Hirshberg and Krimsky measurements are techniques that use the relative positions of corneal light reflexes to identify and estimate eye alignment deviations. They are particularly useful when evaluating young children.

The basic concept is that a penlight is held directly in front of the patient and the corneal light reflexes are observed. If the light reflexes are symmetrical, then no eye turn is present. An asymmetry indicates the direction and magnitude of an eye turn, depending upon the position of the reflexes.

The Hirshberg technique uses the estimated displacement in millimeters to estimate the degree of deviation. The Krimsky technique uses loose prisms to move the deviated reflex back to the "normal" position as a means of measuring the deviation.

1 This test is performed with a penlight or a muscle light. The light must be bright enough to project a good reflex onto the cornea of the patient. Dim the room lights if necessary.

2 Have the patient fix on a distance or near target, depending upon which mode you are measuring. When measuring a child, you can have the parent, or a helper, get the child’s attention with a toy. The penlight is used to create the reflex, it is not used for fixation. An accommodative target, such as a toy for children, or a near card for an adult, should be used as the near target.

3 Hold the penlight directly in front of the patient, slightly below his line of sight. Observe the corneal reflex on each eye relative to its position on the pupil or the iris. Compare the position of the reflex on the right eye with the position of the reflex on the left eye.

If the positions are symmetrical, the patient does not have a deviation. Below are examples of symmetrical reflexes.

If one reflex is displaced temporally (pictured below), relative to the other reflex, then an esotropia may exist.

If one reflex is displaced nasally, then a exotropia may exist.

If one reflex is displaced inferiorly, then a hypertropia may exist.

4 Estimate the magnitude of the deviation by estimating the millimeter displacement of the reflex. This can be done visually using your knowledge that the typical cornea is 11 to 12 mm in diameter, limbus to limbus, and by measuring the size of the pupil. One millimeter of reflex displacement equals approximately 15 prism diopters of eye alignment deviation.

For example: Consider the patient pictured below. Suppose we have measured the pupils to be 4mm across. The left eye is the fixing eye; the reflex is more or less in the center. The reflex in the right eye is a little beyond the temporal edge of the pupil. The distance from the center of the pupil to the edge is 2mm. We multiply 2 times 15 to arrive at an estimated eso deviation of 30 PD.

Loose prisms are used to move the reflex on the deviating eye to a position that is symmetrical with the reflex on the fixing eye.

This is the same example discussed above. The reflex on the right eye is displaced temporally, indicating a right esotropia. A base out prism is placed over the right eye to move the reflex back toward the center.  A prism bar can be used to gradually increase the power and observe the shift in position of the reflex.  In this case, it should take a 30 D prism to move the reflex to symmetry.  When placing the prism, remember that the prism "points" in the direction of the deviation.