The cornea protects the eye from germs, dust, and shields it from UV radiation. It is also an outer lens that directs and focuses light so we can focus better. This thin structure is divided into five layers: epithelium, bowman’s layer, stroma, Descemet’s membrane, and endothelium.
Different Parts of the Cornea
Epithelium and Bowman’s layer: The epithelium is an important barrier for foreign material, while at the same time, it allows nutrients to enter the cornea. It is also connected to nerve endings, making it sensitive to pain. Directly beneath it is the Bowman’s layer, which is made up of a strong layer of fibrous tissue known as collagen.
Stroma and Descemet’s Membrane: If your cornea were injured, this layer would protect it and form a scar as it heals. The stroma under the Bowman’s layer is the thickest layer and is also made up of collagen and water. It not only provides protection, but also allows light to pass its unique shape. LASIK and PRK procedures target this layer for vision correction. Under this layer is a membrane that holds part of the Descemet’s Membrane below it.
This is yet another layer of proactive, strong sheet that shields against infection and injury.
Endothelium: The endothelium is a thin inner layer that constantly pumps fluid out of the stroma to keep the cornea clear and to prevent it from getting hazy. The cornea can recover from minor injuries because there are so many protective layers, however, if the endothelium is damaged, then a corneal transplant is required. Apart from injury, there are several diseases that can affect the cornea.
What are Refractive Errors?
These include astigmatism, nearsightedness and farsightedness. During this process, light is bent by the cornea and lens to focus the light on the retina. After light hits the retina directly, it is converted into signals and sent to the brain. In people with refractive errors, the light does not bend or hit the retina in the right place, which results in imperfect vision for the patient.
What are Some Ways the Cornea can be Impaired?
The several conditions that can damage the cornea include:
Also known as keratitis, it is a rare condition where the cornea becomes infected and can result in serious damage. Corneal infections are rare, but they can be treated with anti-microbial eye drops, while severe infections may persist longer and may require stronger antibiotic, antifungal, or antiviral treatments. If left untreated, it can erode the cornea and a transplant may be the only option.
Dry eye is characterized by a decrease in tear quality and production, causing people with this condition to experience a lack of moisture and discomfort in their eyes. The main symptom of dry eye is a scratchy or sandy sensation within the eyes. Other symptoms include excess tearing, periods of dryness, stringy discharge, pain and redness of the eye. This condition is common in dry environments, the use of specific medications, or certain conditions such as menopause or rheumatoid arthritis. Recommended treatment for dry eye are artificial tears, ointments to add moisture to the eye, and wearing wrap-around glasses while outside to prevent dryness. In severe cases of dry eye, temporary blocking of the eyelid puncta with punctual plugs is an effective treatment option, as well as topical cyclosporine therapy, which is used to enhance tear production.
There are 20 different types of corneal dystrophies exist. Corneal dystrophy is a condition that can affect the clarity of multiple parts of the cornea. The condition causes loss of normal vision due to a cloudy buildup of the cornea. The different types of dystrophies can affect various parts of the cornea in various different ways.
Some corneal dystrophies include:
Fuch’s dystrophy: this involves the gradual deterioration of the endothelium cells for no apparent reason. While these cells deteriorate the endothelium is unable to pump water out of the stroma and the cornea begins to swell. The epithelium retains water, as a result, which can cause severe pain and vision issues. This condition begins with blurred vision on and off throughout the day, and as it worsens, blurred vision will become constant.
Treatment of this condition starts with a decrease in swelling with the use of saline eye drops, ointments, or soft contact lenses. A corneal transplant might be necessary if the disease interferes with the person’s everyday activities.
Keratoconus: This form of corneal dystrophy is the most common in the U.S. and commonly occurs in young adults and teenagers. Keratoconus develops when the middle of the cornea begins to thin and eventually bulges out, forming a cone shape. The bulging of the cornea changes how light is bent and can cause refractive errors as well as scarring and swelling of the cornea, which ultimately causes vision damage. Initially, keratoconus vision issues can be controlled with eyeglasses. As the condition worsens, a transition to special contact lenses is recommended to continue vision improvement. Contact lenses need to fit correctly to improve visual acuity and avoid further damage to the cornea. Corneal collagen crosslinking is another form of treatment that stops the development of keratoconus. However, not everyone can be cured of these symptoms as in some cases the cornea becomes too scarred and unable to handle contact lenses. A corneal transplant is needed to treat some cases of keratoconus.
Lattice dystrophy: This causes abnormal protein fibers to get stored in the stroma, leading to a cloudy vision. Lattice dystrophy generally occurs among children aged 2 to 7. It could lead to epithelial erosion, which in turn could lead to the destruction of the epithelium, making blinking painful.
Granular dystrophy: This causes lesions to form inside the eye that are crumb-shaped that could grow causing discomfort and problems with normal vision. There are two types of granular dystrophy: type I and type II.
Map-dot-fingerprint dystrophy: In this type of dystrophy, the epithelium is not completely developed, making the epithelial cells unable to stick to the epithelium easily. Since the epithelium erodes, the curve of the cornea is altered and the nerve endings in the lining are exposed, leading to severe pain. Other symptoms of map-dot-dystrophy include excessive tearing and sensitivity to light.
This is a pinkish growth on the cornea that is common among adults aged 20 to 40. Usually, people who have Pterygium want to get it surgically removed since it is easily noticeable. However, the Pterygium growth may reappear if the individual is under 40-years-old. To prevent regrowth, doctors use different methods, such a medication called mitomycin-C, or conjunctival autografs.
This is also known as herpes zoster, caused by the varicella-zoster virus, which is also responsible for chicken pox. Once a person recuperates from chicken pox, the varicella-zoster remains in their body in an inactive form. Unfortunately, the virus may become active again in some people, having the ability to infect any part of the body. These infections cause rashes and painful inflammations.
This occurs due to the herpes simplex virus, causing painful sores on the eyelid. Ocular herpes also leads to the inflammation of the cornea. Even though this problem could be treated with anti-viral medications, there remains a big chance this could reoccur.
Iridocorneal endothelial syndrome:
This leads to the development of glaucoma, which alters the iris and causes inflammation of the cornea. Iridocorneal endothelial syndrome is common among women who are aged between 30 and 50.
Treatment of corneal dystrophies:
Descemet’s Stripping Endothelial Keratoplasty (DSEK):
This procedure is also known as the sutureless corneal transplant. In this method, the doctor performs a partial corneal transplant which is kept in place via the natural suction created by the endothelial cells’ pumping action. This procedure is preferred because of faster recovery and a low risk of transplant rejection. It also eliminates the adverse effects of stitches. It is usually preferred for dystrophies that cause corneal swelling.
Phototherapeutic Keratectomy (PTK):
PTK is another method of treatment for damage caused by dystrophies, infection, or scars affecting the cornea. PTK uses an excimer laser to remove the damaged outer layers of the cornea, making tissue healing and growth possible. PTK also corrects and reshapes the stroma lens for better refraction of light. The biggest advantage of PTK is faster recovery compared to a corneal transplant.