Aims: To determine the risk of age-related macular degeneration (AMD) progression posed by the presence of each early AMD characteristic. Methods: A prospective cohort study of 254 participants aged 50 years and older, all with early AMD features at their baseline visit followed for an average of 7 years. Stereoscopic colour fundus photographs were graded for early AMD features using the International Classification System. AMD status was stratified into six exclusive levels along a continuum of disease severity according to drusen type, pigmentary abnormalities, or late AMD. Progression was assessed according to three definitions: a change between or within a severity level, or by side by side grading. Results: The progression rate of early AMD ranged between 3.4 and 4.67% per annum depending upon the definition used. In total, 15 (6%) cases progressed from early AMD to the late complication of AMD. After controlling for age and smoking, cases with soft indistinct drusen at baseline were at a greater risk of progressing from early to late AMD than were cases without this characteristic (OR = 3.72, 95% CI 1.20-11.54; P = 0.02). Conclusion: Our proposed definitions of AMD progression give rates that are consistent with current knowledge of progression and its determinants. Each early AMD characteristic conveys its own risk of progression to an eye, with soft indistinct drusen carrying the greater risk. An international consensus on what defines AMD progression would greatly help the research community when trying to assess the importance of new risk factors and the effectiveness of novel interventions.
Bibliographical noteFunding Information:
The CHARM Study is a recipient of a Project Grant from the National Health and Medical Research Council of Australia. Additional support is provided by the Perpetual Trustees Australia Ltd (Ramaciotti Foundation), ANZ Executors & Trustee Company Ltd (The Hugh DT Williamson Foundation under the Medical Research and Technology in Victoria Program), The Royal Victorian Institute for the Blind, The Royal Victorian Eye & Ear Hospital Research Committee, The Lions Club of Victoria, and The Australian Institute of Health and Welfare.