Maddox rod
Also called Maddox rod test, Maddox rod phoria, multiple-groove Maddox rod, double Maddox rod
The Maddox rod is a lens made of a row of parallel high-powered cylinders, and it turns a point of light into a line at right angles to the cylinders. Placed before one eye, the rod dissociates the two eyes so that the direction and size of a phoria can be measured with prism.1,2
The eye behind the rod sees a red line and the other eye sees the white light, so the two images cannot be fused, and the patient reports where the line sits.1,2 Because the rod dissociates the eyes fully, the Maddox rod cannot tell a phoria from a tropia, which is what a cover test does.1
By convention the rod goes before the right eye.3 A line to the right of the light means an eso deviation, and a line to the left means an exo deviation.3 With the line horizontal, a line below the light means the right eye is higher.3
More detail
With the cylinders horizontal the line is vertical and measures horizontal deviations, while with the cylinders vertical the line is horizontal and measures vertical deviations.3 The deviation is neutralized with prism whose base points away from the deviation, at 6 m and at 33 cm.1,2 The Maddox wing is a different instrument for near testing with a built-in scale, and two rods, one before each eye, measure torsional deviations.1 Done in free space with the glasses on, the test also rules out a vertical phoria caused by tilting the head behind the phoropter.3
Sources (3)
- Kanski, Clinical Ophthalmology (2024), ch. 18
- Eperjesi and Rundström, Practical Binocular Vision Assessment, ch. 6
- Carlson and Kurtz, Clinical Procedures for Ocular Examination, ch. 4
Reviewed October 2026