How Vision Works by Kailey Sawyer

There are three main structures on the outermost part of the eye; the cornea, iris and pupil. The cornea focuses light waves and activates the iris muscle to constrict the pupil. The pupil is a structure that focus’s light. The pupil dilates when there is increased amount of light and constricts when there is a decreased amount of light. After the light goes through those four structures it finally hits the inner part of the eye; the lens, retina, and photoreceptors. The lens is the first structure of the inner eye, it serves to focus the light further to enter the retina. The retina is near the optic nerve and lines the back of the eye. The structures lining the top of the retina are called photoreceptors. There are two types of photoreceptors, rods and cones. Cones work best in bright light and help the neurons to perceive color. Rods on the other hand, work best in low light and are responsible for seeing movement in ones peripheral view. After the light passes through all structures of the eye, it is then turned into neural signals from the optic nerve and sent to the brain (Open Stax College, 2014).

Pediatric Eye Conditions
(Bienfang, Kelly, Nicholson, & Nussenblatt, 1990):

Night Blindness (nyctalopia): Is caused when transition of nerve impulses from brightness (cone dominated) to darkness (rod dominated) is delayed or does not perform at all. 
Nearsighted (Myopia): Is caused when the eyeball is too long.

Farsightedness (Hyperopia): Is caused when the eyeball is too short.

Lazy Eye (Amblyopia): Is caused when one eye does not process neural pathways correctly.

Cross-eyed (Strabismus): Is caused when the eye muscles do not work correctly. This can happen when there is a disruption of nerve pathways from brain to eye muscles.

Color Blindness: when the cones are absent or do not work. A person with normal vision has three different kinds of cones: red, green, and blue.

 

• References

  
  

  Bienfang, D. C., Kelly, L. D., Nicholson, D. H. & Nussenblatt, R. B. (1990).

  Ophthalmology. New England Journal of Medicine, 323(14), 956-967.

  OpenStax College (2014). Psychology. Houston, TX: Rice University.