Deviations from the normal parallelism of the visual axes may be divided, for the sake of convenience, into phorias, tropias and squints. In this arrangement the tropias are defined as more than a phoria and less than a squint. These are the deviations which frequently cause profound disturbances.
I shall briefly cite a case of esophoria and one of exophoria as an example.
The case of esophoria was that of a man of 27 years, large of frame and vigorous, who was highly educated and cultured and had a delicately balanced nervous system. His business was suffering on account of his inability to give it the required attention. He had diplopia of 20 prism degrees for distant and near vision with the red glass. With the Maddox rod there was esophoria of 20 degrees for distant and near vision. There was an inconstant diplopia which was the same in all
DAVIS WT. ESOPHORIA AND EXOPHORIA AS THE CAUSE OF OBSTINATE ASTHENOPIACURE BY SURGICAL AND OTHER MEANS. Arch Ophthalmol. 1933;10(4):455-464. doi:10.1001/archopht.1933.00830050031005