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J.P. Levine, M. Keshet; Comparing Change in Intraocular Pressure After Dilation With Tropicamide Alone versus Tropicamide and Phenylephrine . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4465.
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To measure the change in intraocular pressure in normal eyes dilated with tropicamide 1% alone versus those dilated with tropicamide 1% and phenylephrine 2.5%.
Intraocular pressure (IOP) was measured in 48 eyes of 24 subjects using Goldmann applanation tonometry. Patients with a known diagnosis of open angle glaucoma, a shallow appearing anterior chambers on slit lamp examination, a peripheral iridotomy, or an anterior chamber intraocular lens in either eye were all excluded. Patients on any IOP lowering medication were also excluded. Following a baseline IOP measurement for each subject, both eyes received one drop of tropicamide 1% while one randomly selected eye also received one drop of phenylephrine 2.5%. The intraocular pressure measurements were repeated 30–40 minutes after dilation. Differences between the IOP change in the tropicamide group (Group T) versus the tropicamide plus phenylephrine group (Group P) were analyzed using the paired t–test. Linear regression analysis was used to compare the change in IOP with baseline IOP. As in previous studies, a 6 mmHg change in IOP was considered clinically significant while a P value < 0.05 was considered statistically significant.
There were 24 eyes in Group P and 24 in Group T. The average IOP (mmHg) for Group T was 15 ± 2.9 at baseline and 14.7 ± 3.0 after dilation ( P = 0.1). The average IOP for Group P was 15.5 ± 3.7 at baseline and 14.7 ± 3.7 after dilation (P = 0.4). The IOP change ranged from –6 – +4 for eyes in Group P and from –4 – +4 in Group T. The difference in IOP change between fellow eyes for a given subject ranged from 0 – 6 and was not statistically significant ( P = 0.3). Out of the 48 eyes studied, none had an increase in IOP > 4. Out of the 24 eyes from Group P one had an IOP change of –6. There was an inverse correlation between baseline IOP and the increase in IOP for the group as a whole (n = 48, r = –0.34, P < 0.02).
This study demonstrates that dilating non–glaucomatous eyes with phenylephrine and tropicamide has no greater effect on IOP than dilating with tropicamide alone. For the group as a whole, lower baseline IOP significantly correlated with a greater increase in IOP. Further study is necessary to investigate whether or not this correlation holds true in eyes with ocular hypertension or glaucoma.
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