 Adequate pupil dilatation was needed for screening and treatment of retinopathy of prematurity ROP in premature infants.In general clinical practice, mydriatic drugs were instilled many times until the pupil reached the maximum size. However, poor mydriasis were found in many eyes despite maximum instillation was used. From the clinical observation, we found the packing of mydriatic drugs in lower conjunctival fornix was much more effective to dilate the pupil than instillation in some patients. The purpose of this study was to compare the mydriatic effect of 2.5 phenylephrine and 1 tropicamide by conventional instillation and lower conjunctival fornix packing in premature infants. 