The Study of relationship between binocular vision and near point of convergence while near vision

Background: Binocular vision anomalies are the most common visual problems that are along
with several symptoms such as headache, asthenopia, and pain in the eyes, intermittent diplopia,
intermittent blur vision, print swimming and other symptoms. Because of high prevalence of these
anomalies a regular examination and visual screening program including on some tests for
assessment and determination of these anomalies is necessary. The aim of this study was
assessment of relationship between near point of convergence (NPC) and near binocular vision
symptoms.
Material and methods: In this cross sectional study 124 students of different majors in
paramedical and health faculty of Mashhad University of medical sciences that had inclusion
criteria were studied. The subjects were selected using simple random sampling. The subjects were
divided to two groups (with and without symptoms) according to their own reporting. Visual acuity,
refractive errors and NPC were determined using snellen chart, retinoscopy( cyclopentolat 1% if
necessary) and small isolated letter "E" of approximately 20/30(6/9) size from snellen reduced
chart. The data were analyzed by SPSS version 13 using descriptive and analytical (mann-withney
test and ROC curve) statistics.
Results: The subjects were 60% (75) female and 40% (49) males. In this study 61.1% (82) and
33.9% (42) of subjects were with and without symptom respectively. The mean of NPC in with and
without symptoms group were 11.7± 6.01 and 8.4±3.95 centimeters respectively. The difference in
near point of convergence was statistically significant in the two groups. The cut-off point of NPC
was determined 9.5 cm using ROC curve.
Conclusion: According to high prevalence of binocular vision anomalies especially in students,
determination of NPC has an important role in differentiation of symptomatic from asymptomatic
subjects. Hence, NPC is suggested to be evaluated specially in persons that have long near vision
tasks. Cut-off point 9.5 cm is suggested to binocular vision screening.