Ординатура / Офтальмология / Английские материалы / Notes on Veterinary Ophthalmology_Crispin_2005

FELINE OPHTHALMOLOGY

vascular keratitis, xerosis (corneal desiccation), recurrent ulceration and diffuse conjunctivitis may all be seen (Figure 4.9)

•In most cases there is a tenacious ocular discharge, but this is less conspicuous in cats than dogs, especially in the early stages

•STT 1 values <5mm/min, but remember that values are generally lower than those of dogs

•Feline herpes virus-1 (FHV-1), symblepharon formation and dysautonomia should be ruled out

Treatment

•Tear replacement therapy in most cases

•Parotid duct transposition is rarely used, but is a useful surgical alternative in selected cases

Figure 4.9 Keratoconjunctivitis sicca in a Domestic Shorthair. The cornea is of slightly lacklustre appearance and the camera flash is disrupted. A tacky ocular discharge and chemosis are present. The condition was unilateral and the cause unknown.

CONJUNCTIVA

In the normal cat there is very little exposed conjunctiva. It is usually confined to part of the nictitating conjunctiva and a small area of bulbar conjunctiva visible at the lateral canthus.

DISEASES OF THE CONJUNCTIVA

Epibulbar dermoid

Epibulbar dermoids may be the result of incomplete fusion of the eyelids, with displacement of skin elements into the dermoid. In cats they are usually located on the skin or conjunctiva in the region of the lateral canthus, but they may be found at other sites, and corneal involvement is also encountered. Certain lines of Birman cats show a genetic predisposition, and combined eyelid defects and dermoids in the Burmese cat may also be inherited.

Treatment

Surgical excision, as described previously for the dog (Section 3, pp 101–105).

Symblepharon

Conjunctival adhesion of the palpebral, bulbar or nictitating conjunctiva, to each other or to the cornea, is termed symblepharon and, whilst very rare in dogs, it is extremely common in cats (Figure 4.10). Symblepharon is most frequent following neonatal infection, particularly that caused by feline herpes virus. Less commonly, severe conjunctival inflammation, chemical and thermal injuries can cause this problem at any age.

Figure 4.10 Symblepharon formation in a young Siamese cat. The adhesions are extensive and have obliterated the dorsal and ventral fornices as well as occluding the upper and lower puncta. Note the ‘conjunctivalisation’ of the cornea as a consequence of destruction of the limbal stem cells during the acute phase of inflammation. The cat had suffered from severe conjunctivitis (presumed FHV-1) as a kitten and both eyes were affected.

Clinical features

•The adhesions are usually between the upper and lower eyelids and third eyelid, upper and lower eyelids and bulbar conjunctiva ± cornea (i.e. all the epitheliumcovered tissues of the ocular surface)

•The fornix is often obliterated, so the nasolacrimal puncta may also be nonfunctional and tear production may also be affected because of occlusion of lacrimal gland ductules

•Symblepharon is usually seen as a distinct entity, but may also occur in conjunction with other ocular defects such as microphthalmos

Treatment

•Surgical section of the symblepharon is simple, but the adhesions usually reform rapidly and corneal opacities may be more marked than they were originally. These disappointing results reflect the pathogenesis, notably the destruction of limbal stem cells at the time of acute inflammation. In consequence, corneal epithelium cannot be generated for repair and conjunctival epithelium resurfaces the cornea, causing ‘conjunctivalisation’ of the cornea

•The clinical picture is of ocular surface failure, characterised by conjunctival overgrowth, corneal epithelial defects, vascularisation and scarring

•Therapeutic soft contact lenses delay the postoperative complications, but do not prevent them. It is therefore sensible to avoid surgery in most cases

FELINE OPHTHALMOLOGY

FELINE OPHTHALMOLOGY

•Animals with poor or absent vision, impaired eyelid and globe mobility may benefit from complex blepharoplastic procedures and such cases should be referred

•Limbal autograft transplantation offers the most rational future treatment for a variety of ocular surface disorders, including symblepharon

Chemosis

As the cat has a loosely-arranged conjunctiva, conjunctival oedema (chemosis) may be of spectacular appearance and a ubiquitous accompaniment to many types of conjunctival disease. In addition to addressing the underlying problem it is important to prevent conjunctival desiccation.

