Figure 10-5 Downward slant of the palpebral fissures, often associated with a V-pattern horizontal deviation. (Courtesy of

Edward L. Raab, MD.)

Clinical Features and Identification

A and V patterns are determined by measuring alignment while the patient fixates on an accommodative target at distance, with fusion prevented, in primary position and in straight upgaze and downgaze, approximately 25° from the primary position. Proper refractive correction is necessary during measurement because an uncompensated accommodative component can introduce exaggerated convergence in downgaze.

An A pattern is considered clinically significant when the difference in measurement between upgaze and downgaze is at least 10 prism diopters (Δ); for a V pattern, the difference must be at least 15Δ. The difference is larger for a V pattern because normally there is some physiologic convergence in downgaze.

Most, but not all, patients with pattern strabismus have apparent overaction of the oblique muscles (OEAd or ODAd).

V Pattern

The most common type of pattern strabismus, V pattern occurs most frequently in patients with infantile esotropia. Usually, the pattern is not present when the esotropia first develops but becomes apparent during the first year of life or later. V patterns also may occur in patients with superior oblique palsies, particularly if they are bilateral, and in patients with craniofacial malformations.

A Pattern

The second most common type of pattern strabismus, A patterns occur most frequently in patients with exotropia. A patterns are more common than V patterns in patients with infantile strabismus associated with craniofacial malformations, trisomy 21, and myelomeningocele.