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Tropicamide Eyedrops Cannot Be Used for Reliable Diagnosis of Alzheimer's Disease

      Objective

      To evaluate the mydriatic effect of tropicamide eyedrops as a diagnostic test for Alzheimer's disease.

      Material and Methods

      In a double-blind, placebo-controlled study, we assessed pupillary responses in 22 normal control subjects, 23 patients with probable Alzheimer's disease, 4 patients with isolated memory difficulty, and 6 patients with nonAlzheimer's dementia. Three separate studies were performed, the second and third on a subset of the original group. With use of infrared binocular pupillography, after 5 minutes of dark adaptation, we averaged pupil size during a 1-minute interval for baseline determinations. We then instilled 0.01 % tropicamide into one eye. In the first two studies, we averaged pupil size for a 1-minute period at 5-minute intervals for 30 minutes, followed by a pupil light reflex test. In the third study, we measured pupil size every 5 minutes for 45 minutes and omitted the light reflex test.

      Results

      No significant difference was noted in pupil dilatation between normal subjects and patients with Alzheimer's disease and between patients with non-Alzheimer's dementias and the Alzheimer's disease group in all three studies. Furthermore, on reperformance of the test in the same patients, more than 50% changed from a group above or below 13% pupil dilatation (a cutoff reported to distinguish Alzheimer's disease from normal control subjects) to the opposite group.

      Conclusion

      Results of this study indicate that pupil measurement after instillation of tropicamide cannot be used as a reliable diagnostic test for Alzheimer's disease. Moreover, test-retest reliability with use of dilute tropicamide eyedrops is questionable.
      AD (Alzheimer's disease), MMSE (Mini-Mental State Examination)
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      Linked Article

      • The Eyes Don't Have It in Alzheimer's Disease
        Mayo Clinic ProceedingsVol. 72Issue 6
        • Preview
          In 1994, Scinto and colleagues1 proposed that pupillary responses to dilute tropicamide, a cholinergic antagonist, could be used as a noninvasive diagnostic test for Alzheimer's disease (AD). In an article in Science that generated a flurry of media excitement, the authors reported a pronounced hypersensitivity of pupil dilatation to dilute tropicamide in their patients with clinically diagnosed or suspected AD but not in a group of healthy elderly control subjects. The difference in pupillary responses between the groups was robust enough to distinguish among individuals.
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