12/10/2023 0 Comments One pupil dilated one normalHydroxyamphetamine (1%) may distinguish third from first- and second-order neuron etiologies. Third-order neurons may indicate carotid pathology or cavernous sinus lesions, or other abnormalities such as a lesion of the sixth nerve. Second-order neurons may be affected by the pathology of the lung, thyroid, sympathetic chain, and other causes. First-order neurons, which originate in the hypothalamus, may be affected by the hypothalamic, brain stem, cervical cord lesions, or other causes. The sympathetic pathway for mydriasis is long. Neither of the above agents is any value in the localization of the lesion in the sympathetic chain. Apraclonidine relies on super denervation sensitivity the minimum time is 36 hours, and it may take a week or longer. The normal pupil will be unchanged or slightly smaller. Apraclonidine has different findings thirty to 45 minutes after use, the abnormal eyelid will rise, and the pupil dilates to “reverse” the deficit. The pupil in Horner will minimally dilate or not dilate at all post-drop anisocoria of 0.8mm or more is positive. Cocaine blocks norepinephrine reuptake, resulting in pupillary dilation 45 to 60 minutes after use. Four percent to 10% of cocaine may be used as one confirmation of the diagnosis, and 0.5 to 1% apraclonidine is also used. No abnormality of pupillary constriction to light or near occurs. Dilation lag of the pupil in the dark may be helpful (greatest at 5 sec and less at 25 sec). Classic clinical findings are unilateral miosis, ptosis, and anhydrosis, which may be present in any combination and also be incomplete and difficult to ascertain. Horner syndrome (HS) involves an abnormally small pupil. If non-dilute pilocarpine fails to constrict the pupil, then the pupil is pharmacologically dilated. This previously was thought to help differentiate this form of mydriasis from TNP, but newer results cast some questions on this. Dilute pilocarpine will cause constriction in a dilated pupil of greater than two weeks due to denervation of the neuromuscular junction. The muscarinic agent pilocarpine, both dilute (0.05-0.15%) and non-dilute (1 to 2%), acts on the neuromuscular junction of the pupillary constrictor to cause miosis. A dilated pupil can be tested pharmacologically. The diagnostic approach first involves a careful ophthalmological examination. Generally, medications taken systemically will not cause anisocoria since both pupils will constrict or dilate but can cause anisocoria if the medication gets into only one eye. Small pupils may be caused by opiates, clonidine, organophosphates, pilocarpine, and prostaglandins. Dilating agents are nasal vasoconstrictors, scopolamine patches, glycopyrrolate deodorants, and various herbals, such as Jimson weed. Pharmacologic agents may cause both mydriasis, which is more common, and miosis. There are no cranial nerve palsies in tonic pupil cases. The diagnosis of a tonic pupil is usually clinical. Anatomical abnormalities may exist to cause this entity. The tonic pupil is often benign but may eventually become miotic. The affected pupil demonstrates a response with poor constriction to light but significantly better to accommodation this is referred to as light near dissociation. The pupil is large and more commonly occurs in young women. Tonic pupil, or Adie pupil, is a well-known cause of anisocoria. TNP is an example of a large, abnormal pupil. Magnetic resonance angiogram (MRA) has a threshold of 3 to 5mm and may indicate other pathologies. Diagnosis is radiological with computed tomogram (CT) or magnetic resonance imaging (MRI). Patients usually experience pain with this entity. The most well-known, life-threatening cause of TNP is a posterior communicating artery aneurysm causing pressure on the third nerve. Isolated pupillary dilation is not classically considered a third nerve palsy however, careful evaluation for subtle ptosis or abnormal extraocular movement is necessary to eliminate a TNP using this criterion. Important etiologies of anisocoria include third nerve palsy, Adie pupil, pharmacologic mydriasis, pharmacologic miosis, traumatic mydriasis, physiologic anisocoria, and Horner syndrome.Ī third nerve palsy (TNP) may spare the pupil or cause it to dilate with no reaction to light or convergence.
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