Bacteria do not invade normal, healthy corneas, but they may opportunistically invade once a corneal ulcer or abrasion is present. This is the reason that topically applied antibiotics are always recommended when an ulcer is present- to prevent infection. Once an infection is present, this is very serious. The worst bacterial corneal infections may cause rapid progression in ulcer size and depth, and even “melting” of the cornea to corneal perforation (rupture) in as little as a day or two. These types of ulcers require very intensive medical treatment (antibiotics applied to eye from 4 times daily to every hour around the clock depending on severity) and many even need urgent corneal surgery. Your general veterinarian is usually able to assess whether an ulcer is deep and infected and needs to be seen by a veterinary ophthalmologist urgently.
Reactivation of previously dormant herpesviral infection has been implicated in a number of eye conditions, including corneal ulcers. This is almost exclusively a cat problem, though it has also been reported in the dog and horse. Herpesvirus is one of the most common causes of both conjunctivitis (which often develops first) and corneal ulcers in cats. These are typically superficial ulcers, but like any ulcer, may become invaded by bacteria. When a viral ulcer is suspected, both anti-bacterial and anti-viral medications may be prescribed. Unlike a simple corneal ulcer, viral ulcers are often slow to heal, though most eventually do so. Since herpesvirus outbreaks in adult cats are usually the result of reactivation of dormant herpes infection obtained during kittenhood, immune-suppression is implicated. This could be the result of stress, illness, individual variation, or the use of immune-suppressive medications.
These corneal ulcers are initially similar to simple ulcers. They are shallow ulcers, which do not appear infected, and are not particularly immediately dangerous. However, unlike superficial ulcers, they remain present, making little to no progress over more than a week. Defective cell adhesion, due to a combination of age and heredity, has been blamed. Certain breeds of dogs (Boxers, Corgis, Bulldogs) are predisposed and they are usually middle-aged or older when they become affected.
Treatment is directed at stimulating the cells to heal through
1. simple debridement with cotton swabs (lowest success rate, usually performed at your pet’s general veterinarian)
2. a more intensive corneal debridement sometimes called a keratotomy (usually the first step through a veterinary ophthalmologist and at least 75% successful), or
3. a keratectomy (highly successful, but a surgical procedure requiring anesthesia so second resort for most veterinary ophthalmologists).
Corneal degeneration is characterized by abnormal deposits (usually a combination of calcium and fats like cholesterol) within the superficial and deep layers of the cornea and is seen most commonly in older dogs. This may occur in one or both eyes and often has no apparent cause, although this may be associated with low thyroid levels (hypothyroidism) or chronic eye disease. They appear as white, granular spots which usually do not substantially interfere with vision, at least initially. When first seen, the spots are usually simply monitored unless they are causing pain. Sometimes, eye drops can be used to bind calcium and slow the progression of opacity. In rare cases, usually in dogs over 12 years old, affected eyes may become suddenly painful with ulceration occurring as a reaction or sloughing of the abnormal material. Once ulceration occurs, surgery (keratectomy) or a procedure (diamond burr debridement) may be recommended to completely or partially remove the deposits. If untreated, the ulceration may progress, even resulting in rupture of the eye in the most severe cases.
A large plastic collar is recommended for all ulcers to prevent rubbing at the eye causing further healing delay and increased risk of infection. Yes, your pet can manage to do everything he needs to do while wearing one!