The Complications of Age-Related Macular Degeneration Prevention Trial (CAPT): rationale, design and methodology

Abstract

Background The Complications of Age-Related Macular Degeneration Prevention Trial (CAPT) is a randomized clinical trial to evaluate whether prophylactic laser treatment to the retina can prevent the complications of the advanced stage of Age-Related Macular Degeneration (AMD), the leading cause of irreversible blindness. Methods CAPT is conducted in 23 clinical centers and in three central resource centers. The primary outcome measure is change in visual acuity; secondary outcomes include the incidence of complications of AMD, changes in other measures of visual functioning and vision-related quality of life. In total, 1052 patients with two high-risk eyes were enrolled. One eye was randomized to receive laser treatment and the other eye to observation. All patients were treated immediately after randomization and again at 12 months, dependent on clinical status. All patients are followed via study visits and telephone calls for a minimum of five years. Study visit procedures include established tests of visual function conducted by examiners masked to the treatment assignment of each eye, a biomicroscopic examination by CAPTophthalmologists, and photographs of each eye taken according to protocol and assessed by masked graders in a centralized Photograph Reading Center. Results This paper describes the CAPT study, including study rationale, operational structure, and measures implemented to ensure standardization of assessments, adherence to protocol, quality assurance, and maintaining follow-up. Several features related to study design and procedures that are specific to CAPT are highlighted, including clinic selection and judgements regarding patient eligibility. Conclusions An intervention that can reduce the risk of advanced AMD by 30% in the eyes of people with two high-risk eyes may halve the rate of bilateral blindness from AMD. It would also yield substantial savings in expenditures devoted to treating advanced AMD and the disability it causes, and enhance the quality of life for people at risk.