Developing and Evaluating Threshold Algorithms for the Moorfields Motion Displacement Test (MDT)

Abstract

 

Purpose:

 

To compare different algorithms for establishing threshold in the multi-location Moorfields Motion Displacement Test (MDT) in terms of precision and efficiency.

 

Methods:

 

The MDT is a test of motion hyperacuity for glaucoma detection and runs on a standard computer. There are 32 line stimuli, each scaled by age and eccentricity, corresponding to a Humphrey 24-2 location. To date a standard staircase algorithm (1-1 stair) is used to estimate thresholds at each location in minutes of arc. Fourteen patients with mild to moderate glaucoma (mean age: 64.5yrs) and 13 age-matched controls (experienced users) performed a MDT with a 1-1 staircase, a new weighted binary search (WEBS) and an adjusted staircase (2-1) in random order. Speed for each algorithm was defined as the average time taken to terminate per location. Later, a reference threshold was obtained at 7 locations from frequency-of-seeing curves in the same subjects: 15 presentations at each displacement magnitude (method of constant stimuli) on a monitor with higher resolution but with stimuli adjusted to have equivalent energy (Verdon-Roe et al. 2006 IOVS 47:4847-55). Precision for each testing strategy was estimated to be the SD of the differences between the algorithm threshold and the reference value. An 'efficiency' value (product of mean number of presentations and variance from reference threshold) was calculated for each strategy (Treutwein 1995 Vision Res 35:2503-22), with ideal efficiency at zero.

 

Results:

 

The 2-1 and WEBS tests strategies were 11% less accurate than the standard staircase for healthy subjects but WEBS was 16% faster. The 2-1 and WEBS tests had improved precision coupled with faster test times (18% reduction with WEBS) for glaucoma patients yielding significantly improved test efficiency.  

 

Conclusions:

 

The WEBS test strategy for the MDT can help reduce test time with little loss in precision resulting in greater test efficiency

 

Keywords: perimetry