Keratoconus Progression and Scleral Lenses

History

This 23-year-old keratoconus patient had been successfully wearing scleral lenses that were fit in 2020. In January 2022, when he returned for a refit, we found that his keratoconus had significantly progressed.

The image above is a cross-section view of his left eye, in which we can observe visible thinning and mild opacification at the apex. His previous visual acuity from July 2020 was 20/25^-1 OU. His right eye presented a similar pattern, so only the left eye will be covered here.

Corneal Biomicroscopy

Slit lamp examination OD and OS revealed flattening at the apex. The patient had broken his right lens and had suspended lens wear on both eyes for three days.

The fluorescein pattern OS was normal, there was no staining. We suspected that both eyes had an episode of progression, as he had been quite stable since 2017 when he was first fit with scleral lenses. There were no changes in the cornea overall except for those already noted at the apex. Figure 2 shows the mild opacification, which is difficult to observe from the front with white light.

Evaluation of the Scleral Lens Fit

The previous scleral lenses from 2017 and 2020 had an optimal corneal clearance. The central cornea was also thicker at that time (Figure 3) OD and OS. The scleral lens parameters in 2020 were:

OD: Base curve (BC) 44.00D (7.76mm), power –2.75D, overall diameter (OAD) 17.5mm, optic zone diameter (OZD) 13.5mm, sagittal height (sag) 5.439µm

OS: BC 45.00D (7.50mm), power –3.50D, OAD 17.5mm, OZD 13.5mm, sag 5.642µm

The patient arrived for his visit in January 2022 not wearing his lenses. We used his own lens to evaluate the fit OS, which presented touch at the apex. It was clear that keratoconus progression had increased his corneal sag height, so the scleral lens sag was insufficient to vault the corneal apex. We observed the fitting relationship immediately after he applied the lens, as we wanted to see how it fit upon application. Figure 3 shows the same lens as it fit in 2020, and Figure 4 shows how close it now was to the apex OS.

I call this “an excessively perfect fit,” as the lens was contouring the entire cornea very well; but, it was dangerously close to the cornea at initial application, and we know that scleral lens settling will occur over time and that the lens will inevitably touch the cornea.

Corneal Anterior Tomography

Corneal tomography presented more evidence of keratoconus progression and mild opacity at the apex, which was localized to the visual center of the cornea in front of the pupils. The anterior sagittal curvature map (Figure 5) shows that the entire cornea has a curvature that is far from normal or from a regular keratoconus pattern.

The anterior tangential map shows the specific area where the keratoconus apex is located (Figure 6).

The corneal density average reveals the area where we observed a mild opacity, which inevitably compromises his best-corrected visual acuity with his scleral lens (Figure 7).

Discussion

It is unknown whether the mild opacity resulted solely from the lack of corneal biomechanical resistance or whether the scleral lens touch contributed. This may warrant investigation and discussion, as the scleral lens does not move, but the lens was exerting force against the apex. The patient also was asymptomatic. The pandemic restrictions and fear of exposure to COVID-19 were factors that the patient said were reasons why he delayed his follow-up visit.

Our experience with scleral lenses has taught us that the scleral lens shell offers protection against insults to the cornea that may contribute to reducing the biomechanical resistance of the cornea. Especially when larger scleral lenses are used, the higher sag value is more forgiving, as it vaults the cornea even after hours of scleral lens wear.

Conclusion

We refitted this patient with the following scleral lens parameters:

OD: BC 50D x 45D (6.75mm x 7.50mm), power –10.75D, OAD 17.5mm, sag 6.162µm, VA 20/30^-1

OS: BC 52D x 45D (6.49mm x 7.50mm), power –10.50D, OAD 18.5mm, sag 6.395µm, VA 20/25^-1

Figure 8 show the resulting optimal fit OS. We instructed the patient to have more frequent follow-up visits in the next few months to monitor whether progression was still occurring.