pediatrics
Strabismus
Diagnosis of Strabismus
Physical and neurologic examinations at well-child checkups Tests (eg, corneal light reflex, alternate cover, cover-uncover) Prisms Strabismus can be detected during well-child checkups through the history and eye examination. Evaluation should include questions about family history of amblyopia or strabismus and, if family or caregivers have noticed deviation of gaze, questions about when the deviation began, when or how often it is present, and whether there is a preference for using one eye for fixation. Physical examination should include an assessment of visual acuity, pupil reactivity, and the extent of extraocular movements. Slit-lamp examination is done to detect signs of cataract, and funduscopic examination is done to detect signs of structural defects or pathology of disorders such as retinoblastoma. Neurologic examination, particularly of the cranial nerves, is important. Thecorneal light reflex testis a good screening test, but it is not very sensitive for detecting small deviations. The child looks at a light and the light reflection (reflex) from the pupil is observed; normally, the reflex appears symmetric (ie, in the same location on each pupil). The light reflex for an exotropic eye is nasal to the pupillary center, whereas the reflex for an esotropic eye is temporal to the pupillary center. Vision screening devices such as photoscreeners may be used by trained lay personnel to identify children at risk. When doing thecover test,the child is asked to fixate on an object. One eye is then covered while the other is observed for movement. No movement should be detected if the eyes are properly aligned, but manifest strabismus is present if the uncovered eye shifts to establish fixation once the other eye, which had fixed on the object, is covered. The test is then repeated on the other eye. In a variation of the cover test, called thealternate uncover test,the child is asked to fixate on an object while the examiner alternately covers one eye and then the other, back and forth. An eye with a latent strabismus shifts position when it is uncovered. In exotropia, the eye that was covered turnsinto fixate when the cover is removed; in esotropia, it turnsoutto fixate when the cover is removed. Deviations can be quantified by using prisms positioned such that the deviating eye does not need to move to fixate. The power of the prism is used to quantify the deviation and provide a measurement of the magnitude of misalignment of the visual axes. The unit of measurement used by ophthalmologists is the prism diopter. One prism diopter is a deviation of the visual axes of 1 cm at 1 m. Strabismus should be distinguished from pseudostrabismus, which is the appearance of esotropia in a child with good visual acuity in both eyes but a wide nasal bridge or broad epicanthal folds that obscure much of the white sclera nasally when looking laterally. The light reflex and cover tests are normal in a child with pseudostrabismus. Neuroimaging may be necessary to identify the cause of acquired cranial nerve palsies. In addition, genetics evaluation may be beneficial for certain ocular malformations. 