The prevalence of tropia, phoria and their types in a student population in Iran

ABSTRACT

Purpose

The aim of this study is to determine the prevalence of tropia, phoria, and their types in Islamic Azad University students in Shahrekord, Iran.

Methods

Of 826 students that were invited, 752 participated in this cross-sectional study (response rate = 91.04%). After applying exclusion criteria, statistical analyses were performed on the data of 726 individuals. All participants underwent optometric tests including measurement of visual acuity, objective and subjective refraction, as well as binocular vision and ocular health examinations. The unilateral and alternate cover tests were done to detect the tropia and phoria at 6 m and 40 cm, respectively.

Results

The overall prevalence and 95% confidence interval (CI) of tropia, exotropia, and esotropia were 1.5% (0.8 to 2.7), 1.2% (0.6 to 2.4), and 0.3% (0.1 to 1.1), respectively. The prevalence of esotropia was significantly higher in older age groups (24 years old) (p = .040) . The prevalence of exotropia was significantly higher in females (0.039) and in myopic individuals (p = .001). The overall prevalence and 95% CI of phoria, exophoria, and esophoria were 12.9% (10.7 to 15.6), 11.7% (9.6 to 14.3), and 1.2% (0.6 to 2.3), respectively. There was a significant difference in the overall prevalence of exophoria according to the age (0.021). The prevalence of esophoria was significantly higher in females (p = .039). The prevalence of exophoria was significantly higher in myopic participants (p = .003). Exophoria and exotropia were the most common types of phoria and tropia, respectively.

Conclusion

The prevalence of strabismus in university students was similar to the Iranian general population but lower than other countries. One in every 10 students had phoria, which was much lower than similar reports on Iranian populations; however, due to near-work activity, these students are prone to asthenopia, early visual fatigue, and decreased productivity. Therefore, it is suggested that university students also undergo screening programs to detect the cases of tropia and phoria.

KEYWORDS:

• Strabismus
• Tropia
• Phoria
• Cross-sectional study
• Iran

Acknowledgments

This study was the result of an MSc thesis in optometry entitled “distribution of binocular vision disorders and their effects on lifestyle of Sharekord Azad University students” approved by Mashhad University of Medical Sciences.

Conflict of interest

No conflicting relationship exists for any author.

Additional information

Funding

This project was supported by Mashhad University of Medical Sciences.