Last Updated on January 6, 2021 by Julia Wilson
The retina is the thin, transparent layer of light-sensitive tissue which lines the rear (posterior) wall of the eye, and works similarly to that of the film in a camera. Photosensitive cells known as rods and cones convert light into electrical impulses and transport them to the brain via the optic nerve.
Anatomy of the inner eye
The vitreous humour is a gel-like substance which fills the interior of the eye, helping it keep its shape. The retina has nine neurosensory layers including rods and cones (responsible for vision) which are located in the innermost layer and the retinal pigment epithelium (RPE) behind the photosensitive layer.
In the centre of the retina is the optic nerve, which travels from the retina to the brain where it transmits visual information.
The choroid is a layer of tissue behind the retina which is rich in blood vessels to the retina with oxygen and nutrients.
There are three types of retinal detachment, including:
- Rhegmatogenous retinal detachment (RRD) occurs when there is a tear in the retina which leads to vitreous humour seeping through the tear and behind the retina, separating it from the underlying retinal pigment epithelium.
- Exudative (serous) retinal detachment is due to a build-up of fluid between the photosensitive layer and the retinal pigment epithelium. The most common causes of exudative retinal detachment are inflammatory conditions.
- Traction retinal detachment occurs when the retina is pulled off the retinal pigment epithelium due to tractional forces. The most common cause of traction retinal detachment is diabetes.
There are no breed predilections, it is seen more in older cats, but that is no doubt due to the increased incidence of systemic diseases such as hypertension and hyperthyroidism, which occur as cats age.
Retinal detachment can be primary (spontaneous or traumatic) or secondary to systemic diseases.
Hypertension (high blood pressure): The most common causes of retinal detachment in senior cats. High blood pressure causes fluid to leak from the blood vessels behind the retina, which over time causes it to separate from the underlying layer it is attached to (serous retinal detachment). Hypertension may be primary or secondary to chronic kidney disease and hyperthyroidism.
Hyperviscosity syndrome (HVS): This condition causes the blood to become thicker than usual due to increased proteins (hyperproteinemia), most often associated with multiple myeloma. This can lead to ruptures in the small blood vessels behind the retina.
Advanced diabetes: Uncontrolled blood sugar levels can damage the tiny capillaries in the retina vessels (neovascularisation). These blood vessels are more prone to leaking blood into the vitreous humour (the gel-like substance inside the eye). Scar tissue can form which at times can contract and pull the retina away from the underlying retinal pigment epithelium. This condition is known as diabetic retinopathy.
Trauma: Blunt force, penetrating injury or surgical trauma from a previous eye operation.
Cancers: Lymphoma, multiple myeloma (cancer of the plasma cells), tumours of the eye (most commonly melanoma or ciliary body adenocarcinoma) and aggressive metastatic cancer which can infiltrate the subretinal space which is located between the photoreceptors and the retinal pigment epithelium (RPE).
Ethylene glycol toxicity: Ethylene glycol can cause retinal detachments due to secondary to depositions of crystals within the retina.
Glaucoma: An increase in intraocular pressure within the eye, glaucoma can stretch and detach the retina as the eyeball increases in size.
Vasculitis: Inflammation of the blood vessels which can cause inflammatory exudates to localise in the space between the retina and epithelium.
Idiopathic: Unknown cause.
Retinal detachment isn’t painful to your cat, and it is quite easy for the condition to go unnoticed. It may occur in one (unilateral) or both eyes (bilateral). When both eyes are affected, it is generally due to an underlying systemic disease. Humans with a retinal detachment often report floaters and flashes.
- Sudden blindness or reduced vision: You may notice your cat becoming more clumsy or walk into furniture and walls.
- Odd-sized pupils (anisocoria): The pupil of the affected eye is slow to dilate (enlarge), or remains dilated if the cat has a total retinal detachment. Bilateral pupil dilation will be present in cats with detached retinas in both eyes.
- Hyphema: Bleeding in the front of the eye may be present.
The veterinarian will perform a complete physical examination. A thorough ocular examination will include testing the menace response to evaluate a behavioural response making a threatening gesture with the hand at one eye, and evaluating the pupillary light reflexes by shining a light into the eye(s), which should cause the pupils to constrict (become smaller).
- Have you noticed any other symptoms?
- Does the cat have any known medical disorders?
- How old is the cat?
- Is the cat taking any prescribed or non-prescribed medications or supplements?
- Baseline tests: Biochemical profile, complete blood count, and urinalysis to evaluate the organs and look for signs of infection, poisoning or inflammation.
- Ophthalmoscopy: Also called a funduscopy, ophthalmoscopy is an examination of the back part of your cat’s eye health using an ophthalmoscope.
- Tonometry: A measure of the intraocular pressure in the eye to evaluate for glaucoma.
- Blood pressure check: This is performed in a similar way to humans, with an inflatable cuff placed on the cat’s front leg or tail.
- T3 and T4 tests: Blood tests to check levels of T3 and T4 thyroid hormones in the blood to evaluate for hyperthyroidism.
- Imaging: Radiographs and/or ultrasound of the chest and abdomen to look for tumours.
- Bone marrow biopsy: If the veterinarian suspects multiple myeloma. This would reveal an overabundance of plasma cells.
The goal of treatment is to address the underlying issue and where possible, repair the retina. Your veterinarian will refer you to a specialist eye veterinarian (ophthalmologist) to perform retinal surgery.
- Cryopexy – A procedure in which the ophthalmologist uses extreme cold to freeze the retina around the tear. This causes the area to swell and forms scar tissue when it heals. It is this scar tissue that seals the retina to the wall of the eye.
- Scleral buckle surgery – The surgeon places a piece of silicone on to the sclera (the white portion of the eye) to push it towards the break or tear in the retina, the fluid is drained, and the tear is frozen during this process.
- Pneumatic retinopexy – The surgeon injects an air or gas bubble into the centre of your eye, to push the retina back in place. The tear is sealed with laser or cryosurgery.
- Vitrectomy – The vitreous is removed from the eye and replaced with a gas bubble which pushes the retina back in place against the wall of the eye keeps allowing it to heal. The tear is then repaired by cryosurgery or laser.
As well as repairing the tear or detachment, it will be necessary to treat the underlying cause.
The prognosis can vary depending on the speed of treatment and the underlying cause. The prognosis is poor if the retina has been detached for more than 24 hours, in which case it may be necessary to remove the eye (enunciation). This is an unfortunate outcome; however, cats can adapt very well to the loss of their sight.
- Administer medications as directed by your veterinarian.
- Keep your cat indoors and restrict activity during recovery.
- Regular follow-ups to monitor your cat’s progress and blood pressure.
- Restrict activity until the retina has re-attached.