Ocular abnormalities are prominent features in both the Marfan syndrome and in homocystinuria. The most frequent ocular manifestation, ectopia lentis, was found in 79% of eyes with the Marfan syndrome and in nearly 90% of eyes with homocystinuria. The direction of lens dislocation is sufficiently different in the two disorders to enable the clinician to make a tentative diagnosis, although the degree of overlap makes biochemical confirmation necessary. In homocystinuria, the displaced lens is likely to be detected early in life, tends to move inferiorly, and almost one-third eventually are completely dislocated into the vitreous or anterior chamber. In contrast, in the Marfan syndrome dislocated lenses may remain undetected until the fourth or fifth decade, tend to be displaced superiorly, and rarely are found in either the anterior chamber or the vitreous. Surgery for dislocated lenses in these disorders is frequently complicated by vitreous loss. Postoperative visual acuity is improved in approximately 60% of eyes, however. Spontaneous retinal detachments occur with a high frequency in both disorders, but no significantly increased risk was demonstrated for aphakic patients. Treatment for ectopia lentis in homocystinuria and the Marfan syndrome should consist of repeated correction of refractive errors until the dislocation causes excessive reduction in visual acuity. Chronic mydriasis, particularly in homocystinuria, is contraindicated because of the significant threat of anterior chamber dislocation and secondary pupil-block glaucoma. The danger of thromboembolism in patients with homocystinuria dictates that biochemical confirmation should be made in all patients with ectopia lentis, and local anesthesia utilized for lens surgery whenever possible.
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