Diseases Of Different Organs
A large number of conditions affect the dog’s eyes and range from retinal changes to problems associated with the structure at the front of the eye. Deeper changes are rarely immediately obvious; the effects are mainly in a degree of vision difficulty, apparent as reduced visual acuity or disturbed vision. Distorted vision presents many difficulties as the dog may see objects in a different place and fail to avoid obstructions. Professional attention is necessary. The front chamber and outer covering of the eye is subject to injury and penetration by foreign bodies. Occasionally there is hemorrhage into the front chamber following an accident, resulting in a ‘curtain’ of blood in front of the lens. Although most cases resolve, urgent attention is needed to prevent blindness. Most eye injuries and infections cause inflammation and discharge, with the eye firmly closed. Veterinary examination is urgent; food should be withheld as the dog will probably have to be anaesthetized before the extent of the damage can be explored. Severe inflammation of the outer eye surface is known as Keratitis and can arise from injury or infectious disease. Occasionally, ulceration follows which may take a long time to treat successfully; if left rupture of part of the eye may result. Keratitis should not be confused with protrusion of the third eyelid, although that condition may be an accompanying factor. The third eyelid (Membrana nictitans) acts as an additional protection for the eye; when the eye is closed, the third eyelid automatically moves across. If the eye is inflamed and partly closed, the third eyelid often shows as a ‘shutter’ across part of the globe.
Eyelids are usually inflamed when the eye is infected or injured. Allergies also cause swelling. The effect, on exposure to the allergen, may be sudden. Any of the three eyelids may be injured; it is not rare to see a piece of the third eyelid torn away and lying across the eye surface. A small gland in the third eyelid often becomes enlarged, causing the eyelid to appear prominent, sometimes turning outwards. Surgery is often needed to correct this condition and is usually effective. See also Ectropion and Entropion.
This term aptly describes a well-defined condition of the normally transparent cornea. The condition is associated with a specific virus infection or occurs after the use of certain live vaccines in some susceptible breeds, particularly but not exclusively in Afghan Hounds. Only about twenty per cent of infected animals are affected, and the condition usually resolves itself in a few days. In some cases the condition persists and may become permanent. Any discoloration or clouding of the eye is a matter for veterinary examination.
Breakdowns in vision are commonly due to injury, aging, infections, disease, or inherited factors. See also Cataract, Collie Eye Anomaly, Conjunctivitis, Eye Diseases, and Progressive Retinal Atrophy.
The effects of failing eyesight may not be readily apparent as the dog easily adapts to changing circumstances. Much depends on whether vision is distorted or lessened. Distorted vision is likely to result from changes at the front of the eye, particularly lens dislocation, when the dog sees objects in a different place and may bump into them. Even so it may adapt to the location of familiar furniture, and distorted vision may not be immediately obvious to the owner. The process of lessening visual acuity is usually gradual, and often due to age. Dogs with little or no eyesight can negotiate obstructions in their household with apparent ease.
Injuries to the eye stem mainly from road accidents and fights; they are generally unsightly or the eye is held so tightly closed that the extent of the problem is difficult to establish. On occasions the eye may be dislocated completely from its socket, especially in breeds with protruding eyes, such as Pekingese and Pugs. The eye can sometimes be replaced with prompt veterinary attention, although it will almost certainly suffer some damage, but often removal of the eye is the only course of action. The dog may be more comfortable with the eye removed, the result being no worse than blindness in one eye. Dogs recover remarkably quickly, and the level of pain experienced with most eye conditions seems to be much less than in comparable human situations.
In order to transmit and focus light on to the retina, the lens must be transparent. Degenerative changes may result in a cataract when the lens becomes opaque and visible as a cloudy reflective area deep in the eye. Usually both eyes are affected, and as less light passes on to the retina, vision is much reduced. Reflex constriction of the pupil when a light is shone on it is greatly lessened. Dogs with poor vision manage to cope well in most circumstances Cataracts are often associated with other eye diseases, particularly in cases of inflammation; they may also occur as complications or simply with general changes of age, especially in Labradors and Poodles. Once inflammatory conditions have been controlled, there is little prospect of dissolution of cataracts, and surgical removal of all or part of a cataract may be necessary. However, dogs still have effective vision with the lens removed, provided there are no extensive degenerative changes of other structures.
Collie Eye Anomaly
Rough and Smooth-Coated Collies are prone to what is thought to be faulty development of the retina. Most structures at the back of the eye are affected, and the result may vary between mildly defective sight and total blindness. The condition is almost certainly inherited.
The eye is normally lubricated with tears from the lachrymal gland which drain from the eye through ducts. Excessive tear production or poor drainage results in discharge from the eye. Insufficient tear formation to lubricate the eye gives rise to a condition called Kerato- conjunctivitis Sicca or dry eye. The normally healthy moistness of the eye is replaced with a thick, sticky discharge, and local inflammation may lead to ulceration and permanent opacity of the cornea.
Early treatment is needed to keep the eye moist and stimulate tear secretion. In severe or persistent cases, surgery is sometimes advised. This involves transplantation of a duct from a salivary gland (the parotid) to lubricate the eye and is usually effective.
The position of the edge of the eyelid, with its attached eyelashes, in its relation to the eyeball is of importance to certain eye conditions. If the eyelid is turned out too much it exposes a piece of the delicate conjunctiva, an occurrence which may appear appealing in breeds such as Bloodhounds and St Bernard’s, but soreness is likely if the eyelid turns out too much. Corrective surgery consists of removing a small crescent piece from the affected eyelid, usually the lower one. It is a delicate operation which may need modification.
When the eyelid turns inwards, the eyelashes make contact with the eyeball and cause inflammation and irritation. The condition is more common and more of a nuisance to the dog than Ectropion, especially in Chows and other breeds where a diamond-shaped eye is considered a desirable characteristic. Surgical correction is more necessary with in-turning than with out-turning of eyelids because of the damage to the globe of the eye and the likelihood of impaired vision. A crescentic piece is removed from the outside of the eyelid, and it may take more than one operation to achieve the necessary result. Both upper and lower eyelids may be affected.
Lacrymal Duct Blockage
The lacrymal ducts drain most of the tears which lubricate the eyes. Drainage, through a small opening at the inner corner of each eye, may become obstructed either because the duct is too narrow to accommodate tear production or as a result of an inflammatory condition. Some of the tears produced evaporate, but the remainder flow down and stain the dog’s face. On light-coloured dogs, particularly Poodles, the stains look unsightly, but are not harmful in any way. Surgical clearance of the blocked duct under a general anesthetic is often necessary, followed by treatment to reduce inflammatory changes in the lacrymal duct.
Progressive Retinal Atrophy
Usually referred to as PRA, this is an inherited condition more prevalent in certain breeds, particularly the Miniature and Toy Poodle, and the Briard, than in others. There are several types of retinal atrophy; general deterioration of the retina usually afflicts Poodles, and central deterioration is seen in some Briards, Labradors and Collies. The generalized form of retinal atrophy may first be seen as ‘night blindness’, as that part of the eye most used to see light intensity deteriorates first. Central retinal atrophy does not usually progress to blindness and, unlike generalized atrophy of the retina, vision may be much better at the peripherals than in the center. Vision in dull light may be better than in bright daylight. The changes are irreversible, and as yet no treatment is available to arrest the progression of the condition. However, other changes within the eye, such as cataracts. May need treatment. Vigorous attempts are being made by breed societies and veterinary associations to try to reduce the extent of PRA, the object being to identify clinical cases and encourage breeding from stock certified to be sound.