12 - Visual acuity and contrast sensitivity

Abstract

Visual acuity tests have been used for over 150 years and contrast sensitivity tests for nearly 50. Yet the methods for both types of test are still improving. Acuity tests are shifting from Snellen acuity to the widely recommended logMAR charts, which leads to greater reliability and easier statistical analysis. Adaptations to logMAR testing, such as the use of vanishing optotypes and employing low luminance viewing conditions, are proving useful in the detection of subtle visual function deficits. Contrast sensitivity has shifted away from using sine-wave gratings to characterize the contrast sensitivity function (CSF) to using a single measure of large-letter contrast sensitivity. With the advent of smartphone and tablet-based vision tests, it is now even easier to measure acuity in the field or at home and possible to measure the CSF in as little as 5 minutes. However, so far, the electronic acuity tests are proving to be unreliable, and it is yet to be determined whether there is an advantage to measuring the entire CSF rather than just measuring peak sensitivity with large-letter charts. This chapter reviews current recommendations and outstanding issues for visual acuity and contrast sensitivity tests.