This test is indicated when the pupils appear to be unequal in size.

The practitioner should be positioned directly in front of the patient slightly below the line of sight. Ambient illumination should be low so that the only available light is that reflected from the ophthalmoscope beam. Turn on the ophthalmoscope to full intensity and set it to the largest available beam.

  • Instruct the patient to look at a distant target and not at the ophthalmoscopy light.
  • From a distance of about one metre, shine the ophthalmoscope beam onto the patient’s face so that both pupils are illuminated at the same time.
  • Look through the aperture of the ophthalmoscope at the patient’s pupils.
  • Orange red reflexes, due to the reflectiom of light from the retina, should be seen within each pupil.
  • Observing these red pupillary reflexes will enhance the ability to detect small differences in pupil size between the eyes.
  • Observe the size of each pupil, noting which eye has the larger pupil and estimating the amount of the difference in millimetres – this is the bright condition.
  • Gradually reduce the illumination level of the ophthalmoscope while observing the red reflexes and comparing the sizes of the pupils.
  • Continue to reduce the illumination until the red reflexes are barely visible.
  • Observe the size of each pupil, estimating the amount of the difference in millimetres – this is the ‘dim’ condition.

Repeat steps 2 through 7 one or two times to confirm the observations.
If no difference in anisocoria is observed, end the test. If a difference in anisocoria is detected, the amount of anisocoria is quantified as follows:

Increase the room illumination until you are just able to see the pupils with unaided eyes. Using the PD rule, measure the size of each pupil. The size difference is the amount of anisocoria in dim illumination.Increase the room illumination to its maximum amount. Using the PD rule, measure the size of each pupil.

The size difference is the amount of anisocoria in bight illumination. With the patient looking straight ahead at the fixation target, use the PD ruler to measure the size of the palpebral aperture in millimetres. Note the position of the upper and lower lid of each eye relative to the limbus and the cornea. Instruct the patient to fixate on your finger and have him follow it gradually into upward gaze. Compare the intersections of the lower lids with each limbus. Note which lid clears the limbus first or if they clear the limbus simultaneously.

Record the size of each pupil under bright conditions. Record the difference in pupillary sizes (amount of anisocoria) under bright conditions. Record the size of each pupil under dim conditions. Record the difference in pupil size under dim conditions.

If the difference in pupil size is the same under dim and bright conditions, record ‘anisocoria equal in dim and bright’. This would suggest physiological anisocoria. Record the size of the difference in millimetres.If the anisocoria changes according to the ambient lighting conditions then it is likely to be pathological.

Record the size of each palpebral aperture in millimetres in straight-ahead gaze. If the apertures were equal, and both intersect the limbus in the normal position approximately 2 millimetres below its top, record ‘no ptosis of the upper lid’.

If the lower lids cleared the limbus at the same time when the patient looked upward, record ‘no ptosis of lower lid’. If one lid cleared the limbus sooner than the other, it indicates a ptosis of the more elevated lower lid. Record ‘ptosis of the lower lid’ and indicate the eye whose lid cleared second.

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