Diabetes mellitus can occur in dogs and can lead to the development of cataracts.
What is diabetes mellitus and how can it affect the eyes?
Diabetes mellitus is a disease complex that is characterised by an increased level of glucose (sugar) in the blood. Glucose levels are not only elevated in the blood but also in other parts of the body including the tears and the fluid that fills the inside of the eye. Diabetes mellitus therefore also leads to changes inside and around the eye. The most common and severe problem is the development of diabetic cataracts. Less noticeable are a mild inflammation of the conjunctiva – the thin mucous membrane lining the eyelid – (conjunctivitis) or a reduced tear production, that may lead to infections over time.
What is a cataract?
A cataract describes the clouding of the lens. Comparable with the lens system of a camera, the lens is part of the eye’s structure that allows light to enter the eye and focus it inside, specifically onto the retina, which is equivalent to the film in a camera. The retina is where the light is turned into a nerve signal that is then sent to the brain.
Figure 1: Left eye of a dog with diabetes mellitus that has developed a cataract. Note the white appearance of the centre of the eye. Both eyes were affected and the dog was blind.
When the lens becomes cloudy or ‘opaque’, the light cannot enter the eye properly and the patient loses its sight. This happens in most diabetic patients. Diabetic cataracts can develop slowly over months but often deteriorate very quickly, sometimes even within a few days. The large amount of sugar in the lens leads to swelling and whitening of the tissue. As a consequence the dog’s eyes look white in the centre and vision is severely reduced or lost.
Are cataracts painful?
Usually patients are comfortable, however sometimes a sudden onset cataract can cause inflammation inside the eye, making the eye uncomfortable and red. This is particularly the case when the swelling of the lens has been so severe that it ruptures (comparable with an overfilled balloon).
Can cataracts in diabetic dogs be avoided?
Generally there is very little that can be done to prevent diabetic cataracts from occurring. Good diabetes management may help to delay the onset of the condition, but this is very difficult to achieve in dogs. A food supplement called Ocu-GLO Rx that provides vitamins and antioxidants may also help to delay the onset of diabetic cataracts. However, once formed, cataracts have to be surgically removed to restore sight.
Can cataracts be operated on?
The technique used for cataract surgery in dogs is very similar to the technique used in people. It is called ‘phacoemulsification’ and allows the lens to be removed through one or two very small incisions into the eye. Most patients will also receive an artificial lens, which takes over the function of the lens that is removed.
Figure 2: The same eye as in figure 1, one month following cataract surgery. The dog can now see again.
Patients that cannot receive an artificial lens will still be able to see but will be long-sighted. That means that it will be easier for them to see objects in the distance compared to close objects that may appear blurry.
What happens if my diabetic dog develops a cataract?
Figure 3: A full eye examination is required to assess the cataract and the general eye health of a patient before cataract surgery can be recommended.
If a diabetic dog suddenly develops a cataract, he or she should be examined by a veterinary ophthalmologist to see if cataract surgery is likely to help restore vision. This examination is particularly important to rule out other eye conditions which may influence the surgery.
As the cataract also stops the ophthalmologist being able to examine deeper structures inside the eye, additional tests may be required to examine the inner parts of the eye.
Tests like an ultrasound that creates a picture of the eye or an ‘electroretinogram’ that tests the function of the retina (very similar to the way an ECG tests the heart’s rhythm) may be required to decide if a patient is suitable to have cataract surgery. Ultrasound allows the examination of the inner structures of the eye that may not be visible because of the cataract.
What does cataract surgery involve?
Most patients will need to be hospitalised for cataract surgery. This helps in the preparation of the patient for the surgery as well as to monitor the recovery process. Unlike people, all animals have to be anaesthetised for cataract surgery. The operation is done under an operating microscope that can magnify the small structures of the eye enough to operate inside the eye safely.
Figure 4: This is an ultrasound image of an eye with cataracts. The lentil shaped structure in the middle of the eye is the lens.
After the operation, patients need frequent eye medication (antibiotics to prevent infection and anti-inflammatories to reduce inflammation). The anti-inflammatory medication is likely to be continued for several weeks or months and sometimes years following the surgery. Particularly during the first two weeks following the operation, dogs have to be kept very quiet to allow wound healing as very small suture material is used to close incisions to the eye.
The success rate of cataract surgery is generally good. However as with any operations, complications can occur occasionally and they may be seen several months to years following the operation. This is the reason why patients should be re-examined regularly following cataract surgery and any change to the eye should be reported to the ophthalmologist.