Snellen acuity primarily tests which type of spatial frequencies?

Snellen acuity primarily tests which type of spatial frequencies?

• A. High resolution spatial frequencies
• B. Low resolution spatial frequencies
• C. Both high and low
• D. None of the above

Answer: (A)

Resolving fine detail is what Snellen acuity measures. Letters are made up of thin strokes and sharp edges that correspond to high spatial frequencies in the image they present to the eye. When viewing at the threshold of recognition, the limiting factor is your ability to resolve those fine details, not just the overall shape. Low spatial frequencies carry gross, global shape information, which isn’t enough by itself to identify small letters at high contrast. So, Snellen acuity primarily tests high resolution spatial frequencies.

Resolving fine detail is what Snellen acuity measures. Letters are made up of thin strokes and sharp edges that correspond to high spatial frequencies in the image they present to the eye. When viewing at the threshold of recognition, the limiting factor is your ability to resolve those fine details, not just the overall shape. Low spatial frequencies carry gross, global shape information, which isn’t enough by itself to identify small letters at high contrast. So, Snellen acuity primarily tests high resolution spatial frequencies.