Cornea

The cornea, according to the University Hospital Southampton NHS Foundation Trust, is the clear outer layer of the eye. The cornea is smooth, clear as glass and has a very solid structure. It has two functions. The first is to protect the eye from injury and infection, and the second is to control and focus the entry of light into the eye. It It is the curved transparent layer of the eye that plays a major role in vision. (1)

Definition and Overview

The human eye's cornea acts as its outermost layer and is both transparent and protective. The cornea, along with the sclera, serves as a barrier between the eye's health and potentially hazardous elements including germs, dirt, and other environmental variables.

It also has a function to filter out some of the ultraviolet radiation from the sun.

However, since it does not have the full effective power in terms of protection, the best way to protect its health is to wear wrap-around sunglasses when outside.

In addition, the cornea provides refraction of light as it enters the eye. This refraction process, facilitated by the curved edge of the cornea, is very important so that the eye can focus on objects at different distances. If the cornea is damaged, for example, by disease, infection, or injury, sores can occur, causing disruptions or blockages in the light path and ultimately affecting healthy vision and quality of vision. (2)

Procedures

The transparency of the cornea may be impaired due to congenital, hereditary, or subsequent traumas and infections. There are some diseases that cause pain, burning, stinging, and light sensitivity by reducing the visual quality of the cornea. These diseases are;

• Pterygium

Pterygium arises due to the excessive proliferation of conjunctival tissue, which subsequently invades the cornea, leading to discomfort and inflammation.

• Keratoconus

Keratoconus occurs when the cornea undergoes distortion, resulting in a severe impairment of vision characterized by significant blurriness. (3)

• Keratitis

It refers to the inflammatory response characterized by redness and swelling of the cornea, which is the transparent front part of the eye responsible for refracting light.

• Dry eye

The condition is an inadequate production of tears to maintain adequate moisture on the ocular surface. This insufficiency of tears may result in discomfort and visual impairments.

• Corneal dystrophies

A group of conditions known as corneal dystrophies are characterized by an accumulation of external material on the cornea, which causes vision to become blurry. (4)

Many corneal conditions can be treated with prescription eye drops or pills. However, advanced corneal diseases are treated with different corneal treatment procedures including

• Laser treatment

Ophthalmologists may opt for a laser procedure called phototherapeutic keratectomy (PTK) to reshape the cornea, remove scar tissue, and improve vision for some corneal dystrophies and other disorders.

• Corneal transplant surgery

In cases where the damage to the patient's retina cannot be proportioned, doctors may remove the damaged portion and transfer it with healthy corneal tissue from a donor.

• Artificial cornea

Doctors may potentially decide to employ a keratoprosthesis (KPro) to replace a damaged cornea as an additional option to a corneal transplant, which is also depends on the patient's health condition. (5)

Candidates

Good vision is associated with having a clear, smooth, and healthy cornea. In cases where the cornea is injured, swollen, or damaged, light is blocked from focusing toward the eye, causing blurred vision or the perception of glare. In cases where the cornea cannot heal itself, it needs external medical treatments. The following requirements must be met by the patients to whom these treatments will be administered.

• Having corneal scarring due to injury or infection
• Having corneal ulcers or "sores" from an infection
• Having keratoconus, a medical disorder that causes the cornea to enlarge
• Having thinning, clouding, or swelling of the cornea
• Having hereditary eye diseases such as Fuchs' dystrophy and others
• Having problems caused by a previous eye surgery
• Having eye pain, blurred vision, redness, hypersensitivity

Patients who have these are generally considered eligible for corneal treatment procedures. (6,7)

Risks and Side Effects

Cornea treatments are generally safe, however, some risks and side effects can occur after treatments. These risks and side effects include 

• mild, gritty discomfort
• visual disturbances 
• red marks on the white of the eye (8)
• sensitivity to light (photophobia)
• vision problems – clouded or particularly foggy vision
• eye pain
• glaucoma
• retinal detachment, 
• vitreous hemorrhage (9)

Post-Procedure and Follow-up

In the days after the corneal surgery, follow-up controls should be visited. Surgical stitches may or may not need to be removed. In general, it depends on the patient's progress with healing, the condition of his or her eye, and the type of stitches used. Initially, it's essential to attend regular follow-up appointments. (10)

Recovery

Following the surgical procedure, it is customary to provide patients with a night band to wear for a few weeks to protect the eye for a good healing process. In addition, for any corneal treatment, antibiotics or steroid eye drops should be administered daily. Usually, patients require these drops for a few months, but occasionally, they may last longer than a year. These drops serve to relieve inflammation and swelling while also preventing infection and rejection.

Results

While most patients can expect positive long-term results after corneal operation, a number of variables, including as the patient's general health and the underlying cause of their problem, must be taken into consideration. Despite successful treatment, the risk of complications and corneal rejection may persist for a protracted duration, emphasizing the importance of regular follow-up care. 

To monitor and maintain optimum vision health, it is essential to schedule annual checkups with an eye doctor.

In addition, it is critical to emphasize that, regardless of the kind of cornea therapy obtained, ongoing observation and follow-up care are necessary for reducing the risk of complications or recurrences related with the underlying problem.