Neuro-ophthalmology Questions of the Week: Anisocoria – Horner Syndrome & Cocaine

1. How much anisocoria is necessary for the diagnosis of Horner’s syndrome to be made using cocaine drops?
a. 0.3 mm
b. 0.5 mm
c. 1.0 mm
d. 1.5 mm

2. What is the approximate mean odds ratio for the Cocaine pharmacologic test for Horner syndrome assuming a postcocaine anisocoria of at least 0.8mm?
a.   10:1
b.  100:1
c. 1,000:1
d. 10,000:1

3. Which of the following races may not dilate well with topical cocaine?
a. Asians
b. African Americans
c. Caucasians
d. Native Americans

4. Does the cocaine test for Horner syndrome result in a positive urinary test for cocaine?
a. Yes
b. No

Fig. 5.3. Right Horner’s Syndrome3


Correct Answers:
1. b. 0.5 mm
2. d. 10,000:1
3. b. African Americans
4. a. Yes


“… the cocaine test to be highly effective in separating normal subjects from patients with Horner’s syndrome. The chances of having Horner’s syndrome increased with the amount of cocaine-induced anisocoria. Through the use of logistic regression analysis, we determined the odds ratio of having Horner’s syndrome compared with not having it for each 0.1-mm increment of anisocoria measured after cocaine administration. A postcocaine anisocoria value of 0.8 mm gave a mean odds ratio of approximately 1050:1 that Horner’s syndrome was present (lower 95% confidence limit ° 37:1).  We found that simply measuring the postcocaine anisocoria provided a better prediction of Horner’s syndrome than taking the trouble to calculate the net change in anisocoria. Odds ratios should help the clinician decide if the result of a cocaine test is indicative of Horner’s syndrome.”1


“Of 24 normal patients 20 had less than 0.5 mm of asymmetry in response to two drops of 10% topical cocaine five minutes apart. “The development of anisocoria of more than 0.5 mm is necessary for the diagnosis of Horner’s syndrome to be made using cocaine.” Individual variation between the two normal eyes, “although minimal, does exist in white patients. No such conclusion could be drawn for black patients because of their overall lack of response to the application of topical cocaine routinely used. The cocaine test may not be appropriate for use in black patients to diagnose Horner’s syndrome.”2

In the only two black control subjects (with dark brown irises), the pupils dilated by only 0.3 mm or less, which was confirmed on repeated testing.” 3  

“Patients should be informed that their urine may test positive for cocaine, if assayed according to US federal guidelines and using the protocol employed in this study, up to 2 days after undergoing testing for Horner syndrome.”4

1. Critical evaluation of the cocaine test in the diagnosis of Horner’s syndrome – Kardon et al, – Arch Ophthalmol. 1990;108:384-387
2. The cocaine test in normal patients. Friedman JR, Whiting DW, Kosmorsky GS, Burde RM. Am J Ophthalmol. 1984;98:808-81
3. Cocaine Testing for Horner’s Syndrome. Click to Cure Cancer.
4. Duration of positive urine for cocaine metabolite after ophthalmic administration: implications for testing patients with suspected Horner syndrome using ophthalmic cocaine. Jacobson DM, Berg R, Grinstead GF, Kruse JR. Am J Ophthalmol. 2001 Jun;131(6):742-7.

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