The Single Symbol Book is designed for testing children and adults who have difficulties in perception of symbols in lines. The visual acuity values measured with single symbols are often several lines better than the line acuity values in persons with impaired vision and thus overestimate the quality of visual functioning. Single optotype line sizes from 20/200 to 20/8 (6/60 to 6/2.4) equivalent, 0.10 to 2.50. Includes isolating mask, response key, training cards, and instructions. 13 offset pages for easy flipping.
10 feet/3 meters testing distance
Lea Symbols Visual Acuity Test System developed by Lea Hyvarinen, M.D. The Lea Visual Acuity Test System is the only complete set of visual acuity tests for near and far distance vision for all patient groups 18 months and over. The tests are based on four symbols which blur equally at the threshold. The symbols are easy to name, sign or point to on the Key Card or flash cards (included with every test except 52152 3-D Symbols or 52168 Symbol Domino Cards).
The tests are designed to create a play situation where the child never experiences failure. When no longer correctly recognized, the symbols transform into circles appropriately called "rings" or "balls" by the child. The child can still perceive that he/she is answering "correctly", while the examiner can easily detect the acuity threshold.
5" x 5" (12.7 cm x 12.7 cm).