Contrast sensitivity is the ability of the visual system to detect large but faint targets. There are
some pathological conditions that reduce contrast sensitivity without impairing visual acuity,
and the test will help in the identification of these conditions. However, reduced contrast
sensitivity and reduced visual acuity often occur together, so that some (by no means all)
children with visual impairment also have reduced contrast sensitivity. Tests for the two
functions are therefore complementary and obtaining a measure of both will give a fuller
description of visual deficits than will one alone.
A child with visual impairment who retains good contrast sensitivity will benefit from
enlargement of tasks – he or she sees large faint objects well. A child with an equivalent acuity
but with reduced contrast sensitivity has a much more severe impairment, and will not get the
same benefit from enlargement. Large objects as well as small objects are difficult to see. So a
measurement of contrast