Critical detection of the accommodative convergence to accommodation ratio by photosensor-oculography

The cyclopean eye in vision: the new and old data continue to hit you right between the eyes

We argue against recent claims by Erkelens and van Ee (Vision Res., in press) and by Erkelens (Vision Res. 40 (2000) 2411) that "the concept of the cyclopean eye is em leader always irrelevant as far as vision is concerned" (p. 1157) [corrected] and that "perceived direction during monocular viewing is based on the signals of the viewing eye only" (p. 2411), respectively. In Experiment 1, we presented a pair of small lights on a visual axis and measured the absolute visual direction of the near light with reference to different parts of the face. The near light appeared in front of the bridge of the nose or very near it, contrary to what was expected from Erkelens and van Ee's claim that monocular stimuli are seen in their correct locations. In Experiment 2, we replicated Erkelens' experiments with measurements of phoria and analyses of eye movements. The results confirmed his finding that the cyclopean illusion occurred rarely in the monocular condition, but our phoria and eye movement data provided the basis for a very different interpretation. Our data show that the oculomotor signal in his particular monocular condition was considerably weaker than in his binocular condition; therefore, the rarity of the monocular cyclopean illusion is not surprising. Moreover, since both claims above are based on an over-generalization of the results of Erkelens' study, neither claim is persuasive.

Closed-loop and open-loop accommodative vergence eye movements

We examined accommodative vergence eye movements under conditions in which feedback about retinal-image slip was and was not present (i.e. closed-loop and open-loop conditions). We found that (a) in both conditions the two eyes started to move at the same time; (b) in the open-loop condition, vergence continued in both eyes; and (c) in the closed-loop condition, vergence continued in the occluded eye only, and the magnitude and velocity exceeded that of the occluded eye in the open-loop condition by a factor of two.

Clinical and computer-assisted analyses of preoperative and postoperative accommodative convergence and accommodation relationships

A group of 329 patients who underwent bilateral medial rectus muscle recession for esodeviation were analyzed for factors most closely correlated with the outcome. The data evaluated included age of onset of strabismus, refractive error, year of surgery, age of surgery, sex, preoperative esodeviation, and clinical assessment of preoperative and postoperative heterophoria. Linear regression analysis was used to evaluate the relationships of these parameters. Computer-assisted logistic regression analyses and discriminant analyses were used to assess predictive variables for a postoperative increase or decrease in the accommodative convergence and accommodation (AC/A) relationship represented by the clinical assessment method.