eMedicine Specialties > Ophthalmology > Extraocular Muscles
Esotropia and Exotropia, V-patterns
Updated: Sep 26, 2006
Introduction
Background
Duane first described V-pattern strabismus in 1897. Other investigators also studied these phenomena, contributing to the understanding of them. In 1944, Costenbader and colleagues recommended measuring the horizontal deviations in upgaze and downgaze as part of all routine motility examinations.
Two types of V-patterns can occur. V-pattern esotropia is an esodeviation with greater esotropia in downgaze than in upgaze. V-pattern exotropia is an exodeviation with greater exotropia in upgaze than in downgaze. See Images 1-2.
Comitant horizontal deviations are those in which the angle of deviation is the same in all gaze positions. Incomitant horizontal deviations are those in which the angle of deviation varies in different gaze positions. Horizontal deviations may have lateral incomitances and vertical incomitances. In lateral incomitances, significant differences exist in the amount of horizontal deviation in primary gaze versus side gaze, whereas, in vertical incomitances, significant differences exist in the amount of horizontal deviation in upgaze versus downgaze.
When the eyes diverge more than 10 prism diopters (PD) from upgaze to downgaze, an A-pattern is present; when the eyes converge more than 15 PD from upgaze to downgaze, a V-pattern is present.
Other types of vertical incomitances, which are less common, include X, Y, and lambda patterns. This discussion is limited to V-pattern strabismus.
Pathophysiology
Multiple factors may be responsible for V-pattern strabismus, and, in a given individual, one or more factors may contribute toward its cause.
Inferior oblique muscle overaction
The most widely accepted mechanism contributing to the causation of V-pattern strabismus is associated with inferior oblique muscle overaction and/or relative underaction of the superior oblique muscles. Inferior oblique muscle overaction produces significant horizontal deviation in upgaze. In upgaze, the horizontal action of the inferior oblique muscles is abduction; therefore, inferior oblique muscle overaction produces relative divergence in elevation. A V-pattern results in greater exotropia (or less esotropia) in upgaze and greater esotropia (or less exotropia) in downgaze. Not all V-pattern strabismus is associated with oblique muscle dysfunction. See Images 7-8.
Facial and orbital configuration
An association exists between individuals with hypoplasia of the malar bones, anti-Mongoloid lid slants, and S-shaped contours of the lower lid, and overaction of the inferior oblique muscles and V-pattern strabismus. Patients with craniosynostosis have shallow orbits, and the angle between the visual axis and the insertion of the inferior oblique muscle is increased. This increased angle increases the abduction ability of the inferior oblique muscles in upgaze, resulting in a V-pattern. Contributing to this condition is the complex interplay of these factors with excyclotorsion of the globe.
Effect of the pulley systems
Upward displacement of the pulley systems around the lateral rectus muscle may cause V-pattern strabismus.
Horizontal muscle overaction
Initially, this theory was believed to be responsible for V-pattern strabismus, but no convincing evidence supports it. In V-pattern esotropia, the medial rectus muscle was believed to overact, thereby increasing esotropia in downgaze, and, in V-pattern exotropia, the lateral rectus muscle overaction was responsible for increased exotropia in upgaze.
Vertical rectus muscle imbalance
One theory states that V-pattern strabismus occurs because of underacting superior recti muscles and corresponding overacting inferior oblique muscles. This hypothesis was applied when nasal and temporal displacements were used to treat A- and V-patterns. This theory has been abandoned.
Abnormal oblique muscle insertions
Alterations of the angle of the insertion of the oblique muscle with the visual axis can reduce cyclorotation and abduction forces and increase the vertical function of the oblique muscle.
Anomalous horizontal rectus muscle insertions
Among the suggested causes of V-pattern strabismus are anomalies of the horizontal rectus scleral insertions. They may be inserted above or below the usual positions.
Acquired form
V-patterns are acquired after superior oblique muscle palsy and are a prominent feature of bilateral superior oblique muscle palsies.
Frequency
United States
Although the exact prevalence of V-pattern strabismus in a given population is not known, 12.5-50% of patients with horizontal strabismus have an associated A- or V-pattern. V-pattern esotropia is not as commonly seen as V-pattern exotropia.
Mortality/Morbidity
Patients may experience diplopia that affects their everyday activities, such as driving and reading. In addition, the inability of patients to fuse in different gaze positions can interfere with other activities, including sports and recreation. The cosmetic appearance of V-pattern strabismus coupled with its social implications may be bothersome to patients. Over time, the associated anomalous head position could lead to secondary neck pain and similar problems.
Race
No racial predilection exists.
Sex
No sexual predilection exists.
Age
No age predilection exists.
Clinical
History
The most common presenting signs of V-pattern strabismus are as follows:
- Inward or outward deviation of the eyes
- Abnormal eye movements in different gazes
- Asthenopia (eyestrain)
- Abnormal head posture, chin down in V-pattern exotropia and chin up in V-pattern esotropia
- Diplopia in older children and adults
Physical
The physical examination includes a general eye examination combined with a detailed ocular motility examination. The ocular motility examination, performed with the refractive error corrected, consists of the following:
- Note any abnormal head position.
- Perform cover tests with prisms in the primary position, 30° upgaze and 30° downgaze at near and at distance.
- With ocular rotations, look for associated underaction or overaction of oblique muscles.
- Perform a head tilt test if V-pattern strabismus is noted in patients with suspected bilateral superior oblique palsy.
- Measure torsion in patients with suspected inferior oblique muscle overaction to check for excyclotorsion.
- When required, perform sensory testing, including distance and near stereoacuity, and other tests.
Causes
See Pathophysiology.
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References
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Further Reading
Keywords
V-pattern strabismus, vertically incomitant horizontal deviations, A-pattern, V-pattern, horizontal deviation, upgaze, downgaze, angle of deviation, V-pattern esotropia, V-pattern exotropia
