PCO = posterior capsular opacity. This occurs after cataract surgery due that membrane forms the new lens fibers in the normal lens. Once the lens is removed we don't want new lens fibers as they cause PCO. So surgeons scrape and polish the posterior capsule and IOL manufacturers have modified IOL edges to prevent lens fibers from growing over PC and turning cloudy. Prior to about 2001 more than 90% of people got significant PCO and needed yag capsulotomy. After 2001 due to improvement just mentioned the % is 15-20% I did two Yag capsulotomies in the morning clinic. No way to predict how fast they will grown, some don't progress, ERM= epiretinal membrane not effect PCO but whatever reduced or distorted vision is due to ERM will not be helped by Yag laser.