ND= negative dysphotopsia. You should have a surgeon that is familiar with both positive/negative dysphotopsia, the incidence of each with IOLs of different design and lens material. Sam Masket MD of Los Angeles CA is a world expert on PD and ND. He has designed his own IOL which is supposed to prevent ND. You and your surgeon might want to research it further especially if you have had ND since 2012. LINK http://www.ophthalmologytimes.com/modern-medicine-feature-articles/novel-iol-may-be-key-preventing-negative-dysphotopsia