Lab 10

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South Mountain Community College *

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160

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Biology

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Dec 6, 2023

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docx

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Summer 2020 Biswas BIO160 Name: _______Evelyn Alvarado_______________________ Date: ________________ Lab 10. Testing the Special Senses online lab This is a modified version of the lab done in person in class The special senses include vision, smell, taste, and hearing. In this lab, we will be testing these senses to see how well they are working. In some of these activities, you would watch the accompanying video and finish the handout. In the rest, you can do them on your own using everyday items. Here is the link to the video VISION Activity I: Retina Anatomy The retina is the neural/sensory tunic (layer) of the eye. It contains specialized receptor cells, called photoreceptors, which respond when stimulated by light energy. There are two different types of photoreceptors – rods and cones. Cones are concentrated in the retina directly posterior to the pupil in an area called the macula lutea. The macula lutea contains some rods in addition to the cones, however, the middle of the macula lutea contains only cones. This area is called the fovea centralis. When you are looking directly at an object, the image of that object is hitting the cones. Cones are the photoreceptors responsible for visual acuity, which is the ability to distinguish the difference between two different things, and the detection of color. Rods are primarily located in the periphery of the retina; the area outside of the macula lutea. Rods are more sensitive than cones, so they are able to detect images in dimmer areas than cones. You cannot read or detect color with rods, but you can detect movement in darker environments. One area of the retina does not contain rods or cones. This area is the optic disc. The optic disc is a hole in the periphery of each eyeball that serves as a passageway for blood vessels and neurons to enter and leave the eye. Since there is a hole in that location, photoreceptors cannot exist there. Procedure 1. Look at the picture of the retina and label the following areas on the picture below and note which areas have rod or cones or both. 1

Summer 2020 Biswas BIO160 Activity II: Testing Visual Acuity Visual acuity is the ability to distinguish the difference between two different things, such as letters. Photoreceptors, called cones, are responsible for visual acuity. Eye doctors test visual acuity by using a Snellen chart, which you are probably familiar with if you have ever been to an eye doctor. A Snellen chart consists of lines of letters that get progressively smaller towards the bottom of the chart. The chart is read from 20 feet away and each line on the chart is labeled with a measurement of vision, which depends on which line the reader can accurately read: 20/10, 20/20, 20/30, etc. Someone with average eyesight (20/20) will be able to read the line labeled “20/20” from 20 feet away. If someone has 20/30 vision, they will be able to read the line labeled “20/30” from 20 feet away, which has bigger letters than the line labeled “20/20”. So, what do these numbers mean? Let’s compare someone with 20/20 vision to someone with 20/30 vision. If someone with 20/30 vision can read the line labeled “20/30” from 20 feet away, someone with 20/20 vision would be able to read that same line of text from 30 feet away. Therefore, someone with 20/20 vision has better vision than someone with 20/30 vision. Conversely, if someone with 20/10 vision can read the line labeled “20/10” from 20 feet away, someone with 20/20 vision would have to be 10 feet away from the chart to read the same line of text. Therefore, 20/10 vision is better than 20/20 vision. Materials needed: Watch the part of the video Testing visual acuity using a Snellen chart. Then answer the questions. Data : Fill in the chart with the visual acuity of each of eye based on viewing the Snellen chart. Left eye Right eye D, N, F, P, T, H P, H, U, N, T,D, Z 2 Blood vessel Macula Fovea Periphery Optic disc

Summer 2020 Biswas BIO160 Questions: 1. The test subject had which of the following in his left eye? a. Above average vision (20/15) b. Average vision (20/20) c. Below average vision (20/30) 2. The test subject had which of the following in his right eye? a. Above average vision (20/15) b. Average vision (20/20) c. Below average vision (20/30) 3. Based off his reading using both eyes what kind of vision do you think does the subject have? a. Above average vision b. Average vision c. Below average vision 4. What type of photoreceptor is responsible for visual acuity? a. Rods b. Cones Activity III: Activity V: Testing for astigmatism Astigmatism is a problem in which the surface of the cornea or the lens is not perfectly round. When light hits these abnormalities, it bends and refracts (spreads out) so a single image does not reach the retina at the back of the eye. This results in blurred or distorted images. Materials needed: ● Watch the part of the video with subject reading the Astigmatism chart Procedure: 1. Close one eye and look at the astigmatism chart with your open eye. 2. Report on the table below whether the test subject has astigmatism in that eye or not. a. If all the lines appear the same, the test subject does not have astigmatism in that eye. b. If some of the lines appear wavy, or if some lines are darker than others, then the test subject has astigmatism. 3. Repeat the test with the other eye and record the results below. Data/Questions: 3

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