Ectopia lentis is when the lens is displaced from its normal position, centered behind the iris. When the lens is displaced but remains in the pupillary area, it is considered subluxated. A luxated or dislocated lens is one that is completely displaced from the pupil. The zonules are fibers that extend from the ciliary body to hold the lens in position. Any disorder or trauma of the zonules may result in lens dislocation.

These patients become progressively myopic, often with large astigmatism and decreased vision. Patients may also complain of monocular diplopia and are at risk of developing amblyopia, glaucoma, and retinal detachment.

Ectopia lentis can be inherited as an isolated condition, usually autosomal dominant (simple ectopia lentis). 

More commonly, lens displacement is associated with systemic syndromes, such as Marfan syndrome, homocystinuria, and Weill-Marchesani syndrome. It can also be associated with other ocular disorders such as aniridia, pseudoexfoliation syndrome, and congenital glaucoma. Other less common conditions associated with ectopia lentis include Ehlers-Danlos syndrome, sulfite oxidase deficiency, hyperlysinemia, congenital syphilis, Apert's disease, ectopia lentis et pupillae, spherophakia, iris coloboma, retinitis pigmentosa, and Reiger syndrome. 

The most common cause of acquired lens displacement is trauma.