Vergence anomalies in a sample of high school students in South Africa

Abstract

AimTo study the prevalence of nearpoint vergence anomalies (convergence insufficiency, convergence excess and fusional vergence dysfunction) and association with gender, age groups, grade level and study site (suburban and rural).MethodsThe study design was cross sectional and data was analyzed for 1201 high school students aged 13–19 years who were randomly selected from 13 high schools in uMhlathuze municipality. Of the total sample, 476 (39.5%) were males and 725 (60.5%) were females. The visual functions evaluated included refractive errors, heterophoria, near point of convergence, accommodative functions and fusional vergences. Possible associations between vergence anomalies and demographic variables (gender, age groups, school grade levels and study site) were explored.ResultsPrevalence estimates were 11.8%, 6% and 4.3% for low suspect, high suspect and definite convergence insufficiency, and 1.9% for the pseudo convergence insufficiency. Convergence excess prevalence was 5.6%, and fusional vergence dysfunction was 3.3%. The prevalence of low suspect CI was significantly higher in suburban than in rural participants (p = 0.01), the reverse was the case for pseudoconvergence insufficiency while the prevalence of convergence excess was significantly higher in the younger than in the older age group (p = 0.02). No other category showed any statistically significant associations with vergence anomalies.ConclusionThe prevalence estimates for vergence anomalies in a sample of black high school students in South Africa were relatively low. Only study location and age influenced some vergence anomalies. Identification and referrals are important steps toward diagnosis and treatment for vergence anomalies. Further studies to compare vergence anomalies in various racial populations will be relevant.

Stereoacuity and refractive, accommodative and vergence anomalies of South African school children, aged 13–18 years

“…The sample size was derived from the original study -part of which has been published. 5,26,27 Information sheets and consent forms were written in both English and the children's indigenous language (isiZulu). Only black South African children of either gender were eligible to participate in the study.…”

“…Students who returned their approved parental consent and assent forms were enrolled for the study which also complied with the Declaration of Helsinki regarding research on human subjects. 5 For the entire study, students were excluded if they had suppression on the Worth-4-dot, strabismus, ocular diseases, nystagmus, motility problems, any systemic conditions or were on any systemic medication that might affect near vision function.…”

“…Validated optometric instruments were used and techniques were applied as described in our previous publications. 5,26,27 The eye examination techniques comprised two main stations. All vision testing was performed between 08:30 and 13:30.…”

“…3,4 Near point vergence anomalies are disorders of binocular vision that cause an inability to sustain comfortable bifoveal fixation 5 and include convergence insufficiency (CI), convergence excess (CE) and fusional vergence dysfunction (FVD). 5 The refractive error, accommodative and vergence mechanisms are all part of the visual efficiency system. 3 During fusion, decreased visual acuity (VA), uncorrected refractive error as well as sensory and motor fusion anomalies are thought to influence stereoscopic ability.…”

“…Consequently, a breakdown of the system could result in manifestation of symptoms of asthenopia that may affect visual efficiency and academic performance in school children. 3,5,8 Poor stereoacuity is associated with vision anomalies as well as with reading difficulties in kindergarten and firstgrade school children. 6 Besides its use as a clinical tool for detecting anomalies in the visual system, good stereoacuity is associated with better long-term stability of alignment and reduced risk for, and lesser severity of, amblyopia, improved achievement of sensorimotor developmental milestones, efficient reading ability and improved quality of life.…”