The lens is held in its normal position behind the iris and pupil by tiny strands called "zonules". Disruption of the zonules can cause the lens to move out of its normal position (luxate). When a lens is only partially held by some zonules, it is referred to as a subluxated lens. When a lens is no longer held by any zonules, it is called a luxated lens.
Two general categories of lens luxation are defined according to whether or not the luxation was the first eye problem (primary lens luxation) or whether it was caused by another eye condition (secondary lens luxation). Primary lens luxation is seen more commonly in certain breeds (e.g. Jack Russell Terriers, Miniature Fox Terriers, Tenterfield Terriers and Cattle Dogs) where the defective lens zonules weaken and break over time. Trauma to the eye or head can also cause lens luxation, although it is not usually the primary cause. Trauma severe enough to cause lens luxation usually also causes other obvious eye problems.
Lens luxation can be secondary to other eye diseases such as glaucoma or uveitis. Elevated pressure inside the eye (glaucoma) or inflammation inside the eye (uveitis) can cause the zonules to weaken and the lens breaks free. Interestingly, a luxated lens can also cause glaucoma. Sometimes when we see a patient with multiple eye problems for the first time, it is difficult to tell which problem came first: the luxated lens or another eye condition!
Treatment of a luxated lens depends on the general health of the eye, the position of the lens, and whether or not the patient can still see out of the affected eye. If the lens is loose but is still behind the iris, we sometimes use medications which constrict the pupil in order to trap the lens in its proper position. If the lens has moved in front of the iris, then surgery may be recommended to remove the lens.
Prior to the surgical removal of a luxated lens (lensectomy), preoperative electronic testing of the back of the eye must be done to make sure the retina is working properly. This is to ensure the patient will be able to see after surgery. Lensectomy is done under general anaesthesia with the use of an operating microscope. An incision is made in the edge of the eye and the lens is removed using a small spoon shaped device called a lens loop, or a probe with a frozen tip is inserted into the eye to capture the lens. The lens adheres to the end of the probe in the same way your tongue would stick to a frozen lamp post in the winter! The surgeon then pulls out the lens in one piece. The corneal incision is sutured closed.