The cornea has several layers, the outer layer called the epithelium, the central layer referred to as the stroma and the inner (back side of the cornea) layer called the endothelium. Each of these layers has its own function, the epithelium protects the cornea, as somewhat of a buffer. Its cells have a life span of 45-50 days are are constantly being replaced.
The stroma makes up 95% or more of the corneal thickness and gives the cornea its incredible strength and clarity. The stroma’s level of hydration is critical to its clarity. It is the tissue in the stroma that is removed during LASIK.
The endothelium is a single cell thick. Humans are born with approximately 4,000 of these cells. The cells aren’t regenerated during our life. These cells have a very important job, they control the hydration of the stroma and are responsible for keeping the cornea clear. If these cells fail or too many of them are lost, the stroma will swell and become opaque.
The endothelial cells die as part of the regular life cycle of the cornea, but they do so at a very slow rate. When a cell dies, its neighbors grow larger in order to keep the back side of the stroma covered with endothelial cells. We now have the ability to track the health and wellness of these cells as well as track their death and the size of the remaining cells.
This information allows me to make much more informed decisions about contact lens wear (as lack of oxygen due to contact lens wear can accelerate the death of these cells) and know much more about the health of my patients’ corneas. Utilizing a “Specular Microscope” I am able to gather baseline information and follow and detect subtle changes in the status of the cornea. As part of our commitment to protecting the vision and visual wellness of our patients, we now perform a screening endothelial examination in all of our eye exams for any patients who are likely to have any issues with their cornea.