contact lens case reports
Managing Cone Dystrophy with Tinted Contact Lenses
By PATRICK J. CAROLINE, FAAO, & MARK P. ANDR�, FCLSA
A 28-year-old patient, R.T., presented with a history of cone dystrophy diagnosed at age four. His best corrected visual acuities were 20/200 OU, with a negligible refractive error of plano -0.50 x 90 OU. The anterior segment examination was normal OU except for nystagmus
-0.50 x 90 OU. The anterior segment examination was normal OU except for nystagmus and marked squinting secondary to photophobia. R.T. failed our color vision tests. Posterior segment examination revealed no foveal light reflex and a small crescent of peripapillary atrophy OU (Fig. 1).
About Cone Dystrophy
As illumination increases, the visual performance of the rod mechanism rapidly decreases, a property known as rod saturation. With daylight illumination in normal eyes, there is minimal rod function, but cone function is at its peak for maximum visual acuity and color vision. However, in patients with cone dystrophy, the defective cone mechanism forces the patient to rely on the minimal daylight rod function for vision. Additionally, cone dystrophy patients experience photophobia under normal photopic conditions. These patients squint in attempt to reduce retinal illumination levels and prevent rod saturation, thereby increasing their visual function.
In 1986, Corning Medical Optics introduced a series of photochromic filter spectacle lenses. They decrease photophobia and improve vision in patients with a variety of ocular disorders. These filters have two possible disadvantages -- an undesirable cosmetic appearance and optical aberrations related to the spectacle vertex. Fortunately, incorporating the desired filter into a soft or rigid contact lens can successfully overcome these problems.
In the Red
Red contact lenses function by absorbing the shorter wavelengths (up to 550nm) while allowing nearly all the longer wavelengths to be transmitted. At higher light levels, viewing with the filters enhances vision by eliminating the wavelengths to which the rods are especially sensitive. This reduces the rod saturation effect relative to viewing without the filter. A concern with the red filter contact lenses is the confusion with learned color responses in patients whose color vision is intact. However, this is not a major concern with cone dystrophy patients since color function is markedly decreased.
We fitted R.T. with red-filter plano soft contact lenses tinted by Adventure in Colors, Inc. in Golden, Colorado (Fig. 2). He had no objective improvement in visual acuity with the lenses, but reported a considerable improvement in visual performance, which he attributes to a decrease in photophobia and a subjective increase in contrast sensitivity. He wears the lenses full time and has affirmed that they provide him with a significant improvement in his ocular comfort and overall visual performance. CLS
FIG. 2: Red photochromic filter soft contact lens.
FIG. 1: Retinal photograph of the patient's right eye.
Patrick Caroline is an assistant professor of ophthalmology at the Oregon Health Sciences University and an assistant professor of optometry at Pacific University. Mark Andr� is director of contact lens services at the Oregon Health Sciences University.