Glaucoma in Pets
Glaucoma is characterised by increased intraocular pressure in the eye, resulting in sight loss and pain. It is not only happening in old animals; young animals might be affected too! The balance between the production and drainage of the vitreous (The vitreous body is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates) is disturbed. There is too much liquid in the first eye chamber, causing an increased intraocular pressure. The regular eye pressure should be between 15 and 22 mm Hg. As a result of the high intraocular pressure, the nerve of the eye will get damaged. The increased pressure will also reduce the blood flow in the retina (at the back of the eye, crucial for eyesight), which may result in retina detachment. The nerve damage and retinal detachment will lead to sight loss and sometimes even blindness. In acute cases, the retinal detachment and sight loss can happen within 48 hours.
Clinically signs are traditionally divided in acute and chronic; in reality, most cases of acute glaucoma are superimposed on chronic glaucoma rather than occurring as singular events. Normally it has a gradual progress.
Classification of Glaucoma
– Primary Glaucoma; It is a hereditary disease. The following breeds are predisposed: American Cocker Spaniel, Basset Hound, Chow Chow, Labrador Retriever, Shar-Pei. Primary glaucomas also occur in cats, but rarely. DNA tests for dogs are available.
– Secondary Glaucoma; If another disease in the eye causes glaucoma. The reason can be a cataract, an infection in the eye or neoplasm (cancer). In cats, the most common cause of glaucoma is an inflammation in the eye or tumor.
Diagnose and treatment
Diagnostic procedures are critical to managing the glaucomas and include tonometry, ophthalmoscopy, and gonioscopy (done by an ophthalmologist with a special lens). In the daily practice, tonometers are used to estimate the intraocular pressure, which is reasonable consistent in most species. Ophthalmoscopy permits detection of damage to the eye. Gonioscopy is done by an ophthalmologist with a special lens and helps for the classification of glaucomas (primary or secondary) and determines the most appropriate medical and surgical treatment.
Most dogs with early onset or moderate chronic glaucoma will not visit the clinic as the signs are subtle: sluggish to slightly dilated pupils and the start of enlargement of the eye (buphthalmia). To detect glaucoma in its early phase, tonometry can be routinely performed on high-risk breeds of dogs as part of the annual check-up. Signs of glaucoma include dilation of the pupil, thickening of the small blood vessels of the eye globe, cloudiness of the eye (corneal oedema). Pain is manifested by behavioural changes (lethargic, less active, grumpy) and occasional pain around the eye rather than increased tear production. Glaucoma is known to be a very painful condition.
Glaucoma can be treated medically or surgically depending on the classification of glaucoma. The goal is to preserve the vision and to minimalize the pain, as glaucoma is known to be very painful. Different medication is available, eye drops, ointments, tablets, etc. The medical treatment is focused on:
– Decreasing the production of the vitreous
– Improvement of the drainage of the fluids
– Prevention of a secondary bacterial infection (with antibiotics)
– Pain relief.
Lowering the eye pressure with medical treatment is successful in most of the cases although might be disappointing in the long term and surgical treatment might be the only option left in that case. The prognosis of glaucoma is guarded. End-stage glaucoma with enlargement of the eye and blindness quite often results in enucleation (removal of the eye).