What is a cataract?
A cataract is an opacity of the lens inside the eye. The lens is usually clear and transparent and 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 like having a cataract. In humans, cataracts are one of the most common causes of blindness, especially in developing countries.
What causes a cataract?
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 poor nutrition may cause cataracts too.
What are the clinical signs of cataracts?
- Deteriorating vision or poor vision may take the form of being more “clumsy” around the house, having a change of personality (lethargy or aggression), reluctance to go into the dark or do their normal daily activities.
- 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.
How do we treat 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.
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 into the rest of the eye. Sometimes medications can control inflammation and help control the associated pain. Long term untreated 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.
How successful is cataract 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 10-15% of cases may not work and some animals may even require further surgery or additional medications.
- 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.
What tests will be needed to ensure they are good candidates for surgery?
- Before considering doing cataract surgery we need to make sure that the chances of success are as high as possible. We will evaluate the retina with 2 tests – an ocular ultrasound to make sure it is in normal position, and an ERG (electroretinogram) to see if it is functioning normally.
- An ERG measures the electrical conductivity of the retina. This test is like an ECG for the heart. Because the retina is not visible with complete cataracts this test allows us to ensure the film at the back of the camera is functioning.
- In older dogs with retinal degeneration the ERG response is often reduced. This does not mean cataract surgery shouldn’t or can’t be performed. In these cases, your Veterinary Ophthalmologist will discuss the pro’s and cons of cataract surgery for your pet.
- Ocular ultrasound shows the anatomy of the eye and allows us to measure the lens to plan for the intraocular implant (artificial lens). This test also allows us to look for lens capsule tears or retinal detachments. Any abnormalities will change surgical technique and may decrease the success rate.
- Depending on the breed of dog or prior history further tests may be recommended or performed. Our veterinary Ophthalmologists may discuss these with you at your pets consultation. These include but are not limited to Gonioscopy and ultrasound Biomicroscopy.
- Gonioscopy uses a small lens on the surface of the eye to visualise the iridocorneal angle (drainage angle) of the eye. This may determine if your pet is at higher risk of developing glaucoma (elevated intraocular pressure). Some breeds are more predisposed to this. Cataract surgery can still be performed however we may recommend certain medications to manage the pressure within the eye. Even with normal gonioscopy, glaucoma can still develop.
- Ultrasound biomicroscopy (UBM) is a high resolution ultrasound that again allows assessment for the drainage angle.
What are the complications of cataract surgery?
- Ongoing inflammation in the eye.
- Retinal detachments.
- Glaucoma.
- Infection inside the eye.
These complications are like 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.
What does the aftercare involve?
The procedure is a day stay procedure and your pet will go home the same evening. Initially topical medications up to four times daily and oral medications are administered to your pet. An Elizabethan collar will be provided and must stay on for 2 weeks after the surgery to allow the corneal incisions to heal. Rechecks will be performed on day 1, within the first week and then fortnightly for 1 month. With each successful recheck the time between appointments may be extended. With successful cases monitoring will be performed long term once to twice yearly. Some cases may require more frequent assessment. Our Veterinary Ophthalmologists will discuss what monitoring regime is best for your pet.
For diabetic dogs blood sugar management may be affected. It is important that your pet continues to receive good monitoring and insulin management with your primary care Veterinarian.
