Vision Physiology Post Lab Assignment
20/20 vision is normal vision and means that from 20 feet away, the person can see what an average person can see at that distance (Guitierrez, 2014). In the visual acuity test from lab we measured our vision. To do so my lab partner stood 20 feet away from the Snellen chart, which is organized by letters that gradually decrease in size, and read off the letters. She was able to read through the second to last line, which means she has 20/20 vision. 20/10 vision differs on the other hand because it is better than normal vision. It means that from 20 feet away, the person can see what a normal person would be seeing at 10 feet (Guitierrez, 2014). In the visual acuity test from the lab we only measured up to 20/15 vision, but because my lab partner was able to see the print clearly at 20/15, I believe she would also have been able to see the smaller print at 20/10 vision.
The blind spot in the eye is also called the optic disk and is a white spot located beside the macula lutea. The optic disk the place where the optic nerve or the axons of the ganglion cell layer connect to the eye. The blind spot is so named because it contains no photoreceptors (only blood vessels and nerve endings) so it cannot detect light (Regan et. al).
In lab, we observed the blind spot by using a card labeled with a cross and a dot. I closed one eye, focused on the dot, and moved the card closer to my face. Eventually, when I brought the card close enough I noticed that I could not see the cross anymore. This occurred because of my eye’s blind spot. At that point the card’s proximity to my face focused the image of the cross on my blind spot where there are no photoreceptors (Guitierrez, 2014).
Color blindness is the inability to see color or a specific color. Many times the color will be seen as grey instead of its normal shade. The condition results from one or more of the cone photoreceptors not functioning properly or missing entirely. Genetically the problem arises from incorrect copying of DNA during development. The genes that determine red from green are very similar and position very close to one another. Therefore, it is not uncommon for one or more of the color genes to be abnormal (Regan et al. , 2016).
Color blindness is much more typical in males than females because color genes are found on the X chromosome only. Males have only one X chromosome which means that if a color gene like red or green is incorrect the mutation will be expressed. Females by contrast have two X chromosomes increasing the likelihood that at least one correct gene will be present (Regan et al. , 2016). My lab partner and I are both female and we were both able to see the number 5 outlined by red and green dots in the color blindness test. Therefore we are not red-green colorblind.
