Contact Lens Case Reports
OCT Aids in Contact Lens Fitting
BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FAAO
Anterior segment optical coherence tomography (AS-OCT) has proven to be a valuable tool in scleral lens fitting and follow up. The instrument serves two primary functions: 1) it provides sagittal height data of the anterior segment up to a 15.5mm chord, and 2) it provides visualization and measurement of the fluid-filled space between the posterior lens surface and the anterior surface of the eye.
Historically, OCT instruments that could provide these functions were costly, and their use was therefore limited to research centers only. However, Carl Zeiss Meditec now offers the Anterior Segment Premier Module, which converts its posterior segment Cirrus HD-OCT family into anterior segment devices. The module uses two external lenses: the anterior chamber lens provides a wide-angle view (out to a 15.5mm chord), while the cornea lens provides a high-resolution view of the cornea over a chord of 9.0mm (Figure 1).
Figure 1. The anterior chamber and corneal profile views with the Cirrus HD-OCT.
Clinically, we use the anterior chamber lens to obtain a wide-angle view and measurement of the anterior segment sagittal depth. If the sagittal depth at the 15.0mm chord is 3,850 microns, we add an additional 350 microns for apical clearance and select an initial diagnostic lens with a sagittal height of 4,200 microns.
We then use the cornea lens to measure the amount of central and peripheral clearance with the diagnostic lens. Clinical experience has taught us that scleral lenses “settle” into the bulbar conjunctiva approximately 130 microns throughout the day. However, we have noted significant differences among patients, and settling effects can vary anywhere from 70 to 240 microns.
AS-OCT can be used in the fitting and post-fitting follow up of a wide range of rigid and soft contact lenses. Figure 2 shows the central 9.0mm and the lens edge profile of a daily disposable soft lens. Figure 3 shows a patient wearing a scleral lens with significant apical clearance who has no symptoms of post-lens fogging versus a patient who reports post-lens fogging following four hours of lens wear. Finally, Figure 4 shows the center and edge profile of a custom soft contact lens for keratoconus. CLS
Figure 2. A central (top) and peripheral (bottom) view of a daily disposable soft lens.
Figure 3. A scleral lens patient who has no post-lens fogging (top) and a patient who has symptomatic fogging (bottom).
Figure 4. The central (top) and peripheral edge profile (bottom) of a custom soft lens for keratoconus.
Patrick Caroline is an associate professor of optometry at Pacific University. He is also a consultant for Contamac. Mark André is an associate professor of optometry at Pacific University. He is also a consultant for CooperVision.