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Eyes with glaucoma filtering blebs have more dysesthesia
Risk factors include young age, superonasal bleb location, poor lid coverage and bubble formation, a study shows.
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MIAMI — According to a study conducted here, eyes with glaucoma filtering blebs experience more dysesthesia than eyes without filtering blebs.
This was a prospective cross-sectional observational study conducted to determine the prevalence and risk factors for glaucoma filtering bleb dysesthesia. Study results were recently published in the American Journal of Ophthalmology.
Included in the study were 97 patients who had unilateral trabeculectomy, either alone or combined with cataract surgery. To be included in the study, patients must have had a trabeculectomy at least 3 months before the study began.
After patients were enrolled in the study, they were given a self-report Dysesthesia Scale. They rated the frequency (0 to 5) and severity (1 to 5) of the following symptoms in each eye: ocular pain, discomfort, burning, foreign body sensation and tearing. Other data — age, gender and race of the patient, affected eye, type of surgery (trabeculectomy alone versus cataract extraction with trabeculectomy), antifibrotic agent used and time between surgery and entrance into the study — were taken from the patients’ charts.
Bleb assessment
Patients were examined at the slit lamp to assess bleb size (small, medium, large), location, thickness (thin, medium, thick), presence or absence of bubbles, percent coverage of the bleb by the eyelid and the presence of epithelial defects or dellen adjacent to the bleb.
All patients had intraocular pressure (IOP) measured using a Goldmann applanation tonometer. Those conducting the study did not know patients’ responses to the Dysesthesia Scale when performing the examination.
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“Slit-lamp photographs were taken with the slit beam centered on the area of steepest bleb-corneal angle, and the angle was measured using a protractor,” said Donald L. Budenz, MD, one of the researchers.
Dysesthesia scores for the trabeculectomy eye and the unoperated control eye were compared. A normal dysesthesia score was one that was within two standard deviations of the mean dysesthesia score for the unoperated eye. Researchers used analysis of variance (ANOVA) to determine which variables contributed to bleb dysesthesia and Pearson correlation coefficient to determine the effect of variables on dysesthesia score.
The study included 97 patients; there were 44 right eyes and 53 left eyes in the operated group.
“Sixty-nine patients underwent trabeculectomy with a limbus-based conjunctival flap, and 28 underwent combined trabeculectomy with cataract extraction using a fornix-based conjunctival flap,” he said.
Patients’ average age was 67.8 years (range 17 to 90 years), and age was negatively correlated with dysesthesia score at a statistically significant level. Patients were questioned between 3 months and 23.75 years after trabeculectomy. No correlation was found between time since trabeculectomy and dysesthesia score for the operated eye. ANOVA did not show any association between bleb dysesthesia score and gender, race, type of glaucoma procedure (limbus-based trabeculectomy or fornix-based combined procedure) or use of antifibrotic agent.
“The mean total dysesthesia score was 11.1 in the affected eyes and 3.4 in the unaffected eyes; 67% of patients had a dysesthesia score in the affected eye that was greater than two standard deviations above the mean dysesthesia score in the contralateral eye,” he added.
Predisposing factors
Superonasal location of bleb, presence of bubbles and less lid coverage were predisposing factors to dysesthesia. Additionally, superonasal blebs were found to cause significantly more dysesthesia than superior blebs. While the increased cornea-bleb angle did not correlate with dysesthesia, the mean cornea-bleb angle was higher in patients who had bubbles compared to those who did not. Dellen and epithelial defects were not assessed, because not enough patients were enrolled with these conditions.
“The reason that superonasal blebs cause more dysesthesia is unknown. As suggested by a negative correlation between percent of the bleb covered by the eyelid and bleb dysesthesia, perhaps any bleb that is exposed would predispose to bleb dysesthesia. Because filtering bleb dysesthesia occurs more commonly in superonasal blebs, whenever possible, perhaps a superior location should be selected,” Dr. Budenz said.
For Your Information:Reference:
- Donald L. Budenz, MD, can be reached at the Bascom Palmer Eye Institute, 900 NW 17th St., Miami, FL 33136; (305) 326-6384; fax: (305) 326-6337; e-mail: dbudenz@med.miami.edu.
- Budenz DL, Hoffman K, Zacchei A. Glaucoma filtering bleb dysesthesia. Am J Ophthalmol. 2001;131:626-630.