Approach to amblyopia and strabismus (pediatrics): Clinical sciences

Amblyopia, sometimes called “lazy eye”, refers to decreased visual acuity in one or both eyes that prevents normal development of the visual cortex. It’s crucial to identify amblyopia at a young age before it becomes difficult or even impossible to treat. Common causes of amblyopia include strabismus, or misalignment of the eyes; as well as deprivation and refractive error.

Now, if a pediatric patient presents with a chief concern suggesting amblyopia or strabismus, first perform a focused history and physical examination, including visual acuity and red reflex testing.

Visual acuity testing techniques vary by age. For children under age 2, you can assess the pupillary response to light, as well as the ability to track, or fixate on and follow an object. After age 3, most children can recognize and match objects on cards; and when they are older, they can read an eye chart. For younger children or those who are unable to cooperate with standard testing, consider instrument-based screening with a photoscreener or autorefractor.

Remember to perform vision screening monocularly, at a specified distance, and make sure your patient wears corrective lenses if they were prescribed.

Now, to perform the red reflex test, view both eyes through an ophthalmoscope, and look for a symmetric red reflection from the retina. You’ll find it helpful to turn off or dim the lights to ensure the pupils are dilated.

Alright, let’s look at some findings you might see in children with amblyopia or strabismus. Although young children are often asymptomatic, history might reveal blurred vision or vision loss, and caregivers might describe a “lazy” or deviated eye, as well as squinting, or head tilt, also called ocular torticollis. Infants may demonstrate a lack of eye contact. The physical examination typically reveals a unilateral or bilateral decrease in visual acuity. For verbal children, testing with a standard vision chart may reveal a two-line difference in vision between both eyes. For infants or preverbal children, signs of visual loss include decreased following or fixation and a fixation preference. With these findings, consider amblyopia.

Next, assess for a history of eye deviation, and if present, consider strabismus amblyopia. Then, perform corneal light reflection and cover-uncover tests to look for corneal misalignment.

To test corneal light reflection, have your patient look straight ahead, and shine a light directly onto the cornea of both eyes. If the light reflex is symmetric and centered in each pupil, the eyes are straight; but an asymmetric reflex suggests pupillary deviation or misalignment.

To perform the cover-uncover test, have your patient fixate on an object in the distance, and then cover and uncover each eye. If the uncovered eye drifts after you cover the opposite eye, your patient has ocular misalignment.

Now, if neither of these tests shows evidence of ocular misalignment, consider pseudostrabismus, which means there appears to be misalignment when the eyes are in fact straight. Some anatomic characteristics that can give the false appearance of ocular misalignment include a flat, broad nasal bridge; prominent epicanthal folds; or a narrow interpupillary distance. If any of these features are present, your patient has pseudostrabismus. This benign condition doesn't cause amblyopia, and it typically diminishes as the child grows.

Here’s a clinical pearl! Intermittent strabismus is a normal finding during the first few months of life, but if strabismus is constant, or if it doesn’t resolve after 4 months of age, your patient requires further evaluation.

On the other hand, if the corneal light reflection test or cover-uncover test demonstrates persistent corneal misalignment, diagnose strabismus, also known as heterotropia.

Here’s a high-yield fact! While performing the cover-uncover test, you may discover an intermittent or latent misalignment, called heterophoria. In this case, misalignment or deviation only occurs during periods of fatigue or stress. Heterophoria can occasionally result in eye strain, headaches, or double vision, but it does not cause amblyopia.

Alright, once you diagnose strabismus, your next step is to assess the consistency of eye deviation. If ocular deviation is equal and consistent regardless of gaze direction, your patient has a comitant tropia. To determine the specific type, assess the direction of ocular deviation. If either eye deviates inward, diagnose esotropia. This is the most common type of ocular misalignment in children. On the flip side, if either eye deviates outward, diagnose exotropia.