Ординатура / Офтальмология / Английские материалы / Notes on Veterinary Ophthalmology_Crispin_2005

FELINE OPHTHALMOLOGY

(b)

(a)

Figure 4.2(a,b) In the cat illustrated in (a) the eyes were normal and the subtle anisocoria (inequality of pupil size) was of central origin (diffuse inflammation). In (b) a normal external eye is shown.

ANATOMICAL DIFFERENCES FROM THE DOG

•There are no true eyelashes, and modified skin hairs close to the upper eyelid margin serve in this capacity

•The third eyelid has both striated and smooth muscle, so that there is some voluntary control over its movements

•The cornea almost fills the palpebral aperture, the third eyelid is unobtrusive and there is little visible bulbar conjunctiva

•It is possible to view the drainage angle directly without needing to use a goniolens

•The iris is generally less heavily pigmented than that of the dog, and the distinction between the pupillary and ciliary zones is not always clearly defined

•The pupil is round when dilated and a vertical slit when constricted

•The tapetum is larger and more reflective than that of the dog, and the iridocytes (tapetal cells) are rich in riboflavin

•The optic nerve head is almost always unmyelinated, so it is round in shape and slightly recessed

The combination of voluntary control over third-eyelid movement, a very effective pupil-constriction mechanism and a reflective tapetum make it essential to examine the cat’s eye, and the fundus especially, with as low a light intensity as possible. This is also the case if a mydriatic is used. Subtle fundus lesions will be obscured if the light is too bright because of the mirror-like effect of the tapetum. As emphasised previously, physical and neurological examination may be just as important as ophthalmic examination in determining if the eyes and their adnexa are normal (Figure 4.2a,b).

The common feline ocular and adnexal conditions, and those that are important to recognise because of the serious implications of misdiagnosis, are summarised in Box 4.1.

FELINE OPHTHALMOLOGY

•Visualisation of the deep orbit is less easy in cats than dogs, so the optic nerve is clamped blind and it is most important to avoid excessive traction on the globe and optic nerve during removal.

•Excessive traction while the optic nerve is intact may cause damage to the other optic nerve via the optic chiasma, so that the fellow eye is blinded at the time of surgery.

•Otherwise the surgery is similar to that in the dog.

Orbital neoplasia

Clinical signs

Some 90% of orbital tumours in cats are malignant. Orbital tumours are often of epithelial origin (usually squamous cell carcinoma), or reach the orbit by extension from neighbouring tissues (e.g. from the eye into the orbit, along the optic nerve into the orbit, from the nose into the orbit) (Figure 4.3). Tumours may also reach the orbit as a result of spread (metastasis) from elsewhere (e.g. multicentric lymphoma).

Management

All cases are best referred if there is a prospect of retaining a functional eye, or if the extent (and nature) of the tumour is unclear. Orbital tumours in cats are difficult to manage and the prognosis is usually grave.

Figure 4.3 Orbital neoplasia in a Domestic Shorthair. There is prominence of the third eyelid and dorsolateral deviation of the right globe. Taken in conjunction with the haemorrhagic discharge from the right nostril, the primary site of the space occupying mass is most likely to be nasal with orbital extension through the medial orbital wall. The tumour was subsequently confirmed as a nasal adenocarcinoma at postmortem examination.

EYELIDS

CONDITIONS OF THE THIRD EYELID

(NICTITATING MEMBRANE)

Generalised disease

Dysautonomia

Dysautonomia (an autonomic polygangliopathy) may be associated with unilateral or bilateral third eyelid prominence, although dilated pupils and absence of the pupillary light response are the most constant ocular features.

Chronic diarrhoea

Chronic diarrhoea is sometimes associated with a self-limiting, bilateral, third eyelid protrusion. The cause is unknown. Viral disease has been suggested, but never proved. Debility, weight loss and reduction in the amount of retrobulbar fat, do not produce the obvious third eyelid prominence seen in the dog.

Prominence of the third eyelid – summar y of causes

•Anatomical: e.g. small eye

•Pain: produces globe retraction and consequent protrusion of the third eyelid

•Inflammation and infection: extensive symblepharon formation may be associated with enophthalmos and third eyelid prominence

•Systemic and generalised problems: e.g. tetanus, dysautonomia and chronic diarrhoea

•Primary and secondary neoplasia: very rare

•Retrobulbar space occupying lesions: e.g. inflammation and orbital neoplasia

•Horner’s syndrome: third eyelid prominence, together with enophthalmos, narrowing of the palpebral fissure, ptosis and miosis

•Drug-induced: e.g. phenothiazine tranquillisers

CONDITIONS OF THE UPPER AND LOWER EYELIDS

Ophthalmia neonatorum

The eyelids of neonatal kittens remain fused for some time after birth (usually 4–12 days). Occasionally, infection behind the closed eyelids results in neonatal conjunctivitis (ophthalmia neonatorum), which is invariably caused by feline herpes virus (FHV-1).

