The Crowded Symbol Book is designed for testing children and adults who have difficulty reading the optotypes on the big charts. This test is the smallest line test when the central symbol is used as the test symbol. The four symbols surrounding the central symbol interfere with the recognition of the central symbol closely the same way they do in line acuity charts. Because of the crowding effect, it often allows measurement of line acuity of young children much earlier than the visual acuity charts and thus helps in detecting amblyopia or impaired vision early. Line sizes range from 20/63 to 20/16 (6/19 to 6/4.8) equivalent, 0.63 to 1.25. Includes a response key, instructions, and 16 offset pages.

Dimensions: 5" x 5" (12.7 cm x 12.7 cm).

Testing distance: 10 feet/3 meters.