Ординатура / Офтальмология / Английские материалы / Notes on Veterinary Ophthalmology_Crispin_2005

GENERAL AND CANINE OPHTHALMOLOGY

Figure 3.19 (a) Keratoconjunctivitis sicca (dry eye) in a two-year-old West Highland White Terrier, the breed most commonly affected by the immune-mediated type of dry eye in the UK. Both eyes were affected. A profuse and tacky mucoid discharge is adherent to the cornea of the right eye. The Schirmer tear test reading in this eye was 0 mm/minute and 5 mm/minute in the left eye.

(b) The left eye responded to topical cyclosporin and this treatment was maintained, whereas it was discontinued in the right eye after two months’ of treatment brought about no improvement and a parotid-duct transposition was performed. The right eye is illustrated some two years after parotid duct transposition.

Clinical signs

•The eye is usually uncomfortable, rather than frankly painful, although frank pain and corneal ulceration may accompany acute onset KCS

•Disruption of the corneal reflex and lacklustre appearance of the cornea

•Superficial keratitis with neovascularisation, oedema and, eventually, secondary pigmentation; in chronic KCS corneal desiccation (xerosis) also occurs

•Diffuse conjunctivitis

•Mucopurulent ocular discharge (yellow or green in colour and of tenacious consistency)

•Secondary bacterial infection

•In neurogenic dry eye the nostril on the affected side, or both nostrils in bilateral cases, are dry and crusty. Acquired KCS of neurogenic origin is sometimes associated with chronic middle ear disease

Diagnosis

•Breed, age and sex; systemic and ophthalmic history including any previous treatment

•Clinical signs

•A Schirmer I Tear Test should always form part of the work-up for animals with an ocular discharge, or any indications of ocular surface disease – it is important to test both eyes

Medical treatment

•The KCS can be managed medically by careful cleaning of the eyes to remove the tenacious discharge, followed by frequent application of a proprietary ocular lubricant such as carbomer 980 (polyacrylic acid)

•Preparations containing mucolytics, such as acetylcysteine, can be of value initially if excessive amounts of mucin are present

•Topical antibiotic treatment may be necessary in the early stages, as secondary bacterial infection is common

•Drugs that have immunosuppressive activity and stimulate tear production (e.g. topical cyclosporin) are the most useful, especially for possible immune-mediated KCS. A commercial preparation of cyclosporin ointment is available for clinical use and this is now the treatment of choice for most cases of KCS. The drug has a beneficial effect on mucin secretion as well as stimulating aqueous production. Cyclosporin should be applied twice daily for at least six weeks to assess the adequacy of response and the Schirmer tear test repeated during this time. Responsive cases require twice daily treatment for life

•The parasympathomimetic agent pilocarpine may be beneficial, by the oral or topical route, in KCS of neurogenic origin, but is of no value for immune-mediated types

•Topical corticosteroids may be helpful in initial management, provided that no corneal ulceration is present. Some of the proprietary preparations contain ocular lubricants as well as corticosteroids (see Appendix 2)

Surgical treatment – parotid duct transposition

•If the loss of tear production is absolute and permanent, or the owners cannot manage medical therapy, or the clinical signs are not kept under control with medical treatment, then parotid duct transposition should be considered. If the surgeon is not thoroughly familiar with the technique, it is sensible to practise it first or refer the patient.

•Case selection is important, for example an excessively wet eye may result when parotid duct transposition is carried out in greedy animals and, in all cases, it is usual to divide the feeds up over a 24-hour period to provide optimal lubrication.

•Parotid duct transposition is carried out under general anaesthesia and should only be performed after checking that the parotid salivary gland actually produces saliva, that the pH of the saliva is not too alkaline (ideally less than 8.4, from clinical experience) and after discussing the possible postoperative management at some length with the owners.

•Possible immediate complications of parotid duct transposition include those associated with poor case selection and surgical mistakes.

•Chronic postoperative problems include excessively wet eyes and face, periorbital hair loss, skin excoriation and corneal deposition (usually calcium salts). Very rarely, if the results are not satisfactory, the parotid duct can be ligated either to reduce the flow of saliva or stop it altogether.

•If patients are chosen carefully the results of parotid duct transposition are very rewarding (Figure 3.19(b)).

