Article

PRESCRIBING FOR ASTIGMATISM

IMPROVE COMFORT AND VISION IN BOTH EYES

A common challenge that we face in contact lens evaluations is improving the comfort of patients’ contact lens wear. Thankfully, we have many options in contact lens and ocular surface technology to remedy that hurdle. However, one specific challenge that is difficult to fix—even with the best advancements available—is the case of a patient who needs different lens options for each eye, (e.g., a spherical soft lens for one eye and a toric soft lens for the other). No matter how perfect the fit, vision, and lens material may be, the spherical lens is just going to be more comfortable most of the time.

What approaches and techniques can we use to support our patients’ desire to have the best comfort and vision?

Cornea Size and Shape

Sagittal depth is a buzzword in contact lenses that isn’t just for scleral contact lenses. We need to be aware of a patient’s corneal diameter and depth to provide a lens that has adequate draping over the limbus. To achieve rotational stability, deeper corneas need a larger lens diameter, even when they have an average horizontal visible iris diameter (HVID). Lenses that are too shallow or too small in diameter will move significantly with the blink, spin freely, and may show edge fluting. There are daily disposable toric lenses available up to 15mm in diameter to accommodate large and deep corneas.

Toric Stabilization Designs

Each lens manufacturer has its own “secret sauce” when it comes to toric stabilization design. Some toric lenses use prism ballasting—either at the 6 o’clock position using the lower lid for balance or using a modified prism ballast—while others utilize different techniques for stabilizing the lens on or between the lids. Having knowledge of the design can be helpful in cases in which patients report lens awareness. If they are most aware in the area of the lens that holds the ballast (usually a thicker portion of the lens), consider switching the design to relieve the sensation in that area.

Care Systems Make a Difference

Practitioners have been taught that hydrogen peroxide care systems are the gold standard recommendation for their contact lens patients. That still holds true for those who have chemical sensitivities. However, solutions with wetting agents have been shown to improve comfort and vision quality during contact lens wear (Yang et al, 2012). Because some patients who have astigmatic refractive errors are not yet able to use daily disposable lenses due to their axis or higher astigmatism, practitioners need to be aware of how care systems can maximize their wearing experience.

High-Def Vision and Comfort

Obtaining the very best vision is beneficial when practitioners are attempting to maximize comfort of a toric lens. First, clearer vision in a well-fitting, stable toric lens is going to lead to less eye touching or lens adjusting by the patient. In the current times, hygiene is of the utmost importance to protect patients’ ocular and overall health. Second, several studies have reported that when visual acuity decreases, ocular surface discomfort increases (Purves et al, 2001), despite the neurological lack of interaction between vision and ocular surface sensations (Basuthkar Sundar Rao and Simpson, 2015). Therefore, be sure that a toric lens has been evaluated and adjusted for both over-refraction and lens rotation findings before encouraging a patient to go home and just adapt. CLS

For references, please visit www.clspectrum.com/references and click on document #297.