The clinic nurse notes that following several eye examinations, the physician has documented a diagnosis of legal blindness in the client’s chart. The nurse reviews the results of the Snellen’s chart test expecting to note which of the following?
A. 20/20 vision
B. 20/40 vision
C. 20/60 vision
D. 20/200 vision
Correct Answer: D. 20/200 vision
Legal blindness is defined as 20/200 or less with corrected vision (glasses or contact lenses) or visual acuity of less than 20 degrees of the visual field in the better eye. The WHO describes individuals with low vision as having a best-corrected vision of 20/60 or worse, and blind as best corrected vision worse than 20/400, whereas legal blindness is identified as 20/200 in the United States.
Option A: Although 20/20 visual acuity has been referred to as “perfect vision,” it is important to remember that this is only one aspect of vision and does not include other elements such as depth perception, peripheral vision, and colorblindness.
Option B: In the United States, visual acuity screening will typically begin as early as age 3. There is a critical line that the child should be able to complete on a visual acuity chart by age group. The critical line for children between the ages of three to four is 20/50, four to five is 20/40, and five or older is 20/30.
Option C: An individual with 20/60 vision would be able to distinguish the same optotype at 20 ft that another individual with normal (20/20) vision distinguishes at 60 ft. In the logMAR, visual acuity is reported as a single number where 0.0 is standard vision. Visual acuity decreases as the number increases and improves as the number decreases.
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