Measurement of letter acuity in preschool children.

Measurement of visual acuity remains the most frequently used technique for the assessment of vision in both adults and children. Visual acuity is usually measured clinically in adults using a Snellen chart. However. this technique demands a level of cognition and literacy which is beyond the majority of young children. The measurement of visual acuity in preschool children presents an additional set of problems but it is important that measures of acuity arc made with sufficient precision and accuracy to provide the clinician with valid information. While visual acuity can be measured in infants and very young children using behavioural and clectrophysiological techniques, clinical measurement of letter acuity usually commences when the child is old enough to interact and co-operate with the examiner. By 3 years of age 67% of children will cooperate with visual acuity testing, and by the age of 3.5 years a level of 80% compliance is achieved. The need to detect and correct visual disorder5 during childhood has been recognized for many years by eye-care professionals. Although identification of reduced visual function due to ametropia is important, the detection and treatment of amblyopia is essential