CANINE LACRIMAL SYSTEM PROBLEMS – THE WET EYE

GENERAL AND CANINE OPHTHALMOLOGY

GENERAL AND CANINE OPHTHALMOLOGY

Figure 3.20 Epiphora (tear overflow) in an American Cocker Spaniel. This eight-year-old dog had only recently developed epiphora, so congenital causes can be discounted despite the dog’s somewhat imperfect eyelid anatomy. In this case dacryocystitis had developed after conjunctivitis. Staphylococcus spp were cultured from material irrigated from the nasolacrimal duct and the condition resolved soon after a course of topical antibiotic drops was instituted.

Aetiology of developmental abnormalities of the nasolacrimal drainage system

Poor or imperfect anatomy

•Long-nosed dogs (‘pocket’ effect at medial canthus), especially when the dog has both a long nose and small eyes

•Tight apposition between the cornea and eyelid margin, especially if combined with a prominent eye

•Medial canthal entropion

•Hairs on the caruncle

•Distichiasis and trichiasis

•Abnormal location of lacrimal puncta

Imperforate puncta and micropuncta

Imperforate puncta and micropuncta are common, and it is usually the lower punctum that is affected. There is a breed predisposition in the English Cocker Spaniel and Golden Retriever and epiphora is first noticed at an early age. The diagnosis is usually straightforward in that the punctum is either absent or very small, the dog is young and the owners have noted persistent tear staining (unilateral or bilateral) from an early age.

Treatment of imperforate puncta and micropuncta

•Treatment is not always required in mildly-affected cases

•Surgery is used to enlarge existing puncta or to create puncta when they are absent

•With the patient anaesthetised, the correct site is identified by careful inspection or by cannulating the upper punctum and injecting saline or viscoelastic material to raise a bleb in the region of the occluding conjunctiva

•Any occluding conjunctiva is removed with scissors, usually as a single piece

•Topical antibiotic-corticosteroid eye drops are given for three days postoperatively

Aetiology of acquired nasolacrimal problems

•Internal blockage may affect nasolacrimal drainage (e.g. foreign bodies and inflammation)

•External influences such as nasal and tooth-root problems, space-occupying lesions, surgery and trauma may also produce nasolacrimal obstruction

Treatment of acquired nasolacrimal problems

•Depends on the site of blockage and the cause, so careful investigation is necessary

•Some aspects of investigation and treatment require general anaesthesia

•Foreign bodies such as barley awns can be difficult to remove because of their shape and their tendency to disintegrate. It is important to avoid flushing the foreign body into the narrow intraosseous portion of the nasolacrimal duct and to ensure that all the material has been removed

•Complex cases should be referred

CONJUNCTIVA

The conjunctiva is a thin, variably-pigmented, mucous membrane. It has a rich vascular supply and bright-red, freely-branching blood vessels are visible in the nonpigmented areas. The blood flow is from fornix to limbus. Vessels move with the mobile bulbar conjunctiva and the blood flow is from fornix to limbus. In disease, conjunctival vessels may invade the superficial cornea. Sensory nerve supply is from the ophthalmic division of the fifth cranial nerve and pain fibres are somewhat sparse.

The conjunctiva is freely mobile except for areas of closer attachment at fornix, limbus and eyelid margins. Because of the loose arrangement, conjunctival oedema (chemosis) and subconjunctival haemorrhage form readily after insult.

Conjunctival epithelium contains goblet cells that contribute mucin to the preocular tear film. There is also a contribution (transmembrane mucin) from surface epithelial cells. The conjunctival stroma is divided into a superficial (adenoid) layer and a deep (fibrous) layer. Lymphoid tissue is rich in the superficial layer of adults, but may be sparse, or absent, in neonates. Conjunctival-associated lymphoid tissue (CALT) is associated with immune-mediated conjunctival responses.

Palpebral conjunctiva covers the inner surface of the upper and lower eyelids, terminating in the mucocutaneous junction at the eyelid margin and reflecting at the fornices as bulbar conjunctiva, which covers the anterior portions of the globe, except for the cornea. Nictitating conjunctiva covers both surfaces of the third eyelid.

