Maximizing Vision: Managing Underachieving Scleral Lenses
BY MARIA K. WALKER, OD, MS, & DAVID A. BERNTSEN, OD, PHD, FAAO
The vision and comfort achieved with scleral contact lenses are often unmatched by other specialty lens options. But despite their often-remarkable outcomes, there are occasions in which vision with a scleral lens does not meet expectations. Many causes of suboptimal vision with scleral lenses are manageable; recognizing and remedying these causes before accepting “good enough” acuity can maximize the benefits of this modality.
Residual astigmatism can result in visual distortions, ghosting, and a poor endpoint on spherical over-refraction. When present, residual astigmatism originates either from the crystalline lens or from contact lens flexure, the latter of which can occur in 10% to 15% of scleral lens wearers (Messer and Edrington, 2011). Lens flexure can be identified using a keratometer, which should provide spherical curvatures when there is no flexure.
If flexure is occurring, increasing the lens center thickness by 0.15mm to 0.20mm is typically sufficient to stabilize the lens (Messer and Edrington, 2011). Other options for reducing flexure include increasing peripheral lens thickness by 0.1mm (Lee et al, 2014), decreasing overall lens diameter (van der Worp, 2010), and designing a peripheral haptic zone (Visser et al, 2006).
If the astigmatism is internal and clinically significant (≥0.75D), a front-surface toric scleral contact lens should be designed. Various manufacturers offer toric scleral lenses. It is important to clarify the fitting technique with laboratory consultants prior to ordering; some toric scleral lenses are fitted using a fitting set to evaluate lens rotation and stability, while others are ordered empirically. If a toric scleral lens is rotationally unstable with the default design parameters, toric haptic zones can be incorporated (if not already) to stabilize rotation (Visser et al, 2006).
Excessive Lens Vault
Minimizing the depth of the scleral lens tear film reservoir is commonly encouraged to maximize oxygen availability to the cornea (Michaud et al, 2012; Compañ et al, 2014; Jaynes et al, 2015; Michaud et al, 2015). Although we do not see clinically significant corneal edema with great frequency with scleral lens wear (Compañ et al, 2014), we must consider it as a potential cause of reduced vision. All scleral lens patients should be carefully evaluated for evidence of and susceptibility to corneal edema. If transient edema is suspected, the highest-Dk lens material possible should be used in manufacturing the lens, wear time should be reduced, and the patient must be monitored closely.
Vaulting the cornea more than 250µm to 300µm can sometimes cause visual distortions and unstable over-refractions that are not related to edema. These patients typically complain of glare (light scatter) and a “fishbowl” effect (to which they usually adapt). Additional complications, such as midday fogging, can occur with vaults greater than 400µm. The goal when fitting these lenses should be no greater than 200µm of apical clearance after settling and as little clearance as possible in the mid and far periphery (i.e., about 20µm after settling) (Tan et al, 2015).
Intermittent blur can be induced by corneal edema, but it is far more likely to result from the accumulation of precipitate matter within the tear film reservoir, colloquially termed midday fogging (MDF; Figure 1) (Caroline & André, 2012; Miller, 2013).
Figure 1. Midday fogging observable using optical coherence tomography imaging (left) and slit lamp examination (right).
Patients who have MDF experience a progressive clouding of their vision. The frequency is variable; some experience MDF several times per day, while others experience MDF on an intermittent cycle. MDF has been associated with dry eye, excessive lens vault, and lens edge tightness (McKinney et al, 2013). The origin of this matter is unknown, although there is evidence of increased esterified cholesterol within the tear fluid in some patients who experience MDF (Walker, 2014). Furthermore, the debris appears to be entering/forming through the perilimbal conjunctiva, where the lens often lands on the ocular surface (Walker, 2014).
More research is needed to understand MDF. In the meantime, the following lens design modifications and handling protocol changes can be tried to manage this condition:
1. Instruct patients to use a preservative-free artificial tear as the application solution, either alone or in combination with standard preservative-free saline.
2. Modify the lens design to reduce (limbal) clearance.
3. Instruct patients to perform an “eye wash” with saline prior to lens application and periodically over the top of the lens throughout the day (every one to two hours) to flush the ocular surface of debris.
Surface Debris and Non-Wetting
One of the most common causes of reduced vision with scleral contact lenses, especially in new wearers, is surface debris or non-wetting (Figure 2). Non-wetting is usually remedied with proper education that scleral lenses are extremely susceptible to oil and debris deposition and must be properly conditioned overnight to preserve surface wettability.
Figure 2. Scleral lens surface non-wetting.
If a patient uses proper cleaning techniques and is still experiencing problems, use of a monthly extra strength cleaner and/or weekly use of a hydrogen peroxide system can be recommended, but the patient should still continue to condition the lenses prior to application.
Due to elevated higher-order aberrations in irregular corneas, these patients often experience halos and glare, which are generally worse at night due to increased pupil size. Evaluating the position of the lens and the optical center in relation to the pupil can help determine whether the optic zone of the lens can be increased to reduce symptoms.
If the glare/halos remain severe at night, you can prescribe 1 drop 0.15% brimonidine to be taken 30 minutes prior to the visually-demanding activity (i.e., driving) to reduce pupil size (Chaglasian and Autry, 2012; Thordsen et al, 2004; Edwards et al, 2008).
Future Applications of Scleral Lenses
Scleral lenses provide eyecare practitioners with an opportunity to offer superb vision and comfort to patients who have corneal disease, and the modality continues to expand as ideas and technology advance. Research at the University of Rochester and the University of Houston on incorporating higher-order aberration correction into scleral lenses to improve vision in keratoconus (Sabesan et al, 2013; Marsack et al, 2014) will further increase their utility.
As practitioners, while we work with the current technology to optimize patients’ visual experience, we can look forward to continued advancement of this remarkable modality. CLS
For references, please visit www.clspectrum.com/references and click on document #240.
Dr. Walker is a clinical instructor and PhD candidate at the University of Houston College of Optometry. You can reach her at email@example.com. Dr. Berntsen is an associate professor at the University of Houston College of Optometry. He has received research funding from the Johnson & Johnson Vision Care Institute and Alcon.