From suppression to stereoacuity: a composite binocular function score for clinical research.

PURPOSE: This study aimed to validate a binocular function score that is based on common clinical measures of visual function, providing a more complete analysis of binocular outcomes, against laboratory-based dichoptic tests of threshold stereoacuity and depth of suppression.
METHODS: Scores on a composite binocular function (BF) score derived from clinical stereoacuity measures (Randot Preschool Stereoacuity Test and Randot Butterfly) and the Worth 4 Dot test were determined in adults (n = 20; age 24.8 ± 7.2 years) and children (N = 77; age 8.3 ± 1.7 years) with abnormal binocular vision from strabismus or amblyopia. Adults had threshold stereoacuity measured with a novel, computerised dichoptic psychophysical test of stereopsis. Depth of suppression (dichoptic eye chart inter-ocular contrast balance test) was determined in both adults and children.
RESULTS: Clinical Randot stereoacuity was measurable in 50% of adult and 61% of child participants. Threshold stereoacuity was measurable in 65% of the adult participants. The presence of suppression or simultaneous perception (flat fusion or diplopia) was measurable in all participants, enabling assignment of a BF score to all participants in both groups. In adults, the BF score was highly correlated with the psychophysical threshold stereoacuity measure (ρ = 0.71; p < 0.001). In both adults and children, there was also a high correlation between the BF score and inter-ocular contrast balance (adult ρ = 0.90; child ρ = 0.86; p < 0.001).
CONCLUSIONS: The composite BF score is a convenient and valid scale of binocularity that can be used to extend the stereoacuity measure in cohorts where nil stereoacuity is common and thus could be considered as an outcome measure in clinical trials.