How do these factors affect visual acuity?
- The object and its illumination
- The optical system including the pupil
The object and its illumination
The distance of the object affects visual acuity – the further away the object, the image projected onto the retina is smaller and of lower minutes of arc.
The contrast of the image also has an effect – the higher the contrast of the image, the better the visual acuity as the image stands out more against the background. The lower the contrast ratio, the lower the visual acuity.
Visual Acuity also increases as luminescence increases, because they are similar in ratio.
We ran a study with all members of staff at Gordon’s Glazing Windows Glasgow and found that many people had fantastic vision. Great news!
The optical system including the pupil
The pupil size affects visual acuity and resolution of the image. In low-light conditions, the pupil increases in size and this decreases visual acuity by projecting the image onto the retina as blurred and not sharp. However low visual acuity is also the case if the pupil is too small, where diffraction occurs (not all of the image is sharp/clear, causes a blur at the edge of the shadow of the object).
(To detect a small bright spot, detection is greatly dependent on the quantity of light rather than the exposure time. However, to detect a line, the acuity, (reciprocal width of the line) is proportional to the exposure time. There is no simple acuity-exposure time relationship for the resolution of the target).
(During steady fixation, the eyes are in constant motion. Under these conditions, retinal images traverse a distance of about 3 minutes of arc in one second).