Stimulus type vs. convergence measures
Reviewed by Fiona Rowe

The aim of this study was to investigate if near point of convergence (NPC) would improve when a fixation target with centrally placed 3-D features (to increase binocular disparity stimulus) was used in comparison to a target using only centrally placed 2-D features. NPC was measured in 23 subjects (21 females, two males, average age of 30±7.36 years). The 3-D target provided significantly better average NPC values and less remote values of repeated measures of break point NPC. The authors conclude that their results demonstrate vergence control is reduced when the central part of the target only contains 2-D features. 3-D features appear to act as a fusional guidance for fixation. 

Effect of 3-dimensional central stimuli in near point of convergence.
Glimne SAM, Öqvist Seimyr G, Brautaset RL.
STRABISMUS
2015;23(3):121-5.