How to Measure Ocular Alignment Virtually

Ocular alignment: the alternate cover test can be performed by instructing the patient to hold their head steady, fix their eyes on the camera (or a more distant target - the closer the fixation target, the more of an exodeviation the examiner will see), and use their cell phone (or a spoon) to occlude one eye and then the other eye, back and forth. This test can be also be completed with the patient's head held at 20o off center in the horizontal and vertical planes, which may help in localization of abnormalities (e.g. differentiating the alternating hypertropias of bilateral 4th nerve palsies from alternating skew deviation [https://collections.lib.utah.edu/details?id=1383125&q=skew+deviation&fd=title_t%2Cdescription_t%2Csubject_t&facet_setname_s=ehsl_novel_gold]). Look for a horizontal (when the eye under cover is crossed in so that it has to move outward when uncovered to take up fixation - ESO [https://collections.lib.utah.edu/details?id=1256238]; when the eye under cover is deviated outward so that it has to move inward when uncovered to take up fixation - EXO [https://collections.lib.utah.edu/details?id=1253803]) or vertical (generally named after the side of the higher eye - e.g., if the right eye is uncovered and has to come down to fixate on the target, this is a right hyperdeviation) movements of the uncovered eye. The eso-, exo-, hyper is further classified as a tropia (misalignment present with both eyes open - use a cover-uncover technique on each eye individually) or phoria (misalignment present when binocular vision is broken with alternate cover testing but no misalignment with cover-uncover). Any change in deviation or lack thereof helps in the localization.