The cornea is the clear outer layer of the eye that covers the pupil, iris, and anterior chamber. It is made of tough, transparent tissue and is responsible for focusing most of the light that enters the eye. The cornea has a slight curvature, and as light enters the eye, the shape of the cornea refracts (bends) it, which helps the eye focus on objects that are close or far away. The cornea also acts as a filter, screening out some of the most damaging ultraviolet (UV) wavelengths in sunlight, which protects the lens and the retina from injury due to UV radiation.

The cornea has five layers: the epithelium, Bowman’s layer, the stroma, Descemet’s membrane, and the endothelium. The epithelium is the outer layer of the cornea, which stops any material from entering the eye and absorbs oxygen and nutrients from tears. The stroma is the thickest layer of the cornea, behind the epithelium, and is made up of water and protein. It is elastic but solid and gives the cornea its domed shape. The cornea tends to repair itself quickly from minor abrasions, but deeper abrasions may cause scars to form on the cornea, which can cause the cornea to lose its transparency, leading to visual impairment.

In summary, the cornea plays a crucial role in vision by refracting light and focusing it onto the retina. It also acts as a filter, screening out harmful UV wavelengths in sunlight. The cornea has five layers, and the epithelium is the outermost layer that protects the eye from foreign matter and absorbs oxygen and nutrients from tears.