The epithelium sticks to the basement membrane, which also separates the epithelium from the stroma. The corneal stroma comprises 90 percent of the thickness of the cornea. It contains the collagen fibers organized into lamellae. The lamellae are in sheets which separate easily. Posterior to the stroma is Descemets membrane, which is a basement membrane for the corneal endothelium. The endothelium is a single cell layer that separates the cornea from the aqueous humor. Corneal healing
A healing of a corneal ulcer involves two processes: migration of surrounding epithelial cells followed by mitosis (dividing) of the cells, and introduction of blood vessels from the conjunctiva. Superficial small ulcers heal rapidly by the first process. However, larger or deeper ulcers often require the presence of blood vessels to supply inflammatory cells. White blood cells and fibroblasts produce granulation tissue and then scar tissue, effectively healing the cornea. Superficial and deep corneal ulcers
Corneal ulcers are one of the most common eye diseases in dogs. They are caused by trauma, detergent burns, and infections. Other eye conditions can cause corneal ulcers, such as entropion, distichiae, corneal dystrophy, and keratoconjunctivitis sicca (dry eye). There have been at least two cases where corneal ulceration was caused by canine herpesvirus.Superficial ulcers involve a loss of part of the epithelium. Deep ulcers extend into or through the stroma and can result in severe scarring and corneal perforation. Descemetoceles occur when the ulcer extends through the stroma, exposing Descemets membrane. This type of ulcer is especially dangerous and can result in perforation.
A corneal ulcer, or ulcerative keratitis, is an inflammatory condition of the cornea involving loss of its outer layer. It is very common in dogs and is sometimes seen in cats. In veterinary medicine, the term corneal ulcer is a generic name for any condition involving the loss of the outer layer of the cornea, and as such is used to describe conditions with both inflammatory and traumatic causes. Corneal anatomy of the dog and cat
The cornea is a transparent structure that is part of the outer layer of the eye. It refracts light and protects the contents of the eye. The cornea is about one-half to one millimeter thick in the dog and cat. The trigeminal nerve supplies the cornea via the long ciliary nerves. There are pain receptors in the outer layers and pressure receptors deeper. Transparency is achieved through a lack of blood vessels, pigmentation, and keratin, and through the organization of the collagen fibers. The collagen fibers cross the full diameter of the cornea in a strictly parallel fashion and allow 99 percent of the light to pass through without scattering. There are four important layers in the dog and cat cornea. The outer layer is the epithelium, which is 25 to 40 micrometers and five to seven cell layers thick. The epithelium holds the tear film in place and also prevents water from invading the cornea and disrupting the collagen fibers. This prevents corneal edema, which gives it a cloudy appearance. It is also a barrier to infectious agents.