Cataracts and Lens Diseases in Animals

Cataracts and Lens Diseases in Animals

A cataract is an opacity of the lens inside the eye. The lens is usually clear and transparent and lens helps focus an image on the back part of the eye called the retina. The same concept happens in a camera, with the lens focusing an image on the film in the back of the camera. A camera with a foggy lens is somewhat similar to having a cataract. In humans, cataracts are one of the most common causes of blindness, especially in developing countries.

Cause of Cataracts
Cataracts can be caused by many things. Often we cannot be 100% sure of the cause. Most cataracts seen at the Eye Clinic for Animals are inherited from the parents (in the genes) but other causes such as diabetes, injuries, inflammation, drugs and nutrition may cause cataracts too.

Signs of Cataracts
Owners usually report deteriorating vision of their pets. Poor vision may take the form of being more “clumsy” around the house, having a change of personality (lethargy or aggression) and reluctance to go into the dark amongst other things. Sometimes our clients notice a white area in the pupil (the black circle in the middle of the eye), or their referring veterinarian notices the problem during a routine physical examination.

Treatment of Cataracts
In the past people have tried all sorts of medications to clear cataracts. With our current medical knowledge, surgery is the only cure for cataracts. This doesn’t mean you must have cataract surgery on your animal, as some cataracts are too small to warrant surgery. The decision as to whether your pet should have surgery can be discussed with one of our eye specialists.

Assessment for Surgery
Early assessment of cataracts is important for 2 reasons: Firstly, to assess the retina, the light-sensitive membrane at the back of the eye, to ensure it is normal. This can be done most easily when the cataracts are not too dense, enabling us to see the retina with an ophthalmoscope. If the cataracts are too dense we may need to do a more specialised test called an electroretinogram or ERG. Secondly, with the newer surgical equipment we use today, success of cataract surgery is greater when the cataracts are still in the early stages and the longer that cataracts are left before operating incurs a poorer chance of surgical success.

What happens if my animal doesn’t have surgery?
Cataracts can be irritating inside the eye if left in place, as the components of the lens are inflammatory and can leak from the lens capsule in to the rest of the eye. Sometimes medications can control inflammation and help control the associated pain. In the long term however the inflammation may lead to glaucoma (increased pressure in the eye) and uncontrollable pain may occur. In these cases the eye may need to be removed. So even if you decide not to have cataract surgery please stay in touch with us to monitor the progression of the cataract in your animal.

Tests prior to Surgery
Before considering doing cataract surgery we need to make sure that the chances of success are as high as possible. We may need to test the retina to see if it is in its normal position by ultrasound, and to see if it is functioning normally by doing an electroretinogram, or ERG. This test measures the electrical conductivity of the retina, similar to how an ECG is a common measure of the electrical conductivity of the heart. Just like a camera with a foggy lens, we need to make sure the film at the back of the camera is in its normal position, and working normally. These tests are often done at a different time to the surgery itself. If you are not considering doing cataract surgery then there is also no point in doing these preliminary tests.

Cataracts Surgery
Cataract surgery in animals is almost identical to that in humans. Some people think that cataract surgery is called laser surgery, but it actually involves the use of ultrasound energy using a process called phacofragmentation. After being anaesthetised your pet will have hair clipped from around the eye for sterility reasons. A small area on the leg will also be clipped for catheter placement to break up the lens and remove the fragments. This surgery is performed under an operating microscope and require many years of practice to master. In some cases after the lens is removed an artificial lens may be placed in the eye. Not all dogs are candidates for an artificial lens. The decision to place an artificial lens is often a decision made by the surgeon during surgery depending on various factors. An artifical lens will help animals with close-up vision,  however animals without an artificial lens are still sighted and still function wonderfully. The surgery itself usually will take about one and a half hours per eye.

