In part one of this two-part series (click here ), I detailed pre-fitting clinical considerations for post-surgical keratoconus (KCN) patients. Part two discusses contact lens selection, as it pertains to these patients.

Contact lens fitting after corneal transplant involves determination of corneal shape, refractive error, and tear film integrity. Contact lens fitting can begin as early as six months after surgery. We can expect to see corneal steepening as the sutures loosen or are selectively removed. Therefore, the patient should be informed that there is a chance fit or prescription changes will occur within the first year.

We are fortunate to have at our disposal increasing parameters and the design options of soft, hybrid, rigid gas permeable, and scleral lenses to meet these patients’ needs. Soft lenses will generally require the most adjustment, as they conform to corneal shape, followed by corneal RGPs, and hybrid lenses. Sclerals, which vault the cornea, will likely not require significant or frequent adjustment.

Soft lenses
Consider soft lenses for patients whose corneal topography is more “regular” and whose best-corrected spectacle vision is in the range of 20/40 or better without significant ghosting. To gauge the severity of irregularity, use a standard keratometer or topographical placido disk image to identify keratometric mire.

Custom soft lenses, available in virtually any prescription or design, can be lathed in hydroxyethylmethacrylate-based (“conventional” polymers) or silicone hydrogel materials, making them comfortable for a variety of patients. These lenses are for daily wear only and are typically replaced on a quarterly or semi-annual basis. Consider the latter for grafts about which neovascularization or low endothelial cell count are concerns.

An additional benefit of soft lenses: They work well in patients who have significant meibomian gland dysfunction or atrophy. This is because non-wetting of RGP materials can be a frustrating problem for patients who have comorbid ocular surface disease, for example secondary to Stevens-Johnson syndrome or other autoimmune conditions.

Fitting tip. Optimizing the tear film addressing lipid layer deficiency and employing punctal occlusion and/or non-steroidal anti-inflammatories drops is a good approach to achieving success with all lens materials.

Hybrids
Recent advances in hybrid manufacturing make these lenses an ideal option for patients who have slight-to-moderate corneal astigmatism and/or mild corneal irregularity. Hybrid lenses can correct up to 6 diopters of corneal astigmatism. Consider this option for grafts which do not exhibit a “steep/flat profile” or are not significantly oblate (“e’ value less than 0) in order to avoid mechanical irritation to the graft-host junction.

The gas permeable center (130 Dk) is surrounded by a silicone hydrogel skirt (84 Dk), optimizing comfort, vision, and corneal physiology.

Fitting tip. As dehydration of the soft skirt and eventual binding due to low GP-skirt junctional clearance (inducing hypoxia) may occur with these lenses, close monitoring is necessary. I recommend the following schedule: one week, then monthly for the first three months, six months post-fitting and semiannually thereafter.

Rigid gas permeable
Rigid gas permeable lenses are for patients who wore them before surgery and/or who have mild-to-moderate corneal irregularity (either prolate or oblate) with mild-to-moderate astigmatism. Consider either small (less than 10 mm diameter or large (intralimbal) designs for grafts with 4 diopters or less (bitoric for more than 2.5 diopters) of corneal astigmatism, and for corneas with eccentricity values between 0.3-0.7) This is because they provide a reduction in higher-order aberrations and high-quality optics. Another benefit: They perform well in patients who have marginal tear film thickness. Unlike for patients who have evaporative dry eye (and therefore are at risk for “lens non-wetting”), my experience is that RGP lenses are often better tolerated than soft lenses in aqueous-deficient dry eyes, as they allow for tear exchange and provide a thin reservoir between the back surface of the lens and the cornea.

Fitting tip. Limit bearing on the graft-host junction to promote adequate tear exchange, and consider corneal shape, astigmatic level and pattern, and interaction with the lids. (See Table 1). Additionally, contemplate reducing the diameter if there is decentration of the lens due to force from the upper lid. Increase the diameter to otherwise improve centration.

Scleral
Scleral lenses completely vault the cornea, facilitating the fitting of a complex corneal shape.

Fitting tip. A central clearance of 200 µm and limbal vault of 50 µm promotes adequate corneal oxygenation.¹ Optimize patient comfort by customizing lens haptics. OM

Table 1

Reference:

1. Michaud L, van der Worp E, Brazeau D, Warde R, Giasson CJ. Predicting estimates of oxygen transmissibility for scleral lenses. Cont Lens Anterior Eye. 2012;35:266-271. doi: 10.1016/j.clae.2012.07.004.