Patients with a history of radial keratotomy (RK) surgery often experience visual dissatisfaction from irregular astigmatism and unstable refractive error. RK was first introduced in the United States in the 1980s. Popularized by Dr. Svyatoslav Fyodorov in the former Soviet Union in 1974, RK was believed to be a long-term solution for myopia, but the number of procedures performed has greatly diminished due to unsatisfactory long-term results and the advent of laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) surgery. However, as post-RK patients continue to develop hyperopic and astigmatic shifts decades after surgery, many are still seeking stable refractive options.
Patients often experience diurnal refractive shifts with long-term increases in hyperopia and astigmatism. Fluctuations in intraocular pressure (IOP) and subsequent changes in corneal curvature are thought to be responsible for those changes. Approximately 60% of patients in the Prospective Evaluation of Radial Keratotomy (PERK) study cohort experienced diurnal fluctuations at the 10-year follow-up visit (Kemp et al, 1999).
While the gradual increase in hyperopia is not well understood, peripheral corneal ectasia and compensatory central flattening are speculated to play a role. RK incisions never fully heal and may increase in width over time, so refractive shifts are widely variable due to biomechanical instability of the cornea (Chhadva et al, 2015).
Contact Lens Options
Soft Lenses Similar to spectacle correction, soft lenses generally do not provide adequate correction of diurnal visual fluctuations. However, for patients who have mild-to-moderate refractive shifts, different soft lens prescriptions can be prescribed for different times of the day. Multiple refractions are necessary to evaluate diurnal variation and day-to-day refractive consistency. Due to large amounts of astigmatism, brands offering extended cylinder ranges should be considered. High-Dk materials are also recommended due to the tendency of patients to develop neovascularization within incisions (Figure 1).
Corneal GP Lenses GP lenses mask irregularities and fluctuations in corneal curvature and can provide more stable and crisp visual correction. High amounts of corneal astigmatism can also be corrected without concerns of lens rotation and diurnal changes in topography. Due to central flattening from RK incisions and resulting oblate corneal topography, a reverse geometry design is often required. Larger-diameter intralimbal lenses (>10.5mm) may be needed to enhance lens centration and reduce lens ejection.
Scleral GP Lenses These lenses may be the best visual solution for patients who have intolerance to corneal GPs, issues with lens ejection, or severe corneal ectasia. As with corneal GPs, a reverse geometry design is often needed to properly vault the oblate cornea. Patients should be carefully monitored for corneal staining. As previously stated, high-Dk materials are indicated due to the risk of incisional neovascularization. Scleral lens patients who are prone to conjunctival prolapse may be at higher risk of developing neovascularization. CLS
For references, please visit www.clspectrum.com/references and click on document #257.