Augmented and Virtual Reality Systems - pág.24

Entering the Eye

The human eye is a complex optical sensor but relatively easy to understand when thought of as functionally similar to a camera. Light enters through a series of optical elements, where it is refracted and focused. A diaphragm is adjusted to control the amount of light passing through an aperture, which ultimately falls onto an image plane. As shown in Figure 3.2, the human eyes performs the same basic functions, with the cornea and crystalline lens providing focus while the iris serves as the diaphragm, adjusting appropriately to allow just the right amount of light to pass through the aperture. Instead of coming to rest on film, the inverted light field falls onto the extremely sensitive retina.

Figure 3.2 This illustration shows a vertical cross section through the human eye revealing major structures and chambers.

The Cornea

Light from all directions within the visual field initially enters the eye through the cornea, a transparent, dome-shaped structure, the surface which is composed of highly organized cells and proteins. Most of the refraction of light by the eye (~80%) takes place at the air-cornea interface because of its curvature and the large difference in the indexes of refraction. Set behind the cornea is another transparent structure called the crystalline lens, which is a fine focus mechanism because its shape can be changed, thus providing variability to the effective focal length of the optical system (Delamere, 2005). The space between the two optical elements, known as the anterior chamber, is filled by a clear, watery fluid called the aqueous humor, which is produced by the ciliary body. The aqueous humor provides nutrients (notably amino acids and glucose) for the central cornea and lens because they do not have their own blood supply.