Appendix 1
The Maddox Rod Test
This test is used to uncover latent squints (phorias). The test may be performed with a handframe, a
vision tester or a trial frame but the principle in all is the same. If a candidate is given two dissimilar
targets to view at the same time, the stimulus to fusion is absent and phorias are uncovered.
The Maddox rod is a disc of red glass in which are molded grooves. When a distant spot of light is
viewed with the disc in front of one eye, a red line will be seen by the eye covered with the lens, whilst
a spot of light will be seen with the other eye. The line will be at right angles to the grooves to that when
these are horizontal the line will appear vertical. A candidate with no latent deviation will see the
coloured line pass through the spot of light (orthophoria), whereas a candidate with latent squint
will see the light source to one side of the line.
The Maddox rod with rotating prism is held in front of the right eye and the candidate is asked to look at
a point source of light 6m (20 ft.) away in a darkened room. Both eyes must be open and squinting should
be avoided. The candidate is asked which side of the line the dot is seen. If it is to his right, esophoria is
present and if to the left, exophoria. The candidate is then asked to “put the line on the light” by adjusting
the rotating prism. The examiner reads off the degree of phoria from the scale on the device.
The test is repeated with the disc turned to the vertical position. The light will now be seen either
above or below the line and may be adjusted by the candidate in the same way. If the red line is above the
light there is left hyperphoria, if below the light, right hyperphoria.
If the candidate sees several lines, there are aberrant light sources and, if they cannot be suppressed, the
correct line can be indicated by turning the spot light on and off several times. Some candidates are aware
that the line should pass through the spot and may try to hide their phorias. This should be suspected if a
candidate with an abnormal cover test sees the line directly through the light. In this case the lens can be
adjusted so the dot and the line do not coincide and the candidate’s response should be noted.
Definitions
- Orthophoria – No tendency to deviate.
- Esophoria – Tendency of the eye to turn in.
- Exophoria – Tendency of the eye to turn out.
- Hyperphoria – Tendency of one eye to turn up or the other eye to turn down.
Demonstrations of the Maddox rod Test may be seen on the video The Vision Examination for Aviation
Medical Examiners.
|
