Bill Harvey: Missing out on accuracy by some distance

I have recently undertaken a number of practice visits and have noticed a couple of things about acuity charts that seem to crop up time and time again. The first is the number of practices that use a projector chart upon a flat grey metallic screen. Presumably because the lens or bulb housing has tarnished to some extent, the letters projected are no longer fully black and in a few cases I have seen the pre-reg having to dim the room lights in order for the patient to see the letters better. As Snellen notation is based upon the viewing of a high contrast target, such adaptation brings the whole accuracy of acuity measurement under question.