Fuchs Corneal Endothelial Dystrophy and Corneal Edema
Situated at the front of the eye, the cornea is the transparent dome overlying the colored iris of the eye. The cornea is composed of thin layers of tissue that allow light into the eye and focus the rays of light entering the eye. The cornea and the lens of the eye, a separate structure located just behind the iris, are responsible for creating a sharply focused image on the back of the eye so that we can see clearly. The cornea is responsible for roughly two-thirds of the focusing power of the eye, with the lens responsible for the remainder.
Clarity of the cornea is essential for sharp vision. Clarity of the cornea is largely dependent upon two factors: regular arrangement of protein fibers of the cornea, and the constant removal of fluid from the cornea. The endothelium of the cornea is a single layer of cells along the inner surface of the cornea that continuously pumps fluid from the cornea, keeping the cornea clear. When these cells are injured, they cannot regenerate, and fluid will accumulate in the cornea, resulting in swelling (edema) of the cornea and progressive clouding of vision.
Corneal edema can sometimes develop after eye surgery, especially after cataract surgery. Some terms for corneal edema after cataract surgery include “pseudophakic corneal edema,” “pseudophakic bullous keratopathy,” and “aphakic bullous keratopathy.” Also notable among the causes of corneal edema is Fuchs corneal endothelial dystrophy, sometimes also termed “Fuchs dystrophy.”
Abnormal swelling of the cornea is more likely to occur in people 50 years of age and older. Early symptoms of corneal edema might include blurred vision or haloes, often in the early morning. Very mild corneal edema may not require any treatment. In some cases, a physician may recommend use of a concentrated saline eye drops to draw fluid from the affected eye, thereby reducing the corneal swelling. Ultimately, if swelling of the cornea progresses to a level that a person’s vision is substantially impaired, a corneal surgeon can transplant either the entire cornea or just the abnormal endothelial (inner) layer of the cornea from an organ donor. Surgeons have performed cornea transplants for more than 100 years, and more than 40,000 are currently performed in the United States each year.
Corneal transplantation procedures vary slightly, depending on underlying eye diseases, presence of corneal scarring, or history of eye surgery. The procedures, when paired with glasses or contact lenses, can often restore vision to a significant degree. In contrast to cataract surgery, corneal transplant procedures tend to be performed for more significant impairment of vision, as corneal transplant procedures and their recovery are much more involved.
Patients with corneal edema usually notice blurred vision or haloes around lights. Early on, this blurriness is often worse in the morning, just after waking up, but improves over the course of the day. Initially, fluid collects in the stroma of the cornea, the middle layer of tissue that comprises most of the cornea’s thickness. In advanced cases of corneal edema, blistering can emerge on the cornea’s epithelium, its outermost surface layer. Blistering of the cornea, also known as “bullous keratopathy,” can cause episodes of eye pain or the sensation of a foreign body on the eye.
The timeframe for the progression of corneal edema can vary greatly, depending upon the underlying cause for the edema. For instance, someone undergoing cataract surgery might notice a rapid onset of cloudy vision due to corneal edema. By contrast, mild corneal edema in the setting of Fuchs dystrophy might go unnoticed, or progress only minimally over 20 years before a patient notes hazy vision.
The innermost layer of the cornea, known as the endothelium, consists of a single layer of cells. These endothelial cells pump fluid out of the cornea, maintaining a clear cornea by keeping its fluid content low.
Fuchs corneal endothelial dystrophy, cataract surgery, or infectious agents such as the herpes simplex virus can cause abnormalities of the corneal endothelium. Diseases of the corneal endothelium can irreversibly damage endothelial cells, and corneal endothelial cells do not regenerate when they are injured and lost. Therefore, injury to the corneal endothelium impairs its ability to regulate fluid. Corneal swelling is more likely to develop, resulting in failing vision.
Some early designs of lenses implanted during cataract surgery also caused injury to the endothelium, resulting in a high volume of corneal transplants in previous decades; however, these specific lens implant designs are no longer manufactured. Herpes simplex virus type 1, a common virus causing cold sores and fever blisters, can also cause injury to the cornea, including the corneal endothelium.
Corneal edema can also occur in patients who have previously undergone a corneal transplant for any eye disease, either because the patient’s immune system has rejected the corneal transplant or because the transplanted cornea has failed over time. It is also important to note that corneal edema can also be seen in the setting of some vision-threatening diseases, such as uncommon types of glaucoma, although these less common causes of corneal edema would be easily excluded on an eye exam by an ophthalmologist.
Age plays a role in corneal edema, which is diagnosed most commonly in people over 50 years old.
People genetically predisposed to corneal edema due to underlying Fuchs dystrophy are more likely to develop corneal edema, particularly around the time of cataract surgery or other eye surgeries, and degradation of vision could emerge earlier.
Cataract surgery instruments and practices have improved markedly in recent years; however, these still can injure the cornea’s endothelial cell layer and precipitate the development of corneal edema. A person who has Fuchs dystrophy and cataracts is often at a particularly high risk of developing corneal edema at the time of cataract surgery.
A patient’s symptoms and eye disease history may suggest the presence of corneal edema. On examining a patient, an ophthalmologist may notice corneal clouding as the cause of a patient’s hazy vision. Fuchs dystrophy is typically noted by the presence of typical exam findings on a close exam on the corneal endothelium.
Corneal swelling is usually evident on examination in the clinic with a slit-lamp microscope, using a thin beam of light to illuminate and visualize the individual layers of the cornea. Patients with corneal edema are often referred to a specialty center such as the UW Medicine Eye Institute for management by a cornea specialist.
Corneal edema often results in worsening vision.
There is no preventative treatment for corneal edema.