Success rates of Cataracts Surgery
Published success rates for cataract surgery in both eyes at the same time so that one eye, or both, has vision at 1 year after surgery is over 90%. Success rates for doing just one eye are about 85%. This is certainly quite a high success rate compared to almost any other surgery in the body. However this also means that even in uncomplicated cataract surgeries sup to 15% of cases may not work and some animals may even require further surgery. Most cataract surgery patients do well after surgery. These pet owners are undoubtedly some of our happiest clients. Their now visual pet is suddenly more energetic, happy and experiences a better quality of life. Not all cataract patients have successful outcomes. There is always a risk of complications in any surgery. For the majority of our clients the incidence of complications is acceptable.

The most common reasons for a lack of vision after cataract surgery are ongoing inflammation in the eye, retinal detachments and glaucoma. There are other less common complications and these all may contribute to the 15% cases that fail. These complications are similar to those seen in human cataract surgery. In the worst case scenario, glaucoma or infection after surgery may not only result in lack of vision postoperatively, but also uncontrollable pain with the need to remove the eye.

Post Surgery
Usually after cataract surgery your pet will be going home the same day, as this is a day procedure. When we do send your pet home it is essential that you use the medications we prescribe at the frequency we suggest. Failure to use the medications as directed even for as little as a day or two can result in uncontrolled inflammation, glaucoma and retinal detachments. For the first 1-2 weeks it is important to keep your animal quiet and to limit the exercise your pet has to strict leash walks, preferably with a chest harness rather than a throat collar which can increase the pressure in the eyes. You should keep your animal out of bright light as this may cause discomfort. The eye should be cleaned once daily using a warm compress. At first we may be using medications at least 4 times daily. Over time this decreases, but often both eyedrops and oral tablets are prescribed after surgery.

Your first revisit will usually be 1 or 2 weeks after the surgery, however in some instances we may want to re-check the following day. After this there will usually be another at one month or so after surgery. Subsequent revisits will depend on the progress of the case.

Vision after Surgery
If all goes well your pet may have vision as early as the next day after surgery. Some cases may however take a few weeks to fully regain vision due to the degree of inflammation present and also your pet “learning” to see again.

Lens Luxation
The lens is held in its normal anatomical location by small spoke-like structures called “lens zonules”. If these zonules break, then the lens can be free to move in the eye either forward (anteriorly) or backwards (posteriorly). When the lens moves from its normal location, it is said to be luxated, or if some zonules remain strong and the lens is able to pivot in place then it is subluxated. The issue with this is, if the lens moves anteriorly then it can block the normal fluid drainage from the eye, causing very high eye pressures (known as glaucoma).. This is not only very painful but can render the eye irreparably blind if left untrated.

What causes Lens Luxation?
Lens luxation can occur either due to an inherited defect in the structures that consist of the zonules (ie primary lens luxation), and this is most commonly observed in terrier breeds of dog. Lens luxation can also occur when the zonules become weak or diseased from inflammation in the eye, and can be from trauma, infection, cataracts and many other causes.

Treatment of Lens Luxation
Lens luxation is ideally treated surgically, to remove the lens entirely. In these instances, a replacement lens can not be placed. The removal of the lens can be done via a few methods, and the exact methodology is dependent on a few factors, including if the eye is visual, and if the lens is luxated anteriorly or posteriorly. This can be performed by making an incision in to the cornea and retrieving the lens through the front of the eye, or by enterring the eye from its back portion first and then retrieving the lens from the front. The rationale behind entering from the back, is that the lens has adherence to the jelly-like cushion at the back of the eye called the vitreous humour, which is adhered to the retina. The lens luxating can predispose the effected eyes to a retinal detachment, and similarly the removal of a lens surgically can cause retinal detachment. By entering the back of the eye and removing these connections however, retinal detachment becomes less likely. If the lens is located in the posterior segment, then an option may be to try and “close the pupil” to prevent the lens from heading to the front of the eye (where it causes issues). However, these medications would be life long and the lens can still find its way to the front of the eye despite our best efforts.