Purpose: To introduce a new in vivo quantitative measurement of posterior capsule opacification (PCO) after extracapsular cataract surgery and also to analyze the correlation between opacification density and the patient’s visual acuity. Methods: Prospectively, the opacification density value in the central 3-mm portion of the posterior capsule was quantitated by means of an area densitometry with the Scheimpflug photography system (EAS-1000). The EAS-1000 examination was performed on 40 eyes with clinically significant PCO both before and after undergoing Nd:YAG laser posterior capsulotomy, and on 10 eyes without PCO. The correlation between the opacification density value and the visual acuity was analyzed with a linear regression analysis. Results: The mean opacification density values ± SD were 48.8 ± 29.5 computer-compatible tapes (CCT) steps in the PCO group before capsulotomy, 15.5 ± 7.8 CCT steps in the PCO group after capsulotomy, and 12.9 ± 4.9 CCT steps in the non-PCO group. The mean opacification density value in the PCO group before capsulotomy was significantly greater than that in the PCO group after capsulotomy or than that of the non-PCO group. A linear regression analysis determined that the opacification density value also correlated well with the visual acuity (R 2 = .808). Conclusions: We have established a new in vivo quantitative measurement of PCO. Because the opacification density value obtained by this measurement correlated well with the patient’s visual acuity, we consider this measurement to be useful in both the research and clinical management of PCO.