Most children with strabismus do not experience diplopia. This symptom warrants referral to an ophthalmologist. If the examination suggests a cranial nerve palsy, or if other neurological symptoms are present, the child should be seen promptly.

What Shouldn’t Be Missed

Acute cranial nerve palsies may be due to idiopathic intracranial hypertension or other intracranial diseases. Prompt evaluation and treatment may improve the prognosis for both vision and the underlying disorder.

• 1. Physiological diplopia. This is a normal phenomenon that is most commonly noted by bright and observant children around ages 5 to 6 years. The eyes normally focus on objects in a single plane, and these are seen as single images. Objects in front of or behind the object of attention appear to be double, but most people do not notice this. The diplopia can be demonstrated by holding one finger up at arm’s distance in front of your face, with another object (e.g., something on the wall) in the background in line with your finger. If you focus on your finger but pay attention to the object in the background, the background object will appear double. Conversely, if you focus on the background object but pay attention to your finger, the finger will appear double (Figure 11–1). Most of the time these double images are ignored, but children may become aware of them and report them to their parents.
  
• 2. Breakdown of a phoria. Many normal individuals have a phoria. A phoria is a tendency for the eyes to become misaligned when one eye is covered. The eyes are straight during normal viewing conditions with both eyes open. With a phoria, when one is covered it drifts off center (either inward or outward). The eye returns to its normal position when the eye is uncovered (Figure 11–2). In some patients, usually in association with severe illness or trauma, the ability to control the phoria is temporarily lost, and they develop manifest strabismus (esotropia or exotropia) and diplopia. This usually resolves in conjunction with recovery from the underlying problem.
  
• 3. Fourth nerve palsy. This is most often congenital and not associated with other neurological problems.
  
• 4. Third nerve palsy. Acquired third nerve palsy may result from many different neurological problems.
  
• 5. Sixth nerve palsy. Most common causes are transient sixth nerve palsy of childhood (often associated with preceding viral illness) and increased intracranial pressure.