The Step VEP has a Consistent VA Relationship with Psychophysics for all VA, Age, and Aetiology and Increases the Completion Rate of Paediatric VA Assessment to 96%

Abstract

Purpose: : To compare Step VEP and Psychophysical VA in a paediatric clinical group, to examine the influence of age, VA, and aetiology of visual impairment on their relationship and on the chance of completing the test.

Methods: : 100 children had their VA measured using Step VEPs and an age and ability appropriate Psychophysical test. The success in completion was graded and their aetiology categorised by anatomical location of primary damage. Those successful in both tests and with organic vision loss were included in statistical analysis. Multiple regression modelling was used to screen age, psychophysical VA, psychophysical modality, and aetiological group for association with Step VEP VA. Bland-Altman analysis was then used to quantify accuracy, precision, and bias in the relationship between methods for each subgroup and for previously published studies comparisons of VEP and Psychophysical VA. Finally, Odds ratios were used to compare rates of test completion and partial completion.

Results: : 59 children successfully completed both assessments and had organic vision loss. Age, VA, and aetiological grouping did not influence the relationship between VA measured using Step VEPs and Psychophysics. Psychophysical modality was influential leading to the following equations:VA_Optotypes=0.56 VA _Step (r²=0.75, F=60.93, p=0.000)VA_{Preferential Looking} = 0.45 VA _Step (r²=0.82, F=156.85, p=0.000)Bland-Altman analysis confirmed that the relationship was consistent over the range of VA. The review of previously published studies revealed that this has not previously been demonstrated in a paediatric patient group.Both Step VEPS and Psychophysical tests were successfully completed by 85%, (85/100) of children, though not the same 85, resulting in a combined success rate of 96% (88/92). Of the incomplete Step VEPs, most were partially successful, compared to only half of the incomplete Psychophysical assessments. Finally, Poor VA was the only limit found on success of Step VEPs.

Conclusions: : 1) Step VEPS can be interpreted the same way for every child requiring assessment.2) Attempting both Step VEP and psychophysical VA assessment improves the chance of success over either test alone.3) Incomplete Step VEPS were more likely to be partially complete than incomplete psychophysics allowing VA better than ... to be expressed in most patients.

Keywords: visual acuity • electrophysiology: clinical • neuro-ophthalmology: cortical function/rehabilitation