Unequal Pupils (Anisocoria)

When anisocoria is greater in bright light than in dim light, the larger pupil cannot constrict properly. Causes include blunt trauma to the eye, open-angle glaucoma (p. 148), and impaired parasympathetic nerve supply to the iris, as in tonic pupil and oculomotor nerve paralysis. When anisocoria is greater in dim light, the smaller pupil cannot dilate properly, as in Horner's syndrome, which is caused by an interruption of the sympathetic nerve supply.

Tonic Pupil (Adie's Pupil)

A tonic pupil is large, regular, and usually unilateral. Its reaction to light is severely reduced and slowed, or even absent. The near reaction, though very slow, is present. Slow accommodation causes blurred vision. Deep tendon reflexes are often decreased.

Oculomotor Nerve (CN III) Paralysis

The dilated pupil (about 6-7 mm) is fixed to light and near effort. Ptosis of the upper eyelid and lateral deviation of the eye, as shown here, are often but not always present. (An even more dilated [8-9 mm] and fixed pupil may be due to local application of atropine-like agents.)

Horner's Syndrome

The affected pupil, though small, reacts briskly to light and near effort. Ptosis of the eyelid is present, perhaps with loss of sweating on the forehead of the same side. In congenital Horner's syndrome, the involved iris is lighter in color than its fellow (heterochromia).

Blind eye

Blind eye

Blind eye

Blind eye


Equal Pupils and One Blind Eye

Unilateral blindness does not cause anisocoria as long as the sympathetic and parasympathetic innervation to both irises is normal. A light directed into the seeing eye produces a direct reaction in that eye and a consensual reaction in the blind eye. A light directed into the blind eye, however, causes no response in either eye.

Small Irregular Pupils

Small, irregular pupils that do not react to light but do react to near effort indicate Argyll Robertson pupils. They are usually but not always caused by central nervous system syphilis.

See also Table 16-15, Pupils in Comatose Patients, p. 621.

TABLE 5-10 ■ Deviations of the Eyes

Deviation of the eyes from their normally conjugate position is termed strabismus or squint. Strabismus may be classified into two groups: ( 1 ) nonparalytic, in which the deviation is constant in all directions of gaze, and (2 ) paralytic, in which the deviation varies depending on the direction of gaze.

Nonparalytic Strabismus

Nonparalytic strabismus is caused by an imbalance in ocular muscle tone. It has many causes, may be hereditary, and usually appears early in childhood. Deviations are further classified according to direction:

Divergent Strabismus (Exotropia)

Convergent Strabismus (Esotropia)

cover-uncover test

A cover-uncover test may be helpful. Here is what you would see in the right monocular esotropia illustrated above.

Corneal reflections are asymmetric.

Paralytic Strabismus

Paralytic strabismus is usually caused by weakness or paralysis of one or more extraocular muscles. Determine the direction of gaze that maximizes the deviation. For example:

A Left Cranial looking to the right Nerve VI Paralysis

looking straight ahead looking to the left

Eyes are conjugate.

Esotropia appears.

Esotropia is maximum.

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