March 2008

 

OPHTHALMOLOGY NEWS

 

Targeting photophobia


by Matt Young EyeWorld Contributing Editor

 

 

Photophobia harder to eliminate during surgery for exotropia

The treatment of photophobia after exotropia surgery remains elusive

Surgeons may be able to get rid of exotropia with surgery, but accompanying photophobia is a lot more elusive. A new study published in the December 2007 issue of Optometry and Vision Science found that successful surgery treated binocular photophobia in 53.5% of patients. “Clinicians should educate patients in terms of the possibility of persistence of postsurgical photophobia,” reported lead study author Helen Lew, M.D., Department of Ophthalmology, College of Medicine, Pochon CHA University, Korea. The good news is that even if patients were undercorrected, they still could lose their binocular photophobia symptoms. “The exact degree of reduction does not appear important,” Dr. Lew noted. More than light irritation Researchers looked at 162 basic type intermittent exotropia patients who underwent surgical correction. The mean distance angle of exodeviation pre-operatively was 30.6 prism diopters. The mean near angle of strabismus was 31.3 prism diopters pre-operatively. Mean stereoacuity was 428.9 s.

Angles of deviation were measured with best-corrected vision at near and distance pre-operatively and post-operatively. Patients were divided into high-grade stereopsis (better than 60 s) and low-grade or no stereopsis (worse than 60 s). Binocular photophobia was more common in patients with strabismus of greater than 25 prism diopters, and low-grade or no stereopsis. Bilateral lateral rectus muscles were recessed according to angles of strabismus. Follow-up occurred for at least six months. If a patient’s angle of deviation measured at the last follow-up was less than 10 prism diopters, the correction was understood to be satisfactory. Patients were then questioned about binocular photophobia. They were asked if they had monocular eye closure in bright light and if this was lessened by the surgery. If the monocular eye closure stopped occurring in bright light after surgery (according to the parents), then the patients were put into a “disappearance” group. In total, 96 (59.2%) patients had binocular photophobia before surgery. Of those, 57.2% experienced disappearance of photophobia symptoms post-op. Further, 81 of the 96 were corrected satisfactorily, but only 46 (56.8%) demonstrated a disappearance of photophobia. Meanwhile, among the 15 patients deemed unsatisfactorily corrected, nine (60%) still showed a loss of photophobia. “The likely explanation for this is that even thought they were undercorrected, the angle of strabismus after correction was [less than] 12 to 16 prism diopters, which was considerably smaller than the deviation before surgery,” Dr. Lew wrote. “Some reduction in angle may help the patient to use the suppression mechanism or the fusional process even under the bright environment, but the exact degree of reduction does not appear important.” Dr. Lew, however, could not pinpoint any specific factor that accounted for the photophobia disappearance. The factors studied were composed of sex, age, near and distance angle of strabismus, stereopsis, and fusion in the satisfactory group. Dr. Lew explained why photophobia seems to occur in the first place. “It has been assumed that when an exotropia patient is outdoors and looking at infinity, there are no near clues to stimulate convergence,” Dr. Lew wrote. “Bright sunlight dazzles the retinas so that fusion is somehow disrupted, causing the deviation to become manifest and resulting in monocular eye closure to avoid diplopia.”

Dr. Lew continued: “In this situation, the distance angle of strabismus reflects the strabismus condition more than the near angle. The finding that patients with stereopsis worse than 60 s were more likely to have photophobia suggests that photophobia is related to high visual functions like stereopsis distinct from exotropia or diplopia itself.”

Needless to say, Dr. Lew noted, binocular photophobia is a difficult problem that necessitates further research. “We do occasionally notice this problem,” said Sujatha Mohan, M.D., Rajan Eye Care Hospital, India. Interestingly, she said, light-colored eyes experience more photophobia, such as when a person is driving. However, if a patient has a small pupil size, from 2.5 to 3 mm, it’s not much of a problem, she said. After exotropia surgery, even in patients that experience photophobia, symptoms dissipate over time, likely due to their brains adjusting to the phenomenon, she said. Another problem related to exotropia, she finds, is binocular summation, particularly in patients that have childhood exotropia and surgery takes place after a relatively long period of time. Even some patients with multifocal lenses sometimes have problems unifying the images they see. But over time—perhaps as long as six months—the brain better accepts the images it is presented with, she said.

Editors’ note: Dr. Lew has no financial interests related to this study. Dr. Mohan has no financial interests related to her comments.

Contact Information

Lew: eye@cha.ac.kr

Mohan: +91 044 2834 0500, rajaneye@md2.vsnl.net.in

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