Subconjunctival haemorrhage

This is commonest in cats after blunt or penetrating trauma (see Section 2, pp 40–41).

Conjunctival neoplasia

Conjunctival neoplasia is rare

The commonest neoplasm to encroach on the conjunctiva is squamous cell carcinoma (Figure 4.8). Primary conjunctival tumours include papilloma, adenoma, adenocarcinoma, basal cell tumour, haemangioma, haemangiosarcoma, lymphoma, neurofibroma, neurofibrosarcoma, fibroma, fibrosarcoma and malignant melanoma. Tumours that can metastasise to the conjunctiva include lymphoma (Figure 4.11) and adenocarcinoma.

CONJUNCTIVITIS

The diagnosis of conjunctivitis is not difficult, but effective management depends upon establishing the precise aetiology. It is important to emphasise that respiratory tract viruses are widespread in the cat population, so the isolation of potentially pathogenic viruses should correlate with the clinical presentation and history. The history should include an assessment of the cat’s age, vaccination status and lifestyle and whether there are other cats at risk or affected. Clinical appearance may be helpful, but is likely to be remarkably similar with a range of different causes, so laboratory confirmation of infectious causes is of value.

Aetiology

•Infectious agents – Chlamydophila felis (formerly known as Chlamydia psittaci var. felis) is the commonest cause of infectious conjunctivitis in cats in the UK. Respiratory tract viruses such as FHV-1 and, possibly, calicivirus may also be causes of conjunctivitis (Figures 4.12 and 4.13)

•Tear-film abnormalities

•Other causes of conjunctivitis are less common in cats, but note the possibility of allergy (e.g. to topically-applied drugs in particular), trauma and foreign bodies

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FELINE OPHTHALMOLOGY

Figure 4.13 Infectious conjunctivitis caused by Chlamydophila felis in a young cat. This typically presents as a unilateral problem, and in this cat, at this early stage, is affecting the left eye only.

Clinical signs

•Active hyperaemia of conjunctival vessels and conjunctival inflammation

•Chemosis

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

•Variable degrees of irritation, blepharospasm, excessive lacrimation and pain

•Chronic changes include follicle formation, conjunctival thickening, ulceration and persistent discharge (Figure 4.14)

a local manifestation of impeded venous return with an orbital mass, as part of a systemic vascular response or associated with cardiovascular disease

•Conjunctival infiltration by a tumour, most commonly lymphoma, can be confused with conjunctivitis and biopsy may be required for accurate diagnosis

INFECTIOUS CONJUNCTIVITIS

Viral

Feline herpes virus type 1 (FHV-1) (Figure 4.12)

•The most important virus associated with ocular disease in cats

•In neonates (up to four weeks of age) a cause of ophthalmia neonatorum

•Usually the whole litter is affected, but the severity may vary between kittens

•Complications of neonatal infection may be severe and include symblepharon formation as a result of conjunctival epithelial necrosis, corneal ulceration, corneal perforation, keratoconjunctivitis sicca, occluded lacrimal puncta and obliteration of the fornices (because of symblepharon), endophthalmitis and panophthalmitis

•In young kittens, infection is usually associated with respiratory signs (rhinitis, tracheitis, bronchopneumonia)

•Acute, usually bilateral, conjunctivitis is the most frequent ocular manifestation in older kittens and cats

•Initially the ocular discharge is serous, but becomes purulent within a week of the onset of the clinical signs

•Most cases also show signs of upper respiratory tract infection

•Uncomplicated infections usually take some two weeks to resolve.

