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.
Highlights
Exophoria was significantly associated with astigmatism (χ2 = 11.1, df = 3, p = 0.01); while esophoria was significantly associated with myopia (χ2 = 25.7, df = 1, p = 0.01), astigmatism (χ2 = 34.2, df = 1, p = 0.01) and anisometropia (χ2 = 38.7, df = 1, p = 0.01)
The distribution of heterophoria and its correlation with fusional vergences and refractive errors were investigated in a sample of schoolchildren aged 13–18 years
These findings suggest that decompensation and the corresponding manifestation of symptoms are likely to occur at the mild levels of phoria and fusional vergences
Summary
Open Access well as sensory and motor components of fusion.[1] Fusional (disparity) vergence is the vergence stimulated by retinal disparity that is aimed at maintaining single binocular vision.[1,2] Dissociating the eyes removes the disparity cue used by fusional vergences to compensate for the misalignment and causes a shift in the appropriate phoria position.[3,4]. 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. Purpose: The aim of this study was to determine the prevalence of heterophoria and investigate its associations with fusional vergences and refractive errors 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.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.