Effect of melanin on traumatic hyphema in rabbits

Objective: To investigate the role of melanin in influencing the clearance of traumatic hyphema and in the incidence of rebleeds following the hyphema s. Methods: Hyphemas were induced in 30 eyes of New Zealand white albino rabbi ts using an Nd:YAG laser. A total of 3.75 mg of synthetic melanin suspended in 0.1 mt of balanced salt solution was introduced into the anterior chamb ers of 16 animals. A total of 0.1 mt of balanced salt solution was injected into 14 control eyes. Hyphema levels were measured by a masked observer (V .D.B.) daily for 15 days. Pairs of animals were sacrificed at 1, 3, 5, 10, and IS days and the eyes studied histologically. Results: Hyphemas were consistently produced in all eyes with mean +/- SD l evels of 1.44 +/- 0.22 mm and 1.57 +/- 0.24 mm in the melanin-treated and c ontrol eyes, respectively. The clearance of hyphemas in the melanin-treated eyes was significantly prolonged throughout the study (P < .001). The rate of rebleed in the melanin-treated group was 18.8% and in the control group was 7.1% (P < .01). Histologically, both groups showed variable degrees of blood in the anterior chambers and trabecular meshwork. In addition, the m elanin-treated eyes showed free melanin, melanin-laden macrophages, and an inflammatory response in the anterior chamber and trabecular meshwork that was greater than that in the control eyes. Melanin-treated eyes with reblee ds showed organized hemorrhage with neovascularization. Conclusions: The presence of melanin results in a significantly prolonged c ourse of hyphemas and may influence the rate of rebleeds. Occlusion of the trabecular meshwork with melanin-laden macrophages and inflammation may be the mechanisms responsible for these effects. Clinical Relevance: The release of melanin into the anterior chamber during ocular trauma may be partly responsible for the susceptibility of darker-p igmented individuals to more serious complications following a traumatic hy phema.