EyeWitness Fall 2010 - 4

FEATURE ARTICLE

A GP Multifocal Primer
Jason Jedlicka, oD, faao

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About thE Author Dr. Jedlicka completed a contact lens residency at Pennsylvania college of optometry in 1997 and an ocular Disease fellowship in 1998 at minnesota eye consultants. He is the Director of the contact lens service at the University of minnesota, Department of ophthalmology, and the managing Partner of consultative eye care, a referral practice in the minneapolis area. He is a clinical adjunct faculty member for Pennsylvania college of optometry and illinois college of optometry.

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Figure 1. Aspheric lens design

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Figure 2. Concentric lens design

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Figure 3. Translating lens design

Fitting multifocal GP lenses can be a rewarding experience for you and your patients. Many people over the age of 40 desire to have good vision without glasses, but few are willing to step up and take on the challenge. Learning the pros and cons of each lens type, learning what lens designs would be best for each patient based upon their individual ocular measurements, choosing the best design and knowing how to adjust the fit to optimal results can make for happy patients that will send all their friends and colleagues to you.

itting GP contact lenses for our prepresbyopic patient population can sometimes seem like a “hard sell.” The main reason is that we can often correct the vision acceptably with soft lenses when the fit is otherwise straight forward. However, as our patients begin to experience loss of accommodation, the affects are two-fold: they tolerate less imperfection in their visual correction and they can no longer see things at close distances. Both of these changes should drive us to reconsider GP lenses for many in the “Over 40” population. GP lenses for presbyopia can be fitted in different forms. Single vision lenses can be used in conjunction with reading glasses or as monovision. Multifocal lenses can be used in a multitude of fashions, with lenses set to equal correction or modified to enhance near, intermediate, or distance vision in one eye or the other. In the pages to come, we will focus our attention on the GP bifocal and multifocal lens options that exist today, patient and lens selection, and the basics of how to fit them. Multifocal contact lenses work by having a change in prescription occur over the surface area of the lens. This can either be a straight change from one power to another power, or a progression of power. In the first part of this article, we will differentiate the basic types of lens design. How well the lens designs will work depends on the size and shape of the eye they are being fit to as well as the lid
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position and tension. It also depends on the visual demands of each patient. Part two of our discussion will focus on choosing the right lens for individual types of patients. Finally, once we understand the lens options and how to select for each patient, we will cover the basic strategies for fitting each type.

Types of Multifocal GP lenses
We can generically consider GP multifocals to fit into one of 3 categories: aspheric, concentric, or alternating (translating). To avoid confusion, we need to be clear that all of these lenses may exhibit some degree of translation when fit properly, and that a translating DESIGN is specific to the alternating vision category. So when we discuss “lens translation,” we are indicating that there will be some degree of movement of that lens in the north-south direction. When we discuss translating designs, we are specifically referring to the alternating genre of lenses. Aspheric lenses use a variable rate of curvature across the lens surface to achieve a change in power. This results in one area of the lens having the distance correction, one area having the near correction, and a progression of power between zones to allow for distance, intermediate, and near vision (Figure 1). In a typical back surface aspheric GP multifocal, the steepest part of the lens is in the center, and the lens flattens as you move out in any direction toward the edge. This
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Table of Contents for the Digital Edition of EyeWitness Fall 2010