Augmented and Virtual Reality Systems - pág.30

These impulses continue into the axons of the ganglion cells, through the optic nerve and disk, and to the visual centers in the brain.

Rod and Cone Density

There are approximately 100?120 million rod and 7?8 million cone photoreceptors in each retina (Riggs, 1971). As shown in the distribution graph in Figure 3.9, most cones are concentrated in the fovea, while rods are absent there but dense elsewhere. Despite the fact that perception in typical daytime light levels is dominated by cone-mediated vision, the total number of rods in the human retina far exceeds the number of cones (Purves et al., 2001).

Figure 3.9 This graph shows why we see color (photopic vision) most clearly in our direct line of sight. The peak number of cones occurs in the fovea, where it reaches approximately 150,000 cones per square millimeter.

It is important to note that there are no photoreceptors in the optic disk, more accurately known as the optic nerve head. This lack of photoreceptors means there is no light detected in this area, resulting in a blind spot for each eye. The blind spot for the left eye is located to the left of the center of vision and vice versa for the right eye. With both eyes open, we do not perceive the blind spots because the field of view of each eye overlaps with the other, although they still can be experienced. Follow the instructions in the caption of Figure 3.10 to find your blind spots.

Figure 3.10 To find the blind spot for each eye, start by placing this book flat on a table. Cover your left eye and look at the dot on the left side of this image.