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For most patients with abnormal blood vessels in the eye, either as a delayed complication from a fungus infection called histoplasmosis or from unknown causes, surgery will not likely improve vision. However, for those patients whose vision had been poor just prior to operating, surgery may increase the chances of improving or stabilizing it. These conclusions are part of the results of the Submacular Surgery Trials (SST), funded by the National Eye Institute (NEI), part of the National Institutes of Health.
Eye researchers taking part in the SST investigated the benefits and risks of retinal surgery to remove lesions consisting of new blood vessels, scar tissue, and associated bleeding in different groups of patients. This condition, known as choroidal neovascularization, or CNV, occurs mostly in people older than 50 as a complication of age-related macular degeneration (AMD). A smaller number of people, including many in their primary working ages of 30 to 50, have CNV that is not caused by AMD. These patients have centrally located CNV in one eye, from either unknown causes or from the ocular histoplasmosis syndrome.
Exposure to spores of Histoplasma capsulatum is rather common for people living in or near the Mississippi and Ohio River valleys. Most of those who become exposed experience mild flu-like infections with no lingering, noticeable effects. If the eyes are affected, small lesions called 'histo' spots can occur that might lead to growth of new blood vessels and scar tissue in the retina.
Two papers from the SST on surgery for CNV not caused by AMD appear in the November issue of the Archives of Ophthalmology. A total of 21 clinical centers participated in this part of the trials. For all 112 patients' eyes that had surgery, 55 percent had improved or stable vision after two years, compared with 46 percent of 113 patients' eyes that did not receive surgery but showed improved or stable vision anyway during the two-year period.
While the trial showed a slight benefit overall of surgery, when the researchers looked more closely at patients with vision improvements after surgery, they identified a subgroup that surgery would most benefit: those with poor vision just prior to surgery. The observation confirmed the researchers' pre-trial impression that the level of vision in the eye prior to surgery would be an important predictor of success. Two years after surgery, 76 percent of the patients whose eyes had visual acuity worse than 20/100 (capable of reading only the largest letters on a standard eye chart) had improved or stable vision, compared with 50 percent of those who did not have the surgery but whose vision had also improved after two years. Thus, the chance after two years of improved or stable vision was 50 percent better with surgery than without it.
The SST results favoring surgery for patients with less than 20/100 vision establishes submacular surgery as the only treatment proven to be effective in a large study to treat eyes with central CNV from ocular histoplasmosis or unknown causes. Currently, many similar eyes are treated with photodynamic therapy with a light-sensitive medication, but this treatment has yet to be tested in randomized clinical trials among ocular histoplasmosis patients. When the SST began, photodynamic therapy was not available.
During the 1980s, four clinical trials were sponsored by the NEI and conducted by the Macular Photocoagulation Study Group. For patient's eyes with CNV due to either ocular histoplasmosis (two trials) or unknown cause (two trials), the trials demonstrated that laser treatment prevented severe vision loss when the CNV was away from, or close to, but not under the center of the retina.
The patients in the SST trial also answered questionnaires and surveys to record how their vision affected their quality of life, before and after the surgery. Patients who had surgery reported more improvement in quality of life than patients who did not have surgery.
Six papers have been published so far on the results from the clinical trials conducted by the SST researchers. Four SST papers on surgery for AMD patients appear in the November issue of the journal Ophthalmology.