Assessment of diplopia through Hess screen

Hess chart is the test used to assess diplopia (squint). It shows the position of the non fixing-eye in all positions of gaze when the other eye is fixing.

The image can be separated in widely differing ways. The most usual way is to separate the image by means of fixation objects in complementary filter goggles in complementary colors (red & green).

The red filter reflects all lights and allows only for the transmission of the red light while the green filter allows only for the transmission of the green light.

Performing an examination:

  1. The patient will be asked to sit 50 cm in front of the screen so that its mid-point is situated in his main direction of gaze, that is the primary position of gaze.
  2. The patient wears red and green goggles with the green lens in front of the left eye.
  3. The room lights will be dimmed to a level were the patient cannot see the markings on the Hess screen through the goggles.
  4. The patient is asked to direct the light spot of the green laser pointer, which he guides himself using the hand he writes with, onto the red fixed point.
  5. When the fixation point changes the patient changes his direction of gaze and tries to target the fixed point again.

This is a completely non-invasive test and do not consist and potential side effect to the patients.


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