Near Point of Convergence in Iranian Schoolchildren: Normative Values and Associated Factors
1a Noor Research Center for Ophthalmic Epidemiology , Noor Eye Hospital , Tehran , Iran.
2b Department of Optometry, School of Rehabilitation Sciences , Iran University of Medical Sciences , Tehran , Iran.
3c Department of Medical Surgical Nursing, School of Nursing and Midwifery , Shahid Beheshti University of Medical Sciences , Tehran , Iran.
4d Noor Ophthalmology Research Center , Noor Eye Hospital , Tehran , Iran.
5e Department of Optometry, School of Paramedical Sciences , Mashhad University of Medical Sciences , Mashhad , Iran.
6f Ophthalmic Epidemiology Research Center , Shahroud University of Medical Sciences , Shahroud , Iran.
7g Department of Epidemiology and Biostatistics, School of Public Health , Tehran University of Medical Sciences , Tehran , Iran.
Purpose: To determine the distribution of near point of convergence (NPC) and its related factors in 6 to 12-year-old children.
Methods: In a cross-sectional study in 2015, the urban and rural children of Shahroud, north of Iran, were sampled. All rural schoolchildren were invited to the study, and in the urban area, we conducted random cluster sampling. Examinations included measurement of uncorrected and corrected visual acuity, manifest, subjective, and cycloplegic refraction. NPC and near point of accommodation (NPA) were measured with the best optical correction.
Results: Of the 6624 sampled schoolchildren, 5620 participated in the study, and after applying the exclusion criteria, the final analysis was conducted on data from 5444 students; their mean age was 9.24 ± 1.71 years (6-12 years) and 53.6% (n = 2918) of them were male. Mean NPC was 8.08 cm [95% confidence interval (CI): 7.96-8.19]; 8.07 cm (95% CI: 7.92-8.22) in males and 8.08 cm (95% CI: 7.91-8.25) in females (p = 0.954). NPC significantly recessed with age (p < 0.001). Mean NPC in emmetropic, myopic, and hyperopic children were 8.13, 7.04, and 8.23 cm, respectively (p < 0.001). The multiple linear regression model revealed significant associations for NPC with age (coefficient = 0.10, 0.95% CI: 0.05-0.15, p < 0.001), spherical equivalent refraction (coefficient = 0.17, 95% CI: 0.10-0.24, p < 0.001), and NPA (coefficient = 0.83, 0.95% CI: 0.76-0.90, p < 0.001).
Conclusion: Mean NPC in 6-12-year-old Iranian children was 8.08 cm, which is worse than values reported in previous studies. Mean NPC showed a slight recession with age. Myopic schoolchildren had the least remote and hyperopes had the most remote NPC values. More remote values of NPA were associated with receded NPC.
Keywords: Children; distribution; near point of convergence.