The eye and its constituent structures are capable of taking in light, imaging the light, and converting the visual signal into an electrical signal. The latter information can be manipulated by the brain to produce the multi-colored image that we perceive.

Light first enters a transparent and bulging structure called the cornea. The cornea is the covering structure of the eye. In addition to this protective function, the cornea is the primary light focusing structure of the eye. The cornea is made up of four layers of connective tissue with a layer of epithelium (the same tissue that covers the skin) on the surface. The four layers, from the front of the cornea to the back, are: Bowman's (anterior limiting) membrane, stroma (also called substantia propria), Descemet's (posterior limiting) membrane, and the endothelium. Even with multiple layers, the cornea remains...