Avoiding a Speedbump

Keratoconus is a noninflammatory disease characterized by progressive thinning and steepening of the cornea.¹ A surgical procedure that is sometimes employed to flatten the cornea in patients with mild keratoconus is insertion of intrastromal corneal ring segments (ICRS). Some surgeons use ICRS in conjunction with corneal crosslinking (CXL) in the hopes of flattening the central cornea and arresting any further ectasia.² Contact lenses are often still required to improve BCVA after ICRS implantation; however, depending on the position of the segments, fitting may be more difficult due to induced irregular elevation of the cornea secondary to the implants.^3,4

CASE EXAMPLE

A 25-year-old White male with significant ocular history of bilateral keratoconus presented for his annual contact lens examination without complaint. The patient had a significant ocular surgical history, having had ICRS inserted in his left eye 6 years earlier and CXL performed in both eyes. He reported using olopatadine HCl 0.2% (Pataday Once Daily Relief, Alcon) in both eyes. His posterior ocular health examination was unremarkable, and he reported good systemic health and no systemic medication use.

The patient’s presenting scleral lenses had shallow tear clearance centrally in both eyes. In the left eye, there were areas of inadequate vault, causing the lens to touch the cornea over the patient’s ICRS in the 6:00 clock position midperiphery. With OCT, the fit of the scleral lens in his right eye had 90 µm of central clearance, and the lens in his left eye had 109 µm of central clearance, with corneal touch inferiorly and in the periphery (Figure 1).

The patient’s right cornea displayed mild central striae consistent with keratoconus (Figure 2) and embedded ICRS in the mid-stroma from the 2:00 to 7:00 clock positions in the left eye (Figure 3). Upon removal of the patient’s habitual scleral lenses, the cornea in his left eye had epithelial disruption in the 6:00 clock position midperiphery, which stained with sodium fluorescein (Figure 4). The conjunctiva was white and quiet, the cornea was free from infiltrates, and the anterior chamber was quiet in both eyes.

Slit-lamp examination of the habitual scleral lens on the left eye, corroborated by OCT evidence, indicated that the lens was touching the area of corneal epithelial defect. The area of touch likely led to rubbing of the inferior cornea and subsequent development of the epithelial defect seen upon examination. ICRS implants can often make contact lens fitting more difficult due to the raised and irregular cornea in the areas of insertion.⁵ Of note, the area of touch occurred over an anteriorly placed aspect of the ICRS.

A new scleral lens fitting was performed in-office with the goal of better matching the patient’s corneal shape using a prolate lens in the right eye, and an oblate scleral lens in the left eye. The patient was advised to use nonpreserved artificial tears in his left eye four times daily for a week and to discontinue lens wear in the left eye until his new lenses arrived.

Follow-Up Visits

Over the course of the next two follow-up visits, the patient’s scleral lens fit was refined (Table). At each visit, the patient denied any symptoms of redness, pain, or irritation in either eye since his initial presentation. The patchy epithelial defect found in his left eye at the initial visit was resolved.

DISCUSSION

Several case studies have demonstrated that superficially placed ICRS can be associated with epithelial breakdown of the cornea.^5,6 Ferrer et al proposed that this phenomenon may be secondary to the ICRS reducing diffusion of nutrients to the epithelium, resulting in epithelial defects. This differential diagnosis may be ruled out in this case, however, as the epithelial defect seen upon initial presentation in the left eye did not continue to present at subsequent visits once proper scleral lens clearance was established.

Scleral lenses are designed to vault the cornea, land on the sclera, and maintain a fluid reservoir between the corneal surface and the lens. Rigid gas permeable scleral lens designs may be employed to improve vision and comfort in patients with corneal ectasias and irregularities. As with other rigid lens designs, these lenses provide superior optics by creating a smooth refracting surface. Although new materials have higher oxygen permeability, it is important to fit the lenses to vault the cornea without an excessive tear reservoir, as this limits oxygen permeation to the ocular surface. To prevent induction of a hypoxic state, it is calculated that scleral lenses should be made of the highest Dk materials available and vault the cornea no more than 200 µm to 250 µm centrally once the lens settles.⁷

A major consideration when fitting scleral lens designs is the nature and location of the corneal irregularity and elevation. It should be noted that it is often difficult to achieve even corneal vault, and that in such cases, concessions must be made between minimal and excessive tear vault in different areas of the cornea. Choosing an appropriate lens design will aid in achieving a more even fluid reservoir across the cornea. A prolate design, in which the central base curve is steeper than the peripheral curves of the lens, is most appropriate in cases of central steepening and elevation. In contrast, an oblate, or reverse-geometry design, is more suitable when the elevation and steepening is in the peripheral corneal, such as in the case of pellucid marginal degeneration, or in this patient’s case, where the ICRS created additional elevation and steepening in the peripheral cornea.

TAKEAWAYS

In situations where there are multiple points of differing corneal elevation and steepening, it is especially important to consider mechanical aspects of contact lens fitting and potential risks to the patient. Although rigid scleral lenses help patients achieve excellent vision and comfort, little is known about their long-term effects on corneal health; therefore, patients should be monitored.⁸ Patients with ICRS should also be followed closely, as extrusion, neovascularization, and epithelial defects have been linked to the implants.^6,9,10