A patient has a high frequency cutoff of 20 cycles per degree on the CSF. What is the patient's Snellen acuity?

To determine the Snellen acuity based on the high frequency cutoff provided, it's important to understand the relationship between contrast sensitivity function (CSF) and visual acuity. The high frequency cutoff is the point at which a patient can no longer perceive changes in contrast for visual patterns, and this frequency is often used to estimate visual acuity.

A high frequency cutoff of 20 cycles per degree suggests that the patient has reasonably good ability to resolve fine details in their vision. Studies indicate that a cutoff of around 20 cycles per degree correlates with Snellen acuity of approximately 20/30. This means that at a distance of 20 feet, the patient can discriminate the same detail that a person with normal vision could discriminate at 30 feet.

The other options would correspond to different high frequency cutoffs; for example, a high frequency cutoff at 40 cycles per degree would typically indicate better acuity, around 20/20, while a cutoff lower than that would suggest poorer acuity, such as 20/40 or 20/60. Thus, based on the provided high frequency cutoff, the patient's Snellen acuity is best represented by 20/30.