Vision

• Eyes transduce energy in the electromagnetic spectrum into APs.

• Only wavelengths of 400 – 700 nm constitute visible light.

• Neurons in the retina contribute fibers that are gathered together at the optic disc, where they exit as the optic nerve.

Refraction

• Light that passes from a medium of one density into a medium of another density (bent).

• Refractive index (degree of refraction) depends upon:

• Comparative density of the 2 media.

• Curvature of interface between the 2 media.

• Refractive index of air = 1.00

• Refractive index of cornea = 1.38

• Image is inverted on retina.

Accommodation

• Ability of the eyes to keep the image focused on the retina as the distance between the eyes and object varies.

Changes in the Lens Shape

• Ciliary muscle can vary its aperture.

• Distance > 20 feet:

• Relaxation places tension on the suspensory ligament.

• Pulls lens taut.

• Lens is least convex.

• Distance decreases:

• Ciliary muscles contract.

• Reduces tension on suspensory ligament.

• Lens becomes more rounded and more convex.

Category: Physiology Notes