The axial lengths of 24 consecutive adult eyes with unilateral central retinal vein obstruction (CRVO) were compared with those of contralateral unaffected eyes and those of a control population. The lengths of the two eyes of persons with a unilateral CRVO were not significantly different. By contrast, eyes of persons with CRVO averaged 0.67 mm (approximately 2 diopters) shorter than their control counterparts (P = .03). This anatomic difference may be a factor in the development of CRVO.