Grating acuity tests
In infants, young children and children and adults at early developmental level visual acuity cannot be measured with optotype tests because of communication difficulties. Then an estimate of the function of some parts of visual pathways can be made by using grating acuity measurements with detection and discrimination tests.
The LEA Gratings is an easy test to assess detection grating acuity. The test can be used at different distances and with two different presentation techniques:
LEA Gratings can be used at different distances. When a grating is moved closer to the child or person to be tested, its frequency decreases. When it is moved farther, its frequency increases. This is shown in the adjacent picture. A 1 cpcm (one cycle or pair of black and white lines on one centimetre of the surface) grating has a frequency 1cpd (cpd= number of cycles per degree of visual angle) at 57cm distance and a frequency of 2 cpd at a distance of 114cm.
Grating acuity is a different function than optotype acuity: The stimulus covers a much larger area of the visual field than does an optotype and detection of presence of a striped pattern is a brain function different from discrimination of forms. Therefore grating acuity values should never be converted to optotype acuity values.
The Lea Grating Acuity Test as a discrimination test can be used in assessment of visual functioning of children at school age, sometimes also of well functioning preschool children. The task during the measurement is to tell or show the orientation of the lines on the test, which is shown in four diffent orientations: horizontal, vertical and two diagonal directions.
This test has proven useful in testing vision of children who have brain damage. Some of them can not process many straight lines at ones, the test surface is seen as a network of distorted lines or only a small area of the grating can be perceived or the lines are not perceived at all. This information on the limited capacity of processing large numbers of parallel lines cannot be found in any other test situation.
For more information, see the Instructions Section: LEA Gratings, LEA Grating Acuity Test, LEA Low Contrast Grating Acuity Test and LEA Low Contrast Gratings, the detection acuity test at low contrast levels.
Edited on 1.7.2009