What can cause the eye to drift up and perhaps slightly inward?

The condition described, where the eye drifts upward and slightly inward, is typically associated with a dysfunction of the cranial nerves that control eye movement. Specifically, impairment of cranial nerve IV, also known as the trochlear nerve, can result in an inability to properly innervate the superior oblique muscle of the eye. This muscle plays a key role in depression and intorsion (inward rotation) of the eye.

When there is congenital impairment of cranial nerve IV, the affected eye may exhibit a characteristic position known as hypertropia, where it is positioned higher than the other eye. As a result, this can cause an observable drift upward and may result in slight inward deviation due to compensatory mechanisms of other muscles attempting to stabilize the gaze.

Other factors can cause eye drift or misalignment, but they do not specifically produce the same upward and inward drift characteristic of a trochlear nerve issue. For example, intraocular foreign bodies typically affect vision or cause inflammation rather than direct muscle weakness. Traumatic effects can cause more generalized eye movement issues depending on the location and severity but are not as specific as cranial nerve impairment. Optic nerve injury primarily affects vision rather than the alignment of the eyes, focusing on visual signals