Is Vernier Acuity more Sensitive than Grating Acuity to Visual Impairment in Adolescents?

Abstract

 

Purpose

 

Vernier acuity, often referred to as a “hyperacuity”, may be more sensitive than grating acuity in detecting visual deficits such as amblyopia in young children. Thus, we compared vernier acuity (VeA) and grating acuity (GA) tests to recognition acuity (RA) in adolescents with visual impairment, hearing loss, and cognitive disabilities.

 

Methods

 

24 optometry students from the New England College of Optometry and 10 adolescents (16 eyes) attending Perkins School for the Blind were tested in each eye for RA (crowded letters), VeA (Drover et al OVS 2010) and GA (Teller Acuity Cards) in 2 sessions. Acuities were analyzed in logMAR. Test-retest reliabilities were examined with Bland-Altman method (bias, 95% Limits of agreement, LOA). To directly compare VeA and GA to RA in adolescents, their raw data were normalized taking the difference from the normal value for age (Delta-Normal, ΔN). ΔNs were analyzed with correlations and means.

 

Results

 

Adult mean (SD) logMAR acuities (RE, session 1) were: RA -0.11 (0.05) (20/16); VeA: -0.24 (0.15); GA: -0.09 (0.05). Test-retest analyses of the adolescent data (in logMAR) showed minimal bias and similar 95% LOA (0.66 for RA; 0.69 for VeA; 0.56 for GA). For adults, test-retest 95% LOA for RA was 0.28 logMAR. Correlations of adolescents’ ΔN for VeA and GA with RA (session1) were significant and similar (VeA with RA, r=0.78; GA with RA, r=0.83). Mean ΔNs were also similar and not significantly different (RA: -0.79±0.34; VeA: -0.89 ± 0.44; GA: -0.76±0.31).

 

Conclusions

 

Test retest reliabilities are similar for RA, VeA and GA tests in a small sample of adolescents with visual impairment and other disabilities. Normalized VeA and GA acuities have a similar relationship to normalized RA and are not significantly different on average. Thus, vernier acuity may not have an advantage over grating acuity in adolescents with visual impairments due to ocular and neurological causes, who have other disabilities. However, for other causes of visual deficits, for example, amblyopia, vernier acuity may be more sensitive than grating acuity.

 

 

Vernier acuity cards with stimuli, forming a second-order shape of a six-pointed star or a flower (Drover et al 2010). Acknowledgments: Eileen E. Birch, PhD. and Yi-Zhong Wang, PhD. who provided the stimuli.

 

 

Photograph of examiner testing an adolescent participant with vernier acuity cards.

 

Keywords: 754 visual acuity • 584 low vision • 759 visual impairment: neuro-ophthalmological disease