Hirshberg test determines the approximate positions of the visual axes of two eyes at near. This method is used to identify strabismus if no other more precise procedure can be used. Traditionally in practices, a penlight is used to be shone into the eyes and the practitioner estimates the deviation of the retinal reflex. People get confused about deviations and ocular positions, so the application reports the direction of the deviation.
Equipment and set-up:
Press the button to turn on the penlight and direct it toward the client´s eyes from a distance of about 50 centimetres. Instruct the client to look at the light, observe the corneal light reflex from the both eyes, while placing your eyes directly behind the penlight. The degree of strabismus can be roughly estimated by measuring in millimetres the decentration of the reflex from the centre of the pupil. One millimetre of the deviation of the reflex is equal to 22 prisms.
Interpreting the results:
Move the reflex on both eyes so as seen on the client’s cornea. The result will be therefore interpreted automatically. One millimetre of the deviation of the reflex equals 22 prisms. You can measure the angle of strabismus by placing the prisms in the direction in which the reflex of the deviation needs to move to match the fixating eye. The goal is to get the symmetrical position of the two corneal reflexes from both eyes. The method is called the Krimsky Test.
- reflex is in the centre of the pupil (no deviation – record no decentration)
Position of the corneal reflex relative to position of angle Lambda in the fixation eye:
- slightly nasal to the centre of the pupil (exotropia)
- slighty temporal to the centre of the pupil (esotropia)
- slighty superior to the centre of the pupil (hypotropia)
- slightly anterior to the centre of the pupil (hypertropia)