Professor, Royal Veterinary College, Department of Veterinary Clinical Sciences
Hatfield, Hertfordshire, UK
'The diseases of the eye constitute a very important, but most unsatisfactory division of our work, for the melodies of this organ, although few in number, are frequent in their appearance. They are sadly obstinate and often baffle all skill.' W. C. Spooner, 1852.
Almost 150 years have lapsed since this judgment on ocular disease in veterinary medicine was delivered, and most of it remains true to this day. The exceptions relate to skill and the paucity of ocular disease. Our treatments of the 'melodies of this organ' have improved as aetiologies have been explored and research has produced therapies both medical and surgical. However, the development of the pedigree dog in its numerous shapes and sizes has provided today's clinician with a wide range of ocular diseases to treat. These diseases are determined genetically and have been unwittingly produced either through the desire to refine a specific anatomical feature or as a by-product of the close breeding involved in obtaining a specific feature. The problems, therefore, have arisen either as the result of an earnest desire to measure up to a Breed Standard, or they arose accidentally in a selection process focused on improvement. Thus, microphthalmos may be the result of producing a small ellipsoidal palpebral fissure, while progressive retinal atrophy has appeared within certain breeds because specific lines have been selected for intensive breeding to perpetuate their outstanding breed features. It is reasonable to expect that today's pedigree dog should be able to enjoy a normal life free from pain, discomfort and other incapacity. That would be the measure of real progress, but in some breeds we have a situation in which the effects of natural selection and evolution have literally been reversed.
The two dictating factors in eyelid conformation are size, and hence the shape, of the palpebral fissure and the position or size of the globe. Thus entropion, ectropion, the diamond eye configuration and anomalies of the membrana nictitans tend to be dictated primarily by the requirements of the Breed Standard, while other defects like distichiasis and aplasia of the lacrimal puncta occur as the result of intensive breeding programmes involving affected animals.
Several breeds are involved, the incidence varying from extremely high in the Chow-Chow and Shar-Pei, to low in breeds like the Labrador and Golden Retrievers. Entropion is a deformation of the eyelid in which there is inward rotation of part of the palpebral margin such that eyelid hair is brought into contact with the cornea and/or the bulbar and membrana conjunctival surfaces. Invariable there is discomfort or pain and the patient may present in blepharospasm. Conjunctivitis, superficial keratitis and corneal erosion are all possible consequences and sight can be permanently impaired as the result of scar and pigment formation if the defect is not corrected. It is normally the lateral part of the lower eyelid that is involved, but constant blepharospasm can induce further inward rotation of the palpebral fissure. Extensive involvement is seen with regularity in the Chow-Chow and in the Shar-Pei. Fortunately, corrective surgery is effective and skin or skin and orbicularis oculi muscle resection is well practised. Eyelid tacking, which has been extensively utilised in the neonatal lamb, can be used in very young puppies, but a number of these patients subsequently require the more traditional approach to achieve correction.
Here the lower eyelid is everted away from the globe to expose the membrana nictitans and the ventral conjunctival surfaces. Exposure of this tissue results in chronic conjunctivitis, and the lagophthalmos may detract from the efficient distribution of the precorneal tear film. Exposure keratitis and even corneal ulceration may ensue and drainage of the tear film via the nasolacrimal duct may also be impaired. It is due to the large palpebral fissure which is a required feature of the Breed Standard for several breeds. Thus, ectropion is expected in breeds like the St. Bernard, the Bloodhound, the Mastiff, the Basset Hound and the Clumber and English Cocker Spaniels and its incidence will remain high unless considerable change in the conformation of the head in these breeds is effected. The Breed Standard of the Clumber Spaniel, for example, asks for the eyes that should be enophthalmic with prominence of the membrana nictitans. The weight of the large hanging pinnae combined with the heavy jowls simply pulls the palpebral fissures ventrally over the globes leading to loss of support for the lower eyelid. Similar commentary applies to the other breeds, and the recent Breed Standard changes are not radical enough to effect real improvement.
Surgical correction is possible, but the success of the techniques used is governed considerably by the weight of the facial skin. Simply shortening the palpebral fissure by full thickness wedge resection does nothing to stablise the lateral canthus and techniques that shorten the lower eyelid and provide support by cicatrix formation at the lateral canthus offer the best chance of success.
The Diamond Eye Configuration
This severe conformational defect is a combination of entropion and ectropion, and is the direct result of a large, unsupported palpebral fissure. It is simply an exaggeration of the conditions that produce ectropion and is found consequently in those breeds in which ectropion readily occurs. Deficiency of the lateral retractor muscle allows the lateral canthus to hang loosely in a position well below the normal line of the palpebral fissure. This loose tissue distorts easily, particularly where there is no support from an enophthalmic and somewhat microphthalmic eye. Entropion of the lateral parts of the upper and lower eyelid is the result, and this is combined with ectropion of the central part of the lower eyelid. Conjunctival exposure and inflammation result in chronic ocular discharge, and corneal scarring and pigmentation inhibit sight. Often the eye is not visible and sight is largely a matter of touch for many affected patients. Surgical correction is difficult and the extreme examples simply cannot be helped enough. A combination of eyelid shortening and lifting procedures together with rhytidectomy and facelifting techniques may alleviate the condition, but the real solution lies in the acceptance of the fact that this condition is a serious defect and that only radical change in conformation can effect significant improvement. It requires something of a U-turn by those currently involved in the well-being of the affected breeds, but even if this were to happen overnight it will be many years before real improvement is seen.
Unlike the previous eyelid conditions, distichiasis is not related to conformation. The corneal irritation, inflammation and ulceration that can accompany this condition are due to the presence of accessory or ectopic cilia on the margo-intermarginalis of the palpebral fissure. The cilia arise singly or in groups from the meibomian gland orifices, having found origin within the distal tarsal plate tissue of the eyelid. Not all distichiasis is of clinical significance for in many patients the cilia 'float' harmlessly in the precorneal tear film. However, in others the hairs cause trigeminal irritation and possible corneal damage. Distichiasis is commonplace in several breeds, with the English and American Cocker Spaniels and the Miniature Long-Haired Dachshund being significantly involved. Simple plucking or cutting of the hairs offers temporary relief only, and root removal by electrolysis is not always successful. Cryotherapy, in which the roots are destroyed by freezing the distal tarsal plate through the palpebral conjunctiva, can be successful, but techniques that involve dissection to remove the roots are governed by the thickness of the eyelid.
The several keratopathies which are considered to be inherited include chronic superficial keratitis (pannus or CSK), the epithelial and endothelial dystrophies, the lipid dystrophies, keratitis pigmentosa and keratoconjunctivitis sicca whilst there is a clear breed predisposition associated with conformation in the aetiology of corneal ulceration in the brachycephalic types.
There is only one conclusion and that is that where our desire to produce a desired feature in our dogs has led to discomfort and loss of function, that feature should be changed or at least modified to allow man's best friend to live a healthy pleasant life.