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Lausanne, Switzerland-Disorders of accommodation can be caused by disruption of neuroregulation. While many patients present with an insidious and mild accommodative insufficiency, often accompanying a systemic illness, the acute onset of severe and bilateral loss of accommodation is a more serious condition and may indicate the presence of a midbrain lesion.
Unilateral accommodative loss most often results from a lesion of a peripheral nerve, which is not likely to involve a midbrain lesion, according to Aki Kawasaki, MD, who spoke about the neurologic causes of accommodative disorders.
The two main categories of accommodative disorders are accommodative insufficiency and accommodative spasm.
"In the category of accommodative spasm, most cases are functional (psychogenic) in origin or develop after a head trauma," she continued.
Insufficient accommodationDr. Kawasaki presented a typical case. A 32-year-old woman complained of sudden difficulty reading out of her right eye. She held the near test card about 2 feet from her right eye to be able to read it, compared with 6 inches from her left eye, indicating insufficient accommodation in her right eye.
In addition, anisocoria was noted. Her right pupil was large and unreactive to light. There was no evidence of ocular nerve palsy or intraocular inflammation, but careful slit-lamp examination revealed sectoral palsy of the iris sphincter. Additionally, the right pupil demonstrated cholinergic supersensitivity to dilute pilocarpine. Thus, in this patient with acute unilateral accommodative insufficiency, the cause was found to be acute Adie's tonic pupil.
Detecting and diagnosing accommodative insufficiency can be difficult because patients present with vague symptoms. They may complain of ocular fatigue or eye strain, periorbital aching or generalized headaches, and Dr. Kawasaki noted that accommodative insufficiency should be considered in the differential diagnosis of cases such as these.
When attempting to determine the origins of an accommodative insufficiency, Dr. Kawasaki advised that ophthalmologists ask three questions:
"Mild and bilateral accommodative insufficiency may accompany an acute illness, and this is a common scenario with children who have developed a viral syndrome," she said. "This accommodative insufficiency is a nonspecific manifestation of the illness, it does not represent damaged neural pathways, and it comes on insidiously and will eventually resolve as the patient's condition improves."
In marked contrast is the scenario of a healthy young adult or child who suddenly cannot read. These patients are very aware of and worried by the sudden loss of their near vision. The pupils in these patients are usually poorly reactive to light, but in some cases, the pupil light reflex is normal.
"In the case of acute and bilateral accommodative insufficiency, the physician must consider a midbrain lesion," she emphasized.
Two particularly common lesions in children and young adults are acute hydrocephalus and tectal tumor. In both cases, the dorsal rostral midbrain is disrupted in the regions where the integrating and output centers for accommodation and pupilloconstriction reside, she stated.
From a neurologic standpoint, unilateral accommodative insufficiency usually indicates the presence of a peripheral nerve lesion, according to Dr. Kawasaki. And be- cause the neural impulses for accommodation and for pupillary constriction are carried in the same peripheral nerve pathway, unilateral loss of accommodation is nearly always associated with loss of pupilloconstriction.