Crowding ratio in young normally sighted children.

Purpose: To determine normal values of the crowding ratio (CR) in children.

Methods: Of 62 normally sighted primary school children aged 4-12 years old the CR was determined both for distance and near vision. The examinations were performed using commonly available test charts based on the LEA symbols.

Results: At near, the CR was significantly better than at distance and for all ages <2.0. The upper limit of the CR at distance was <2.0 from age six.

Conclusion: With commonly available tests the CR can easily be determined in school age children. For children >6 years of age, a CR > 2.0 (i.e. at least 3 lines difference between the result of a single optotype acuity test and a line acuity test) is suspicious and warrants further investigation. It may, for example, be a sign of cerebral visual impairment (CVI).