contact lens Q&A

In a Bind with RGPs

BY CHRISTOPHER SNYDER, OD, MS
JUNE 1998

RGP lens sticking or binding is always associated with a lens position that's not centered on the cornea, typically trapping mucus under the lens, yet rarely affecting vision or comfort significantly (Fig. 1). The most common symptom described by patients is that the lens is more difficult than usual to remove from the eye. Lens binding never seemed to occur with PMMA lenses, so it likely has something to do with the different materials or the larger diameters of RGP lenses.

While this phenomenon is often associated with overnight lens wear, it may occasionally present in daily wear patients. The lens binding associated with extended wear is typically evident upon eye opening in the morning. The lens tends to break free within a matter of minutes, and patients often aren't even aware that the phenomenon has occurred. Since daily wear lens binding tends to develop while the lens is worn during the day, it may have a different causative mechanism than extended wear binding.

A daily wear RGP patient presented with her lenses seemingly stuck to the cornea. What causes this phenomenon?

ANSWER: Helen Swarbrick, Ph.D., who has done most of the research on this clinical phenomenon, has shown that there is essentially no space between the posterior lens and the epithelium when the lenses bind down. She has theorized that the lens immobilization is a function of the physics of thin films, wherein a great amount of force is required to slide two surfaces relative to each other when there is a thin film of fluid between them. When the RGP lens is in a decentered position and there's a thin film between the lens and the cornea (consisting of the sticky, mucus component of the tears with the aqueous squeezed out), moving the lens takes slightly more force than the eyelids are able to impart.

My theory is that a thin coating of deposits builds up over time on the central back surface of the lens. This slows lens movement, impedes tear exchange under the lens and may enhance the thin film effect. I've noticed that these patients are typically middle- or advanced-age females, so I wonder if there's a connection between tear chemistry and hormonal changes.

What should you do when you encounter lens binding?

ANSWER: Upon lens removal, an indentation ring is evident (Fig. 2). Corneal topography detects mild distortion associated with binding, so avoid performing a refraction for spectacles within an hour after removal. After an hour, the impression ring fades from view without any residual effects.

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Polishing the posterior lens surface with in-office modification equipment is a quick and effective way to solve this clinical problem. Enhanced daily surfactant cleaning, periodic enzyme soaking and in-office polishing on a routine basis (at least yearly but more often for some patients) keeps patients happy in their RGPs!

Dr. Snyder is a professor of optometry and serves as chief of contact lens patient care at the School of Optometry at the University of Alabama at Birgmingham.