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. 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. Due to the optical properties, the streak of light is seen perpendicular to the axis of the cylinder.

The Maddox rod test should be used in cases of:

The method of assessing near and distance fixation is similar.

Method for measuring horizontal deviations:

Method for measuring vertical deviations:

1. The patient is held for granted to hold the Maddox Rod in front of their right with the cylinders vertical, making the red line horizontal.
2. The patient is then asked whether the white light is superimposed on the red line or if it appears above or below the red line.

Examples of recordings are shown below:

MR: sc (F) L/R 5∆ eso 8∆ (FR)

MR: sc (F) L/5∆ eso 8∆ (FR)

MR: sc (F) 5∆ BD 8∆BO (FR)

sc: without correction
- F: far
- N: near
- FR: fixing right
- FL: fixing left
- BD: base down prisms
- BU: base up prisms
- BO: base out prisms
- BI: base in prisms
- eso: esotropia
- exo: exotropias
- L/R: left hypertropia or right hypotropia
- R/L: right hypertropia or left hypotropia

The double Maddox rod test can also be used to assess torsion and measure cyclotropias.

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Wikipedia