To compare choroidal thickness in patients with regressed retinopathy of prematurity (ROP) with healthy controls using enhanced depth imaging optical coherence tomography (EDI OCT) METHODS: Twenty-four children and young adults (41 eyes) with regressed ROP≥stage 3 had undergone EDI OCT with Spectralis FD-OCT as part of their clinical record. Their refraction, best-corrected visual acuity, and ophthalmoscopic findings were recorded. Corresponding data was collected prospectively from 33 healthy controls (58 eyes) who had been born at term. Choroidal thickness was measured independently by two observers subfoveally and at 1500 μm nasal and temporal to the fovea using EDI OCT.Mean subfoveal choroidal thickness, adjusted for refraction, was 271.1 μm (95% CI, 247.8-294.5) in the ex-ROP group, which was significantly thinner than 327.4 μm (95% CI, 293.8-360.9) in controls (P=0.008). Similarly, mean adjusted temporal choroidal thickness was 257.2 μm (95% CI, 240.2-274.2) in ex-ROP's vs 320.5 μm (95% CI, 288.6-352.3) in controls (P=0.001). There was no statistically significant difference in the nasal measurement. In the ex-ROP group, there was no significant correlation between subfoveal choroidal thickness and gestational age (r(s)=0.16, P=0.46) or birthweight (r(s)=0.03, P=0.90). In eyes without copathology in addition to regressed ROP (29 eyes, 19 patients), there was no significant correlation between subfoveal choroidal thickness and visual acuity.Our findings of thinner subfoveal and temporal macular choroidal thickness in regressed ROP support the case for choroidal involvement in the pathogenesis of this condition.