This patient has a right esotropia. In Hirschberg testing you read the corneal light reflex, the small bright dot the penlight makes on the front of the eye. When both eyes are straight, that dot sits centered in each pupil. The left dot is centered, so the left eye is on target. The right dot is pushed toward the ear. The textbook rule is direct: an eye that is turned in shows a reflex displaced temporally. So the right eye is turned in, and an in-turned eye is an esotropia.
The word ending matters too. Both eyes are open during this test, so any turn you see is out in the open. That is a tropia, a manifest deviation, not a phoria. A phoria is hidden while both eyes are open and only shows when you break fusion with a cover. Size is estimated from how far the dot has moved. Each 1 mm of shift stands for roughly 7 degrees on a round globe, which equals about 15 prism diopters. Because corneal size and curvature vary, these are estimates only. Cover tests are more exact, and light reflex tests can be fooled by a misshapen pupil or by unusual retinal anatomy. For that reason the textbook says to use cover testing whenever the patient can cooperate. Hirschberg still earns its place with infants, with very young children, and with anyone who cannot sit for a cover test.
Two short rules carry the day. Reflex toward the ear means the eye is turned in. Reflex toward the nose means the eye is turned out. Reading the corneal light reflex is a core part of the COA ocular motility content area.
Incorrect Answers
- A. The left reflex was centered, so the left eye was straight. A phoria is also hidden with both eyes open and cannot be seen this way.
- B. Nothing points to the left eye. Its dot sat in the middle of the pupil while it held fixation.
- C. An out-turned right eye would push its reflex toward the nose. This reflex moved toward the ear instead.
Testing Pearls
- Centered corneal reflexes in both pupils mean the eyes are straight.
- A temporally displaced reflex means an in-turned eye; a nasally displaced reflex means an out-turned eye.
- Every 1 mm of displacement is about 7 degrees, or about 15 prism diopters.
- Krimsky adds prisms to Hirschberg so the deviation can be measured.
- Use Hirschberg when a patient cannot cooperate, then confirm with cover testing when possible.
References
- American Academy of Ophthalmology. Ophthalmic Medical Assisting: An Independent Study Course. Chapter 9, Ocular Motility.
