Clinical Features and Identification of Pattern Strabismus
The presence of A and V patterns is determined by measuring alignment while the patient fixates on an accommodative target at distance, with fusion prevented with the prism alternate cover test, 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 induce exaggerated convergence in downgaze. The examiner should look specifically for apparent oblique muscle overaction (OEAd or ODAd) because of its frequent association with pattern strabismus.
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, this difference must be at least 15Δ because there is normally some physiologic convergence in downgaze.
The most common type of pattern strabismus, V pattern occurs most frequently in patients with infantile esotropia. The pattern is usually not present when the esotropia first develops but becomes apparent during the first year of life or later. V patterns may also occur in patients with superior oblique palsies, particularly if they are bilateral, and in patients with craniofacial malformations.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.