Maddox rod

The Maddox rod test can be used to subjectively detect and measure a latent, manifest, horizontal or vertical strabismus for near and distance. The test is based on the principle of diplopic projection.[1] Dissociation of the deviation is brought about by presenting a red line image to one eye and a white light to the other, while prisms are used to superimpose these and effectively measure the angle of deviation (horizontal and vertical). The strength of the prism is increased until the streak of the light passes through the centre of the prism, as the strength of the prism indicates the amount of deviation present. The Maddox rod is a handheld instrument composed of red parallel plano convex cylinder lens, which refracts light rays so that a point source of light is seen as a line or streak of light.[2] Due to the optical properties, the streak of light is seen perpendicular to the axis of the cylinder.[3]

Maddox rod and pen torch used in Maddox rod testing
  1. ^ Ansons, A. & Davis, H. (2008). Diagnosis and Management of Ocular Motility Disorders, Third Edition. [Wiley Online Library]. doi:10.1002/9780470698839
  2. ^ Maddox rod. (n.d.) Millodot: Dictionary of Optometry and Visual Science, 7th edition. (2009). Retrieved October 19, 2014 from http://medical-dictionary.thefreedictionary.com/Maddox+rod
  3. ^ "The Maddox Rod Test" (PDF). Jomtonline.com. Archived from the original (PDF) on 16 October 2014. Retrieved 13 October 2014.