•Some 80% of infected cats become latently infected, and any form of stress in later life may produce a relapse; virus may be shed intermittently and chronic asymptomatic carriers are common

•Recrudescence of infection is likely in chronically infected cats and any form of stress (e.g. re-homing, cat shows, introduction of new cats, lactation, general anaesthesia and surgery), endogenous immunosuppression (e.g. FeLV and FIV) and exogenous immunosuppression (e.g. corticosteroids, cyclosporin and chemotherapy) may produce a relapse

•The clinical signs in chronically affected cats are diverse; they include epiphora, lowgrade conjunctivitis and ulcerative and non-ulcerative keratitis

Feline calicivirus (FCV)

•Feline calicivirus is a much less common cause of viral conjunctivitis than FHV-1 and there is some doubt as to whether it is a genuine conjunctival pathogen

•Cats of any age are affected, but FCV infection is commoner and more severe in young kittens

•Ocular signs may be associated with other pathogens

•Clinical signs of infection largely relate to the effects of the virus on the upper respiratory tract, typically producing rhinitis and a serous nasal discharge

•Vesicles that rupture to produce clearly delineated ulcers are commonly found in the mouth (e.g. tongue and oral mucosa)

•Asymptomatic carriers are common, and, since the virus is excreted constantly, it is relatively easy to confirm infection in animals with clinical signs

FELINE OPHTHALMOLOGY

FELINE OPHTHALMOLOGY

Diagnosis of viral conjunctivitis

•Clinical signs

•Virus isolation from conjunctival swabs and oropharyngeal swabs

•PCR (polymerase chain reaction) provides the most sensitive and specific test for viral identification and the detection of asymptomatic carriers

•Intermittent excretion of FHV-1 means it is difficult to confirm infection in many cases, whereas calicivirus is excreted constantly

•Serology is of no value in vaccinated animals

Treatment of viral conjunctivitis

•Topical antiviral treatment for FHV-1 is described under Cornea. Calicivirus is not sensitive to the antiviral drugs that are currently available.

•Nasal and ocular discharges should be removed by regular, gentle cleaning and topical antibiotic applied to control secondary bacterial infection. White petroleum jelly can be smeared below the eyes to prevent skin excoriation

•Nursing care (rehydration and good nutrition)

•Systemic broad-spectrum antibiotic will also be needed when upper respiratory tract involvement is present

•Tear replacement therapy (e.g. 0.2% polyacrylic acid; 0.2% w/w carbomer 940) will be required if KCS is present until tear production returns to an adequate level. Occasionally parotid duct transposition is needed in the long term

Bacterial

Feline chlamydiosis (Figure 4.13)

Chlamydophila felis (obligate intracellular bacterium)

Clinical signs

•The most important bacterial feline conjunctival pathogen

•Clinical signs may be observed in cats from four weeks of age onwards

•Initially unilateral conjunctivitis, several days later it becomes bilateral. Initially there is a serous discharge with obvious chemosis and conjunctival hyperaemia, later the discharge can become mucopurulent and other organisms may be isolated

•There is no corneal involvement, and no primary respiratory disease, although mild rhinitis may be present. In a proportion of cases both respiratory tract viruses and

Chlamydophila felis will be isolated

•Lymphoid follicle formation is common in chronic cases

Diagnosis

•Conjunctival swab, cytobrush, or a Kimura spatula, are used to obtain samples from the ventral conjunctival sac for culture and indirect fluorescent antibody or PCR testing

•Diagnosis is confirmed by chlamydial isolation and by demonstration of intracytoplasmic inclusion bodies in the epithelial cells during the acute phase of the disease. Intracytoplasmic inclusion bodies can be difficult to differentiate from intracytoplasmic pigment granules

•Serology is of limited value in that a low antibody titre is not diagnostic of

chlamydiosis, whereas a high antibody titre may indicate, but does not confirm, infection. Titres may remain high for up to a year after infection

Treatment

•Treatment consists of systemic treatment with the tetracycline group of antibiotics, for example, doxycycline (5mg/kg by mouth every 12 hours for 3–4 weeks) or a combination of amoxycillin/clavulanate (12.5–25mg/kg every 8–12 hours for 3–4 weeks). The tetracycline group should not be used in pregnant queens or kittens.

•Topical tetracycline is no longer made commercially in the UK. It is not always well tolerated in the cat as it may provoke a rapid hypersensitivity response initially and, if its use continues, marginal blepharitis can develop.

