Specialty Lens Fitting in Advanced Keratoconus

The most challenging fits are those for patients who have irregular cornea conditions. In our experience, the advanced keratoconus and post-penetrating keratoplasty corneas are the most common and challenging fits. In this column, I will examine advanced keratoconus, especially those patients who have thin corneal apex. The image shows a scleral lens fit in a keratoconus patient who has a visible nebula at the corneal apex.

Specialty Lens Approach in Advanced Keratoconus

Back in 2002, most practitioners only had specialty GPs for fitting keratoconus, and many contact lens labs had their own designs. A few years later, scleral lens with high-oxygen-permeability became available and since then its popularity has grown. The principal advantage of scleral lens fitting for keratoconus cases is that the lens vaults the overall cornea and rests on the scleral conjunctiva. However, some scleral obstacles require a special haptic design goes around or above it. Additionally, eyes that have high toricity also require adjustments to adjust the haptic to the different scleral angles.

Patients who have a small palpebral fissure may not be able to apply a scleral lens, and most will prefer another option like a specialty GP lens fitting. Specialty GP lens designs can be manufactured at a diameter up to 12.6mm as the GP blank has a 12.7mm diameter. The problem with GPs for patients who have advanced keratoconus is that to achieve corneal clearance and a higher sagittal height (sag), the lens design must have a steeper posterior central base curve (BC). In high advanced cases, this may not even be possible, and the patient may need a corneal transplant. There are some labs that can manufacture steeper designs that can reach up to 75D (4.50mm radius).

Back in 2004, we only had a GP keratoconus design up to 65D (5.19mm radius) available; however, we could manage even higher sag values increasing the optical zone and overall diameter. In 2005, because of a need for a few demanding cases, we developed an even steeper BC up to 75D. In 2006, we began manufacturing the first scleral lens prototypes. At that time, the main need for scleral lenses were for some high irregular post-graft patients that had manual penetrating keratoplasty and, after corneal stabilization, they had irregularities that were present as high anterior elevations all around the graft.

Some patients with successful long-term GP lens fitting sometimes reject the suggestion to try scleral lenses, even when they present with highly advanced keratoconus with thin thickness corneas. In this case, we manage to customize the GP lens in a way that we could offer the best possible fit.

The Specialty Lens Fit Challenge—Examples

Case One This patient was fit with scleral lenses because both corneas presented with a nebula that also created a dot elevation (Figure 2a). He presented with this condition since his first visit with us back in 2000. My father, Saul Bastos, MD, used to cauterize the lesion and smooth the surface so he could wear corneal contact lenses. The problem is that this condition was recurrent, every four months the tissue would grow again. In this case, the patient was successfully refitted with scleral lenses. Figure 2b shows the same eye, right beside the nebula, the posterior keratoconus, and the thinning.

This case requires that the vault over the cornea should prevent scleral lens touch after the lens settles. The images were taken four hours after application. The sagittal curvature map (Figure 3a) reveals the advanced keratoconus; on the average corneal density map (Figure 3b), it is possible to correlate the nebula in black with the image from the Scheimpflug image (Figure 4).

Case Two Patients who have advanced keratoconus and small palpebral fissures and who wear GP lenses usually have a higher sensitivity to light (photophobia). In addition, their upper lids generally will position right over the pupil. This is one of the reasons that these patients are not ideal candidates for scleral lens fitting, especially if they already have already worn GPs for years without complications. These patients also tend to keep their superior lids halfway down because this generates a small improvement on visual acuity (Figure 5). One rule of thumb in these cases is that the best fit is the one that provides an improvement of visual acuity, maintains the corneal physiological health, and is the most comfortable.

These patients present the following signs:

• Increased sensitivity to light (photophobia;
• Steeper anterior curvature from the apex and mid-periphery cornea;
• These corneas tend to present small nebula at the apex;
• Visual acuity obtained generally will reach from 20/60 and up to 20/30;
• Difficult to obtain sharp images as these patients tend to move and squeeze the eye due to the slit lamp light beam.

In this case of a long-term patient who wore GPs for about 40 years, the best possible fit was not what we wanted, but it was what was possible to achieve. And he was quite satisfied with the result. His OD had the most severe keratoconus condition (Figure 6). The GP lens parameters OD was: BC 74 x 50, power of –27.75D, overall diameter (OAD) 9.8mm, an optical zone of 6.0mm and made in the Optimum Extra material with a Dk of 100.

Even though there is excessive fluorescein at the periphery and the lens eventually touched the lower lid may induce air bubbles under the lens. Note that the bubbles immediately disappeared after blinking and, fortunately, the lens remained stable and did not fall or dislodge. In Figure 7, you can observe the slit lamp cross-section view. We used a very steep, customized secondary BC of 50D and a steeper aspheric periphery. Visual acuity reached 20/30^-2, which is excellent in this case. It is very important to instruct the patient who has high advanced keratoconus to avoid eye rubbing.

The Pentacam image presents the map of the anterior sagittal curve (Figure 8a) with a 76.5D as the peak, however, we need to pay attention the immediate surrounding area to initial trial lens. The cornea has a minimum thickness point of 271mm, which can be noted on this map. Also, the Scheimpflug image (Figure 8b) reveals the thin central area at the apex.

Conclusion

This column presents a case in which a GP lens was not an option due to the salient central scar. It also addresses another case in which scleral lenses were not an ideal option due to a small palpebral fissure and because the patient has worn GPs for a few decades. Most practitioners would recommend the second patient for a corneal transplant.

In our everyday practice, we need to have both options and a good specialty lens trial lens set for both GPs and scleral lenses.

Mr. Bastos is the director and clinical instructor of specialty contact lenses at the Instituto de Olhos Dr. Saul Bastos (IOSB) and is the director and specialty lens consultant of Ultralentes, a small laboratory specializing in GP and scleral lens designs in Porto Alegre, RS, Brazil.