contact lens primer
Rigid Contact Lenses Why Fit 'Em?
BY TIMOTHY B. EDRINGTON, OD, MS, FAAO, & JOSEPH T. BARR, OD, MS, FAAO
RGP lenses typically provide crisper high and low contrast vision when compared to soft contact lenses or LASIK. They also tend to be a healthier option for patients' corneal health than soft lenses due to better tear exchange (by approximately ten- to twentyfold) and availability of materials with greater oxygen permeability (Dk). Higher Dk materials are beneficial for patients with high refractive errors in order to minimize corneal swelling and neovascularization.
Many soft lens patients present with dry eye symptoms, especially in the evening. Often, rigid lenses may reduce dry eye symptoms. More specialized lens designs, such as torics and bifocals, are available in RGP materials. Also, custom designs are almost unlimited with RGPs. This allows the practitioner more latitude in fitting and problem solving.
With increased interest in controlling or reducing myopia, rigid lens wear can be successful. For patients whose refractive surgery has resulted in reduced unaided vision, due to residual refractive error or surgically-induced corneal distortion, RGPs provide these patients with their best optical correction. Reverse geometry lenses generally provide a better fit on post-refractive surgery corneas. Also, reverse geometry lenses have become the lens of choice for corneal refractive therapy (advanced orthokeratology). The steeper peripheral curves enhance lens centration while the flatter base curve induces corneal "flattening."
Rigid lenses are indicated for patients with irregular corneal surfaces or irregular astigmatism due to trauma or disease (such as keratoconus). The tear lens formed beneath the rigid lens optically "corrects" the surface irregularity, affording the patient improved vision as compared to a spectacle or soft lens correction.
There are fewer contraindications to rigid lens wear as compared to soft lens wear. Almost every patient requiring spectacles is a good candidate for RGPs. Regardless of the amount of myopia, hyperopia, astigmatism (and axis), rigid lenses can be fitted and manufactured. Rigid lens patients also tend to be more loyal to their practitioner. Poor candidates include patients who desire to be part-time lens wearers, patients who work in dusty environments and patients who are not sufficiently motivated to adapt to rigid contact lens wear.
Patient motivation and practitioner skill become the limiting factors for almost all patients who desire or would benefit from rigid contact lenses.
TABLE 1RGP Advantages and Disadvantages
Enhanced tear exchange
Fewer symptoms of dry eye
More specialty designs
Able to optically correct irregular astigmatism
Able to optically correct corneal distortion due to surgery or trauma
Worse for part-time wear
Increased discomfort with foreign bodies
Can dislodge or decenter during activities such as sports
Difficult to achieve cosmetic and therapeutic tints
Dr. Edrington (tedrington @scco.edu) is a professor and chief of contact lens services at Southern California College of Optometry.
Dr. Barr is editor of Contact Lens Spectrum and assistant dean for clinical affairs at The Ohio State University.