Continuing with our subseries on infections that can be treated with corneal transplants, today we’ll be discussing the worldwide leader of preventable blindness–Trachoma.
What is Trachoma?
Trachoma is a bacterial disease most commonly seen in third world countries or areas of poor hygiene.
It is caused by infection of the bacterium Chlamydia trachomatis, which can be transferred from person to person via direct contact, through sharing of infected washcloths/towels, or via flies who have come into contact with a bodily secretion of an infected individual (tears, snot, spit, etc.).
Chlamydia trachomatis is a bacterium belonging to the Chlamydia family, although it is not the same as the sexually transmitted disease Chlamydia. Chlamydia trachomatis is a disease solely infecting the eyes, more specifically, the conjunctiva of the eyes.
The conjunctiva is the squishy, clear protective layer overlying the sclera (white part of the eyes) and inner eyelids. The main purpose of the conjunctiva is to provide cushion to the eye allowing for movement (up, down, left, right, clockwise, and counterclockwise). Without the conjunctiva, movements would create friction and be quite uncomfortable.
In trachoma, the conjunctiva becomes inflamed and irritated. It then cycles through periods of active and inactive inflammation. Over time, the active phases lead to an accumulation of damaged tissue within the eyes.
Early Stage Trachoma
In the early stages of the disease, the active bacterial infection causes symptoms of eye redness, irritation, light sensitivity, and itchiness of the eye & eyelid margins.
As the inflammatory response ramps up to combat the infection, small raised welts called follicles develop on the underside of the eyelids. You can think of follicles similar to skin hives, however these welts are larger and indicate great amounts of inflammation.
These follicles rub against the cornea each time a person blinks. This creates a shearing force, damaging the cornea and the inner eyelids.
Over time, the inner eyelids begin to scar down. Unlike normal, squishy conjunctiva, scar tissue is inflexible and rigid. The more extensive the scarring, the more stiff the eyelids become.
Middle Stages
In the middle range of the disease course, the scarring causes the eyelid to roll inward on itself in a condition called entropion.
As the lid curls in on itself, it positions the eyelashes so that they are directed in toward the cornea in a condition called trichiasis. Each time an individual blinks, the eyelashes are pushed downward into the cornea, and then dragged upward, which causes serious damage and corneal scratching over time.
All of this extra shearing force from the eyelids and lashes in addition to the inflammation within the eye accumulates to cause corneal scarring.
Later Stages
As mentioned earlier, scarring in the eye is not a good combination. Scarring of the cornea changes its normal transparent appearance to white and cloudy–limiting a person’s vision.
In severe cases, the scarring becomes so extensive that light is no longer able to pass through the cornea to reach the back of the eye. At this point, the patient would be considered legally blind.
How is Trachoma Treated?
The key to treating trachoma is early detection, to treat the disease before it causes scarring of the eyelids and the subsequent counterparts.
In the early stages of the disease, antibiotics are used to kill the bacteria and reduce inflammation. Artificial tears are also frequently prescribed to keep the eyes lubricated and reduce the frictional force from follicles and inflammation.
If the disease is left to progress to the entropion stage, entropion surgery can be performed to restructure the eyelids so that they no longer curl inward. This procedure is typically an outpatient procedure and may entail a small skin graft being taken to help reshape the eyelids.
Additionally, a doctor can epilate (remove) the eyelashes that are growing down into the cornea if a person is suffering from trichiasis.
In the final stages of the disease, a corneal transplant may be the recommended treatment option to replace the damaged, scarred cornea with clear donor tissue. In these stages, the individual will likely also need to undergo entropion surgery and eyelash epilation to ensure the eyelids/eyelashes do not damage the new corneal tissue.
The most commonly used corneal transplant surgery to treat trachoma patients is a full thickness penetrating keratoplasty (PK). We’ll discuss PK’s, in addition to other common types of corneal transplants at the end of this series.
If you found today’s article to be interesting, be sure to check back within the next few weeks to learn more about infectious diseases that can be treated with corneal transplants, next up with we’ll be discussing Herpes and later corneal ulcers!
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