The Scleral Lens Vault
Troubleshooting Reduced Vision
BY GREGORY W. DENAEYER, OD, FAAO
Practitioners and patients alike have high expectations for visual results with scleral contact lenses. This holds true whether the scleral lens is used to manage corneal irregularity or for correcting high refractive error. Dissatisfaction can result when the visual results fall below what was expected. Objective and subjective findings will help to troubleshoot causes for reduced vision, which allows practitioners to make modifications that will improve patient satisfaction.
Reduced Visual Acuity
A common reason for reduced acuity with any scleral lens patient is residual astigmatism. This can result from scleral lens flexure if a patient has a toric sclera but is wearing a spherical-back-surface scleral lens. Topography of the lens in-situ will confirm this fitting issue. Refitting the patient with a back-surface toric design should minimize or eliminate flexure. Residual lenticular astigmatism can be corrected with front-surface toricity.
Higher-order aberrations can also prevent patients from seeing perfectly. Residual positive coma from the internal optics and induced coma from static lens decentration can result in diminished visual performance (Sabesan, 2013; Chen, 2008). Adding front-surface higher-order aberration control, when commercially available, has the potential to improve visual acuity for affected patients (Marsack, 2007).
Finally, any corneal scar that is within the visual axis can diminished best-corrected acuity. Corneal transplant can be necessary if a patient is unsatisfied with vision because of opaque scar tissue.
A common complaint of scleral lens patients is “foggy vision” that is often intermittent in nature. The primary causes of this complication are poor surface wetting, reservoir debris, and corneal edema. A careful slit lamp exam is necessary to make a diagnosis.
Poor Surface Wetting The lens surface should have a continuous even tear layer that doesn’t break up between blinks. Non-wetting is often the result of manufacturer error. All sclerals should be plasma treated to help ensure initial wetting. For patients with ocular surface disease, choose materials with relatively low wetting angles. Recommend backup lenses so lenses can be sent away for repeat plasma treatment without interrupting wear.
Reservoir Debris Gaps that form as a result of a scleral lens that lands unevenly can allow debris to be pumped into the reservoir, which can disrupt a patient’s vision. Refitting the patient with a customized back-surface toric from scleral topography can reduce this complication, as the lens will have improved fitting apposition.
Corneal Edema Finally, patients who have full-thickness corneal grafts with reduced endothelial cell counts can develop corneal edema with scleral lens use. Fit patients who have endothelial cell counts above 800 cells/mm2 (Sindt, 2008), and choose materials with ≥100 Dk. Minimizing center thickness and vault will help to improve transmissibility.
When a patient complains of reduced vision with scleral lens use, take a careful history and detailed exam to troubleshoot the etiology. Make modifications as necessary, but make sure the patient’s expectations are realistic. CLS
For references, please visit www.clspectrum.com/references and click on document #244.
Dr. DeNaeyer is the clinical director for Arena Eye Surgeons in Columbus, Ohio. He is a shareholder of Precision Ocular Metrology LLC, has proprietary interest in Visionary Optics’ Europa and Elara Scleral Lenses, and is a consultant to Visionary Optics and Alcon. You can contact him at email@example.com.