What is a dislocated lens?
Dislocation of a lens is when the lens falls out of its proper position, typically into the vitreous (for a diagram of the lens and its relationship to the vitreous, click here. Normally, the lens is located immediately behind the iris (the colored part of the eye). Patients who have undergone cataract surgery have a lens implant instead of the "native" lens. Either kind of lens -- the native lens or a lens implant -- can become dislocated into the vitreous.
Why does dislocation of the lens occur?
The native lens becomes dislocated most commonly during cataract surgery, when the contents of the lens inadvertently fall into the vitreous (this is an uncommon but well-known complication of cataract surgery). Rarely, the lens spontaneously falls into the vitreous, unrelated to cataract surgery.
Lens implants are typically placed within the lens "capsule", which is the outer lining of the native lens; the cloudy contents of the lens are removed but the capsule is left in place to hold the lens implant. The capsule is held in place by "zonules" -- very fine, string-like structures that connect the capsule to the wall of the eye. Sometimes, the capsule and/or the zonules become weakened, and the lens implant can no longer be held in place, resulting in its dislocation into the vitreous.
How does lens dislocation affect the eye?
The lens -- either the native lens or a lens implant -- is necessary for focusing light on the retina, which allows the eye to see clearly. When the lens becomes dislocated, it can no longer do the focusing, and the vision becomes quite blurry as a result.
If lens material becomes dislocated into the vitreous during cataract surgery, other problems can arise in addition to blurred vision. The eye can become inflamed (inflammation --overactivity of the immune system within the eye -- can cause pain, redness and damage to critical structures within the eye) and the eye pressure can become elevated (high eye pressure is known as glaucoma).
What is the treatment for a dislocated lens?
Vitrectomy surgery is used to treat a dislocated lens. In the case of dislocated native lens material, as in complicated cataract surgery, the retina specialist performs a "lensectomy" as part of the vitrectomy procedure. A specialized instrument known as a "fragmatome" can break up the lens material into tiny pieces and remove it from the back portion of the eye. In the case of a dislocated lens implant, a vitrectomy is combined with removal of the dislocated implant through an incision in the front portion of the eye.
Once the dislocated lens is removed, a new lens implant is often placed. A variety of techniques can be used to insert the new implant. If there is sufficient lens capsule to support a new implant, it can be placed behind the iris, in front of the residual "shelf" of lens capsule. Often, there is insufficient lens capsule to support a new lens implant. In that case, the implant can be placed in front of the iris (this is known as an "anterior chamber lens") or it can be sutured in place, behind the iris. The technique for placement of a new lens implant is determined by several factors, including how much lens capsule remains, whether the patient has glaucoma, and the condition of the cornea.
If a new lens implant is thought to be too risky, or if the patient simply prefers not to have a new implant inserted, a contact lens can be worn, instead.