The distribution of near point of convergence in an Iranian rural population: A population-based cross-sectional study

Abstract

Objective To determine the distribution of near point of convergence (NPC) according to age, sex, and refractive error in a rural population above 1 year of age in 2015. Methods In this population-based cross-sectional study, multistage cluster sampling was applied to randomly select two underserved areas from the north and southwest of Iran and all individuals above 1 year living in these areas were invited to participate in the study. All participants underwent ocular examinations including visual acuity measurement, refraction, binocular vision testing including cover test and measurement of NPC, and slit lamp biomicroscopy. Results Of 3851 who were invited, 3314 participated in the study (response rate: 86.5%). The NPC was 8.42 ± 2.94 cm in the whole population, 8.59 ± 3.07 cm in men, and 8.30 ± 2.84 cm in women. Subjects above 70 years of age had the most remote NPC (mean: 10.44 ± 3.07 cm). The mean NPC was 7.79 ± 2.93, 8.83 ± 2.72, and 9.63 ± 2.70 cm in emmetropic, myopic, and hyperopic participants, respectively. According to the results of a multiple linear regression model, NPC had a positive correlation with age (b: 0.058, p < 0.001), male sex (b: 0.336, p : 0.005), and hyperopia (b: 0.044, p : 0.011). Among the evaluated variables, age had the greatest effect on NPC (Standardized coefficient: 0.402). Conclusion The distribution of NPC in the Iranian population is different from other populations. Since NPC is influenced by age more than any other variable and presented normal values according to age in this study, the results can be used to interpret clinical measurements for diagnosis and treatment purposes.

The distribution of the near point of convergence and its related factors in an elderly population: the Tehran Geriatric Eye Study (TGES)

“…However, the age range these two studies was wide, and individuals over the age of 60 years included small portion of the overall sample. The mean NPC found in the age groups 60-69 years and more than 70 years in the present study was significantly closer (less remote) than the values reported in similar age groups in the study by Ostadimoghaddam et al (11.98 and 13.06 cm, respectively) [2], and Hashemi et al (9.53 and 10.44 cm, respectively) [18]. These differences may be due to subtle differences in NPC testing instructions, for example "tell me when the target becomes double" versus "try to keep the target single as much as possible and report whenever diplopia occurs".…”

“…ignored due to the small effect size, that the amount of in both sexes was clinically comparable [2]. Age is one of the influential factors on the and agerelated recession of NPC has been reported in different studies [2,9,18]. It seems that these age-related changes are mainly due to a decrease in the accommodative effort along with reduced accommodative amplitude and subsequently a decrease in the accommodative vergence [2].…”

“…As mentioned earlier, several studies have examined the distribution of NPC,1-2,9-19 but most of these studies were performed on children and young adult populations whose results cannot be compared with the present study. A review of the literature found only two studies reporting the distribution of NPC in the elderly population over 60 years of age [2,18]. However, the age range these two studies was wide, and individuals over the age of 60 years included small portion of the overall sample.…”

“…To the best of our knowledge, no study in the literature has evaluated the distribution of NPC specifically in the elderly population. Some previous studies have shown an increase in NPC with age [2,9,18], with these changes being more pronounced in the elderly (over 60 years of age) [2,18]. Given the age-related changes in NPC, the use of existing recommendations (mainly reported for children and young adults) to interpret this finding in the elderly population is debatable and may lead to misinterpretation of the index.…”

“…Therefore, information about normal NPC values in the general population is important to increase its diagnostic value and improve clinical interpretation of this index. Several studies have addressed the distribution of NPC and its related factors in different populations [1,2,[9][10][11][12][13][14][15][16][17][18][19]. However, most of the available studies were non-population-based studies, conducted on selected clinical populations and mostly targeted children and young adults.…”