The COVID-19 pandemic is not holding back research. In addition, professional meetings give us a unique opportunity to be exposed to new ideas or to push the boundaries of our knowledge even further.

The field of scleral lenses is no exception. Based on what has been learned over the past 10 years, professionals are increasingly embracing scleral lenses as the modality of choice for treating ocular surface problems, restoring vision to patients, or enhancing the experience of those who wear more conventional lenses but still have problems with acuity or comfort.

The growing popularity of scleral lenses is likely due to the fact that today we know more about conjunctival and ocular surface anatomy than in the recent past. One article deserves our attention here (Walker et al, 2020); it summarizes the current knowledge of the ocular anatomy of the anterior segment and is based on, among other things, work carried out with the aid of modern conjunctival mapping technology. Clearly, this increased knowledge of the ocular surface is leading to changes in the way scleral lenses are designed, manufactured, and fitted, which, in turn, improves their performance, limits complications, and leads to improved patient comfort.

Speaking of technology, the increasingly widespread use of decentered optic zones makes it possible to improve the visual performance of scleral lenses, particularly in the case of decentration. The benefits are obvious when fitting multifocal lenses, but even more so in eliminating the induced aberrations that can occur when scleral lenses are used to compensate for mild-to-moderate corneal ectasia.

The benefits of scleral lenses are not limited to vision and comfort. Recent published work by Ling and colleagues (2021) indicated that scleral lenses may contribute to reducing the rate of corneal grafts in the United States. They analyzed the records of 2,806 keratoconus eyes, and found that only 3.2% of them were referred for surgery.

The authors concluded that scleral and GP lens wearers carry a five times lower chance than other KC patients of having to undergo corneal transplantation. Promoting and fitting sclerals helps reduce the chance of surgical intervention.

Maintain Corneal Integrity

To be safe, prescribing scleral lenses must meet certain conditions to maintain corneal integrity. Hypoxic stress associated with scleral lens wear tops the list of concerns.

This subject has been debated for years and Fisher et al (2021) are shedding new light on it. They confirmed that scleral lenses may induce corneal edema and that it increases as the reservoir becomes thicker; they identified the latter, and not the lens material Dk, as the determining factor.

The most interesting finding of this study is that the level of in vivo edema did not fully match the theoretical models developed by Kim and others (2018). Further work is needed to explain this divergence, which would help to better define the true impact of scleral lens-induced hypoxic stress. At the “Scleral Lens Super Session” at the 2022 Global Speciality Lens Symposium, speakers reminded us that induced edema becomes an important element to consider when dealing with more fragile corneas (e.g., post-grafts and post-radial keratotomy). In these cases, corneal edema can lead to physiological complications.

Alleviating hypoxic stress is achieved by using proper fitting methods, which is what is taught in optometry school. In a recent survey, contact lens educators reported that their average (optimal) fit is characterized by a central reservoir thickness of 206.3µm ± 44µm, not to exceed 350 microns (Harthan et al, 2021). The optimal vault above the limbus is 62.1µm ± 23.6µm, not to exceed 100 microns.

It is reassuring that optometry students are learning the right way; this assumes that these conditions are known to limit hypoxic stress to the cornea and to reduce the risk of midday fogging.

In Conclusion

Many eyecare professionals have made scleral lenses their modality of choice for the irregular cornea. For others, it is never too late to join the parade and offer this safe and comfortable device to patients. CLS

References

1. Walker MK, Schornack MM, Vincent SJ. Anatomical and physiological considerations in scleral lens wear: Conjunctiva and sclera. Cont Lens Anterior Eye. 2020 Dec;43:517-528.
2. Ling JJ, Mian SI, Stein JD, Rahman M, Poliskey J, Woodward MA. Impact of Scleral Contact Lens Use on the Rate of Corneal Transplantation for Keratoconus. Cornea. 2021 Jan;40:39-42.
3. Fisher D, Collins MJ, Vincent SJ. Fluid reservoir thickness and corneal oedema during closed eye scleral lens wear. Cont Lens Anterior Eye. 2021 Feb;44:102-107.
4. Kim YH, Tan B, Lin MC, Radke CJ. Central Corneal Edema with Scleral-Lens Wear. Curr Eye Res. 2018 Nov;43;1305-1315.
5. Harthan JS, Schornack M, Nau CB, Nau AC, Fogt JS, Shorter ES. Current U.S. based optometric scleral lens curricula and fitting recommendations: SCOPE educators survey. Cont Lens Anterior Eye. 2021 Jun;44:101353.