a dry eye patient who needed full coverage and had several areas of elevation (bilateral pingueculas, areas of conjunctival hypertrophy) that were interacting with her already quite sophisticated lenses. We ended up designing a 19.5 mm–wide by
18 mm–high lens.
We have another patient who has already been in the wavefront-guided optics process with another lens but needs a more customized lens shape and yet another with huge elevation irregularities, ie, extreme asymmetrical graft-host junction elevations, where we will build channels into the lens to manage recurring edema.
This more advanced technology is certainly not necessary for the “everyday” scleral lens patient (if that is such a thing), but as an SL practice grows, there will inevitably be at least a handful of patients who really need and want this advanced technology. And I imagine the more you use it, more people will seek you out.