Contact Lens Case Reports

Piggybacking Keratoglobus

By Patrick J. Caroline, FAAO, & Mark P. André, FAAO

Keratoglobus is an extremely rare, bilateral, ectatic condition characterized by a limbus-to-limbus thinning of the cornea, most markedly peripherally and often resulting in extreme protrusion of the entire cornea (Figure 1).

Figure 1. Keratoglobus with extreme corneal ectasia and limbus-to-limbus corneal thinning.

The corneal changes in keratoglobus usually begin early in life, with the diagnosis typically made around ages 12 to 16. The condition reaches maximum severity in the 20s to 30s, after which it tends to remain stationary throughout life. The corneal diameter is usually within normal limits and, unlike in keratoconus, in keratoglobus the cornea is more symmetrical (round) and the astigmatism is often more regular (Figure 2). Also, in keratoglobus the corneal eccentricities remain within normal limits at approximately 0.30 to 0.60 (Figure 3) whereas in keratoconus the eccentricities commonly range from 0.80 to 1.60.

Figure 2. OCT images and corneal topographies illustrating the differences between a normal eye and the three primary forms of corneal ectasia.

Figure 3. Patient's topography, note the more regular and symmetrical astigmatism and normal eccentricity.

A Piggyback Fit

Our patient is a 39-year-old male with a longstanding history of keratoglobus. Throughout the years he has experienced moderate success with his large-diameter, steep, aspheric contact lenses, but more recently his wearing time has been limited to 10 hours a day.

We considered two options: piggyback contact lenses and scleral contact lenses. It has always been our philosophy that patients need to “earn” a scleral lens—that is, we like to rule out more traditional contact lens modalities first. Of course, patients who have ocular surface disease are the exception to that rule because scleral lenses serve as their primary optical and medical treatment.

For this piggyback fit, custom soft lenses were required because of the extreme bilateral ectasia. The final soft lens specifications were OD central base curve radius 5.80mm with a 6.00mm radius in the periphery, plano power, and a 14.8mm diameter and OS 6.00mm base curve radius in the center and 6.20mm in the periphery, plano power, and a 14.8mm diameter. The aspheric GP parameters were OD 56.00 base curve, −17.00D power, and 11.0mm diameter and OS 54.00 base curve, −16.00D power, and 11.0mm diameter (Figure 4).

Figure 4. Patient's piggyback lenses.

Today the patient's visual acuities with the lenses are OD 20/40 and OS 20/30—but perhaps more importantly, he experiences all-day comfort with his contact lenses. CLS

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Patrick Caroline is an associate professor of optometry at Pacific University. He is also a consultant to Paragon Vision Sciences. Mark André is an associate professor of optometry at Pacific University. He is also a consultant for CooperVision.