Rigid Contact Lenses as a Diagnostic Aid for Patients With Reduced Acuity

Rigid lenses are valuable for more than just refractive correction. Here are two cases where they helped shed light on the true etiology of reduced acuity.

BY THOMAS S. DEVETSKI, OD
JANUARY 1999

In modern eyecare practice, clinicians must be cognizant of all available means, both high-tech and basic, of caring for their patients. When treating patients with irregular corneas, it can be difficult or nearly impossible to perform retinoscopy or refract to an accurate best corrected visual acuity. Placing a rigid contact lens over surface irregularity yields a better view of the retinoscopy reflex, aids estimation of potential best corrected visual acuity and also aids in differentiating an anterior segment-related reduction in visual acuity from a posterior segment etiology. As the following two cases demonstrate, any practitioner obtaining less-than-normal acuities from a patient with a questionable etiology should consider using rigid contact lenses as a diagnostic aid, especially if automated corneal topography is not available.

Case 1: RGPs Reveal a Healthy Retina

Our pediatric ophthalmologist referred 7-year-old Jane to our clinic for help in evaluating her refractive status and potential best corrected visual acuity. Her history included injuries to her left eye sustained from a glass soda bottle that shattered in her face. She had undergone repair of a large corneal laceration, cataract extraction with IOL implantation and a scleral buckle procedure for a subsequent retinal detachment. These surgeries left her with an irregular pupil, which included a pigmented membrane near the visual axis. This, in combination with the extreme irregularity from the laceration repair, caused an obscured view of her retina and the retinoscopy reflex. At this stage, her acuity was grossly measured as finger counting at three feet. All attempts at retinoscopy and subjective refraction were unsuccessful, and her practitioners at the time didn't know if her posterior segment would even allow better visual acuity.

On initial examination, I considered autorefraction, corneal topography, manual keratometry and fitting a rigid lens to gain a better retinoscopic view and to obtain a more accurate potential best visual acuity. Neither the autorefractor nor the topographer could obtain a reading, so we anesthetized Jane's cornea and placed a standard Boston Envision lens on it (7.60mm, 9.6mm, -3.00D). With fluorescein, the tear pattern was irregular, almost corrugated, and steep centrally, so I changed the base curve to 8.00mm. This lens showed much less central pooling and a better overall fit with some inferior decentration (Figs. 1 & 2). To my surprise, she could see 20/70 with overrefraction, a telling sign of the favorable status of her retina and macula.

FIG. 1: Jane's cornea with an RGP contact lens.

FIG. 2: Fluorescein view of Fig. 1.

I ordered and dispensed a Boston Envision lens (8.00mm, 9.9mm, plano), with which Jane attained the best acuity of 20/50. After instruction, she could insert and remove the lens with some difficulty, but was very motivated to wear it. At the one-day and and one-week follow-up visits, her acuities were the same and her comfort was much improved. At her one-month exam, she was wearing the lens all day with no adverse effects to her cornea.

Case 2: A Different Diagnostic Path

Six-year-old David, whose right eye suffered a laceration from a tree branch, was referred to us for contact lens fitting after corneal repair. His posterior segment was apparently normal, and his best visual acuity with spectacles was 20/70.

The referring physician's plan was to use a rigid contact lens to neutralize the corneal irregularity and obtain a better acuity. After a long fitting process, however, the acuity remained 20/70, and it became apparent that David's irregular cornea was not the root of his diminished acuity. I then referred him to the pediatric ophthalmologist, who diagnosed a subtle pigment anomaly of his macula, which accounted for the reduction of acuity. In this case, a lower-than-expected visual gain with the use of a rigid contact lens led to another diagnostic path and the patient's true condition. CLS

Dr. Devetski is both a clinical assistant professor and the director of the Contact Lens Service at the University of North Carolina School of Medicine, Department of Ophthalmology, Chapel Hill, N.C.