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G. T. Liu, J. Hillelsohn, M. B. Hymowitz, A. Shrivastava, J. S. Schultz; The Differential Pupillary Response to 2.5% Phenylephrine in Patients Taking Tamsulosin. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2447. doi: https://doi.org/.
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Intraoperative floppy iris syndrome (IFIS) is a syndrome associated with tamsulosin use. Pathologically, it has been suggested that in patients taking tamsulosin, the size of the pigment granules in the melanocyte cytoplasm is irregular, the majority of the iris dilator muscle cells are markedly vacuolated, and no nerve terminals innervating the smooth muscle are present. We are investigating if 2.5% phenylephrine stimulation of pupil dilation above 1% tropicamide is less effective in tamsulosin patients than in control patients. In addition, we are determining whether there is progression of smooth muscle dysfunction in the tamsulosin group.
Subjects currently taking tamsolusin and age-matched controls were recruited in both the Urology and Ophthalmology clinics. Pre-dilation pupil measurements were taken, and subjects were dilated with 2.5% phenylephrine and 1% tropicamide in the right eye (OD) and 1% tropicamide in the left eye (OS). Forty minutes after dilation, pupil size was measured using a Corneal Topographer (TopCon®). Pupil dilation size was then compared OD to OS.
39 tamsulosin subjects and 44 controls completed the study. The average OD-OS difference was 0.61± 0.4. This represents the dilation activity of phenylephrine (alpha-1 adrenergic stimulation of dilator muscle) above tropicamide (antagonism of constrictor muscle). In the controls we found OD-OS difference to be 1.11± 0.45. A T-test comparing these 2 values yielded p < .001. In addition, a correlation between smooth muscle dysfunction and length of time on tamsulosin was observed. Patients who took tamsulosin less than one month had an average OD-OS difference of 0.85 ± 0.5. Patients who were on tamsulosin more than one month had an average OD-OS difference of 0.52 ± 0.32. A Mann-Whitney test yielded p=0.0089.
Patients taking tamsulosin show markedly less dilation with phenylephrine than the normal population. The degree of dysfunction due to tamsulosin may be assessed by the dilation response to phenylephrine. Additionally, the length of time of tamsulosin use may correlate with the degree of iris dysfunction. :
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