Harrisburg Corneal Reflex Test Overview

Aug 28, 2024

Harrisburg Corneal Reflex Test

Overview

  • Also known as the Harsh Bark Test or Corneal Light Reflex Test.
  • Objective Test:
    • Utilizes a pen torch for rough estimation of the angle of manifest strabismus.
    • Uses the first Purkinje image to assess alignment of eyes or potential strabismus.
    • Useful for young, uncooperative patients, or when physicians have poor vision in the deviating eye.

Procedure

  1. Setup:
    • Patient sits 50 cm away from the examiner.
  2. Execution:
    • Examiner turns on the pen light, directing it towards the midline of the nose between the eyes.
    • Patient instructed to look at the light.
    • Examiner observes corneal light reflex from both eyes.
  3. Estimation:
    • Degree of strabismus estimated by measuring decentration of the reflex from the pupil center.
    • 1 mm deviation = 15 prism diopters.

Measurements and Interpretation

  • Conversions:
    • 1 degree = 2 prism diopters.
    • 1 mm = 7 degrees or 14 prism diopters.

Observations and Interpretations

  • Centered Reflex:
    • Interpretation: Ortho position or normal alignment.
  • Decentered Temporally:
    • Interpretation: Esotropia.
  • Decentered Nasally:
    • Interpretation: Exotropia.
  • Decentered Downward:
    • Interpretation: Hypertropia.
  • Decentered Upward:
    • Interpretation: Hypotropia.

Deviation Estimation

  • Reflex between Pupil Center and Pupillary Margin:
    • Estimation: 7 degrees or 15 prism diopters.
  • Reflex at Pupillary Margin:
    • Estimation: 15 degrees or 30 prism diopters.
  • Reflex between Pupillary Margin and Limbus:
    • Estimation: 30 degrees or 60 prism diopters.
  • Reflex at Limbus:
    • Estimation: 45 degrees or 90 prism diopters.
  • Reflex at Sclera:
    • Estimation: More than 45 degrees or more than 90 prism diopters.

Limitations

  • This test provides a rough estimation because it is objective and does not use prism measurements.

Key Points

  • Corneal reflex is opposite to the deviation of the eyes:
    • Eyes move in (Esotropia) = Reflex moves out.
    • Eyes move out (Exotropia) = Reflex moves in.