Vision tests.
Follow me and I will go through the vision tests with you.
The results for all three parts must be recorded on the vision test form.
The first test is the Snellen eye chart test.
- Take the participant over to the eye chart test area.
- Line up their toes to the line on the floor (20 feet).
- Participants can leave on their glasses if they wear them for driving.
Procedure: Look at the wall and read aloud the smallest line you can comfortably read.
- If the participant gets every letter on the first line they try correct have them try the next smaller line. Continue until they miss a letter. At that time, record the one that they were able to read in full (line above).
- If they get the first line they attempt incorrect, have them read the previous line. Repeat as needed until they get one line completely correct. Record this acuity.
- Participant must have 20/40 or better vision using both eyes to participate in the study.
The next vision test is the contrast sensitivity test. Take the participant over to the eye chart test area.
- Line up their toes to the line on the floor (10 feet).
- Participants can leave on their glasses if they wear them for driving.
Procedure: We are going to test how well you see bars at different levels of contrast. Your ability to see these bars relate to how well you see everyday objects. It is VERY IMPORTANT you do not squint or lean forward while you are taking the test.
- Point out the sample patches at the bottom of the chart with the three possible responses (left, right, or straight).
- Cover one eye with an occluder. (DO NOT let the participant use his/her hand to cover the eye since pressure on the eye may cause erroneous contrast sensitivity test results).
- Instruct the participant to begin with Row A and look across from left to right. Ask the participant to identify the last patch in which lines can be seen and tell you which direction they tilt. If the response is incorrect, have the participant describe the preceding patch.
- Use the table in the ENV binder to determine if subjects’ answers are correct.
- Each vertical column of numbers on the second part of the vision test form corresponds to a horizontal row on the chart. Record the last patch the participant correctly identifies in each row by marking the corresponding dot on the form.
- To form the participant’s contrast sensitivity curve, connect the points marked.
- Cover the other eye and repeat all the steps above.
The last vision test is the test for color blindness.
Procedure:
- Take the participant back to his/her desk.
- Place the book containing the plates on the testing apparatus.
Please hold the red end of this handle to your nose and read the number on the following plates.
- Record the participant’s answers on the vision test form.