Table 1.

Generic categories of low vision severity, specified in terms of acuity and contrast sensitivity. Allowing the use of such categorizations simplifies the use of a tools such as ours, at the cost of being able to clearly differentiate between the effects of acuity or contrast sensitivity. These categories are somewhat arbitrary and other authors often use other terms or other levels of low vision. (See [Colenbrander 2003] for more on categories of low vision and Section 5 of this paper for more on acuity and contrast sensitivity.)

Mild	Snellen 20/45 (logMAR 0.35), Pelli-Robson score 1.48
Moderate	Snellen 20/115 (logMAR 0.75), Pelli-Robson score 1.20
Severe	Snellen 20/285 (logMAR 1.15), Pelli-Robson score 0.9
Profound	Snellen 20/710 (logMAR 1.55), Pelli-Robson score 0.6