OHTS Phase 3 will re-examine study participants 20 plus years after enrollment to document clinical status and the incidence and severity of self-reported functional limitations. The 279 participants who developed POAG in OHTS Phase 1 or 2 will have more than 10 years of post-POAG follow-up by Phase 3. The timing of re-examination at 20 years is meaningful because 20 years approaches the median life expectancy of OHT patients in their 60's and 70's and half the median life expectancy of patients in their 40's and 50's. For the first time, patients with ocular hypertension and clinicians will have high quality data about the long-term risk of developing POAG and functional limitations associated with the disease. These data will facilitate patient-centered care so that patients and clinicians can decide on the appropriate frequency of tests and examinations and the potential benefit of preventative treatment.
Glaucoma is one of the leading causes of blindness in the United States and other industrialized countries. It is estimated that 2 million people in the United States have glaucoma and that 80,000 of these individuals are legally blind from the disease. Among African Americans, glaucoma is now recognized as the leading cause of blindness.
Elevated intraocular pressure (IOP), a common condition affecting 3 to 6 million people in the United States, is thought to be the leading risk factor for development of open-angle glaucoma. There is no consensus that medical reduction of intraocular pressure prevents or delays the onset of visual field and/or optic nerve damage in ocular hypertensive subjects.
Despite the lack of convincing evidence for the efficacy of medical treatment in ocular hypertension, approximately 1.5 million glaucoma suspects in the United States are being treated with costly ocular hypotensive medications that carry the potential for serious and even life-threatening side effects.
Clearly, there is a need for a well-controlled clinical trial to determine whether medical reduction of IOP can prevent or delay the onset of glaucomatous damage in ocular hypertensive subjects. Only then can clinicians and patients make rational choices and health care planners ensure that limited medical resources are being allocated in a safe and cost-effective manner.
The Ocular Hypertension Treatment Study (OHTS) is a long-term, randomized, controlled multicenter clinical trial. Ocular hypertensive subjects judged to be at moderate risk of developing primary open-angle glaucoma are randomly assigned to either close observation only or a stepped medical regimen. Medical treatment consists of all commercially available topical ocular hypotensive eye drops.
After completion of baseline measures (IOP, visual fields, disc photos) and randomization, the subjects are followed for a minimum of 5 years with automated threshold central static perimetry (Humphrey program 30-2) twice yearly and stereoscopic optic disc photographs once yearly. Study end points are reproducible visual field loss and/or progressive optic disc damage in either eye of a patient attributed to glaucoma by a Masked Endpoint Committee. All visual fields and optic disc photographs are read in a masked fashion in Reading Centers.
In the 1991 Baltimore Eye Survey, African Americans were shown to have a prevalence of open-angle glaucoma four to five times higher than whites. Given this high prevalence of glaucoma in the African American population, it is important to recruit and follow an adequate sample of African American subjects in the trial (approximately 25 percent of the total patient sample).
At the conclusion of this study, practitioners should be able to make reasonable estimates of risk for individual ocular hypertensive patients and to determine which ocular hypertensive individuals are most likely to benefit from early prophylactic medical treatment.