Evaluation and Comparison of the Dissociated Phoria State at Rear and Distance Fixation of Children, Using Three Different Techniques and the Prediction of Their Binocular State

Purpose: This research, compared the dissociated phoria state at near and distance fixation in free space, using three different techniques; the Howell test, alternate Cover test and Thorington test. Methods: A total of 220 healthy Mexican children from Querétaro, 5.06 to 17.11 years of age, participated in this study. The magnitude of phorias at both distances was quantified using each of the tests, starting from the least to the most disruptive one. The degree of stereopsis, break, and recovery value of the near point of convergence were also analyzed to understand the interaction among them and their impact on the sensorimotor balance of the visual system. Results: Despite their different ways of dissociation, for patients with exophoria or esophoria at near, the alternate Cover test and Thorington provide similar values. If examining the exophoria state at distance, the alternate Cover and Howell test are similar, whereas for the esophoria, the alternate Cover and Thorington give similar results. The break value and the magnitude of exophoria at near can predict the stereopsis degree. The break value and the magnitude of exophoria are related to each other. Gender doesn´t relate to any variable, whereas age, is associated with the degree of stereopsis and the break of NPC. Conclusions: The statistical analysis showed that the alternate Cover and Thorington test, despite their different ways of dissociation, can substitute one another, whereas the Howell test, cannot be interchangeable with the other two. The different way of dissociation this test uses, can be related to the obtained results. By analyzing the crucial elements of the binocular visual system, can help professionals determine the interaction among them and their impact on its sensorimotor balance.