Corneal Ulceration in Cats
Dr. Rhea Morgan
Diagnosis In-depth Your veterinarian will do a complete medical history and perform a thorough ophthalmic examination. Thorough examination provides essential information regarding the cause and severity of the corneal ulcer. It may also highlight other related symptoms or diseases such as those listed above. Parts of the examination are often conducted in a darkened room using a bright light source and some form of magnification.
During the examination, fluorescein stain is applied to the cornea and any excess is rinsed off. Fluorescein stain adheres to any areas where the surface layer of the cornea is missing. Fluorescein staining outlines the ulcer and permits accurate assessment of the size and depth of the ulcer.
If low tear production is suspected as the cause, a Schirmer tear test is performed. A small strip of calibrated filter paper is placed inside the lower eyelid and left in place for one minute. The distance to which tears flow along this filter paper is a measure of the volume of tears produced. This is a safe and non-painful test.
In cases where the ulcer appears infected, special samples may be collected from the cornea for examination under a microscope, for bacterial culture and sensitivity testing, and/or for viral testing. This is particularly important if an ulcer has progressed rapidly, has failed to respond to appropriate antibiotics, or if feline herpesvirus (FHV-1) may be involved.
If special techniques, equipment, and/or training are required, your veterinarian may refer your cat to a veterinary ophthalmologist for further evaluation.
The principal goals in the treatment of corneal ulceration are to identify and treat its cause, to prevent secondary infection, and to encourage healing. Following removal of the inciting cause and appropriate treatment, repair of minor corneal ulcers is often complete within seven days. Patients with slow-healing or rapidly progressive ulcers require more protracted therapy.
The typical therapeutic approach may include the following:
An Elizabethan collar may be applied to the cat. Corneal ulcers can be irritating and your cat can cause more serious injuries to his eye if he scratches it with his paws or rubs it against carpet or furniture.
Bacteria are regularly implicated in the worsening of corneal ulcers, particularly ulcers that get deeper. Therefore, one of the most important treatments for corneal ulcers is the prevention of secondary infection. This involves the application of a topical ophthalmic ointment or eye drop to the eye until the ulcer is healed. One of the more commonly used preparations is a combination of three antibiotics – neomycin, polymyxin, and bacitracin or gramicidin. In more serious ulcers, antibiotic choice may be guided by culture and sensitivity results. It is critical to avoid the topical use of any medications containing corticosteroids when the cornea is ulcerated.
Antibiotics are ineffective against FHV-1. If your cat has an ulcer secondary to FHV-1 infection, the frequent application of an antiviral agent such as idoxuridine, trifluridine (Viroptic®), or vidarabine (Vira-A®) may be recommended.
If an ulcer is deep when it is first discovered, or if it progresses rapidly despite appropriate treatment, surgery may be necessary to save the eye and vision. This may involve referral to a veterinary ophthalmologist.
The most commonly performed surgery for deep corneal ulcers or ulcers that are threatening to perforate the eye is a conjunctival graft performed with the patient under general anesthesia. A small piece of the conjunctiva from near the cornea is sutured into the ulcer. This brings a healthy blood supply to the area and provides mechanical support to the diseased cornea. Grafting decreases the chances of perforation, increases ocular comfort, and speeds healing, similar to what a skin graft does for a severe burn.
For more superficial ulcers, a bandaging type of procedure may be enough to encourage healing. Sometimes a soft contact lens is placed on the eye. The lens covers the ulcer and keeps it protected. If contact lenses are not available, the third eyelid may be temporarily sutured to the top lid so that it covers the cornea. While suturing the third eyelid up also protects the cornea, the cornea is hidden so it is not possible to observe whether the ulcer is improving or worsening. The animal can see through a contact lens, but it cannot see through the third eyelid while it is sutured up.
Another type of protective surgery is the partial tarsorrhaphy, where the external eyelids are temporarily sutured together. The lids can be partially closed, thereby protecting the cornea, but still permitting frequent observation and treatment of the ulcer.
Treatment of dry eye, removal of additional or misdirected eyelashes, and surgical correction of entropion may be necessary in selected cases. These steps also limit the chance of future corneal ulcers.