How to do Maddox rod test?

The Maddox rod test is used to assess for the presence and type of heterophoria (eye misalignment) or heterotropia (strabismus). Here's how to perform the test:

Performing the Maddox Rod Test

The Maddox rod test aims to dissociate the eyes, which means preventing them from working together, so any misalignment can be revealed. It usually involves covering one eye while the other views a light source through the Maddox rod.

1. Setup: Position the patient comfortably, a few meters away from a light source (usually a spotlight or penlight).

2. Application of the Maddox Rod: Place the Maddox rod in front of one of the patient’s eyes, typically the right eye. The Maddox rod consists of a series of strong parallel cylindrical lenses, which convert a point of light into a streak of light perpendicular to the orientation of the cylinders. The grooves of the Maddox rod should be oriented horizontally to assess vertical deviation, and vertically to assess horizontal deviation.

3. Patient Observation: Ask the patient what they see. They will see a streak of light (from the eye viewing through the Maddox rod) and the point of light (from the eye without the rod).

4. Interpretation: This is the critical part. The patient's perception reveals the type and extent of any eye misalignment.

   • Orthophoria: If the streak of light passes directly through the point of light, the eyes are properly aligned (orthophoric) at that distance.

   • Heterophoria/Heterotropia: If the streak of light does not pass through the point of light, there is a misalignment.

     • Horizontal Deviation (Testing for Horizontal Deviation): If the Maddox rod is oriented vertically:
       • Esophoria/Esotropia (Crossed Diplopia): The streak appears to the right of the light.
       • Exophoria/Exotropia (Uncrossed Diplopia): The streak appears to the left of the light.
     • Vertical Deviation (Testing for Vertical Deviation): If the Maddox rod is oriented horizontally:
       • Hyperphoria/Hypertropia (Right Hyper): The streak appears below the light.
       • Hypophoria/Hypotropia (Right Hypo): The streak appears above the light.

5. Measuring the Deviation (Phoria/Tropia): The amount of deviation can be measured using prisms. Introduce prisms in front of one eye until the streak of light passes directly through the point of light. The amount of prism power needed to achieve alignment quantifies the degree of phoria or tropia.

6. Subjective Torsion (Optional): To assess for subjective torsion (cyclophoria or cyclotropia), ask the patient if the streak is parallel to "railroad tracks" (horizontal). If not, the streak is tilted, indicating torsion. The degree of torsion can be subjectively estimated by the patient or measured using other instruments. The patient is asked to turn a knob until the streak is parallel to "railroad tracks."

Important Considerations:

• Ensure the patient understands the instructions.
• The Maddox rod test is subjective, relying on the patient's perception. Accurate responses are essential.
• This test is typically performed at both distance and near fixation to evaluate alignment under different viewing conditions.