Which measurement is performed under monocular conditions?

• A. Hirschberg
• B. Angle lambda
• C. Both
• D. Neither

Answer: (B)

Monocular testing isolates one eye at a time by occluding the other, so the measurement that is performed under monocular conditions is the one that relies on evaluating the relationship of the eye’s own visual axis to its own pupillary axis without the other eye influencing the view.

The Hirschberg test uses the corneal light reflex to estimate how the eyes align when both eyes are fixating on a target; this is essentially a binocular assessment and doesn’t require occluding one eye. In contrast, angle lambda describes the offset between the eye’s visual axis and its pupillary axis, a measurement that is taken with the eye viewed in isolation (monocular conditions) during procedures like retinoscopy or slit-lamp assessment. Therefore, angle lambda is the measurement performed under monocular conditions.