NORMATIVE VALUES FOR THE NEARPOINT OF CONVERGENCE OF ELEMENTARY SCHOOLCHILDREN

Background. Nearpoint of convergence (NPC) values of 8 to 10 cm are wi dely used to diagnose binocular dysfunctions such as convergence insuf ficiency. However, there are no published age-related normative values in the literature to substantiate these values. Methods. Subjects wer e 297 schoolchildren in kindergarten, third grade, and sixth grade who had passed a school-based Modified Clinical Technique vision screenin g. Each child had the NPC break and recovery taken three times using a standardized protocol developed by the Convergence Insufficiency and Reading Study group. The examiners used an Astron International (ACR/2 1) Accommodative Rule with a movable column of 20/30 letters as the ta rget. Results. For each grade, the distribution of NPC break was right skewed, with a concentration of values between 1 and 6 cm. At least 8 5% of the subjects in each grade had an NPC break less than or equal t o 6 cm. NPC break values (mean +/- SD) were 3.3 +/- 2.6 cm for kinderg artners, 4.1 +/- 2.4 cm for third graders, and 4.3 +/- 3.4 cm for sixt h graders, and the means were found to be statistically different (ana lysis of variance, p = 0.031). NPC recoveries (mean +/- SD) for the th ree groups were 7.3 +/- 4.8 cm, 8.7 +/- 4.2 cm, and 7.2 +/- 3.9 cm, re spectively, which were also significantly different (analysis of varia nce, p = 0.027). The recovery distributions were more symmetric and le ss skewed than those for break. For each grade level, there was a stro ng positive relationship between NPC recovery and NPC break, but the d ifference between NPC recovery and break had a low correlation with th e NPC break. Summary. Kindergartners had somewhat better NPC breaks th an third or sixth graders, whereas no clear age trend was present for NPC recovery. A supporting study using a random sample of clinic patie nts (aged 10-12 years) suggests that patients with NPC breaks > 6 cm a re more than twice as likely to be symptomatic than patients with NPC breaks less than or equal to; 6 cm. Based on these results and the NPC break distributions in this study, a clinical cutoff value of 6 cm is suggested for patients of elementary school age. A cutoff value in th e 6- to 10-cm range is recommended for children of elementary school a ge in a screening context. The exact value within this range depends o n the level of concern with identifying patients who have visual signs and symptoms associated with a receded NPC.