Prevalence of heterophoria, tropia, and near point of convergence abnormality in a high school student population in Erbil city center

To determine the prevalence of tropia, phoria, and abnormality of near point of convergence (NPC), along with associated ocular symptoms, in high school students.

This cross-sectional study was conducted in Erbil, Iraq. The target population consisted of high school students selected through a multi-stage cluster sampling method. Comprehensive visual examinations were performed for all students, including measurement of uncorrected and corrected visual acuity, objective and subjective refraction, and distance and near cover tests. NPC was evaluated using a single 6/12 visual target mounted on a centrally positioned Gulden fixation stick. Ocular symptoms were investigated through interviews.

Of the 996 selected students, 921 participated in the study. Of them, 543 (58.96%) were female, and their ages ranged from 13 to 22y. The prevalence of tropia was 3.58% [95% confidence interval (CI): 2.38%–4.78%], observed in 3.44% of males and 3.68% of females. Exotropia (1.95%, 95%CI: 1.06%–2.85%) was more common than esotropia (1.52%, 95%CI: 0.73%–2.31%). The 15.42% (95%CI: 13.09%–17.75%) of students had phoria. Exophoria (13.79%, 95%CI: 11.56%–16.02%) was significantly more prevalent than esophoria (1.63%, 95%CI: 0.81%–2.45%). The prevalence of NPC abnormality in the total study population was 24.97% (95%CI: 22.18%–27.77%). It was 26.72% (95%CI: 22.26%–31.18%) in males and 23.76% (95%CI: 20.18%–27.34%) in females (P=0.307). The most common symptom in phoria was headache (86.62%, 95%CI: 81.02%–92.22%), followed by tired or sore eyes (61.97%, 95%CI: 53.99%–69.96%). The most common symptoms in tropia were blurry vision (93.94%, 95%CI: 79.77%–99.26%) and difficulty concentrating (87.88%, 95%CI: 76.74%–99.01%).

Among Erbil’s high school students, the prevalence of strabismus, particularly the exodeviation type, is relatively high, and a significant percentage of students have NPC abnormalities. Addressing and correcting these binocular vision problems, due to their associated visual symptoms, can lead to an improvement in students’ quality of life and academic performance.