Which of the following is a common ocular manifestation of Marfan's syndrome?

The correct answer is subluxation of the lens, which is a hallmark ocular manifestation of Marfan's syndrome. This condition is characterized by a defect in the connective tissue, leading to various structural abnormalities, one of which includes the dislocation of the lens from its normal position. The subluxation often occurs in an upward direction, and it is caused by the weakening of the zonules that hold the lens in place, a direct consequence of the underlying connective tissue disorder associated with Marfan's syndrome.

While cataracts and retinal detachment can occur in individuals with various systemic diseases, including Marfan's syndrome, they are not as distinctive or commonly associated with the condition itself as lens subluxation. Similarly, glaucoma is less specifically linked to Marfan's syndrome and is not a primary ocular manifestation of the syndrome. This distinctiveness of lens subluxation makes it a key finding when evaluating patients suspected of having Marfan's syndrome, further supporting the choice of this answer.