Vision is blurred if light does not bend or refract correctly and focus directly on the retina. The cornea is responsible for 70% of the refractive power of the eye. The retina receives the light rays and converts them to neural signals that are transmitted by the optic nerve to the brain, where the signals are translated into images. Light rays pass through the cornea and lens and then focus on the retina. SWEENEY, in Biomaterials and Regenerative Medicine in Ophthalmology, 2010 4.2.1 Refractive error In general, when entering a denser medium from a less dense medium, light is refracted toward the normal and when it passes from a dense to a less dense medium, it is refracted away from the normal. This displacement of light rays is called refraction. When a ray of light passes from one medium to another, the light undergoes a change in direction. There are two laws of reflection, namely, the angle of incidence is equal to the angle of reflection and the incident ray, the normal at the point of incidence, and the reflected ray lie in the same plan. This consists merely of a lamp in a box containing a narrow slit that emits rays of light. The behavior of light rays may be investigated by using a ray-box. Light always travels in straight lines although its direction can be changed by reflection or refraction.
Light is an electromagnetic wave and the straight line paths followed by narrow beams of light, along which light energy travels, are called rays. This chapter focuses on light rays and its behavior. J O Bird BSc, CEng, MIEE, CMath, FIMA, FCollP, MIEIE, P J Chivers BSc, PhD, in Newnes Engineering and Physical Science Pocket Book, 1993 Publisher Summary