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LEA Numbers

LEA NUMBERS® Tests were developed for international studies in occupational health and school health services. Letters like the Sloan Letters are used in the Western world and in the old colonies of western empires but not in a large part of the rest of the world whereas numbers are the same world over. The four numbers 5,6,8 and 9 were chosen because they could be designed to blur equally.

LEA Numbers Blur

Notice how the bottom row of objects all look similar? This is the blurring equally of the LEA NUMBERS®.

The experiences that the previous manufacturer and I have had in designing the symbol optotypes helped us when the number optotypes for occupational health were created. However, numerous hours were spent refining the details of each number. Fortunately, we nowadays have the facilities to exchange information via fax, phone and computers thus reducing the time needed in this type of industrial designing. The LEA NUMBERS® were designed to have equal legibility, to blur equally. This makes the threshold value much narrower than in older tests where such easy numbers as 2, 4 and 7 are used.

In clinical use of visual acuity tests letters and numbers are generally used instead of the reference optotype Landolt C or "Ring" although there are countries were Landolt C is used even in pediatric testing. Letter and number optotypes require recognition of the form.

The round numbers 5,6,8 and 9 are more difficult to recognise than it is to detect where the space is in the Landolt C. Calibration of the size of the number optotypes was done by Juvi Mustonen, O.D. and Risto Näsänen Ph.D. at the Vision Laboratory of the Department of Physiology, Helsinki University, Finland.

Assessment of visual acuity usually follows measurement of refractive error, first without, then with correcting lenses, monocularly and binocularly.

 

Additional Resources

Pediatric Vision Consulting

Questions about screening children, ask us about helping you set up a program with our consulting services.

Find out more >>

LEA SYMBOLS® and HOTV Comparison Study

A study from the Illinois College of Optometry compares LEA NUMBERS® and HOTV to screen children.

Read about the results >>

LEA SYMBOLS® References

LEA SYMBOLS®, the international standard for pediatric vision testing and screening. Find sited published studies using the LEA SYMBOLS®.

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