Anomalous Head Posture and Strabismus

Normal Head Posture

The eyes usually remain in (or very near) the frontal plane - gaze away is usually momentary - followed by prompt repositioning of the head to face the object of regard.

Approximately 12 grams of force is required in all muscles, (relatively little effort) to maintain eyes in primary position

Gaze to one side

Try maintaining gaze to one side while keeping your face straight ahead. It is tiring. The natural tendency is to rotate your head, facing (or nearly facing) the object of regard.

Gaze maintained to the side requires more tension on all of the horizontally acting muscles holding the eyes in position.

How do the eyes get to side gaze?

Saccade

During a rapid refixation or saccade the eye muscles contract with up to 100 gm or more at peak velocity of 200 /sec.

Velocity depends on speed of moving object followed, (usually) a few degrees per sec.

Pursuit

The eyes track in a slow following movement.

Oculocephalic

Eye movement is influenced by middle ear static factors. Movement confirms intact muscle/neural arc.

A few degrees/sec. Depends on head movement

Regardless of how the eyes attain a given gaze position, the eye muscles are under more tension in gaze away from primary.

A person may find it necessary to attain a given gaze position or assume an anomalous head posture to achieve comfortable vision - for example: to avoid diplopia, or to find the null to gain better vision in the case of nystagmus.

Compensatory Head Posture for Diplopia: The head (face) moves where the eye(s) movement is limited, for example:

VI N palsy right eye - ET primary position

Greater ET in right gaze, less in left gaze

To avoid diplopia the person turns his face right, while the eyes assume levoversion. The object of regard is straight ahead by egocentric localization. You have to think about this one. Egocentric localization (the relationship between you and what you are looking at) refers to body-posture, etc. not just the direction the face is pointing.

Head posture in right superior oblique palsy. The chin is down and the head tilted left while the eyes look up to the right. This compensates for both the vertical and the torsional defect.

hp strategies

The null point shown here is in right gaze which would result in left face turn. The null point can shift from side to side in periodic alternating nystagmus with a periodicity of several minutes.

Nystagmus may also be damped with convergence which is the basis for "artificial" divergence surgery. This will be discussed later.

In cases of restricted movement of the eye(s) from mechanical restriction or muscle weakness, resulting in diplopia, think of the head as the eyeball. The head moves where the eye cannot. The eyes then move opposite the head (face) direction to avoid the direction of limited movement thereby avoiding diplopia.

Anomalous head posture can occur in congenital ET and is always seen in spasmus nutans. The vision gain is not obvious in these cases.

Editor-in-Chief: Eugene M. Helveston, M.D.

Associate Editor: Faruk H. Orge, M.D.

Editorial Board: Bradley C. Black, M.D.

Edward O'Malley, M.D.

David A. Plager, M.D.

Derek T. Sprunger, M.D.

Daniel E. Neely, M.D.

Naval Sondhi, M.D.

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