Hirschberg Test: Board Review
Master the Hirschberg test: reflex direction, angle estimates, angle kappa and Krimsky testing for NBEO and OKAP.
The Hirschberg test evaluates ocular alignment by observing the:
Hirschberg Test in 30 Seconds
The Hirschberg test rapidly estimates the presence and approximate magnitude of manifest horizontal strabismus by comparing corneal light reflex position between the eyes. It is especially useful when formal cover testing is not feasible. For boards, know the reflex-direction inversion, the degree and prism diopter landmarks and pseudo-strabismus from angle kappa.
How the Test Works
Hold a penlight approximately 33 to 50 cm from the patient's eyes at the midline. The patient fixates on it while you compare the position of the corneal light reflex relative to the center of each pupil. A nasally displaced reflex means the eye is deviated outward, or exotropic. A temporally displaced reflex means the eye is deviated inward, or esotropic, because the reflex shifts opposite the direction the eye has turned.
Estimating the Angle
- Each millimeter of corneal reflex displacement corresponds to roughly 7 prism diopters, or about 15 degrees, of ocular deviation. Boards commonly express Hirschberg landmarks in both degrees and prism diopters, using the approximation that 1 degree equals about 2 prism diopters.
- Reflex at the pupil margin: about 15 degrees, or approximately 30 prism diopters. This is the common small-angle board landmark.
- Reflex at the mid-iris, midway between the pupil margin and limbus: about 30 degrees, or approximately 60 prism diopters. Think moderate manifest deviation.
- Reflex at the limbus: about 45 degrees, or approximately 90 prism diopters. This suggests a large-angle deviation.
4 Facts Exams Always Ask
- The Hirschberg test estimates alignment but does not replace prism cover testing for an exact measurement.
- It is most useful in preverbal children, poorly cooperative patients and patients whose reliable fixation or cover testing cannot be performed because of poor fixation or media opacity.
- A positive angle kappa can make a truly aligned eye appear exotropic because the reflex lies nasally relative to the pupil center.
- The modified Krimsky test places prisms before one eye to neutralize reflex asymmetry, providing a rough quantitative estimate.
The Classic Trap
The most common error is reversing the direction. A nasal reflex does not mean esotropia. The reflex moves opposite the deviated eye, so nasal reflex displacement indicates exotropia. Also compare both eyes and consider angle kappa before labeling a centered patient as strabismic.
Clinical Pearl
Use Hirschberg as the first look, then move to prism cover testing when fixation and cooperation allow it. Asymmetric corneal light reflexes can identify a manifest deviation quickly, but the millimeter estimate is too imprecise for definitive measurement.
Checkpoint 1
A patient's right corneal light reflex is displaced nasally relative to the pupil center. What does this indicate?
Checkpoint 2
A child has a nasally displaced corneal light reflex in one eye but no manifest deviation on cover testing. What is the most likely explanation?
A 2-year-old cannot cooperate with cover testing. With a penlight held at midline, the right corneal light reflex lies at the temporal pupil margin while the left reflex is central. The child steadily fixates on the light.
What is the most likely finding?
Sources & Publisher Info
Last clinically reviewed: August 9, 2026
Diagram created with AI image generation, clinically reviewed for accuracy.
References
- American Academy of Ophthalmology. Basic and Clinical Science Course, Section 6: Pediatric Ophthalmology and Strabismus.
- American Association for Pediatric Ophthalmology and Strabismus. Strabismus educational resources.
- American Academy of Ophthalmology EyeWiki. Strabismus and corneal light reflex assessment resources.
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