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The aim of this study was to evaluate the effect of estrogen on the vascular resistance of the central retinal artery in postmenopausal women, compared with placebo, using transorbital ultrasound with Doppler velocimetry.We performed a prospective, randomized, triple-blinded placebo-controlled study. A total of 51 healthy postmenopausal women (follicle-stimulating hormone, >40 IU/L) with a mean (SD) age of 53.6 (4.8) years were studied. Participants were randomly allocated into two groups: placebo (n = 23) and estrogen (0.625 mg conjugated estrogens; n = 28). Transorbital Doppler velocimetric ultrasound was performed before and after treatment in sitting and supine positions.The mean age was similar in both groups. The pulsatility index of the central retinal arteries had a significant decrease after the use of estrogen, when women were evaluated in the sitting position. Women who received placebo did not show any difference in pulsatility index of the central retinal arteries after treatment. When the same comparison was done with participants in the supine position, no difference was observed in either group.Our study demonstrates that estrogen reduces the vascular resistance of the central retinal artery in postmenopausal women because of a vasodilatory effect.