contact lens primer
Post-RK Contact Lens Care
BY TIMOTHY B. EDRINGTON, OD, MS, FAAO, & JOSEPH T. BARR, OD, MS, FAAO
Many post-radial keratotomy patients could benefit from contact lens wear. Uncorrected refractive error, need for near and intermediate distance correction, fluctuations or drift in refractive error and corneal distortion are common reasons RK patients patients to seek post-surgical contact lens care.
The Role of Soft Lenses
If the patient's RK incisions extend to the vascular-rich limbus, soft lenses are generally contra-indicated due to possible neovascularization along the incision lines. If the incisions do not extend to the limbus, soft lens wear may succeed if the manifest refraction is stable (repeatable at different times of the day and on different days) and vision is acceptable. Carefully monitor neovascularization during follow-up examinations. Also, look for areas of corneal staining, especially centrally, to rule out poor lens draping over the entire corneal surface. If a soft sphere provides acceptable and consistent vision, consider prescribing a silicone hydrogel to optimize oxygen availability. For soft torics, consider a reduced wearing schedule and frequent follow-up exams to minimize and monitor corneal edema and neovascularization.
The Role of Corneal Topography
Perform corneal topography before fitting post-RK patients with contact lenses. Topography provides both baseline findings for comparing corneal changes over time and enhanced understanding of corneal contour and curvature values for selecting an initial diagnostic rigid lens.
Figure 1. Alignment fitting reverse geometry lens on a
Rigid Lens Design
Prescribe the simplest rigid lens design that will optimize vision, comfort and corneal physiology. Consider prescribing a sphere if it provides adequate lens centration with no localized areas of excessive (central or peripheral) clearance or harsh mid-peripheral bearing. Pre-operative keratometry values may help you select the initial diagnostic base curve. You might start with the base curve equal to or slightly flatter than the pre-surgical flat K value. Overall diameters of 9.50mm or greater enhance lens centration.
Because of resulting central flattening, many post-RK patients benefit from wearing reverse geometry lenses. It is generally necessary to empirically order the first lens. Use topography curvature values to determine both the base and peripheral curves. One method is to average the central flatter values using the topography number maps to determine the base curve, then average mid-peripheral curvature findings to determine the steeper secondary curve. Fine tune the lens design by interpreting the fluorescein pattern. The goal is to align with the corneal contour (Figure 1) by minimizing localized areas of excessive clearance and harsh touch. Interpret the area of central cor-neal flattening by topography to determine the optic zone diameter. Typically optic zone diameters for post-RK reverse geome try lens designs are prescribed smaller (6.0mm to 7.0mm) than standard optic zone diameters.
OK, That Didn't Work
Corrective photorefractive keratectomy (PRK) remains an option if the refractive error is stable and if manifest refraction vision is acceptable.
Post-RK corneal contours often require creative lens designs. If rigid lenses decenter excessively, consider large overall diameter, aspheric, piggyback and other designs. Always closely monitor corneal staining and neovascular changes to determine the acceptability of any lens design.
Dr. Edrington is a professor and in the contact lens service at the Southern California College of Optometry. E-mail him at email@example.com.
Dr. Barr is editor of Contact Lens Spectrum and assistant dean for clinical affairs at The Ohio State University.