The Effects of Anisometropic Amblyopia on the FNS and TNO Stereotest Thresholds in Four- to Eight-Year-Olds

PURPOSE: To investigate the relationship between stereoacuity and factors associated with anisometropic amblyopia in children aged 4–8 years. METHODS: 44 participants had their stereoacuity thresholds measured using the Frisby Near Stereotest (FNS) and the TNO Randot Stereotest (TNO). Participants were divided into anisometropic amblyopes and controls (normal uniocular visual acuity (VA) with or without glasses). FNS and TNO stereoacuity thresholds were compared based on different factors, which included interocular acuity difference (IAD), VA levels, and the degree of anisometropia. RESULTS: All 44 participants achieved better stereoacuity with the FNS compared to the TNO (p = 0.045). The control group performed significantly better on the FNS (p = 0.012) and the TNO (p = 0.009) when compared with anisometropic amblyopes. The only statistically significant correlation was found between stereoacuity – as measured with FNS – and IAD (p = 0.009). However, the TNO showed a correlation in the presence of poor VA, larger IADs and a high degree of anisometropia. CONCLUSIONS: Stereoacuity thresholds are significantly affected by poor VA, large IAD and high degrees of spherical anisometropia when trying to distinguish the resolution of a target with the TNO yet the same factors do not appear to affect ability to distinguish the disparity of a target with the FNS. Controls also performed worse on the TNO.