Clinical signs and complications

•Swelling behind the closed eyelids often with escape of pus medially (Figure 4.4(a))

•Other signs of FHV-1 infection as, for example, respiratory disease

•The inflammation caused by FHV-1 is severe and may result in symblepharon, occluded lacrimal puncta, keratoconjunctivitis sicca, corneal ulceration, perforation, endophthalmitis and panophthalmitis

Treatment

•The eyelids can be opened with a blunt-tipped probe or blunt-tipped tenotomy scissors as described previously in the dog. The eyelids should be eased open starting in the region of the medial canthus, working from medial to lateral, and carefully cleaning away any purulent material (Figure 4.4(b))

•A short course of topical antibiotic will be required and any ocular discharge should be removed before antibiotic is applied

•Adequate supportive care should be provided

•If the condition is not treated promptly, the severity of the inflammation results in complications (Figure 4.4(c))

FELINE OPHTHALMOLOGY

FELINE OPHTHALMOLOGY

Symblepharon (see under Conjunctiva, this section, pp 189–90

Agenesis and coloboma

Complete (agenesis) or partial (coloboma) absence of the eyelid or eyelids is not uncommon in cats (Figure 4.5).

•Repair may be effected by a number of techniques, depending upon the extent of the defect. Cases with large defects that cannot be repaired by primary closure should be referred. In some breeds, such as the Burmese, eyelid defects may be associated with dermoids

Entropion

Entropion is relatively uncommon in cats and is usually a result of chronic inflammation, or of spastic type associated with pain. Persian cats are the exception, as they may have congenital entropion, usually of the lower medial eyelid, which may require corrective surgery (Figure 4.6).

Treatment

•Differentiate spastic entropion from anatomical entropion by applying topical local anaesthetic – spastic entropion disappears, anatomical entropion persists

•Perform surgical correction for anatomical (Hotz-Celsus technique) and cicatricial (Y-to-V technique) types of entropion. Treat the underlying cause for spastic types.

Figure 4.6 Entropion affecting the lower medial eyelid in a Persian Cat. This is the commonest site for anatomical entropion and, in this case, is associated with the formation of a corneal sequestrum.

Meibomianitis

Meibomianitis (Figure 4.7), chronic inflammation of the meibomian glands, can cause inspissation of meibomian lipid and consequent formation of chalazia when the glands become overloaded and rupture. The condition is most likely to present as lipogranulomatous conjunctivitis. Cystic glandular changes are also seen occasionally, especially in Persian cats.

Figure 4.7 Meibomianitis (chronic lipogranulomatous conjunctivitis) in a Domestic Shorthair. Lipid histochemistry of biopsy material indicated large quantities of lipid associated with the meibomian glands.

FELINE OPHTHALMOLOGY

FELINE OPHTHALMOLOGY

186 Notes on Veterinary Ophthalmology

Treatment

Usually the removal of the inspissated material by curettage after incising the palpebral conjunctiva is curative.

Eyelid neoplasia

Eyelid tumours are uncommon, and histopathology should always be undertaken. Squamous cell carcinoma is the most frequently encountered eyelid neoplasm, especially in white cats and those with non-pigmented lids (Figure 4.8). These tumours are often locally invasive, but are also potentially metastatic, so careful examination of the whole animal is mandatory. Animals with extensive eyelid involvement should be referred.

Management

•Squamous cell carcinoma responds to a variety of treatments, including local radiotherapy and surgical excision combined with blepharoplasty. Local radiotherapy on its own can be very effective, as is excision combined with cryosurgery and radiotherapy

•For other eyelid tumours (e.g. mast cell tumours) wide-based excision and blepharoplasty is usually the treatment of choice

•All feline eyelid tumours should be submitted for histopathology

to be resolved into those with increased tear production and those with inadequate tear drainage

•Topically-applied fluorescein 1% does not always appear at the ipsilateral nostril, as the nasolacrimal duct is short and fluorescein may enter the oropharyngeal region and be swallowed

•It may be easier to tilt the head downward and examine the ipsilateral nostril, rather than attempting to identify fluorescein in the oropharyngeal region

•Fluorescein is most readily observed using blue light in the dark

Tear distribution problems

Agenesis and colobomatous eyelid defects are the commonest reason for poor tear film distribution.

Increased tear production

Any painful eye condition may increase tear production. Follicular conjunctivitis may cause sufficient irritation to increase tear production when follicles are prominent on the inner surface of the third eyelid. Very rarely, increased production can be caused by inflammation of the lacrimal or nictitans gland.

Inadequate tear drainage

Congenital problems

•Absence or atresia of the lacrimal puncta; the upper and/or lower punctum is affected and other eyelid anomalies may also be present

•Anatomical imperfection is a possible cause of tear-drainage problems. Flat-faced cats such as the Persian are often severely affected (combination of shallow orbit, prominent globe, shallow lacrimal lake and occlusion of the nasolacrimal duct associated with brachycephalic conformation). Anatomical imperfection may also result from trauma or surgery

Acquired problems

•Loss of punctum ± canaliculus through destruction as a result of inflammation or previous surgery. Punctal occlusion in cats with symblepharon formation is reasonably common, but is not readily amenable to surgery, as adhesions reform

•Blockage of any part of the nasolacrimal system occurs because of problems within the system (e.g. foreign bodies, dacryocystitis), or external influences, such as nasal and tooth-root problems, space occupying lesions and trauma

THE DRY EYE – UNDERPRODUCTION AND ABNORMALITIES

OF TEARS

The feline tear film has received little study to date, and it is assumed that, as in the dog, the commonest clinical problem is a lack of aqueous production resulting in keratoconjunctivitis sicca (KCS).

Keratoconjunctivitis sicca

Clinical signs and aetiology

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

FELINE OPHTHALMOLOGY