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).

Diagnosing cerebral visual impairment in children with good visual acuity.

PURPOSE: To identify elements that could facilitate the diagnosis of cerebral visual impairment (CVI) in children with good visual acuity in the general ophthalmic clinic. METHODS: We retrospectively investigated the clinical characteristics of 30 children with good visual acuity and CVI and compared them with those of 23 children who were referred with a suspicion of CVI, but proved to have a different diagnosis. Clinical characteristics included medical history, MRI findings, visual acuity, crowding ratio (CR), visual field assessment, and the results of ophthalmologic and orthoptic examination. We also evaluated the additional value of a short CVI questionnaire. RESULTS: Eighty-three percent of the children with an abnormal medical history (mainly prematurity and perinatal hypoxia) had CVI, in contrast with none of the children with a normal medical history. Cerebral palsy, visual field defects, and partial optic atrophy only occurred in the CVI group. 41% of the children with CVI had a CR ≥2.0, which may be related to dorsal stream dysfunction. All children with CVI, but also 91% of the children without CVI gave ≥3 affirmative answers on the CVI questionnaire. CONCLUSION: An abnormal pre- or perinatal medical history is the most important risk factor for CVI in children, and therefore in deciding which children should be referred for further multidisciplinary assessment. Additional symptoms of cerebral damage, i.e., cerebral palsy, visual field defects, partial optic atrophy, and a CR ≥2 may support the diagnosis. CVI questionnaires should not be used for screening purposes as they yield too many false positives.