Visual Acuity Tests
A great majority of the LEA Tests are visual acuity tests to allow measurement of visual acuity in all clinical situations. One of the most common areas is vision screening in preschool and school age.
The basic visual acuity test is the line test where the distance between the symbols, the optotypes, is equal to the width of the symbols, as recommended by the International Council of Ophthalmology in 1984 and 1988 and WHO 2003.
Near Vision Tests
Thus for near vision acuities we have three different acuity values:
Distance vision tests
Visual acuity for distance vision is measured with tests held at three meter distance. If that distance is too great for a young child, testing can be performed at two meter distance. In older children measurement can made at greater distances up to six meters if the child has vision tasks at that distance.
For testing children 5 years of age and older, the basic test of visual acuity at distance is the 15-line Folding Chart or the back illuminated charts on either the small lightbox or the big EDTRS-lightbox. In these charts there are two or three sets of symbols in the lower rows so that measurement of binocular and monocular values can be made by using different sets of symbols. This prevents memorising. The charts with several sets of symbols in the lower rows are too difficult for 3-4-year-old children. For them there is the chart with 10 lines and only one set of symbols.
If we use seven visual acuity tests of the LEA Vision Test System, it is possible to get seven different visual acuity values when assessing vision of a child with brain damage related changes in oculomotor functions and visual processing.
Back illuminated distance vision charts
In the U.S., the National Eye Institute requires that visual acuity measurements for research purposes are made on visual acuity tests that are back illuminated at a standard luminance level. The light boxes are of two different sizes, the large so called EDTRS light box where a full size visual acuity test can be used and a small light box on which the largest symbols are three lines smaller.
The small light box is easily caried and can be used with both paediatric and adult visual acuity charts at high and low contrast levels. Its use is demonstrated Follow-up of Vision Development of healthy children to detect amblyopia (lazy eye) and eye turn or strabismus.
The LEA SYMBOLS® have been chosen for several screening instruments, such as the INSTA-LINE by Good-Lite, the Massachusetts Visual Acuity Test and the VIP-test. These modifications try to make testing easier for the tester. A typical screening test in several States of the United States contains only those lines of the visual acuity chart that are used in screening symptom free children.
Screening programs and tests for assessment using LEA SYMBOLS® are also a part of computer based tests by:
For more information, see the Instructions Section: LEA SYMBOLS® Visual Acuity Tests.
Edited on 1.7.2009.