4.4 The Human Eye

We have covered enough concepts in this chapter to describe the basic operation of the human eye, which is clearly an important component in any VR system. Here it will be considered as part of an optical system of lenses and images. The physiological and perceptual parts of human vision are deferred until Chapter 5.

Figure 4.24: A simplified view of the human eye as an optical system.

Figure 4.25: A ray of light travels through five media before hitting the retina. The indices of refraction are indicated. Considering Snell's law, the greatest bending occurs due to the transition from air to the cornea. Note that once the ray enters the eye, it passes through only liquid or solid materials.

Figure 4.24 shows a cross section of the human eye facing left. Parallel light rays are shown entering from the left; compare to Figure 4.11, which showed a similar situation for an engineered convex lens. Although the eye operation is similar to the engineered setting, several important differences arise at this stage. The focal plane is replaced by a spherically curved surface called the retina. The retina contains photoreceptors that convert the light into neural pulses; this is covered in Sections 5.1 and 5.2. The interior of the eyeball is actually liquid, as opposed to air. The refractive indices of materials along the path from the outside air to the retina are shown in Figure 4.25.

Figure 4.26: Normal eye operation, with relaxed lens.

Figure 4.27: A closer object yields diverging rays, but with a relaxed lens, the image is blurry on the retina.