Here’s how these maps can be used in myopia control.

Myopia control remains a hot topic among optometrists and patients, especially as the prevalence of myopia continues to increase. Consider: There are 34.1 million Americans who are myopic today, according to the National Eye Institute, and the number is expected to reach 39 million by 2030. That means we can expect more patients to ask us about how to limit its progression.

This subtractive map shows a “smiley face” pattern. This is caused by a lens that is riding too high, causing superior corneal flattening.

Multiple studies have been conducted to determine what steps may be taken to do so. Unfortunately, some of these studies show limited potential or conflicting results. One of the more promising treatments for myopia control is the use of orthokeratology (ortho-k) lenses.

A Crucial Step
Corneal topography becomes a crucial step in determining the correct lens parameters for our patients. Corneal mapping allows us to evaluate important corneal characteristics necessary for an optimal contact lens fit. We can actually evaluate thousands of corneal data points on a single map.

Important factors when determining the ideal candidate for ortho-k lenses are corneal steepness and eccentricity. Patients with steeper corneas and high eccentricity tend to make the best candidates.

Using corneal mapping to look at the distribution of power becomes important when fitting patients for myopia control. The hypothesis is that ortho-k lenses reduce myopia progression by increasing myopic defocus of the peripheral retina. Peripheral myopic defocusing is essentially creating an add power for the patient. This peripheral defocusing is thought to play a role in slowed progression of axial length.

An Example
In our practice, we use the E300 Corneal Topographer from Medmont (and distributed in the United States by Nidek, Inc). The E300 analyzes 102,000 corneal points with a standard deviation of error of less than 2 microns and is capable of measuring the cornea from limbus to limbus.

On the current model, data can be extrapolated out to 17mm. This provides excellent mapping for optometrists fitting specialty contact lenses. Map analysis and display can be customized by the user with up to four images shown per screen.

The E300 allows the user to compare pre- and post-treatment eyes using subtractive maps. These maps allow the user to monitor change in dioptric power, treatment zone position, treatment zone size and lens position.
In addition to being used for fitting contact lenses, the E300 can also be used to evaluate dry eye by measuring tear break-up time with 94% specificity and 82% sensitivity. The E300 by Medmont does have the ability to be integrated into current practice management systems utilizing Medmont Studio.

Christopher Lehman, OD, practices with Clompus, Reto & Halscheid Vision Associates P.C. in West Chester, PA.


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