SOFT PROSTHETIC LENSES are typically used for cosmetic improvement in cases of anterior segment disfigurement. However, as the case presented shows, they can also be used for management of diplopia with adult strabismus.
A 51-year-old female patient was referred by her ophthalmologist for specialty lens fitting. She had a history of myasthenia gravis with secondary strabismus that resulted in intermittent diplopia. The patient also was referred to a strabismus surgeon, but she was interested in a prosthetic occluding soft lens for her left eye for relief of her diplopia.
At that time she was wearing periodically replaced soft lenses fit by her primary care optometrist. Her visual acuity was 20/20 in both eyes. Binocular vision assessment revealed a constant greater than 30 prism diopter left esotropia. Anterior slit lamp examination was unremarkable. The patient has brown eyes (Figure 1A) with equal and round reactive pupils. Measured horizontal visible iris diameter of her right eye was 11.5 mm and photopic pupil size was 4.5 mm.
After discussion, the patient agreed to be fit with a computer-generated soft prosthetic lens for her left eye and to continue standard soft contact lens wear for vision correction of her right eye. A 14.5 mm trial soft lens (Figure 1B) was ordered with an 8.6 mm base curve that incorporated a demo white prosthetic size of 11.5 mm and pupil opening of 4.5 mm.
The trial lens had adequate centration and movement, but the 11.5 mm prosthetic coverage was slightly less than needed to completely cover her iris, and measurement showed that she needed a 12 mm final lens. A color match was determined using a card showing available colored patterns in natural light conditions near a window.
The final lens (38% water content, Dk 9 with a black backing and closed pupil) was ordered and dispensed (Figures 1C and 1D).
The patient had immediate relief from her diplopia and was thrilled with her comfort and cosmetic appearance. She was advised to use a hydrogen peroxide care system for nightly cleaning and replace the lens every year.
Computer-generated prosthetic soft lenses are an efficient choice for patients who need cosmetic improvement or occlusion. They have the additional advantage of superior reproducibility when replacement is needed. Because the Dk value is typically low secondary to the lens polymers commonly used, and the pigment acts as further resistance, the patient should be monitored for hypoxia-related complications.