EyeWitness Fall 2010 - 28

FEATURE ARTICLE

ABCDE
The ABCs of GPs
Phyllis l. rakow, comt, ncle-ac, fclsa

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About thE Author Phyllis rakow is Director of contact lens services for the Princeton eye Group in central new Jersey. she has lectured throughout the United states and canada, writes for numerous publications, has served on the Board of Directors of the clsa, and is currently on the Board of Directors of the ncle.

lthough GP lenses account for only a small percentage of contact lens fits today in North America, their many advantages make them an attractive option for both new and current contact lens wearers. Rigid lenses offer crisp vision, easy care, longer lens life, lower maintenance costs, and high oxygen permeability. In addition, they provide excellent bifocal and multifocal correction, superior toric designs, and the ability to fit a broad range of regular and irregular corneal topography. Most contact lens candidates, though, exposed to a great deal of soft lens advertising, expect to achieve instant comfort, and request soft lenses even if it means sacrificing the many benefits of GPs.

this tutorial on GP materials, design, and fitting is meant to serve only as a guideline and supplement to hands-on clinical practice, for it is with practical experience that contact lens technicians will develop the specialized skills and expertise that will enable them to become valuable assets to the practices in which they work. Look for Part 2 of this article in a future issue of EyeWitness, which will cover GP follow-up care, troubleshooting, and problem solving.

Selecting the GP candidate Good communication between patient and fitter will discuss the patient’s need or desire for precise visual acuity; occupational and recreational activities; ocular surface anomalies, such as dry eye, GPC, seasonal allergies, and blepharitis; motivation; and willingness to adapt to GPs. Patients who have parents, siblings or friends who wear GPs are excellent rigid lens candidates, as they have role models who can provide encouragement and support during the adaptation period and show them that while comfort may take a little longer to achieve with GPs than with soft lenses, the long-term benefits are far greater. Scientists, mathematicians, and engineers, who are used to precision in their careers, appreciate the crispness that GPs provide. Motivation, though, is not the only issue. Before promoting GPs to a patient, it is important for fitters to compare the patient’s refraction and keratometry readings. The corneal astigmatism and refractive astigmatism must be similar in both degree and axis to avoid problems with residual astigmatism and the need for complex toric designs. Patients with againstw w w. c l s a . i n f o |

the-rule or oblique astigmatism are also more difficult to fit with GPs, as the lenses may fail to center properly or decenter down-and-in or down-and-out with each blink. Other marginal candidates are patients with large pupils, who may experience flare around headlights and streetlights at night when their pupils dilate even further; and patients involved in strenuous occupational endeavors or recreational activities such as contact sports, in which the lenses may displace or even be ejected from the eye. Athletes, pilots, police officers, and emergency workers cannot afford to lose a lens at a critical time, and may be better off with soft lenses, even if it means sacrificing some visual acuity. Patients who want contact lenses for parttime or social wear will also do better with soft lenses, since it is difficult to maintain adaptation to rigid lenses when they are worn only intermittently. GP materials It is only since the latter part of the 1970s that gas permeable materials have been available for the manufacture of rigid contact lenses. Prior to that polymethylmethacrylate (PMMA), a biologically inert material, that offered good optics, easy care, and ease of manufacture was used, first for scleral, then for corneal contact lenses. However PMMA transmitted no oxygen to the cornea; what little oxygen the cornea received was strictly through the tear exchange. Most patients developed some degree of corneal edema, with changes in corneal topography, overwearing abrasions, and long-term effects on corneal health and integrity. One of the early gas permeable materials, and one that is still being used today, was silicone acrylate (SA), which was produced by the copolymerization of silicone and methylmethacrylate. The greater the silicone content, the higher the
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EyEWitnEss FALL 2010

EyeWitness Fall 2010

Table of Contents for the Digital Edition of EyeWitness Fall 2010