The characteristics of drusen in 81 patients with bilateral drusen as a manifestation of age related disease were analysed for symmetry between the two eyes. It was found that there was close concordance with respect to drusen size, number, density, and fluorescence which was greater than would have been expected by chance alone. This finding implies that drusen may result from metabolic malfunction specific to the patient rather than the nonspecific result of aging. Discrete abnormal deposits in the inner portion of Bruch's membrane, when large, can be detected clinically as drusen.' Their appearance and distribution may vary widely from one patient to another, and histological studies imply that the composition of the deposits differs from one eye to another.'4'5 However, changes are rarely unilateral, and some symmetry exists between the right and left eyes for the number and type of drusen in the macula area.'620 In most of these studies limited data were obtained, and the aim of this project was to verify these observations. Drusen characteristics were analysed in order to examine whether or not symmetry of drusen exists between the two eyes of a patient which is greater than might have been expected by chance alone. If symmetry were proved, it would imply that drusen may result from metabolic changes specific to the patient rather than being non-specific results of aging.Patients and methods A retrospective study was undertaken of the clinical records, colour photographs, and fluorescein angiograms of a continuous series of 81 patients who were seen in 1983 and 1984 with the following attributes: all were over 50 years of age, they had minimal or no visual symptoms and good visual acuity, and had drusen at each macula but no signs of geographic atrophy, pigment epithelium detachment, or choroidal neovascularisation.Photographs and angiograms of each patient were analysed by two authors independently for number, size, density, and early and late angiographic behaviour of the drusen by means of a grading scheme which has been described.2"22 The posterior pole was divided into two areas: within (central) and outside (peripheral) 1600 im of the foveola. The drusen in these areas were analysed according to their number (fewer than 10, 10 to 20, more than 20), their size (less than S0 [tm, 50 to 500 [tm, greater than 500 [tm), and the distribution was classified as scattered, subconfluent, or confluent. Fluorescence of drusen was assessed as equal to choroidal fluorescence, slightly brighter than choroidal fluorescence, or brightly fluorescent during the dye transit and 3 minutes after dye entry. In most cases the drusen were uniform in size, distribution, and fluorescence in each area; when this was not the case the classification was determined by the largest, most densely