<prompt> Prevalance of cataract at one point of time can be determined by:Longitudinal studyCross-sectional studySurveillanceCohort study  <response>: Ans is b i.e. Cross-sectional study RepeatCross-sectional or Prevalence study - in cross-sectional studies, we survey several individuals at one point in time and collect information on health status, health-related behaviour, and other exposure factors. In this way we can estimate the burden of disease in a group of individuals and try to estimate whether a particular exposure is linked to a disease or health outcome. 