GENERAL AND CANINE OPHTHALMOLOGY

GENERAL AND CANINE OPHTHALMOLOGY

DISEASES OF THE CANINE CONJUNCTIVA

Epibulbar dermoid (see Cornea, this section pp 109–123)

Conjunctivitis

Conjunctivitis is one of the commonest problems encountered in most species (Figure 3.21), but is unsatisfactorily classified unless the aetiology can be determined. It is important to remember that conjunctivitis is often a self-limiting disease, that not all cases require treatment and that, in the dog, it is frequently secondary to some other problem. In many types of conjunctivitis it is common for the ocular discharge to persist for several weeks after the acute signs have subsided, a situation that is sometimes exacerbated when ointments are used for treatment because of ‘mucus trapping’. If the eye is comfortable and no longer inflamed the treatment should not be prolonged solely because of an ocular discharge.

Figure 3.21 Acute conjunctivitis in a dog (Left eye). There is an ocular discharge and the eye is uncomfortable and red because of conjunctival hyperaemia. Conjunctival oedema, most obviously involving the third eyelid, is also a feature. Despite a comprehensive work-up, the cause was not established and the acute signs resolved within seven days without any treatment, although a mild ocular discharge persisted for some three weeks afterwards.

Aetiology of canine conjunctivitis

•Viral – e.g. distemper virus

•Bacterial – usually Gram +ve cocci

•Parasitic – Thelazia spp common in parts of Europe (Italy), Russia, Asia and western America

•Mycotic – e.g. blastomycosis (non-temperate climates)

•Immune-mediated and allergic (e.g. atopy is common)

•Physical (common) and chemical (uncommon)

•Preocular tear film abnormalities (common – see earlier)

•Iatrogenic (home remedies, inappropriate therapy); quite common

•Unknown; common

Clinical signs of acute conjunctivitis

•Conjunctival discomfort (probably itchy rather than frankly painful)

•Active hyperaemia (dilatation) of conjunctival vessels (diffuse redness of conjunctiva) – usually all the conjunctival surfaces are involved (palpebral, nictitating and bulbar)

•Chemosis (conjunctival oedema)

•Ocular discharge (serous, mucoid, purulent, haemorrhagic or combinations of these)

Clinical signs of chronic conjunctivitis

•Follicle formation (lymphoid hyperplasia); occasionally the follicles can be localised to specific areas of conjunctiva, such as beneath the third eyelid

•Conjunctival thickening and conjunctival vascular injection

•A persistent discharge; the nature of the discharge can vary

Differential diagnosis

Conjunctivitis is the commonest reason for a red eye in dogs (Figure 3.21). There are, however, a number of other conditions that can present with an acute red eye and they must be distinguished from conjunctivitis. It is helpful to remember that simple conjunctivitis is not associated with corneal or intraocular involvement. The brief list below highlights the key ocular features that aid differentiation of non-traumatic causes of acute red eye in the dog.

•Keratoconjunctivitis sicca

•Keratitis – corneal involvement, extent and depth of which varies

•Episcleritis and episclerokeratitis – nodular or diffuse, perilimbal oedema ± superficial corneal lipid infiltration

•Scleritis – nodular or, less commonly, diffuse, perilimbal oedema ± deep corneal lipid infiltration ± uveitis

•Anterior uveitis – aqueous flare, iris is oedematous and inflamed, pupil may be constricted

•Glaucoma – non-responsive, dilated pupil, corneal oedema may be present if the intraocular pressure is sufficiently high (>40–50 mmHg)

Protocol for investigation and diagnosis

•History (e.g. unilateral or bilateral, duration, lifestyle, management, treatment, seasonal variation, vaccination status, others at risk or affected)

•Clinical appearance

•Schirmer I Tear Test to check tear production

•Conjunctival scrapes, swabs or cytobrush samples

•Biopsy on occasions

•If ophthalmic stains are to be used to aid diagnosis, they should be applied after the samples have been taken

Conjunctival scrapes may be taken for cytology, and swabs or cytobrush samples for culture and sensitivity. In first opinion practice, scrapes and swabs are usually taken only from those cases that do not respond to treatment. Topical anaesthesia is not normally required for sampling. Swabs and cytobrush samples are usually taken from the ventral fornix and palpebral conjunctival region by firm application of a moist sterile swab. Bacteria can often be recovered from the conjunctival sac of normal dogs, so the results should always be interpreted with caution.

