Corneal ulcers

From Cat
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Right eye 4 mo post-conjunctival grafts
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Left eye 4 mo post-surgery.

Corneal ulceration, laceration, partial thickness and full thickness injuries are a common corneal disease of cats.

The clinical presentation is of acute, usually unilateral onset of pain, blepharospasm and lacrimation. A transient anterior uveitis mediated by an axon reflex within the trigeminal nerve can follow corneal insult. Aqueous loss or haemorrhage may also be apparent. Corneal injury should always be considered in animals that present with injury to the third eyelid.

Examination should establish the site of any corneal injury, the position of the iris, the depth of the anterior chamber, if hyphema is present, the state of the pupil, and whether there appears to be iris and lens damage in addition to corneal damage. Aqueous loss and iris prolapse are common if there has been corneal penetration. Uveitis is usually present, but is not necessarily intense. Lens penetration, with leakage of lens protein and traumatic lens luxation are less common.

Differential diagnoses includes:

Treatment

Medical

Medical therapy consists of either proprietary antibiotic drops or fortified antibiotic solutions.

A mydriatic cycloplegic (e.g. atropine 1%) is usually indicated when there is deep corneal damage and uveitis. While most cats tolerate atropine ointment better than solution, it is better to select drops rather than ointment if there is any possibility of the ointment becoming trapped in the cornea or entering the anterior chamber during the healing process. Once the pupil has dilated atropine is given only as frequently as is necessary to keep it so.

Systemic analgesics are indicated if the eye is painful. Topical local anaesthetics are not used beyond the initial diagnostic and treatment stages as they may seriously compromise corneal healing.

Surgical

Superficial injuries do not require surgical repair, but wound healing will be enhanced if any loose flaps of corneal epithelium are removed with fine scissors after several applications of topical local anaesthetic.

It the extent and the depth of the corneal injury which determines the type of support for corneal wound healing required. Therapeutic soft contact lenses and conjunctival pedicle grafts are the usual means of providing support for healing in those cases in which perforation is likely without some form of corneal support. Third eyelid flaps may be used as an alternative to therapeutic soft contact lenses. Short-term measures to protect the cornea include cyanoacrylate glue and collagen corneal shields.

It is not always necessary to suture penetrating injuries since if the wound is of small diameter continued aqueous loss is unlikely. If there is no leakage of aqueous from the site of penetration and the anterior chamber has reformed, then medical treatment is all that is required - usually topical antibiotic and mydriatic cycloplegic (atropine 1%). Atropine may be used sparingly once pupil dilation has been achieved but the antibiotic would be used initially on an hourly basis until it is clear that healing is proceeding uneventfully.

Many penetrating corneal injuries require primary reconstructive surgical repair. The wound should be inspected carefully and cleaned of foreign debris. Coagulated aqueous invariably covers the corneal wound and this must be removed. Prolapsed iris should be returned to the anterior chamber and it is important to emphasise that abscission of incarcerated iris is rarely if ever necessary. Viscoelastic materials will be of value in expelling intraocular haemorrhage and restoring and maintaining normal anatomical relationships within the anterior chamber - high viscosity viscoelastic materials are the best ones to use. Fine suture material (7/0 - 10/0 monofilament nylon, virgin silk or polyglactin) should be selected and the simple interrupted corneal sutures should penetrate about three quarters of the corneal thickness and may be preplaced to aid the procedure. Secure watertight closure is essential and it is usual to aspirate the viscoelastic material, because leaks are more difficult to detect with viscoelastics, and to reform the anterior chamber with balanced sodium solution and a small bubble of air. Once healing has occurred the sutures can be removed or left, according to their reactivity.

If the corneal defect is extensive, a different suture pattern can be used. A corneal wound of up to 5 mm diameter in its largest diameter can be closed with preplaced horizontal mattress sutures, provided that the wound margins are healthy, but a high degree of astigmatism is inevitable and this technique should not be used if there is excessive tension on the sutures. The same suture pattern can be used to close a descemetocele, but a thick conjunctival/Tenon's capsule pedicle graft may be a better option. Penetrating keratoplasty is also a practical proposition in the cat.

Eye removal is almost never the treatment of choice for acute ocular trauma.

References

1. Barnett, KC & Crispin, SM Feline Ophthalmology (2002) Saunders