The corneal light reflex test, cover test, red reflex, and extra-ocular rotations are four basic tests for strabismus. To perform the corneal light test, project a penlight onto the cornea of both eyes simultaneously while the child looks straight ahead. Compare the placement of the two corneal reflections. When the eyes are straight, the light appears at the same point on each cornea. If a muscle deviation is present, the reflected light appears slightly off center in one eye. Figure 41-13 illustrates the placement of corneal reflections as they would appear for each direction of deviation. In part A, note that the light is centered on the cornea of the left eye but is displaced laterally, or outward, on the right cornea, indicating that the right eye is turned inward, or is esotropic. In B, note that the light is centered again on the left cornea but is displaced medially, or inward, on the right cornea, demonstrating an outward-turning, exotropia of the right eye. In part C the light indicates that the right eye is turned upward, or is hypertropic, and the left eye is straight.
The cover test is performed by having the child look straight ahead at an object 20 feet away (Fig. 41-14). An eye chart is usually used to test children older than 3 years. For younger children, it is helpful to use a colorful, moving object or toy. As the child looks at the target, cover the child's right eye and look for movement of the uncovered eye. If the left eye moves to pick up fixation, it was deviated before placing the cover over the right eye. Repeat the procedure for the left eye, and watch for any movement in the uncovered right eye. If the eye moves inward to pick up fixation, the eye is exotropic. If the eye moves outward to pick up fixation, the eye is esotropic.
The third test involves simultaneous examination of the pupillary red reflexes. This is a useful test to assess ocular
alignment and rule out abnormal ocular media, such as cataracts. The test should be performed in a darkened room with the examiner approximately 18 to 24 inches from the patient. Both red reflexes should be simultaneously assessed and compared using the direct ophthalmoscope. If an abnormality exists in the ocular media, the red reflex will be asymmetric or a white reflex may be present. An abnormal reflex may also signify a high refractive error or a small strabismus. The red reflexes should be equal and symmetric. Ophthalmoscopy also permits direct visualization of the fundus and optic disc. The fourth test checks the extraocular movements in the cardinal positions of gaze (Fig. 41-15). The results of these tests provide a good basis for determining whether there is any misalignment present. This is an important screening for all family physicians to learn, because early intervention can help improve the overall visual and binocular status of the patient.
Table 41-5 lists several forms of strabismus. For congenital esotropia, surgery is the primary treatment for this condition and is performed between 6 and 12 months of age (Fig. 41-16). Esotropia may also be related to refractive error and managed with spectacle correction (Figs. 41-17 and 41-18). Large deviations of exotropia and hypertropia are also managed surgically (Figs. 41-19 to 41-23). (See online text for further discussion.)
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