Hirschberg Test – Squint Video
It is performed by shining a light in the person’s eyes and observing where the light reflects off the corneas. In a person with normal ocular alignment the light reflex lies slightly nasal from the center of the cornea (approximately 11 prism diopters — or 0.5mm from the pupillary axis), as a result of the cornea acting as a temporally-turned convex mirror to the observer. When doing the test, the light reflexes of both eyes are compared, and will be symmetrical in an individual with normal fixation. For an abnormal result, based on where the light lands on the cornea, the examiner can detect if there is an exotropia (abnormal eye is turned out), esotropia (abnormal eye is turned in),hypertropia (abnormal eye higher than the normal one) or hypotropia (abnormal eye is lower than the normal one).
In exotropia the light lands on the medial aspect of the cornea. In esotropia the light lands on the lateral aspect of the cornea. In hypertropia the light lands on the inferior aspect of the cornea. In hypotropia the light lands on the superior aspect of the cornea. A cover test can tell you the extent of the eso/exotropia.
Individuals can suffer from several tropias at once. In Graves ophthalmopathy, it is not uncommon to see an esotropia (due to pathology of the medial rectus muscle) co-morbidwith a hypotropia (due to pathology of the inferior rectus muscle).