In complex or chronic cases, conjunctival biopsy may be performed following topical local anaesthesia. Several drops of proxymetacaine hydrochloride 0.5% should be applied first, then a cotton wool bud soaked in amethocaine hydrochloride 1% is held, for several minutes, against the area to be biopsied. A piece of affected conjunctiva is tented up with small tissue forceps and removed with tenotomy scissors (crushing or distorting the sample should be avoided). The sample is placed flat on very thin card for routine histological fixation so as to avoid distortion.

Canine infectious conjunctivitis

Viral

• Canine distemper virus is the most important cause

GENERAL AND CANINE OPHTHALMOLOGY

GENERAL AND CANINE OPHTHALMOLOGY

•Ocular signs may include bilateral conjunctivitis, ocular discharge, KCS, corneal ulceration, multifocal choriotretinitis, optic neuritis and acute loss of vision

•There is no specific therapy, but the animal should be isolated and nursing care should include adequate cleansing of the eyes and tear replacement therapy

Bacterial

Aetiology and diagnosis

•Although there is a range of possible pathogens, they are most commonly secondary to an underlying predisposing problem such as KCS, eyelid abnormalities and contaminated traumatic injuries

•The diagnosis is made on the basis of the history, clinical signs, conjunctival scrapings and swabs

•The most common bacterial pathogens are Gram +ve cocci (Staphylococcus and, less commonly, Streptococcus). Neonatal conjunctivitis (ophthalmia neonatorum) has been described under Eyelids

Treatment

•Successful treatment depends upon establishing and removing the underlying cause

•For Gram +ve organisms, the commonest situation, topical fusidic acid gel is the first choice and topical chloramphenicol (as drops or ointment) is a useful second choice. If Gram -ve bacteria are involved, then gentamicin solution is the agent of choice. For mixed infections, fucidic acid and gentamicin can be used together

•For confirmed staphylococcal infection, topical corticosteroids are also appropriate, to lessen the hypersensitivity reaction to staphylococcal toxins

Allergic conjunctivitis

Aetiology and diagnosis

•Variety of causes (e.g. atopy, drug sensitivity, food sensitivity, following insect and arachnid bites, insect stings, hypersensitivity to bacterial toxins and unknown)

•The history can be diagnostic when hypersensitivity reactions are immediate

•Intradermal skin testing will be required for diagnosis of possible atopy

Treatment

•Depends upon identifying and removing the allergen(s). Hyposensitisation is effective in some cases, but the range of possible allergens complicates the situation

•Acute allergic conjunctivitis requires early treatment with corticosteroids

•If allergen(s) cannot be identified, then palliative treatment with topical antiinflammatories (e.g. sodium cromoglycate or corticosteroids) is indicated

•Note that with the exceptions already stated (atopy and staphylococcal toxins), the routine use of corticosteroids to treat conjunctivitis may obscure the cause, make correct diagnosis difficult, lengthen the time course of the disease and can prevent resolution of the inflammation

Physical causes of conjunctivitis

Aetiology and diagnosis

•Usually a consequence of consistent trauma from dust, cilia or masses which irritate or abrade the conjunctiva

•History and lifestyle may be helpful – an acute unilateral problem might suggest a

conjunctival foreign body, a more chronic problem may relate to the dog’s environment, including bedding materials like sawdust

•Chronic conjunctival exposure and irritation can also result from poor eyelid anatomy (e.g. ectropion) and other abnormalities, for example, anatomical entropion can also cause conjunctivitis because of chronic irritation

Treatment

Identify and remove the primary cause

Chemical causes of conjunctivitis

Aetiology and diagnosis

•Various causes (e.g. shampoo, insecticidal sprays, antiseptic skin preparation, acid or alkali burns)

•Identify the cause, check the pH of both the conjunctival sac and the offending chemical

Treatment

•When shampoos and weak acids are involved, use bland ophthalmic ointment after first flushing the conjunctival sac with water

•For any alkalis and strong acids, continue to flush the conjunctival sac with water while seeking urgent specialist help and possible referral. Ask the owner to bring the offending chemical with them whenever possible

‘Iatrogenic’ and idiopathic causes of conjunctivitis

Aetiology and diagnosis

•It is always worth enquiring if the owner has used home remedies

•It is important to avoid creating iatrogenic problems by inappropriate medication

•Check tear-film distribution and production if there is any suggestion of ocular surface disease

•Take swabs and scrapes if there are any signs of infection (e.g. mucopurulent discharge)

Treatment

•Stop inappropriate treatment

•Check all the conjunctival surfaces carefully. If follicular conjunctivitis is present, then a dry swab can be used to rub the follicles firmly under topical local anaesthesia – an empirical approach that often leads to their resolution

LIMBUS, EPISCLERA AND SCLERA

THE LIMBUS

The limbus is the transition zone between the orderly arrangement of the cornea and the less ordered tissues of the conjunctiva and underlying episclera and sclera (Figure 3.22(a,b)). It may be a site of chronic proliferative disease and neoplasia. The limbus can also be used as a site for surgical entry into the eye as well as being a common site for accidental intraocular penetration.

