Cornea is the outermost layer of the eyeball, which is a transparent layer and act as the window to the inside part of the eyeball. Cornea structured by some cell layer and connecting collagen tissue. Cornea doesn’t have any blood vessels except in the Limbus at the side part.

The cornea's main function is to refract, or bend, light. The cornea is responsible for focusing most of the light that enters the eye.  The light is received in the neural retina and optic pupil, then transmitted to the brain's neurons.

The cornea is comprised of five layers: the epithelium, Bowman's layer, the stroma, Descemet's membrane, and the endothelium. If there any damage happened in one or more layers, it’ll cause cloudiness in the cornea and causing problems with the eyesight. The cornea got it nutrition for several sources, e.g. tears, Limbus blood vessels, and the aquos from the back of the cornea. On the epithelium layer, there are free ended nerves which causing pain if there any damage in the cornea.

Some disruption or damage that may happened in the cornea:

• Keratitis or corneal infection (ulcer) which caused by viral infection, bacteria, fungus, parasite.
• Bullous keratopathy (corneal swelling / edema) 
• Corneal cicatricial (scars)
• Corneal perforation ( hole in the cornea)

Keratitis

Keratitis is an inflammation of the cornea caused by infection or non-infection, which is the most common disruption ever found. Keratitis caused by infection, usually happened because of infection by bacteria, virus, or parasite. While non-infection keratitis may happen because of immunological abnormalities on the patient, like rheumatic, eyelid inflammation, etc.

Example of things that may cause keratitis :

• Contact lens : make sure you’ve cleaned the lenses according to the manual. The constant use of contact lenses in a long period has a higher risk of keratitis than the daily use. 
• Low immune system: when the body immune system is weak (because of stress, sickness, flu) it’ll cause a higher risk of getting a keratitis (mostly because of virus infection)
• Steroid : Steroid in eye drops, which often used to fix red eye or eye inflammation may increase the risk of getting a keratitis or worsened the keratitis condition in the eye. Recommended to consult every eye condition to get the right medication. 

Complications that may happen because of keratitis :

• Chronic inflammation on the cornea which often recurrent.
• Open perforation on the cornea surface.
• Scar tissue on the cornea. 

All damage and complication on the cornea will cause temporary problems for eyesight or permanent lost of the eyesight. 

Usually to fix the problem, the patients will have to undergo keratoplasty to replace the damaged cornea with a healthy one from a donor.