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Selective laser trabeculoplasty seems to exert a systemic effect that results in the lowering of IOP in the untreated fellow eyes of patients with open-angle glaucoma.
"SLT has replaced argon laser trabeculoplasty as the treatment of choice for open-angle glaucoma over the past 5 years at the Aston Clinic, University of Texas Southwestern, where a trend toward a decrease in IOP values in the opposite eye has been noted by the treating glaucoma specialists. Initial studies evaluating the safety and efficacy of SLT noted that phenomenon as well, leading us to suspect a systemic biologic effect of unknown mechanism. The reduction of IOP in the fellow eye after SLT has not been formally studied, and there are no long-term data with large groups of patients," Dr. Weinstein said.
Dr. Weinstein and colleagues completed a chart review of all patients who had undergone SLT at the Aston Clinic. The investigators recorded any previous surgeries, the age and sex of the patients, corneal thickness, glaucoma medications, diagnosis, degrees of treatment, baseline IOP in the treated and untreated eyes, and IOP at 1 hour, 2 weeks, 3 months, and 6 months. Patients with a history of previous glaucoma surgery in either eye, non-open-angle glaucoma in either eye, or those with any change in glaucoma medications or further surgical intervention in either eye within 6 months after treatment were excluded from this study.
The charts of 128 patients who underwent SLT were reviewed; 39 were excluded because they had a prior history of intraocular glaucoma surgery. In addition, three patients were excluded because they had monocular vision, 10 because they changed medications after SLT, nine underwent SLT in the contralateral or same eye again, one underwent a trabeculectomy, and 23 patients had been followed for less than 6 months.
The average IOP values for the treated eyes were 19.0, 18.7, 16.7, 15.1, and 15.1 mm Hg, respectively, at the preoperative, 1-hour, 2-week, 3-month, and 6-month examinations, Dr. Weinstein reported. The average IOP values for the fellow eyes were 17.1, 16.7, 15.2, and 15.0 mm Hg, respectively, at the preoperative, 2-week, 3-month, and 6-month examinations. Data were available for 43 patients preoperatively and at 6 months, 40 patients at 2 weeks, and 33 patients at 3 months.
Six months after SLT, 43 patients had an average IOP decrease of 3.9 mm Hg (from 19.0 to 15.1 mm Hg) in the treated eye (p < 0.001) and 2.1 mm Hg (from 17.1 to 15.0 mm Hg) in the untreated eye (p < 0.01). The percent of IOP reductions at 6 months were 18.8% (p < 0.001) and 11.2% (p < 0.01), respectively, in the treated and untreated eyes, Dr. Weinstein reported.
The investigators found a positive correlation between the treatment response in the treated and untreated eyes (p < 0.001). Interestingly, patients with higher preoperative IOP values had greater reductions in IOP in both the treated and untreated eyes (p < 0.001 and p = 0.021, respectively) at the 6-month examination. The finding agrees with that of a previous study by Hodge et al. from the University of Ottawa Eye Institute, Ontario, Canada, that showed a correlation between high baseline IOP and SLT success rates 1 year postoperatively.