GENERAL AND CANINE OPHTHALMOLOGY

GENERAL AND CANINE OPHTHALMOLOGY

Figure 3.22(a,b) Scanning electron micrograph (a) and histological section (b) of the normal canine conjunctiva, episclera, sclera limbus and cornea.

Limbal-based changes are invariably the result of inflammation or neoplasia and should be distinguished from pathology of similar appearance involving the cornea and anterior chamber. For example, multicentric lymphoma may be associated with peripheral corneal and iris infiltration and anterior-chamber involvement. Physical examination of the whole animal may help to differentiate local ocular disease such as episclerokeratitis from generalised disease such as multicentric lymphoma.

Inflammator y problems

Benign proliferation of connective tissue is reasonably common at the limbus. It should be differentiated from cysts and neoplasia.

Treatment

Treatment consists of surface-active topical corticosteroids (e.g. dexamethasone, prednisolone, fluorometholone) combined with complete excision or excisional biopsy. Most limbal inflammations are, strictly speaking, forms of episcleritis and/or episclerokeratitis (see this section, pp 107–108).

Neoplasia

Aetiology and diagnosis

•Pigmented limbal (epibulbar) tumours are usually benign, and the majority can be classified as melanocytomas (Figure 3.23), rather than melanomas, based on their behaviour and histological appearance

•In old dogs the growth rate is invariably slow, whereas in younger dogs it may be rapid

•The German Shepherd Dog is the most commonly affected breed

•Gonioscopy is a useful adjunct to routine ophthalmic examination in these cases

Differential diagnosis

•Limbal pigmented neoplasia should be distinguished from scleral defects (e.g. staphyloma and scleromalacia perforans) and post-traumatic uveal prolapse

•Non-pigmented limbal neoplasia should be classified as primary (focal or invasive) or secondary (metastatic) neoplasia and differentiated from inflammatory disease

Treatment

Tumours at this site can be kept under observation if they are static or of slow growth. Those of rapid growth are probably best removed under general anaesthesia by excision. If necessary, a graft (e.g. scleral homograft) can be used to make good the defect and support healing, although a number of different approaches (e.g. cryotherapy, laser photocoagulation, corneoscleral transposition) have also been described. It is unusual to have to sacrifice the eye. If in doubt seek specialist opinion and consider referral.

Figure 3.23 Limbal melanocytoma in a German Shepherd Dog. Note the lipid infiltration of the cornea (arcus) which is a common feature of most limbal, episcleral and scleral pathology, whether it is neoplastic or inflammatory in origin. The serum lipid and lipoprotein profile was normal.

THE CANINE EPISCLERA

The episclera consists of collagen, blood vessels, some elastic fibres, fibroblasts, melanocytes, phagocytic cells and nerves (both myelinated and unmyelinated). The episclera is most developed between the limbus and the extraocular muscle insertions where it blends superficially with the overlying Tenon’s capsule.

Episcleritis

This condition is seen occasionally in dogs and may be diffuse (simple) or nodular and either unilateral or bilateral (Figure 3.24).

Figure 3.24 Diffuse (simple) episcleritis in a dog. Note the radial configuration of the episcleral vessels. There is faint dorsolateral anterior stromal corneal lipid deposition and more marked paraxial medial lipid deposition. In the latter region lipid deposition has been exacerbated by the presence of a small sebaceous adenoma of the lower eyelid, just visible overlying the corneal lipid. The serum lipid and lipoprotein profile was mildly abnormal, mainly because of an increase in highdensity lipoprotein. The eyelid tumour was surgically excised and the episcleritis treated with topical surface-active corticosteroid (fluorometholone).

GENERAL AND CANINE OPHTHALMOLOGY