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Laboratory Sciences
June 1999

Effect of Melanin on Traumatic Hyphema in Rabbits

Author Affiliations

From the Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago. Dr Lai is currently performing his ophthalmology residency at the University of Chicago, Chicago, Ill. Dr Bhavnani is currently in private practice in Fort Meyers, Fla. Dr Edward is now with Ophthalmology Associates, Fort Worth, Tex.

Arch Ophthalmol. 1999;117(6):789-793. doi:10.1001/archopht.117.6.789

Objective  To investigate the role of melanin in influencing the clearance of traumatic hyphema and in the incidence of rebleeds following the hyphemas.

Methods  Hyphemas were induced in 30 eyes of New Zealand white albino rabbits using an Nd:YAG laser. A total of 3.75 mg of synthetic melanin suspended in 0.1 mL of balanced salt solution was introduced into the anterior chambers of 16 animals. A total of 0.1 mL 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 15 days and the eyes studied histologically.

Results  Hyphemas were consistently produced in all eyes with mean ± SD levels of 1.44 ± 0.22 mm and 1.57 ± 0.24 mm in the melanin-treated and control 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 melanin-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 rebleeds showed organized hemorrhage with neovascularization.

Conclusions  The presence of melanin results in a significantly prolonged course 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-pigmented individuals to more serious complications following a traumatic hyphema.