A patient has a Snellen acuity of 20/100. What is their contrast sensitivity in terms of cycles per degree?

In visual perception, contrast sensitivity refers to the ability to discern between finer and finer increments of light versus dark (contrast) in a visual stimulus. It is typically measured in terms of cycles per degree (CPD), which represents the number of stripes (cycles) that can be detected per degree of visual angle.

For a patient with a Snellen acuity of 20/100, their vision is poorer than what is considered normal (20/20 acuity). This level of acuity suggests that the patient can identify the specific letters or details at a distance of 20 feet, which a person with normal vision can see at 100 feet. It's generally understood that as visual acuity diminishes, the individual's contrast sensitivity also decreases.

Research has shown that there are standards or expected values for contrast sensitivity associated with various levels of visual acuity. A patient with a Snellen acuity of 20/100 is often expected to have a contrast sensitivity value around 6 CPD. This means they are likely capable of perceiving patterns that consist of 6 cycles within a one-degree visual angle, which reflects their ability to detect differences in contrast at that acuity level.

Therefore, the contrast sensitivity for a patient with 20/100 vision