Corneal/External Disease

Corneal/External Disease

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The cornea is the eye's outermost layer. It is a clear, dome-shaped window covering the front of the eye.

The cornea has two functions: 1) It helps shield the eye from germs and dust, and 2) It serves as the eye's outermost lens, refracting light and helping the eye to focus. It is responsible for roughly 65-75% of the eye's focusing power.


An adult cornea is only a ½ millimeter thick and is comprised of five layers: the epithelium, Bowman's Layer, stroma, Descemet's Membrane, and the endothelium.


  • The epithelium blocks foreign materials from the eye and helps distribute oxygen and nutrients to the rest of the cornea. This layer contains thousands of tiny nerve endings, making the cornea sensitive to pain when scratched.
  • Bowman's Layer is made up of collagen. If scratched, this layer is prone to scarring that can sometimes lead to vision loss.
  • The stroma accounts for 90% of the cornea's thickness and is composed of collagen. Healthy collagen formation gives the cornea its clarity. When this collagen clumps up, it can cause cloudiness in the cornea.
  • Descemet's Membrane is a thin, strong sheet of tissue that protects against infection and injuries. The cells in this membrane regenerate after injury.
  • The endothelium is the thin, innermost layer of the cornea responsible for pumping water from the cornea and keeping it clear. Once endothelium cells are destroyed (due to disease or injury) they cannot regenerate. If too many endothelium cells are destroyed, blindness can occur and a corneal transplant is the only available therapy.

Common Cornea Conditions 

Corneal and external diseases are those that involve the cornea, the surface of the eye, and sometimes the eyelids. Common cornea and ocular surface conditions include the following:


Most conditions that affect the cornea are treatable, especially when detected early. To schedule an appointment, call 920-327-7000 or request an appointment online

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BayCare Clinic,, is the largest physician-owned specialty-care clinic in northeastern Wisconsin and Michigan’s Upper Peninsula. It is based in Green Bay, Wisconsin. BayCare Clinic offers expertise in more than 20 specialties, with more than 100 physicians serving in 16 area communities. BayCare Clinic is a joint partner in Aurora BayCare Medical Center, a 167-bed, full-service hospital. Follow BayCare Clinic on Facebook and Twitter.