Shiley Eye Institute UC San Diego

The Role of the Cornea and Corneal Endothelial Cells

The cornea is the “windshield” of the eye, essential for maintaining clear vision. Its clarity depends on a specific hydration level, which is tightly regulated by a biological pump operated by corneal endothelial cells (CECs). These cells form a single row on the innermost layer of the cornea and work continuously to remove excess fluid, keeping the cornea transparent.

Corneal Endothelial Cells: Limited in Number and Function

Humans are born with all the CECs they will ever have. CECs do not regenerate or proliferate. When these cells are damaged or die, there are no stem cells to replace them. This limitation makes the health of existing CECs crucial for maintaining corneal function.

Causes of CEC Decline

CEC numbers decrease naturally with age, but other factors can accelerate their loss. Common causes include intraocular surgeries such as cataract surgery, certain eye medications, and a degenerative condition known as Fuchs endothelial corneal dystrophy (FECD). These factors can lead to reduced pump function, resulting in corneal swelling and cloudiness.

Understanding Telomeres

Telomeres are protective caps at the ends of chromosomes, which hold our genetic material. Similar to the plastic tips on shoelaces, telomeres prevent chromosomes from fraying and becoming shorter. When they become too short, cells can no longer divide, leading to cell death or dysfunction.

Telomeres and Corneal Health

The cornea is unique among ocular tissues because it has the shortest telomeres. In patients with FECD, the telomeres of corneal endothelial cells are even shorter than those in individuals without the disease. This accelerated telomere shortening contributes to the premature aging and loss of CECs, leading to the symptoms of FECD.

Linking FECD and Telomeres

One of the hallmarks of FECD is short telomeres; this results in premature (patients are often in their 40’s) loss of endothelial cells in the cornea, causing them to deteriorate faster than usual. This contributes to the loss of endothelial cells and the buildup of fluid in the cornea,

Telomere research gained significant attention after the 2009 Nobel Prize in Physiology or Medicine highlighted its importance. Studies have shown that short telomeres destabilize chromosomes, causing cell death and potentially triggering nearby cells to follow a similar pathway.

Understanding Fuchs Endothelial Corneal Dystrophy

FECD is a bilateral (affecting both eyes) disease characterized by the premature degeneration of corneal endothelial cells. As these cells deteriorate, the cornea can no longer regulate its hydration effectively. This leads to fluid buildup, swelling, and significantly decreased vision.
FECD is one of the most common major eye diseases, affecting an estimated 8 million people in the United States alone. Symptoms often begin in middle age, with progressive vision impairment that may ultimately require corneal transplant.

Natalie A. Afshari, MD, FACS

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Natalie A. Afshari, MD, FACS

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