Common eye conditions in cats – clinical tips (Part 2)

12 April 2024

In this second part of common ophthalmic conditions, Mike Rhodes from Focus Referrals and Chair of the British Association of Veterinary Ophthalmologists takes us through an overview and clinical tips of common conditions seen in cats. This follows part 1 on common eye conditions seen in dogs.

CLINICAL TIP – As a general rule, most ocular disease in cats is associated with feline herpesvirus (FHV-1). PCR testing for FHV-1 can prove problematic due the possibility of false positives and false negatives. Therefore, some ophthalmologists advocate not testing for FHV-1 but instead treating for the virus if the clinical signs are consistent with FHV-1 infection.

1) Entropion

This is inversion of the eyelid(s), resulting in ocular irritation and corneal disease due to direct contact of the eyelid hairs. Entropion is much less common in cats compared to dogs.

Clinical signs include blepharospasm, corneal ulceration and keratitis (where the eyelid hairs contact the ocular surface), corneal sequestrum formation, increased tear production, epiphora and periocular wetting, increased blink rate and self trauma. Treatment options are permanent surgical correction and surgical management of concurrent corneal sequestrum.

CLINICAL TIP – When performing surgical correction of entropion in cats, always take away more eyelid tissue when compared to a similar procedure in a dog. 

2) Conjunctivitis

This condition is relatively common in the cat and is usually primary and infectious (compared with secondary to other ocular or systemic disease processes in the dog).

Clinical signs are conjunctival hyperaemia, chemosis, conjunctival swelling/thickening, conjunctival follicle formation (chronic cases) and ocular discharge (mucoid, mucopurulent, haemorrhagic). Treatment involves addressing and treating the underlying cause. For FHV-1 conjunctivitis, if clinical signs are not severe, then stopping all treatment can allow the cat to fight an effective immune response to the virus. If this fails, either topical ganciclovir (Virgan eye gel 5g tube) or oral famciclovir (Famvir) can be used. Chlamydophila felis associated conjunctivitis is best treated with oral doxycycline (Ronaxan 20mg tablets). In cases of entropion and eyelid agenesis, surgical intervention is warranted. If due to an underlying tear film deficiency, topical lacrimomimetic therapy should be considered. Eosinophilic conjunctivitis can be treated with topical corticosteroids (e.g. Pred Forte, 1% prednisolone acetate) or cyclosporine (Optimmune, 2mg/g cyclosporine). Lipogranulomatous conjunctivitis is best treated via surgical curettage of the nodules.

CLINICAL TIP – The two most common infectious causes of feline conjunctivitis include FHV-1 and Chlamydophila felis; the latter can never cause corneal disease whereas FHV-1 can cause conjunctival and/or corneal disease.

3) Corneal ulceration – indolent superficial ulcers

Clinical signs of these types of ulcer are dendritic corneal ulcer, superficial corneal ulcer with loose, non-adherent epithelial edges, blepharospasm, conjunctival hyperaemia, ocular discharge (serous, mucoid, mucopurulent), corneal neovascularisation and corneal sequestrum formation. For treatment, surgery will be required in cases of entropion or upper eyelid agenesis. FHV-1 related indolent corneal ulcers can be managed with topical ganciclovir (Virgan eye gel 5g tube) or oral famciclovir (Famvir), and a broad spectrum topical antibiotic agent e.g. chloramphenicol. The lose epithelial edges of the lesion should be debrided following the placement of topical local anaesthetic solution (Minims Proxymetacaine hydrochloride 0.5%).

CLINICAL TIP – Feline superficial ulcers are not the same as canine spontaneous corneal chronic epithelial defects. Do not perform a keratotomy or corneal burr in a cat because you are likely to induce a corneal sequestrum which will further delay the epithelial healing process.

4) Eosinophilic keratoconjunctivitis (EK)

This proliferative keratoconjunctivitis is unique to the cat and is marked by eosinophilic inflammation. Clinical signs are often unilateral but can be bilateral, proliferative white/pink, raised lesions arising from the dorsolateral limbus, multifocal white (‘cottage cheese-like’) corneal lesions that retain fluorescein, the affected eyes are often open and comfortable and the third eyelid and upper/lower eyelids can also become involved. Treatment is topical corticosteroids (e.g. Pred Forte) or cyclosporine (e.g. Optimmune). Megestrol acetate can be a very effective alternative but is not recommended as a first-line treatment due to reported side effects.

CLINICAL TIP – The white ‘cottage cheese-like’ corneal lesions often take up fluorescein stain and are falsely diagnosed as corneal ulcers. Typically cats with EK are non-painful whereas cats suffering from ulcerative keratitis exhibit blepharospasm.

5) Corneal sequestrum

This is a condition which presents as an area of corneal discolouration (amber, brown-to-black) and is associated with corneal necrosis. Clinical signs are an area of brown corneal discolouration, blepharospasm, superficial corneal ulceration, progressive corneal ulceration, spontaneous corneal perforation, conjunctival hyperaemia, ocular discharge (serous, mucoid, mucopurulent) and corneal neovascularisation. Treatment should treat the underlying cause if possible, e.g. surgical correction of lower eyelid entropion (see above). Otherwise, conservative medical therapy can be used (see clinical tip).

