EYE EYE

There are many age-related changes which can be recognised in eyes including the following:


Eyelid papillomas

Papillomas or warts are very common in old dogs particularly on the eyelid margins. Excision is indicated when they impinge on the cornea causing irritation, inflammation or self-trauma. Melanomas and carcinomas occur occasionally, but they are rare.



Cysts of the gland of Moll

These cysts are usually small and have a vesicular appearance. They do not cause clinical problems but can be surgically excised if necessary.



Increased tear viscosity

Increasing tear viscosity will reduce the rate of flow of tears across the corneal surface, thus reducing the ability of the tear film to wash away particulate matter that might collect on the surface.



Decreased lysozyme activity

Reduced lysozyme activity may lead to increased susceptibility to infection.



Corneal pigmentation

Corneal pigmentation with melanin is a common condition in dogs and is usually secondary to inflammation or some other corneal or uveal disease. If heavy pigmentation is present it will result in impaired vision.

If a primary cause cannot be identified (e.g. entropion, trauma, distichiasis, trichiasis, neoplasia (melanoma), keratitis sicca etc.) senile corneal degeneration should be considered as a possible cause.

Treatment depends upon the underlying cause. If surgical correction of a primary cause is not possible, corticosteroid therapy can be successfully employed in most cases. Superficially pigmented areas can be excised surgically.



Corneal lipid deposits

Corneal dystrophies are seen in older animals and usually present as bilateral, progressive, degenerative lesions. Lipid deposits may appear in the corneal stroma, and sometimes other materials can become deposited.e.g. calcium. Treatment is rarely indicated but an underlying cause should be sought (e.g. hyperlipidaemia, hypercalcaemia) and treated if possible.




Iris atrophy

This is rare but can lead to blockage of the drainage angle resulting in glaucoma.



Nuclear sclerosis

With advancing age fibres near the centre of the lens become compressed and this, with concomitant loss of water causes an increase in density of the lens nucleus (called sclerosis) which gives a blue-grey tinge to the lens. Nuclear sclerosis affects most dogs over 6 years of age to some degree or other, but transmission of light to the retina is not affected, the fundus is visible on ophthalmoscopic examination because the discoloured lens is still translucent and vision is not seriously impaired. No treatment is needed although there have been unsubstantiated anecdotal reports of nuclear sclerotic lesions disappearing following a change in diet from an adult maintenance ration to one formulated specifically for old dogs.



Cataracts

Senile cataracts are common in dogs and most dogs over 9 years will have some evidence of cataract formation. Usually the opacity progresses slowly and it may affect the nuclear or cortical part of the lens. They are usually blue-grey initially progressing to yellow or even brown with maturity. Despite the obvious opacity vision is often not severely impaired.

(1) Nuclear cataracts form as a result of the normal process of nuclear sclerosis.
(2) Cortical cataracts are most commonly seen in old dogs and are due to the accumulation of fluid within the lens cortex.
(3) Diabetic cataracts may appear earlier in life (from 2 years of age). They are usually bilateral and progress rapidly. The lens changes may be reversed if treated early enough.
(4) Punctate cataracts have been reported in association with hypoparathyroidism and renal insufficiency.

Impaired vision due to cataract formation is manifest as bizarre behavioural changes including barking at imaginary objects.

There is no satisfactory medical treatment for cataracts and various surgical approaches (e.g. extraction, phaecoemulsification) have been recommended.



Asteroid hyalosis

Calcium deposits called asteroid bodies are sometimes seen in the vitreous of ageing animals. They are usually only present in one eye and appear like small white round deposits. The cause is unknown, they do not cause problems and do not require treatment.



Vitreous liquefaction

This degenerative change is often seen in old animals and those that have cataracts.



Loss of rods and cones

An age-related decrease in numbers of rods and cones results in decreased visual acuity, and could result ultimately in visual impairment.



Retinal detachment

Retinal detachment is common in cats and an occasional finding in dogs. It is often bilateral and is usually secondary to hypertension such as occurs in chronic renal failure. Detachment can be slow or sudden and total detachment results in blindness.



Cystoid retinal degeneration

Cystoid retinal degeneration is common, particularly in the region of the ora serata, and it is regarded as a normal ageing process.



Neoplasia

Retinal neoplasia is rare and usually secondary to uveal tract neoplasia when it does occur. Uveal tract tumours are more common and most involve the ciliary body or extensive areas of the uveal tract. Most are malignant and pigmented neoplasms are usually melanomas. Usually only one eye is affected. Differentiating pigment changes of the iris from malignant melanoma can be difficult or even impossible. Because of this, and because melanoma within the eye tend to metastasise slowly (unlike malignant melanoma of oral origin), enucleation should only be performed when the pigmented mass grows rapidly, it develops an irregular contour, causes local discomfort or there are intraocular haemorrhages. When metastasis does occur it can be to the brain, lungs or elsewhere in the body.

In cats lymphosarcoma of the iris may be associated with positive feline leukaemia virus (FeLV) status.

The net effect of slowly progressive age-related changes leads initially to loss of visual acuity then to visual impairment and finally to blindness. Full ophthalmological examination is needed and should be incorporated into any geriatric screening programme. It should include ophthalmoscopy, assessment of pupillary reflexes and the menace reflex.