The cornea is the clear front part of the eye covering the iris, pupil, and anterior chamber. It, along with the lens, refracts light and contributes two-thirds of the eye's total optical power. Nerve endings in the cornea sense touch, temperature, and chemicals, prompting a blink reflex. Without blood vessels, the cornea remains transparent. External diseases like dry eye, infections, allergies, and dystrophies can cloud the cornea. Conditions such as corneal all transplantation, dystrophies, blepharitis, allergies, and trauma also affect it.