A Pilot Study to Provide Proof of Concept of a Novel Monochromatic Sub-Pixel Strategy for the Moorfields Motion Displacement Test (MMDT)

Abstract

 

Purpose:

 

The pixel size of standard LCD monitors limits the resolution of the hyperacuity Moorfields Motion Displacement Test (MMDT) to measure thresholds in young subjects. This study was designed to provide proof of concept of a novel sub-pixel displacement strategy for the purpose of increasing the MMDT dynamic test range.

 

Methods:

 

The MMDT 32-location test was presented on an EIZO GS521 monochromatic monitor (0.165mm pitch). The right eye of two healthy subjects (aged 25 and 20 years) was tested. Frequency of seeing (FOS) curves were generated at 9 locations for whole and sub-pixel motion displacements using a multi-location FOS test strategy. 15 presentations were made for each increment of displacement. FOS curves were generated and 95% confidence intervals (CI) compared between the two strategies (Wilcoxon test; SPSS version 16; log₁₀ probit fit).

 

Results:

 

The sub-pixel strategy extended the lower end of the MMDT dynamic test range at locations where responses at the smallest whole pixel displacement were seen. The finer increments of displacement provided by the sub-pixel strategy significantly narrowed the CIs (P < 0.01). The mean reduction for the 95% CI at the 50% threshold for the two central locations was 23%.

 

Conclusions:

 

The MMDT sub-pixel strategy increases the lower end of the dynamic test range of the MMDT so that thresholds can now be measured across all locations. The greater sampling provided by sub-pixellation means that the role of the MMDT may be extended to threshold testing and monitoring of glaucoma.  

 

Keywords: visual fields • perimetry