Prevalence of heterophoria and its association with near fusional vergence ranges and refractive errors

Abstract

Background: Heterophoria is an error of binocular alignment that manifests only during monocular viewing or in conditions that disrupt binocular vision. Heterophoria is compensated for by fusional vergence through a mechanism that involves both sensory and motor fusion. The distribution of heterophoria has not been studied extensively in schoolchildren in South Africa and studies quantifying the magnitude of association between heterophoria and fusional vergences are scarce.Purpose: The aim of this study was to determine the prevalence of heterophoria and investigate its associations with fusional vergences and refractive errors.Methods: This was a cross-sectional study design and comprised data from 1056 high school students aged 13–18 years, who were randomly selected from 13 out of a sample frame of 60 high schools in uMhlathuze municipality in the province of KwaZulu-Natal, South Africa. The sample comprised 403 (38%) males and 653 (62%) females. The participants’ mean age was 15.89 ± 1.58 years. Visual acuity, refractive errors, heterophoria and fusional vergences were evaluated using conventional optometric techniques.Results: The overall prevalence of orthophoria at distance was 80.1% (95% confidence interval [CI]: 77.7% – 82.6%), that of exophoria was 13.9% (CI: 11.9% – 16.0%), while that of esophoria was 6.0% (CI: 4.5% – 7.4%). At near, the prevalence estimates were as follows: exophoria, 542 (51.3%, CI: 48.3% − 54.2%); orthophoria, 36.6% (CI: 33.9% − 39.5%); esophoria, 12.1% (CI: 10.2% − 14.0%). On the severities of near phoria, the frequencies were as follows: mild (1–7 prism dioptres [pd]), 41% (CI: 38.3% – 44.1%); moderate (8–13 pd), 9.7% (CI: 7.8% – 11.5%); and severe (> 13 pd), 1.1% (CI: 0.6% – 1.8%). For the severities of fusional vergences, the distributions were as follows: positive fusional vergences, mild (15–22 pd), 88.3% (CI: 86.4% – 90.4%); moderate (> 7 to < 15 pd), 10.1% (CI: 8.2% – 11.9%); and severe (≤ 7 pd), 1.6% (CI: 0.9% – 2.4%). For negative fusional vergences, the percentage of anomalous cases (≥ 22 pd) was 14.2% (CI: 12.3% – 16.3%), while that for normal (< 22) was 85.8% (CI: 83.7% – 87.7%). For vertical phoria, the prevalence was 2.7% and 3.6% at near. There was a weak but significant inverse correlation between near exophoria and positive fusional vergence break (r = −0.10, p = 0.01), whereas exophoria and negative fusional vergence break were positively correlated (r = 0.14, p = 0.01). Esophoria was inversely correlated with negative fusional vergence break values (r = 0.13, p= 0.01) and was positively correlated with positive fusional vergence break (r = 0.13, p = 0.03). Chi-square tests showed that exophoria was associated with astigmatism (p = 0.01), while esophoria was significantly associated with myopia (p = 0.01), astigmatism (p = 0.01) and anisometropia (p = 0.01).Conclusion: The data for far and near distance, horizontal and vertical heterophoria were not normally distributed. Orthophoria was most prevalent at far, exophoria at near and there was a significant association between phoria and fusional vergence. The significant associations between phoria and fusional vergence were at lower levels of fusional vergences.

Comparison of vergence mechanisms between university students with good and poor sleep quality

“…The majority of the subjects in this study had orthophoria at distance and exophoria at near. This finding is similar to the study done by Wajuihian [29] , who reported that orthophoria is the most prevalent at distance while exophoria at near among high school students. The heterophoria tends to have an exophoric shift with decreasing viewing distance [30] .…”

Clinical features of Sudanese patients presenting with binocular vision anomalies: A hospital-based study

“…Patients with heterophoria have latent deviation and use motor and sensory fusion to maintain proper alignment. Many authors [9][10][11] reported that fusional vergence (FV), such as positive fusional vergence (PFV) and negative fusional vergence (NFV), have a critical role in controlling exopho-ria and esophoria, respectively. Orthophoria is a rare condition characterized by perfect ocular alignment, which is continued even after the removal of the effect of fusional vergence [9,11].…”

“…Studies have shown that binocular vision anomalies are commonly associated with ocular symptoms such as asthenopia, headaches, eye pain, and blurred vision [9][10][11][12]. These binocular vision anomalies, particularly manifest strabismus, if left untreated, could result in symptoms of confusion and diplopia and might lead to the development of binocular and monocular sensory changes such as suppression, anomalous retinal correspondence, and amblyopia [13,14].…”

Do standard optometric measures predict binocular coordination during reading?

“…Technical instrumentation allows for very precise objective measurement of the individual oculomotor behavior (Gantz & Caspi, 2020;Jainta & Joss, 2019;Kim, Vicci, Granger-Donetti, & Alvarez, 2011). In clinical optometric and ophthalmologic settings, however, methods that need charts, an experienced examiner and which rely mostly on the answers and perceptions of the patient are usually applied to assess individual binocular status (Howarth & Heron, 2000;Hussaindeen et al, 2015;Schroth, 2012;Wajuihian, 2018). In this context, several parameters are required to qualify a patient's individual binocular status: based on visual acuity and refractive measures, heterophoria, vergence and accommodative parameters and asthenopic symptoms need to be assessed.…”