Snell-Sterling visual efficiency scale

visual efficiency scale, Snell-Sterling 

A representation of visual efficiency as a function of visual acuity, in which are taken into account other factors such as perception, experience, etc. in estimating how much vision a person has for a given visual acuity.

Table V2 Relationship between visual acuity and the Snell-Sterling visual efficiency scale (in percentage round figures)
visual acuity				Efficiency		loss of vision
(m)		(ft)		(in %)		(in %)
6/6		20/20		100		0
6/7.5		20/25		96		4
6/9		20/30		91		9
6/12		20/40		84		16
6/15		20/50		77		23
6/18		20/60		70		30
6/24		20/80		59		41
6/30		20/100		49		51
6/48		20/160		29		71
6/60		20/200		20		80
6/90		20/300		8		92
6/120		20/400		3		97
6/150		20/500		1.5		98.5

Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann