A non-inferiority, crossover, randomized controlled trial will be conducted for this purpose. Participants will be randomly assigned to receive either a) microdrops on their first and standard drops on their second screening examination a week later (M/S group), or b) standard drops first and microdrops a week later (S/M group). Microdrops (6.5 μL) will be instilled using a calibrated micropipette, while standard drops (28-34 μL) will be instilled directly through the commercially available plastic multi-dose mydriatic dropper bottle.
The purpose is to test the hypothesis that microdrop instillation of combined phenylephrine 1.67% and tropicamide 0.33% eyedrops causes at least equal mydriasis compared with standard drop instillation of the same mydriatic regimen, which constitutes routine care for pupil dilation during retinopathy of prematurity (ROP) screening in our neonatal intensive care unit. Comparison, also, will be made to the subsequent adverse events and the drug concentration in peripheral blood samples.