Yoked and Differential Prisms to Improve Posture


Ever hear of “Orthopedic Optometry”? No, it’s not a new way to achieve ortho, although it does relate to prism prescribing. I came across the term on VTODs on Facebook a few days ago when Dr. Kiera Garner posted this: “Jonathan Shapiro, FCOptom, FAAO, FEAOO, has developed a method of orthopedic optometry. He invented a polarized eye chart that helps to determine the preferred combination of lens, filter and prism to optimize binocularity and posture.”

Apparently Jonathan is giving a course titled “Integrated Optometry”, and it’s predicated in part on this article he authored in the Canadian Journal of Optometry last year. A significant test component is something that Jonathan previous published in the 1990s called the Parallel-Testing Infinity Balance (PTIB), which is a variation on the Turville Infinity Balance test.

The PTIB is now computerized, and in the article Jonathan describes the method as follows:

The first target (a) has two nonius lines positioned along the horizontal, polarized for each eye. The colors chosen for the arrows are close to each other on the spectrum to avoid spatial displacement from transverse chromatic aberration (TCA). Peripheral locking is maintained by the use of a yellow square. The positions of the nonius lines in relation to the X, and to each other, are compared as the head moves laterally while fixating on the X. The head of the patient is held in the primary position by the examiner to prevent head-tilting. By holding the head during the examination, the examiner can control the speed of movement. The head is moved slowly left and right. If no variations in the vertical positioning of the images are found, the positioning of the lateral and medial recti can be assumed to be level. A major difference in the relative vertical height of the two eyes, at the edge of the vergence movements, indicates an imbalance. If the lateral and medial recti muscles are not aligned, as the head moves to one side, one line will rise or drop. On moving in the opposite direction, the opposing line will move. This action is repeated with the chin depressed and raised. If there is a reduction in the amount of vertical movement during vergences, comparing the primary position to when the chin is depressed or raised, then Yoked vertical prisms are introduced. The power of the Yoked prisms prescribed is determined by the amount needed to reduce vertical movement to a minimum, when the head is held in the primary position. After the Yoked prisms are introduced, the test is repeated with the nonius line positioned vertically, to determine if there is any disruption to the horizontal balance.

The second target (b) is the PTIB. The top black bar, with 2 red lines, is seen binocularly. The squares, with attached red lines, are seen separately by each eye. In this test, the PTIB will show the vertical and horizontal misalignment of the images perceived by each eye during motion. This is noted by the patient as changes in the vertical alignment of the two squares, and/or the relative horizontal positioning of the red nonius lines on the squares with red lines in the black bar. It will also show any cyclorotation or image-size variation. The examination will also highlight possible involvement of the oblique muscles. The head is held in the primary position. If necessary, Differential prisms are used to balance the vertical and hori-zontal imbalances before the head is moved. After the position of the squares is balanced, the head is moved laterally and vertically, as described before. The patient reports if the squares remain on the same level, if they cyclorotate away from the original format, if they change size, or if the red line on the square dislocates from the red line in the black bar above. The information allows the practitioner to infer the actions of the EOM. Whether there is an over- or under-action of a specific muscle is less important than the relation of the paired muscles during tracking. A cyclic rotation, as exhibited on the squares of the PTIB, may be modified when the head is held in a specific position.

Actually you can gain a sense of the “orthopedic” implications of this approach through Jonathan’s course outline:

Investigating the Effect of Facial and Head Structure on Binocular Vision and Cortical Integration (Introduction)

Describing phorias

Types of Binocular Vision

Cortical Integration

Parallel-Testing Infinity Balance (PTIB)

Is stereopsis directly related to Binocular Vision?

Skull structure

HAVX syndromes

Nasal projection

Facial asymmetry

Sterno-Cleido-Mastoid asymmetry

Case studies

Corneal warpage from facial asymmetry

Changes in visual localization from skull shapes during aging

Suggesting treatment regimes

Postural Anomalies – Causes

Sterno-Cleido- Mastoid Asymmetry

Genetic Growth Asymmetry

Birth Canal Stress

Other?

Postural Anomalies – Effect on the Spine and Vision

Spinal changes caused by Sterno-cleido-mastoid shortening

Spinal Changes caused by Genetic Differences

Special cases

Spinal changes caused by Anterior – Posterior asymmetry

Examining and Treating

  • Massaging and stretching the SCM
  • Use of Yoked and Differential Prisms

3 thoughts on “Yoked and Differential Prisms to Improve Posture

  1. Won’t this yield a compensatory Rx? For patients with head injury, won’t this likely lead to a need for increased prism Rx over time?

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