The correct answer is D.
Color blind patients cannot distinguish red from green or blue from yellow. The pictured Snellen eye chart is a quick screening test for both visual acuity and red-green color blindness. Another way of testing for color blindness is using the Ishihara color system which contains numbers or symbols of colored dots within other colored dots. Color blind patients will not be able to see the number or symbol (see image in explanation).
Wrong Answers:
Option A. 20/20 is considered normal vision.
Option B. 20/200 is considered legally blind. 20/200 means that a patient with normal vision would be able to see line 1from 200 feet away.
Option C. For the Snellen vision test, the patient stands 20 feet away, then covers one eye and reads the lowest possible line without squinting.
Learning Point: Visual acuity and color blindness can be quickly tested using the Snellen chart. For Snellen testing, the patient stands 20 feet away from the chart, then covers one eye and reads the lowest possible line without squinting. 20/20 vision is considered normal vision, which means that from 20 feet away, the patient can read lines 1 through 8 correctly, but cannot read line correctly from 20 feet. Color blindness is an X-linked inherited condition that occurs 20x more often in males. Red/green color blindness is the most common form, but yellow/blue is another less common form.
