Gregory W. DeNaeyer OD FAAO FSLS
Keratoglobus is a subtype of keratoconus in which the entire cornea becomes ectatic. These patients are notoriously difficult to fit with (R)GP lens designs because their corneas have extraordinary amounts of sagittal depth. Corneal (R)GP lenses are often unstable and will commonly eject off the eye. Mini-scleral lenses and hybrid lenses usually don’t have enough sagittal depth to adequately vault the corneal surface. In fact, large, full-scleral lenses are usually required to successfully fit the keratoglobus cornea.
A 56-year-old male patient presented with keratoglobus of his left eye (figure 1), which had previously undergone a penetrating keratoplasty. He was wearing a hybrid contact lens that exhibited fluting of the soft skirt secondary to an excessively flat fit (figure 2). The patient’s vision with glasses over his hybrid contact lens was 20/40.
The patient was refit with a full scleral lens. A diagnostic scleral lens with a diameter of 18mm and base curve of 54 diopters exhibited central clearance but mid-peripheral corneal touch. A series of 20mm scleral lenses with base curves of 52, 54 and 56 diopters were then evaluated. The 20mm, 52-diopter lens exhibited mid-peripheral touch (figure 3), while the 54-diopter and 56-diopter lenses vaulted the entire corneal surface.
The amount of vault with the 54-diopter lens (figure 4) seemed inadequate considering that the lens would settle over time, but the 56-diopter lens (figure 5)seemed to vault excessively.
Based upon those observations, a 20mm scleral lens with a 55-diopter base curve was ordered and dispensed (figure 6). The final power of –22.50D gave the patient 20/30 vision.
Discussion figure 3
Successfully fitting keratoglobus requires lenses that will vault large amounts of sagittal height. Using full sclerals with diameters of 20mm or greater are generally required to achieve adequate vault. Scleral lens designs that have large optic zones and a reverse curve will help attain additional sagittal depth and mid-peripheral clearance.
In this case, the 20mm scleral design that was successful for this patient had a 10mm optic zone and a 4-diopter reverse curve. The overall sagittal height of the scleral lens was 7.84mm, or 7,840 microns.
Greg DeNaeyer is a 1998 graduate of The Ohio State University College of Optometry. He completed a hospital based residency at the Columbus VA Medical Center. Greg joined Arena Eye Surgeons in 1999 and is currently the Clinical Director. His primary interest is specialty contact lenses.
Greg is a boardmember of the Scleral Lens Education Society and is a Fellow of the American Academy of Optometry. He is a contributing editor for Contact Lens Spectrum and a contributor to Review of Cornea and Contact Lenses and Optometric Management. Currently his primary research is focused on profilometer designed scleral contact lenses, scleral lenses that correct higher order aberrations, and topical drug delivery devices. He has consulted for Visionary Optics, Essilor, Inspire Pharmaceuticals, B+L, and Aciont.