Visual, Hearing, and Taste Test Lab - The Senses Visual and Hearing Tests and Experiments Activity 1 Demonstrating the Blind Spot A \u200bblind spot \u200bis

Visual, Hearing, and Taste Test Lab - The Senses Visual and...

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The Senses: Visual and Hearing Tests and Experiments Activity 1: Demonstrating the Blind Spot A blind spot is an obscuration of the visual field. It is the place in the visual field that corresponds to the lack of light-detecting photoreceptor cells on the optic disc of the retina where the optic nerve passes through the optic disc. 1. Hold Figure 1 (below) about 18 inches from your eyes. Close your left eye, and focus your right eye on the star, which should be positioned so that it is directly in line with your right eye. Move the figure slowly toward your face, keeping your right eye focused on the star. When the dot focuses on the blind spot, which lacks photoreceptors, it will disappear. 2. Have your partner record in metric units the distance at which this occurs. The dot will reappear as the figure is moved closer. Distance at which the dot disappears: Right eye __25.4cm_________________________________________ Repeat the test for the left eye. This time close the right eye and focus the left eye on the dot. Record the distance at which the star disappears: Left eye __30.48cm_________________________________________ Fig. 1 Activity 2: Determining Near Point of Accommodation Lens elasticity can be tested by measuring the near point of accommodation. The near point of vision is about 10 cm from the eye in young adults. It is closer in children and farther in old age. To determine your near point of accommodation, hold a dissecting pin at arm’s length in front of one eye. Slowly move the pin toward that eye until the pin image becomes distorted. Have your lab partner use a metric ruler to measure the distance from your eye to the pin at this point, and record the distance below. Repeat the procedure for the other eye. Near point for right eye __9cm_______________________________________________________________ Near point for left eye __11cm________________________________________________________________ Activity 3: Testing Visual Acuity Visual acuity, or sharpness of vision, is generally tested with a Snellen eye chart, which consists of letters of various sizes printed on a white piece of paper. The distance at which the normal eye can read a line of letters is printed at the end of that line.
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1. Have your partner stand 20 feet from the Snellen eye chart () and cover one eye with an index card or hand. As your partner reads each consecutive line aloud, check for accuracy. If your partner wears glasses, give the test twice – first with glasses off and then with glasses on. If they wear contacts, just test them with them in. Do not remove contact lenses! 2. Record the number of the line with the smallest-sized letters read. If it is 20/20, the person’s vision for that eye is normal. If it is 20/40, or any ratio with a value less than one, he or she has less than normal visual acuity. (Such a person is myopic
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  • Spring '16
  • Johnson

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