Establishing an Objective Measurement of Visual Acuity with a Computerised Optokinetic Nystagmus Suppression Test

Abstract

Objective Investigating the correlation between subjective and objective VA (visual acuity) elicited with a newly developed computerised optokinetic nystagmus (OKN) suppression test (“SpeedWheel”) in adults.

Methods SpeedWheel presented alternating black/white stripes moving horizontally across a LED screen. Seven VA steps were induced with Bangerter filters placed onto spectacle frames. Magnified eye movements were projected from infrared cameras inside the frames and displayed onto a smartphone. Dots whose size increased in logarithmic steps were superimposed to suppress OKN. Suppression of OKN resulted in the SpeedWheel acuity which was then correlated to Snellen acuity as measured with the Freiburg Acuity test.

Results 28 eyes from 14 individuals were tested. FrACT-E correlated well to SpeedWheel (r: 0.89; p < 0.001). Snellen acuity was never lower than 0.14 LogMAR of SpeedWheel values. Bangerter filters showed greater mean difference to both methods indicating that this filter is not as predictable as suggested by the filter value.

Conclusion SpeedWheel offers a fast (< 80 sec) and reliable alternative option to measure objective VA.

Zusammenfassung

Ziel Die Korrelation zwischen subjektivem und objektivem Visus bei Erwachsenen zu evaluieren. Der objektive Visus wurde mithilfe eines neu entwickelten, computerisierten, optokinetischen Nystagmussuppressionstests („SpeedWheel“) ermittelt.

Methode Der subjektive Visus, welcher durch den Freiburg Acuity and Contrast Test E (FrACT-E) gemessen wurde, wurde mit dem SpeedWheel-Visus in 28 Augen und in verschiedenen, durch Bangerter-Folien induzierten Visusstufen verglichen. SpeedWheel präsentierte auf einem LED-Bildschirm alternierende schwarze und weiße Streifen, welche sich horizontal über den Bildschirm bewegten. Punkte, schrittweise im Durchmesser zunehmend, wurden eingeblendet mit dem Ziel, den optokinetischen Nystagmus zu unterdrücken. Die Augenbewegungen wurden vergrößert auf einem Smartphonebildschirm dargestellt und direkt beobachtet.

Resultate FrACT-E korrelierte gut mit SpeedWheel (r: 0,89; p < 0,001). Der Snellen-Visus war nie unter 0,14 LogMAR des SpeedWheel-Wertes. Der durch den Bangerter-Filter vorausgesagte Visus unterschied sich deutlich von FrACT-E und SpeedWheel.

Fazit SpeedWheel bietet eine zuverlässige und schnelle (< 80 s) Alternative, um den objektiven Visus zu bestimmen.

Key words

neuroophthalmology - visual acuity - optokinetic nystagmus

Schlüsselwörter

Neuroophthalmologie - Visusbestimmung - optokinetischer Nystagmus

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