SKEW deviation

Question 1

SKEW Description

Answer 1

Skew deviation is a vertical strabismus resulting from a disruption of input into the oculomotor (3) and trochlear (4) nuclei.
Torsion is often a feature and other symptoms and signs of central nervous system disease are usually present.

Question 2

SKEW aetiology

Answer 2

Arises from a peripheral or central imbalance of otolith inputs to the oculomotor and trochlear nuclei.
Involves structures from the thalamus and parietal cortex, and lesions rostral to the interstitial nucleus of Cajal.

Question 3

SKEW features

Answer 3

Vertical Strabismus:
Can be transient or permanent; transient deviations common in unilateral INO.
Misalignment can be concomitant or incomitant; resembles any cyclovertical muscle underaction.
Diplopia

Intorsion and Extorsion:
Intorsion of the hypertropic eye (affected) and extorsion of the hypotropic eye.

Torsional nystagmus.
Reflects common occurrence with lesions involving the interstitial nucleus of Cajal (INC).

Bielschowsky Head Tilt Test:
Usually negative in concomitant skew deviation but positive in incomitant skew deviation.

Ocular Tilt Reaction (OTR):
Comprises the triad of skew deviation, ocular torsion, and head tilt.
Depends on a crossed graviceptive pathway and projects to the contralateral interstitial nucleus of Cajal and then to ocular and spinal motor neurons.
Sensitive brainstem sign with localizing and lateralizing value.
Peripheral and Central vestibular lesions result in a head tilt towards the same side as the lesion
Rostral lesions of the MLF and INC (interstitial nucleus of Cajal)result in head tilt towards the opposite side of the lesion
The reason for this is due to the cross over of vestibular nuclei in the contraleteral MLF

Head Tilt:
Head tilt towards the hypotropic eye; does not promote fusion of the vertical deviation.
Not eliminated by correction using prisms or surgery.

Upright-Supine Test:
Compares the size of the vertical deviation in the primary position when upright and lying supine.
A decrease of 50% or more in the size of deviation when supine in 80% of patients with skew deviation.
Fourth nerve palsy shows no significant change in the size of the vertical deviation.

Subjective Visual Vertical:
Patients adjust a luminous line in complete darkness to the upright, earth vertical.

Other Signs:
Other signs of central nervous system disease usually involve the brainstem and cerebellum.
Double vision can be the result of a lesion affecting the premotor, internuclear or infranuclear pathways, the ocular motor nuclei or a skew deviation

Question 4

SKEW vs 4th

Answer 4

upright supine test in 4th doesnt change

BHHT shows no change in skew

intorsion in skew, extorsion in 4th

Question 5

skew mx

Answer 5

Monitoring:
Strabismus can be monitored using a Hess chart.
Unable to fuse with surgery or prisms