A complicated corneal ulcer begins with a superficial corneal ulcer.  Once the protective layer of the epithelium is gone, the ulcer can become infected with bacteria. 

In many cases, these dogs can act painful initially when the ulcer is shallow then act less painful as the ulcer gets deeper. 

Deep stromal corneal ulcers are usually treated with surgery. 

Pertinent Anatomy

• To understand a corneal ulcer, it is important to have a basic understanding of the anatomy of the cornea.  The outer most layer of the cornea is a protective barrier called the epithelium.  Beneath this is a layer that makes up the majority of the cornea called the stroma.  It is the highly structured anatomy of this layer that allows the cornea to be clear.  On the inside of this layer is a thin membrane called Descemet’s membrane.  Internal to this there is only a one cell thick layer called the endothelium.  A corneal ulcer is the loss of a portion of the outer epithelium.  In a simple corneal ulcer, the remaining epithelium will slide over the ulcerated area and heal the ulcer in a few days.  There are several situations in which this does not occur and one of these is the complicated corneal ulcer.

What is a Complicated Corneal Ulcer?

• A complicated corneal ulcer is an ulcer that, in addition to loss of the epithelium, the underlying corneal stroma is lost.  These are usually divided into superficial stromal ulcers (which are less than halfway through the thickness of the cornea) and deep stromal ulcers (which are more than halfway through the thickness of the cornea).
• A complicated corneal ulcer begins with a superficial corneal ulcer.  Once the protective layer of the epithelium is gone, the ulcer can become infected with bacteria.  Certain bacteria produce degrading enzymes that breaks down or ‘‘melt” the stroma of the cornea.  In addition, the bacteria draw white blood cells into the cornea to fight off the infection which can produce more degrading enzymes.  The result is an ulcer that becomes larger and grows deeper into the cornea.  It can extend all the way down to Descemet’s membrane, (termed descemetocele).  This is the last stage before the eye ruptures.

Clinical Signs

• These ulcers  can occur in any animal  but are most often seen in dog breeds that have short noses and prominent eyes such as Pugs, Shih Tzu’s, Lhasa Apsos,  Boston Terriers etc.  These breeds have eyes that bulge out and are less sensitive to the external environment (ie. they do not feel the discomfort of the eyes drying as other breeds do). Therefore, they do not blink as often as needed to spread the tear film properly across their eyes.  The tears, in addition to lubricating the cornea, contain antibodies to help fight off infection. 
• In many cases, these dogs can act painful initially when the ulcer is shallow then act less painful as the ulcer gets deeper.  This is because most of the nerves in the cornea are superficial.  As these ulcers progress, blood vessels may grow into the cornea. 

Treatment

• Treatment usually depends on the depth of the ulcer.  Superficial stromal corneal ulcers are usually treated initially with intensive medical therapy.  A cytology and or a culture test may be used to determine what types of bacteria are present.  Medical therapy usually consists of topical antibiotics several times daily, topical atropine to dilate the pupil and reduce pain, and an artificial tear supplementation.  Sometimes a medication to decrease activity of the degrading enzymes may be used.  If the ulcer is not responding to medical therapy, surgery is usually recommended.
• Deep stromal corneal ulcers are usually treated with surgery.  The surgery most commonly performed is a conjunctival graft.  In this surgery, a section of the conjunctiva, which is the pinkish tissue which covers the white portion of the eye, is brought over to cover up the corneal ulcer.  This provides both structural support to the cornea and nutritional support by a blood supply to aid in healing the ulcer.  If the corneal ulcer is very deep, or ruptured, a corneal graft may be used alone or in addition to a conjunctival graft to provide more support.  Medical therapy after surgery usually consists of the same medications, although at a lower frequency of administration.

Prognosis

• It is common for complicated corneal ulcers to cause significant corneal scarring.  As with any disease, early treatment is key to decreasing this scarring.  After the ulcer is completely healed, medications may be used to decrease scarring.  In most cases, artificial tear supplements may be used on a permanent basis to keep the ulcer from returning, as well as being used prophylactically in the opposite eye.  Early aggressive treatment can save vision in most patients.