The Human EyeKho, Mojica, Mateo

The Human Eye

The Human Eye (biology)

The pupil is an opening which allows light to pass into the eye. It isthe dark hole in the center of your eye. The pupil is controlled bythe iris (the colored part of the eye) which is a muscle that contractsto make the pupil smaller and relaxes to allow the pupil to widen.The pupil’s size relates to how much light there is in a particularsetting. The iris is covered by the cornea. The lens of the eye islocated in back of the iris. The lens focuses the light onto the retina,which acts like a screen. Eyelashes and eyelids protect the eye bystopping dust particles from falling onto the eye itself.

The Human Eye (biology)

There are two types of light sensitive cells on the retina.Rods, are used for black and white vision, and areconcentrated on the sides of the retina. Cones are used forcolor vision, and are concentrated in the center of theretina. Vision is most acute in the area of the retina knownas the fovea centralis.

Rods and Cones

The Human Eye (Physics)

In our eyes, the object is beyond 2F, and the image formedis real, inverted, smaller than the object, and on theopposite side of the lens. We know that the image formedmust be real, because it is projected onto the retina (whichis like a screen). However, we don’t actually “see” theobject as inverted because our brain flips things around sothat we see them as being upright.

The Human Eye (Physics)

We know that lenses are needed to focus an object onto a screen, and in this case the retina. One of the theories of how the eye focuses is the 3 lens system. In this situation, (1) the cornea would have little refractive power, and just serve as a “cover glass” to the eye. (2) The aqueous lens lies on top of the pupil, and has a strong refractive power, because it is a very thick lens. (3) The vitreous lens does a lot of magnification.

Other facts

Its index of refractionchanges because there isa density change withinthe lens itself.

The blind spot, locatedwhere the optic nervemeets the eye, containsno photo-receptors.

Some animals have literal colour blindness. They do not have cones on their retinas.

Sources:

Saskatchewan Education. (1992). Science: A Curriculum Guide for the Secondary Level Physics 20/30

Oracle Quest. Retrieved from http://library.thinkquest.org/C003776/ingles/print/chapter5.htm