Describe the Route and Structures on the Route of Light Passing from the External Eye to the Internal Eye.

Describe the route and structures on the route of light passing from the external eye to the internal eye.

Light passes through the cornea, part of which is a delicate thin layer of collagen fibers, through the opening of the eye called the pupil. The pupil is constricted by pupillary constrictor and dilator muscles based on the amount of light reaching the eyes. Light goes past the lens which is adjusted by the ciliary body muscles. The shape of the lens is adjusted based on whether a person is focusing on an object near or far away. The lens light is then focused on the choroid and retina which is rich with delicate blood vessels. Light hits the fovea on the retina. Light is detected by photoreceptors and rods and cones. Rods detect light in low light, and are not color sensitive. Cones are color sensitive and work in brighter conditions. The rods are on the periphery of the retina and the cones are more concentrated, especially on the fovea. The rods and cones are attached to bipolar and ganglion cells or neurons, that lead into the optic disc. Light is then transmitted via the optic nerve which is medial to the fovea, and also creates a blind spot in our field of vision. Light also passes through the aqueous humor, similar to cerebrospinal fluid, which also keeps the shape of the eye.This is the route of light that passes from the external eye to the internal eye as you can see there are many steps involved.

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