The rectus muscles of infants are smaller than those of adults; muscle insertions, on average, are 2.3–3.0 mm narrower, and the tendons are thinner in infants than in adults. In newborns, the distance from the rectus muscle insertion to the limbus is roughly 2 mm less than that in adults; by age 6 months, this distance is 1 mm less; and at 20 months, it is similar to that in adults.
Extraocular muscle function continues to develop after birth. Eye movements driven by the vestibular-ocular system are present as early as 34 weeks’ gestational age. Conjugate horizontal gaze is present at birth, but vertical gaze may not be fully functional until 6 months of age. Intermittent strabismus occurs in approximately two-thirds of young infants but resolves in most by 2–3 months of age. Accommodation and fusional convergence are usually present by age 3 months.
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.