Contact Lens Case Reports
Managing Height Differentials with Scleral Lenses
BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FAAO
A 46-year-old female underwent a corneal transplant to her left eye to correct a severe post-LASIK ectasia. Postoperatively, the patient had failed with numerous corneal and piggyback lenses and was referred to our clinic for a scleral lens fitting. Optical coherence tomography (OCT) imaging of the patient’s left eye showed significant surface irregularity and a bulge to the graft, with a sagittal height at 15.0mm of 4,300 microns; the average sagittal height of a normal eye at 15.0mm is 3,735 microns. Figure 1 shows the slit lamp appearance at the time of the initial evaluation. Figure 2 shows the axial (power) and the elevation (height) displays of the left eye. In the April 2015 issue, we stated that if the height differential along any given meridian exceeds 350 microns, the patient may be a better candidate for a scleral lens design. In this patient, the height differential was 485 microns.
Figure 1. The patient’s post-surgical bulging graft results in a significant sagittal height—4,300 microns.
Figure 2. The axial (power) display map and the elevation (height) display map showing a 485-micron differential in corneal height.
The patient was fitted with an ICD 16.5 scleral lens from Valley Contax with a sagittal height of 4,700 microns (400 microns higher than the baseline OCT sagittal depth). Figure 3 shows the fluorescein pattern of the initial diagnostic lens. It is easy to see the area of slight fluorescein thinning in the area of the peripheral cornea and the geographic area of near “touch” at 3 o’clock. This is a common finding when fitting patients post-keratoplasty, in which the peripheral cornea is higher than that of normal eyes. In lens designs that incorporate tangent angles in the periphery (rather than radii of curvature), the additional peripheral clearance is created by increasing the peripheral corneal clearance angle 5º to 10º. In scleral lenses, tangent angles work like a drawbridge raising the lens over corneal areas with increased tissue elevation.
Figure 3. The fluorescein pattern of the initial diagnostic lens with inadequate peripheral corneal clearance and the final lens with the 5º, 125-micron increase in peripheral clearance.
Many manufacturers incorporate two tangent angles into the lenses’ periphery—one designed to create clearance across the peripheral cornea and the other across the limbus. A 1º change in the angle (a +1 change) increases the sagittal height of the lens by approximately 25 microns. Most clinicians work in +5º steps, which results in a sagittal height increase of 125 microns.
In this case, we ordered a lens with a sagittal height of 4,700 microns, –15.75D power, 16.5mm diameter, +5 peripheral corneal clearance curve, and a standard limbal clearance curve and scleral landing zone. The patient’s visual acuity was 20/25. She enjoyed excellent comfort and all-day wearing time with the lens. CLS
Patrick Caroline is an associate professor of optometry at Pacific University. He is also a consultant to Contamac. Mark André is an associate professor of optometry at Pacific University. He is also a consultant to CooperVision.