Maddox rod
Also called Maddox rod test, Maddox rod phoria, multiple-groove Maddox rod, double Maddox rod
A lens made of a row of parallel high-powered cylinders that turns a point of light into a line at right angles to the cylinders. Placed before one eye, it dissociates the two eyes so that the direction and size of a phoria can be measured with prism: the eye behind the rod sees a red line and the other eye the white light, the two cannot be fused, and the patient reports where the line sits1,2.
Because it dissociates the eyes fully, the Maddox rod cannot tell a phoria from a tropia, which is what a cover test does1. By convention the rod goes before the right eye: a line to the right of the light means an eso deviation, a line to the left an exo deviation, and with the line horizontal a line below the light means the right eye is higher3.
More detail
With the cylinders horizontal the line is vertical and measures horizontal deviations; with the cylinders vertical the line is horizontal and measures vertical deviations3. The deviation is neutralized with prism whose base points away from the deviation, at 6 m and at 33 cm1,2. The Maddox wing is a different instrument for near testing with a built-in scale, and two rods, one before each eye, measure torsional deviations1. Done in free space with the glasses on, the test also rules out a vertical phoria caused by tilting the head behind the phoropter3.
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