What does 20/CF 6” mean when talking about correctional vision?
largest letter on an eyechart (the one at the very top) is usually a big "E."
This is typically the 20/400 line, meaning that if you cannot read down
the chart to smaller size letters, your vision would be recorded as 20/400.
But what if you can't even see that size letter?
The person measuring your visual acuity would then hold his hand a few feet away and ask if the patient can say when his fingers wiggle. The hand would then be gradually moved further away, all the while asking the patient being tested how many fingers were being held up, changing the number intermittently. If that furthest distance where the number of fingers could no longer be counted correctly were to be 6 feet, the patient's visual acuity would be recorded as Count Fingers at 6' or CFx6'. [Actually, the "20/--" is not used.]
_Written by J. Trevor Woodhams, M.D. - Chief of Surgery, Woodhams Eye Clinic