Two smaller groups 8M to 1.6M for repetitive testing (20/40, 6/12 to 20/8, 6/24 equiv.).
Can be wall-mounted.
ETDRS charts are considered the standard in vision testing. Their high calibration has eliminated many underlying errors that have provided false or compromised results. This ETDRS chart features PV Numbers for optotypes. These optotypes have been calibrated to Sloan Standards and are considered highly reliable. PV Numbers have been chosen because of their equally difficulty, blur at threshold and occupied space in a Snellen 5×5 grid. This ETDRS chart is an acceptable way of testing patients not familiar with the Roman Alphabet, or mute patients.