Anterior and posterior lens luxation are conditions that can range from non-event to major surgery.
DEFINITION OF TERMS
What is it? Let’s break it down. Anterior means front or forward, from the Latin root meaning before, and in this case refers to the frontmost chamber of the eye. It’s no surprise that it’s called the anterior chamber.
Posterior comes from the Latin post, meaning after, and here refers to the rear chamber of the eye.
Lens refers to the flying saucer-shaped structure that normally sits approximately in the middle of the eye, just behind the iris. The iris is the part of the eye that gives us color: blue eyes like all three of my grandchildren and me, and my beautiful wife, Brenda.
Luxation refers to movement of a body part out of its normal location. It comes from the Latin luxus, meaning to dislocate, and luxare, to put out of joint.
NORMAL AND ABNORMAL ANATOMY
A normal lens floats in the posterior chamber of the eye where it hangs suspended in a special gel, vitreous humor, by zonules, tiny fibers which surround the lens and, together, make up the lens’ suspensory ligament.
Zonules may break down for a variety of reasons. Trauma, age and fibrous tissue genetic defects are among the more common reasons. When zonules break down sufficiently that the suspensory ligament is dysfunctional, the lens is no longer confined to the posterior chamber and may float wherever it pleases. If it goes backward it may impact the retina and interfere with vision, even cause permanent retinal damage. If the pupil is wide, such as occurs under bright-light conditions and some forms of blindness, the lens may easily pass through the opening and into the anterior chamber.
The potential for major complications is much greater in anterior lens luxation.
WHAT A PET OWNER NOTICES
What you see as a pet owner depends on the pre-luxation state of the lens. If we started with a normal, clear lens, you may notice nothing until the eye becomes inflamed.
If the lens moves posteriorly an inflammatory response may or may not be initiated. If not, your pet may simply experience a decrease in visual acuity on the affected side. If inflammation is present, however, the white part of the eye, known as sclera (from the Greek, sklera, meaning hard) may be red with blood vessels.
In anterior lens luxation a normal, clear lens may go unnoticed by you, but not by the eye. Inflammation will usually begin very quickly and your first indication will be an inflamed sclera.
A common age-related cause of lens luxation is cataract formation. As the lens changes structure, detachment from the zonules may occur, leading to lens luxation. If a cataractous lens luxates anteriorly, a bright white spot may be noticed by owners. In this case the sclera may have already been red, as inflammatory response to even intact cataracts is commonly observed.
Aqueous humor, the fluid in the anterior chamber of the eye, constantly flows in and flows out. Normal pressure inside the eye is maintained when inflow and outflow are equal. The presence of a lens in the anterior chamber, however, may interfere with outflow, leading to increased pressure and a condition known as glaucoma. Glaucoma is a medical emergency, as permanent retinal damage and permanent loss of vision may occur in as little as a few hours. In this situation buphthalmia, or enlargement of the globe, may be the first thing you see. The pain glaucoma patients experience is incredible, so remember, this is a medical emergency.
TREATMENT OF LENS LUXATION
If a lens luxates posteriorly and is not interfering with vision or stimulating an inflammatory response, one may elect for no treatment at all. Keep in mind that this situation is subject to sudden change.
If treatment is required, simple control of the inflammation may be sufficient. This might be achieved by use of oral and/or topical (drops or ointments) medications.
Inability to control the inflammation and/or presence of vision interference may lead a clinician to decide to recommend surgical lens removal, essentially cataract surgery, which is almost always performed by a board-certified ophthalmologist. Surgery is also the best approach to prevent loss of vision from a lens causing damage to the retina.
If a lens luxates anteriorly several treatment options exist.
The ideal approach is to perform surgical lens removal. Even if glaucoma has permanently eliminated vision, the globe might be saved by removing the lens and reestablishing aqueous humor outflow.
There is one potential roadblock for pet owners considering surgery for lens removal: It’s going to cost around $1750.00, beyond the reach of some.
A surgical alternative is enucleation, surgical removal of the globe. Enucleation is a good alternative for the nonvisual eye, as it is less costly and a procedure almost all general practitioners routinely perform.
Lens luxation is neither a common nor a rare event. Your pet’s doctor hopes your dog and cat never have to experience this condition, but he is ready and capable of handling it, should it occur.
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My cat Taz is 22 years old and has been receiving fluid therapy and prescription diet for kidney failure. He has been doing well for 3 years now. 3 years ago his right pupil became extremely enlarged. He was diagnosed with luxated lens (cataract) in that eye only. The other eye was healthy. Yesterday he began to bump into walls and we noticed the other pupil is now enlarged, too (slightly smaller still than the other). He was checked out by a Veterinarian. The lens on that eye is luxated also (unsure if posterior or anterior). His blood Pressure is fine and his ocular pressures are ok also. There is no redness or cloudiness noted, just pupils are large and he appears to be blind. I know he is old and any treatment is unlikely but do you have any suggestions.
Dear MRJ, After I began reading your comment and saw the part about Taz’s pupils being dilated, I immediately skipped through the rest looking for the words “blood pressure.” When I found them, and saw that the result was normal, I not only breathed a sigh of relief, but felt very confident that your veterinarian is covering all the bases for Taz. That said, hypertension is not ruled out. Blood pressure measurements in pets do not have the reliability and reproducibility we enjoy in human blood pressure measurement. I would like to see repeated blood pressure readings to know for sure that hypertension is not a problem. In addition, having a board-certified veterinary ophthalmologist examine Taz would help. This move means nothing against your primary care veterinarian. It is simply a matter of specialized equipment and specialized training that will allow an ophthalmologist to evaluate Taz’s eyes in ways the general practitioner cannot. While no one is going to be eager to perform surgery on a 22-year old kitty in renal failure, it can be done, it has been done, and (depending on the outcome of the ophthalmologist’s examination), is the most likely way to save his eyes, with or without vision. Please keep us updated on Taz’s progress, Dr. Randolph.