It is not essential that laser users become experts on the biology and physiology of that very complicated organ, the eye. However, it is necessary to know how the laser beam of interest affects the functions of two of the eye’s components: the cornea and the retina. In addition to being knowledgeable about how these two functional parts of the eye interact with various laser beam wavelengths, it is essential that the magnification factor of the complete eyeball assembly be understood. The ability of the eye to focus a certain wavelength range of radiation is one of the most fascinating and remarkable functions of any of the human body organs. Microscopes require extensive apparatus and lens systems to obtain magnifications that approach that capable of the human eye: 100,000 (105) times. This magnification factor is used in laser safety as an engineering constant in calculating optical density values.