<prompt> Minus cylinder lenses are prescribed because ofCheaper to produce and distributePreferred due to meridional aniseikoniaReduces minificationCauses less coma and trefoil  <response>: Aniseikonia is defined as a condition wherein, images projected to visual coex from the two retinae are abnormally unequal in size andor shape. Up to 5 aniseikonia is well tolerated. Meridional aniseikonia - refractive differences only occur in one meridian In a plus cylinder the lens is ground on the anterior surface of spectacle and thus there is more scattering and distoion of image as compared to a minus cylinder which is ground on posterior surface. Thus a minus cylinder is more comfoable to the patient and hence all prescriptions are written with a minus cylinder. Extra edge: - In pt with monocular aphakia wearing contact lens, of aniseikonia is approximately 8 - In aphakia, Aniseikonia is decreased with contact lens than glasses. Hence, IOL implantation is preferred management NOTE- Aneisokonia with IOL- 1-3 