Cataracts in Cats
Dr. Jennifer Welser
Veterinary care includes diagnostic tests and subsequent treatment recommendations. A complete eye examination. Most veterinarians have the tools with which to confirm the presence of a cataract in the lens, but it is often necessary to visit a veterinary ophthalmologist to have a more thorough examination performed using specialized ophthalmic equipment. Such an examination includes fluorescein staining of the cornea, Schirmer tear test, slit lamp biomicroscopy, tonometry, and possibly examination of the retina.
Diagnostic tests are needed to recognize cataracts and exclude other diseases. These tests may include:
Cataracts are classified as incipient (very small), immature (encompassing more, but not all of the lens), mature (encompassing the entire lens) and hypermature (the lens is beginning to shrink down and slowly resorb). The eye exam is important for staging the cataracts and for detecting underlying diseases.
Blood tests are often necessary to search for a systemic disease. Laboratory tests are also used to assess general health prior to any surgery to remove cataracts.
An ocular ultrasound is performed if the retina cannot be examined because the cataract is too opaque, and if surgery is being considered. Prior to surgery it is important to determine if the retina is normal or healthy. If a retinal detachment or changes in the vitreous (jelly-like substance behind the lens) are found, then surgery to remove the cataract may not be worthwhile.
An electroretinogram (ERG) is also frequently performed prior to cataract surgery in order to evaluate the function of the retina. An ERG is especially important in determining underlying retinal disease masked by the cataracts (if the lens is too opaque for all the retina to be examined). If the ERG is abnormal, then the cat is not a good candidate for cataract surgery.
To understand the importance of evaluating the rest of the eye and especially the retina prior to surgery, consider this analogy: A cataract is like a physical barrier to light, similar to a cover over the lens of a camera. This barrier can be physically removed by surgery. In contrast, the retina is like the film in the camera, and the rest of the eye is the camera itself. If the camera or the retina is not working properly, then removing the lens cover (cataract) will not improve the animal's vision. The rest of the camera must be working well, and the film must be good before removing the barrier over the lens will be worthwhile.
Treatments for cataracts may include one or more of the following:
Cataract surgery. At the present time, there is no laser surgery for removing cataracts in either people or animals. Phacoemulsification is the most common technique used in humans and animals to remove a cataract. Once the pupils have been dilated and your pet is under general anesthesia, a small incision is made through the cornea (clear domed front surface of the eye). The lens is housed in a small bag called the lens capsule. A small tear is made in the front capsule and a circular piece of the lens capsule is removed. The phacoemulsification instrument uses ultrasonic waves to break apart the lens and then suck it out. Most of the lens is removed by phacoemulsification, and then the lens capsule (the "bag") is cleaned of any remaining lens material. Frequently an intraocular lens implant (a prosthetic lens) is then placed into the lens capsule.
The lens capsule acts as a bag to hold the implant in place. There are lens implants for both dogs and cats, and these prosthetic lenses return the vision as close to normal as possible. There are some situations when a lens implant cannot be inserted. When no lens implant is used, the animal's vision is still greatly improved by cataract surgery.
The incision through the cornea is then stitched closed after the lens has been removed.
Extracapsular lens extraction. This is another cataract removal technique. It is used either when a phacoemulsification machine is not available, or when a cataract is so hard or old that the phacoemulsification instrument isn't powerful enough to break up and remove the lens. The surgical procedure requires making a larger incision through the cornea and a larger hole in the lens capsule so that the lens can be removed from the bag as a single, whole piece. A lens implant can still frequently be inserted during this type of procedure.
Intracapsular lens extraction. This is another surgical method that involves making a large incision through the cornea and removing the whole lens within its capsule. This procedure is used when a cataractous lens has shifted out of position and is no longer held firmly in place inside of the eye. Because the lens capsule has been removed, if a lens implant is inserted, it has to be sewn into place because there is no capsular bag left to hold it in the center of the eye.
Regardless of which type of procedure is used to remove a cataractous lens, there are many postoperative medications and important home care instructions to be followed after the surgery.
Cataract surgery has a high success rate, as long as the rest of the eye is healthy. The success rate of cataract surgery is decreased if the eye has been inflamed in the past, or is actively inflamed. All uveitis must be controlled before cataract surgery can be attempted, and other eye problems such as retinal disease and glaucoma must also be ruled out.
Risks involved with cataract surgery include those associated with general anesthesia. Anesthetic risks are minimized by evaluating pre-operative laboratory tests, performing a complete physical exam, and taking X-rays of the chest. The information gathered from these tests is then used to develop an appropriate anesthetic protocol.
Anterior uveitis and glaucoma are the two most immediate and common complications encountered in the days following cataract surgery. Many cats are medicated prior to surgery to combat the uveitis that occurs once the eye is opened, and these medications are continued for weeks following the surgery. Pressure within the eye is monitored closely following surgery, and anti-glaucoma drugs are started as needed.
The most common problems that arise long-term after cataract surgery are scarring of the lens capsule that remains in the eye and detachment of the retina. Because of both short-term and long-term problems that may be encountered after cataract surgery, frequent follow-up visits are needed for sometime.
If your pet's cataracts are secondary to some other eye disease, removal of the cataract is frequently not indicated.
Medical therapy may be necessary to control inflammation within the eye, to combat any glaucoma present, and to treat underlying illnesses, even when the cataract cannot be removed. Periodic follow-up examinations are required to keep the eye healthy and the cat comfortable.