•A proportion of previously-infected cats become chronic carriers and may be a possible source of infection for other cats (the organism can be isolated from the urogenital and gastrointestinal tracts), a situation which may pose problems in catteries, especially for breeding colonies. In this type of environment all the cats will require systemic amoxycillin/clavulanate or tetracycline or erythromycin or doxycycline for at least four weeks.

Feline mycoplasmosis

Mycoplasma felis, possibly in association with primary pathogens such as FHV-1 and Chlamydophila felis, may be associated with feline conjunctivitis. Mycoplasma felis alone is unlikely to be a primary pathogen and can be isolated from the conjunctival sac of normal cats.

Clinical signs

Blepharospasm, epiphora and conjunctival hyperaemia, but within 14 days the most striking finding is pallor of the conjunctiva with some thickening and chemosis and a typical pseudomembranous conjunctivitis.

Diagnosis

Confirmation of mycoplasmal conjunctivitis is difficult, as isolation requires specific mycoplasma culture media and the possibility of concurrent pathogens must also be investigated.

Treatment

•Mycoplasma felis is susceptible to tetracycline given topically for 5–7 days, but with the potential disadvantages already outlined above

•The clinical course is shortened to some five days in treated cases; without treatment the time course is some 30–60 days

Other bacteria

•Other bacteria identified (e.g. Pasteurella spp, Staphylococcus spp, Streptococcus spp, Salmonella spp, Moraxella spp) are of uncertain pathogenicity

•Bacterial conjunctivitis may occur secondary to other ocular disease (ocular, adnexal or orbital infection, keratoconjunctivitis sicca, dacryocystitis) and in cats that are stressed or immune compromised

•Pasteurella multocida may be transmitted in fight injuries

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FELINE OPHTHALMOLOGY

ALLERGIC CONJUNCTIVITIS

Allergic conjunctivitis (and allergic blepharitis) is most frequently encountered as a response to topically applied drugs and, less commonly, as a reaction to insect venom. Long-term treatment with topical preparations (e.g. tetracycline) is sometimes associated with periocular pigment loss and marginal blepharitis.

Treatment

•The allergen should be avoided

•Topical antihistamines or corticosteroids can be given, but most cases have resolved completely by 12–48 hours after removal from the allergen

Other causes of conjunctivitis are rare in cats and similar to those already described for the dog

LIMBUS, EPISCLERA AND SCLERA

NEOPLASIA

Primar y

This is a rare site for primary neoplasia. Limbal epibulbar melanoma (scleral shelf melanoma) is the most frequently encountered and, in most cases, and unusually amongst feline tumours, is both slow growing and benign.

Treatment

Sequential observation without intervention, or total resection, or partial resection with radiotherapy or cryotherapy. A graft may be required at the excision site and such cases are usually referred.

Secondar y

Secondary neoplasia associated with the feline leukaemia–lymphoma complex are the most likely to be encountered. For example, scleral deposits of lymphoma can present as a red and often painful eye. Biopsy is diagnostic.

CORNEA

Developmental and early onset corneal problems include inherited neurometabolic disease (e.g. mucopolysaccharidosis, mannosidosis, gangliosidosis). Specific enzyme deficiencies lead to the widespread accumulation of abnormal products in tissues and in the cornea this manifests as pancorneal clouding (Figure 4.15(a,b)).

had facial dysmorphia (a broad flattened face) and disproportionately large paws. (b) The corneal clouding seen in the kitten in (a) was caused by pancorneal mucopolysaccharide accumulation.

Many of the acquired causes of corneal disease in the cat are similar to those found in the dog, although eyelid and cilia abnormalities as causes of ulcerative keratitis are uncommon in cats. Claw injuries are a common cause of feline ulcerative keratitis and bacterial infection is often introduced (Figures 4.16(a,b)). Damage to the feline lens following penetrating injury has been associated with the development of poorly differentiated, malignant, intraocular sarcomas up to several years later.

Feline herpes virus (FHV-1) is a primary corneal pathogen in the cat and it is important always to consider FHV-1 as a possible cause of feline ulcerative keratitis, in addition to other possible causes.

There is no primary pathogen in the dog and, in addition, corneal sequestrum and proliferative keratoconjunctivitis are feline conditions that have no direct parallel in the dog.

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