Phoria measurements using chromatic targets.

Von Graefe phoria measurements were obtained for ten prepresbyopic subjects at 40 cm and 6 m test distances using a vertical column of black letters on red, green, and white backgrounds. Phorias measured at 40 cm using red and white target backgrounds were similar, but the phoria measured using a green target background indicated a change toward greater exophoria. No difference in phoria measurements was found between all targets at 6 m.