Cataracts are much more common but a lens luxation does occur and when it does it definitely creates a problem for the pet.
The normal lens floats in the area of the eye called the posterior chamber, which is the chamber behind the lens. The lens kind of hangs there floating in a thick gel called vitreous humor, and is attached by tiny fibers called zonules. The zonules can be likened to be the spider web with the lens held in place in the middle of it. The gel and zonules together make up the suspensory ligament of the lens.
The zonules that hold the lens in place break down for a number of reasons. Trauma, age, and fibrous tissue genetic defects are the most common. When these tiny fibers break down the suspensory ligament of the lens is dysfunctional, the lens is no longer confined to the posterior chamber of the eye and is free to float around. If the lens floats backwards it may damage the retina causing loss of sight. If the iris is wide such as it gets for night vision the lens can migrate through the iris into the front chamber of the eye called the anterior chamber. An anterior lens luxation usually causes more complications than the posterior chamber lens luxation.
Besides being a painful condition to the pet an anterior lens luxation may stop the inflow and outflow of the fluid of the front of the eye called aquous humor. When the anterior lens luxation occurs the fluid can flow into the anterior chamber but cannot flow out of it, when this happens the pressure of the fluid in the anterior chamber rises sharply creating a condition called glycoma, or increased pressure of the eye. This condition is very painful and may lead to rapid loss of sight. When a pet has a sudden development of glycoma it is a medical emergency of the eye as sight can quickly and errantly be lost.
Treatment for a non-complicated posterior chamber luxation may be handled medically. Treatment for an anterior lens luxation may require surgical removal of the lens, if there is considerable pain or glycoma associated with it.