Vision

Vision

• The retina contains thousands of photoreceptors. There are 2 kinds of photoreceptors:

  • rods - low light, extremely sensitive, all over the retina

  • cones - center of the retina, detection of colors, less sensitive

• To see an image, light passes through the eye and hits the retinal pigment epithelium (RPE) on the back of the eye. The light causes molecular changes that begin an impulse. The impulse travels through the rods and cones, then bipolar neurons, and then ganglion cells before traveling to the brain via the optic nerve.

• The fovea centralis is a tiny pit that contains only one, so it is the point that provides the sharpest image. There are no photoreceptors where the optic nerve meets the eye, this is called the blind spot. Because the blind spot affects different parts of each eye, it is not regularly noticed. The brain fills in the missing image.

• In some individuals, the eye is too long or too short, causing near-sightedness (myopia) or far-sightedness (hyperopia). Corrective lenses help to refract the light so it accurately converges on the retina.

Summary:

• Two kinds of photoreceptors (rods and cones) are found in the retinal pigment epithelium. The optic nerve channels impulses from these receptors to the brain but causes a blind spot in the retina where it attaches. I flight does not correctly focus on the retina, correvctive lenses may be required.