The document discusses reflection of light and its uses in ophthalmology. Reflection occurs when light rays traveling in one medium hit the boundary of another medium and turn back into the first medium. There are two main types of reflection - specular reflection which occurs from smooth surfaces and causes light to reflect at the same angle, and diffuse reflection which occurs from rough surfaces and scatters light in all directions. In ophthalmology, the cornea's anterior surface acts as a convex mirror and reflection is used by instruments like the keratometer.