Effect of Pharmacological Mydriasis on the Intraocular Pressure in Eyes with Filtering Blebs Compared to Normal Eyes: A Pilot Study

AIM: To test the effect of pharmacological mydriasis on intraocular pressure (IOP) in eyes with functioning blebs compared with normal eyes. PATIENTS AND METHODS: The cross-sectional study included 39 eyes, of which 19 eyes had filtering trabeculectomy blebs (group A), and 20 eyes with no previous surgeries (group B). IOP was measured using the Goldmann applanation tonometer before, and 30 min after the application of tropicamide 1% eye drops. RESULTS: In group A eyes, the IOP level changed from 13.68 ± 3.4 mmHg before pupillary dilatation, to achieve a level of 11.95 ± 3.03 mmHg following mydriasis, with an average IOP drop of 1.73 mmHg (p < 0.0001). On the other hand, the pre-dilatation IOP in group B eyes was 15.9 ± 3.00 mmHg, had increased after mydriasis to 18.4 ± 2.9 mmHg, with an average rise of 2.5 mmHg (p < 0.0001). The difference in IOP change following mydriasis between both groups was significant (p < 0.0001). CONCLUSION: Surprisingly, pharmacological pupillary dilatation resulted in a reduction of IOP in eyes with successful trabeculectomy, which is different from the usual effect of raising the IOP as in the control group. This effect has not been previously studied.