CLINICAL TIP – If surgery is not an option to remove a corneal sequestrum then medical management with a topical broad-spectrum antibiotic ointment twice daily e.g. chloramphenicol (Chloramphenicol 1% Eye Ointment) is acceptable in the hope that an associated corneal neovascular response leads to sloughing of the sequestrum from the corneal surface. However, owners need to be warned that in some cases the sequestrum can progress to involve the full corneal thickness, resulting in a focal point of weakness and a spontaneous corneal perforation.

6) Uveitis

This refers to inflammation of the uveal tissue and occurs when the immune privilege mechanisms for the eye become overwhelmed and the blood-ocular barriers breaks down. The principles of uveitis are similar in cats as they are for dogs, but the clinical signs are much less noticeable. Clinical signs are keratic precipitates (often obscured by the third eyelid), anterior chamber fibrin, aqueous flare, hyphaema, hypopyon, rubeosis iridis, iris nodules, iris hyperpigmentation, inflammation of the anterior vitreous, miosis, reduced intraocular pressure, cataracts, chorioretinitis, retinal detachment and anterior lens luxation. Treatment options are topical non-steroidal anti-inflammatory drug e.g. bromfenac (Yellox eye drops), topical corticosteroid e.g. prednisolone acetate (Pred Forte 1% prednisolone acetate), systemic NSAIDs, systemic corticosteroids and systemic immunomodulatory drugs e.g. oral cyclosporine (Atopica).

CLINICAL TIP – Due to the insidious nature of feline uveitis, affected individuals often present very late on in the disease process, manifesting as apparently very different ocular conditions. For example, a corneal ulcer due to chronic secondary glaucoma and globe enlargement – the underlying cause actually being chronic anterior uveitis or an anterior lens luxation – again due to underlying chronic anterior uveitis.

7) Glaucoma

This is much less common in the cat than the dog and is usually secondary, with clinical signs much less obvious in cats than dogs. Clinical signs (acute) are mydriasis, anisocoria (unilateral cases), reduced direct pupillary light reflex. Clinical signs (chronic) are globe enlarges (hydrophthalmos) and corneal ulceration (exposure keratitis, reduced blink). For treatment, the underlying cause should try to be addressed, but cases of feline glaucoma often present at a very advanced stage. Topical treatment is restricted to dorzolamide (Trusopt, dorzolamide hydrochloride 2%) and dorzolamide/timolol combination (Cosopt, dorzolamide hydrochloride 2%/timolol maleate 0.5%). Surgical intervention involves enucleation or laser cyclophotocoagulation (endoscopic or transscleral).

 CLINICAL TIPS – 1) A slightly dilated pupil and associated anisocoria (altered pupil sizes between the two eyes) is the most common indication of early glaucoma in cats.

2) The retrobulbar optic nerve is very short in the cat and so care should be taken during eye removal surgery to avoid placing traction on the optic nerve, which could result in blindness to the other eye (via optic chiasmal damage). This is especially so in chronic glaucomatous cat eyes and so the author often decompresses the globe prior to surgery by carefully removing aqueous humour via a small gauge needle and syringe.

8) Hypertensive ocular disease

The eye is a major target organ for systemic hypertension and so hypertensive ocular disease is not uncommon in cats. Early clinical signs are retinal ‘target lesions’, flat, bullous retinal detachments, retinal haemorrhage (pre, intra and sub), vitreal haemorrhage, iris haemorrhage, mydriasis, reduced direct pupillary light reflex and reduced vision. Chronic signs are total retinal detachment, hyphaema and secondary glaucoma. Treatment involves addressing the underlying cause and treating with anti-hypertensive therapy, aiming for a systolic blood pressure of less than 160mmHg. Oral amlodipine (Amodip) and oral benazepril (Fortekor) can be used.

CLINICAL TIP – Cats with chronic hypertensive retinopathy develop total retinal detachment and associated blindness in the affected eye(s). However, typically one eye detaches a long-time before the other, during which time the cat appears visual. The owner will only notice that the cat has gone blind when the second retina detaches. This is important when giving advice to the owner regarding return of vision once the systemic hypertension is hopefully controlled and the retinas re-attach. If the first retina has been detached for many months, then it is less likely to regain vision as compared to the most recent retinal detachment that should regain vision if treated promptly.

Further information

Due to the low number of topical medications licensed for ocular use in animals, appropriate treatment can be prescribed via the prescribing cascade (https://new.bsava.com/Resources/Veterinary-resources/Medicines-Guide/Prescribing-cascade)

BSAVA Manual of Canine and Feline Ophthalmology https://www.bsavalibrary.com/content/book/10.22233/9781910443170

Acknowledgements

This article was produced by Mike Rhodes, Focus Referrals and Chair of the British Association of Veterinary Ophthalmologists.