Preventing GP Bevel Plaque
contact lens case reports
Preventing GP Bevel Plaque
BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FAAO
The adherence of debris on GP lenses is a complex biochemical function that surface chemists have struggled with for nearly 40 years. While the inherent reactivity of the plastic plays a major role in the deposition story, other external factors such as manufacturing processes, patient care and handling, and individual tear film chemistry can also contribute.
GP Surface Plaques
While many different contaminants have been identified on the surfaces of GP lenses, i.e. proteins and lipids, perhaps one of the more intriguing forms of deposition is often referred to as GP surface plaque. The exact chemical composition of GP surface plaques has never been identified, but it is suspected that their chemical make-up is similar to other mucous-membrane plaques that accumulate elsewhere on the body, i.e. the teeth. Our scanning electron microscopy studies show the debris to be a multilayered material of varying thicknesses that forms fissures on the lens surface that can be mistaken for scratches or cracks in the plastic. Surface plaques can take on two very different clinical appearances. One is a flat, diffuse, grayish film that often covers a large area of the anterior lens (Figure 1), and the other is a thick, elevated, grayish band in the lens periphery, often referred to as a bevel or peripheral flange plaque.
Figure 1. Flat and diffuse surface plaque on the anterior surface of a GP lens.
Our patient is a 24-year-old female with an eight-year history of GP lens wear. Her spectacle prescription was OD +3.50 −1.00 x 175, 20/25 and OS +3.00 −0.75 x 005, 20/25. Visual acuity with her current four-year-old lenses was 20/25 in both eyes. Slit lamp examination showed that both lenses positioned well and moved well with the blink. Both lenses had a thick, circular bevel plaque at the lenticular junction of the lenses (Figure 2). The patient had noted the buildup on the lenses for approximately six months, but she had remained relatively asymptomatic. We everted the patient's lids and found that the tarsal plates were free of any pathology.
Figure 2. Patient's thick, circular bevel plaque. The slight pigment is believed to be makeup from the patient's lids and lashes.
An Ounce of Prevention
Bevel plaques often form on hyperopic lenses in which the anterior power curve is markedly steeper compared to the flatter lenticular flange. The deposit is firmly bound to the lens and cannot be removed with traditional abrasive surfactant cleaning. Even aggressive surface polishing is often inadequate at removing the plaque. It is therefore necessary to order new lenses and to direct patients' attention toward preventing the deposition. We've found it best to instruct patients to use an abrasive cleaner such as Boston Original Cleaner (Bausch + Lomb) at night followed by overnight storage in the Optimum Cleaning, Disinfecting and Storage solution (Lobob Laboratories). This type of cleaning regimen is often effective and less invasive than cotton swab cleaning, which can result in frequent lens breakage. CLS
Patrick Caroline is an associate professor of optometry at Pacific University. He is also a consultant to Paragon Vision Sciences. Mark André is an associate professor of optometry at Pacific University. He is also a consultant for CooperVision.
Contact Lens Spectrum, Issue: April 2010