A 5-month-old infant is brought to your office by her mother. The mother reports that the child has a “lazy eye.” On further inquiry, the mother describes a 1-month history of the child’s eyes turning inward toward the nose. This occurs intermittently and is not noticed by the child’s father. The mother shows several photographs that are inconclusive. The infant’s maternal uncle had strabismus surgery as a child. On examination, the infant protests when either eye is covered, and seems to have an inward deviation of the right eye, more pronounced when looking to the left (Figures 15-1 A,B,C). The patient is able to move the eyes easily in all directions.
Strabismus refers to any misalignment of the eyes. It can be further categorized based on the direction of the deviating eye(s): 1) esotropia—the eye turns inward; 2) exotropia—the eye turns outward; 3) hyper- and hypotropia—the eye turns upward or downward respectively; and 4) cyclotropia or torsional—the eye is rotated clockwise or counterclockwise. Further, the terms used to describe strabismus also depend upon the conditions under which it is present (constant or intermittent) and whether it changes with the position of gaze (comitant or incomitant).
There is geographical variation in the prevalence of strabismus.
Esotropia is more common in Western populations whereas exotropia is more common in Eastern populations.
US population-based studies have found an annual incidence per 100,000 population of 64 in exotropia (corresponding to a prevalence of 1 percent of children aged <11 years), 111 in esotropia (corresponding to a prevalence of 2 percent of children aged <6 years), and 12.9 in hypertropia (corresponding to a prevalence of 0.26 percent of children aged <19 years).
In the US, the incidence of esotropia is highest in children younger than 7 years, whereas the incidence of exotropia is highest in children aged 6 to 9 years, and is also high in adolescents and adults with sensory strabismus.
The prevalence of strabismus is higher in those with intellectual disabilities (44.1%) compared with the general population. The prevalence in white people is 2 percent to 4 percent, but may be lower in Asian populations.1–3 Among Hispanic and Latino children, prevalence is:
2 percent at ages six to 11 months.
2.6 percent at ages 36 to 47 months.
2.8 percent at ages 60 to 72 months.
Among African-American children, prevalence:
1.1 percent at ages six to 11 months.
1.9 percent at ages 36 to 47 months.
3.9 percent at ages 60 to 72 months.4
Proper alignment of the eyes is guaranteed by a normally functioning sensory and motor fusion mechanism. If either of these two systems is perturbed, strabismus may result.
Sensory:
All the nervous impulses that reach the eyes. These factors include the movements of extraocular muscles, psycho-optical reflexes (poorly understood fusional impulses), external influences on muscle tone (endolymph, vestibular system, possible reflexes from neck muscles), and influences of the several nuclear and supranuclear areas that govern ocular motility.
Motor:
Second, there are anatomical factors, which consist of orientation and shape of the orbits; size and shape of the globes; volume of the retrobulbar tissue; functioning of the eye muscles as determined by their insertion, length, elasticity, and structure; and anatomical arrangement of connective tissue, ligaments, and pulleys of the orbit.5
The diagnosis is made with a careful history and physical examination as outlined in the following sections.
History
Age of onset, especially during perinatal period.
Birth history.
Family history.
Associated illness or trauma, especially neurologic.
Associated signs including nystagmus, headache, ptosis, anisocoria.
Constant vs. intermittent.
Change of deviation based on direction or distance of fixation.
Physical examination.
General health and neurologic status.
Head position—ocular torticollis may be induced by ocular misalignment.
Vision, eyelid position, or pupils.
Corneal light reflex or Hirschburg test.
The projected light reflex will be centered on each eye if they are aligned. In esotropia, the light on the inwardly deviated eye will be displaced temporally and in exotropia it will be displaced nasally.
Cover and cover/uncover test.
Cover the apparently straight/fixating eye and observe the fellow eye for a refixation movement.
An esotropic eye will have a refixation movement from nasal to temporal in order to pick up fixation and vice versa.
Ductions and versions.
Check eyes separately and together for ability to move completely.
Penlight exam.
Look for ocular abnormalities of the cornea, iris or lens.
Red reflex test.
Complete ophthalmologic examination including cycloplegic refraction and dilated fundus examination.
