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

Equipment required in Maddox rod testing

Equipment used in Maddox rod testing. Top left (Maddox rod), top right (vertical base up and base down prisms), bottom left (pen torch) and bottom right (horizontal base out or in prisms)

Indication of use

The Maddox rod test should be used in cases of:

Method of assessment

The method of assessing near and distance fixation is similar.

A) Esodeviation, B) Exodeviation, C) Hyper-deviation, D) Hypo-deviation, E) No deviation

Method for measuring horizontal deviations:

  1. When performing the clinical test, the room lights should be dimmed and only one light source should be visible.
  2. When testing at near, the patient is to fixate on light source at 33 cm, which is held at eye level. When testing at distance, the patient is to fixate on a light source at 6m.
  3. Patient is instructed to fixate on the light source with both eyes opened.
  4. The Maddox rod is then placed over the fixating eye.
  5. To measure the horizontal deviation, the Maddox rod is placed in front of the right eye (it is done on both eyes) with the cylinder horizontal, making the red line will be vertical. The patient is then asked whether the white light is superimposed on the red line, or if it is to the left or right of the red line.
Maddox rod test tutorial

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.

Recording

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

Double Maddox rod test

The double Maddox rod test can also be used to assess torsion and measure cyclotropias.[7]

Double Maddox rod test with trial frames
  1. The room lights should be dimmed and only one light source should be visible
  2. Maddox rods are placed into the trial frames, one before each eye
  3. Cylinders are placed into trial frame vertically, making the two red lines horizontal
  4. Vertical prism ( base-up, or base-down) can also be added into the trial frames to separate the two red lines (This avoids confusion if the patients claim that they only see one red line). The degree of deviation and the direction (incyclo or excyclo) can be determined by the angle of rotation that causes the line images to appear horizontal and parallel.
  5. The amount of cyclodeviation is measured in degrees, utilised from the scale on the trial frame
  6. When testing at near, the patient asked to fixate on light source at 33 cm, which is held at eye level. When testing at distance, the patient is to fixate on a light source at 6m.
  7. Patient is instructed to fixate on the light source with both eyes opened
  8. Patient is asked to rotate OR the examiner rotates the cylinders with the axis knob on the trial frame until the 2 red lines are parallel
  9. This test can be repeated for the secondary and tertiary positions of gaze [8]

Advantages

Disadvantages

References

  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. Retrieved 13 October 2014.
  4. ↑ Ansons, A. & Davis, H. (2008). Diagnosis and Management of Ocular Motility Disorders, Third Edition. [Wiley Online Library]. doi:10.1002/9780470698839
  5. ↑ Ansons, A. & Davis, H. (2008). Diagnosis and Management of Ocular Motility Disorders, Third Edition. [Wiley Online Library]. doi:10.1002/9780470698839
  6. ↑ Ansons, A. & Davis, H. (2008). Diagnosis and Management of Ocular Motility Disorders, Third Edition. [Wiley Online Library]. doi:10.1002/9780470698839
  7. ↑ Ansons, A. & Davis, H. (2008). Diagnosis and Management of Ocular Motility Disorders, Third Edition. [Wiley Online Library]. doi:10.1002/9780470698839
  8. ↑ Ansons, A. & Davis, H. (2008). Diagnosis and Management of Ocular Motility Disorders, Third Edition. [Wiley Online Library]. doi: 10.1002/9780470698839
  9. ↑ Ansons, A. & Davis, H. (2008). Diagnosis and Management of Ocular Motility Disorders, Third Edition. [Wiley Online Library]. doi:10.1002/9780470698839

See also

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