CONTACT LENS DESIGN & MATERIALS
DON’T FORGET ABOUT PATIENTS’ VISION
GREGORY J. NIXON, OD, FAAO
Based on most new contact lenses touting enhanced moisture retention properties, I think it’s safe to say that we are practicing in the contact lens era in which comfort is king. While comfortable contact lens wear is most certainly an important variable that impacts proper lens selection, we shouldn’t lose sight of the need to maximize our patients’ vision. As eyecare professionals, we should always strive to give our patients the best possible contact lens experience in both comfort and vision.
Not All Spherical Lenses Are Created Equal
Even though soft spherical contact lenses have only a single power noted on the lens package, that certainly doesn’t mean that all lenses labeled with the same power provide the same optical effect. Many contact lenses labeled as spherical lenses actually have an aspheric optic zone. This asphericity can reduce the impact of aberrations and may help mask some blur from low degrees of uncorrected astigmatism (up to –0.50DC). In my experience, many patients who need higher myopic powers (>9.00DS) have a tendency to note improved overall visual clarity in lenses with aspheric optic zones.
Additionally, optic zone size can have a significant impact on visual performance. Patients who experience nighttime blur or glare from nocturnal pupil dilation, as well as those who have a naturally large daytime pupil size, can benefit greatly from a larger optic zone. Optic zone size is not a parameter that we often think about when selecting a soft lens. However, there are published guides of contact lens listings that currently list a number of commercially available soft lenses with an optic zone size of up to 9.0mm.
Correct Your Low Astigmats
We are blessed with a variety of readily available toric contact lens options in nearly every refractive parameter and in every replacement modality. The reproducibility of these lenses offers predictable, stable lens fits that can provide your astigmatic patients with clear, consistent vision without fluctuation. Take the time to demonstrate these options to your low astigmats who have only 0.75DC to 1.00DC. Providing a clear, distinct optical image for each meridian can make a significant improvement in overall image quality.
GPs Still Play a Role
While many practitioners consider GP or scleral lenses only for highly irregular or diseased corneas, traditional GP lenses still offer considerable optical clarity for normal corneas that have higher degrees of refractive error, especially higher astigmatism. When a patient has ≥2.50D of corneal toricity, a bitoric GP contact lens can be easily designed to provide the ultimate fit that positions well on the eye with little impact from lens rotation. Plus, a bitoric GP will dramatically reduce issues of spectacle blur compared to a spherical GP fit on a higher-toric cornea.
The complexities of designing a bitoric lens have been minimized by a number of readily available resources. An easy-to-use online lens calculator is available at www.gpli.info/lens-calculator. Additionally, the consultants at your GP lab are a great resource to help with designing bitoric lenses.
Embrace Your Role
We should relish the opportunity to provide our patients with the best vision possible. When choosing a contact lens, we should devote just as much concern to the optical design as we do to the material for the best overall performance. CLS
Dr. Nixon is the associate dean for Clinical Services and professor of clinical optometry at The Ohio State University College of Optometry. He is also in a group private practice in Westerville, Ohio. You can reach him at email@example.com.