Cataract surgery eye biometry test. IOL Master test being carried out on a patient prior to cataract surgery. This is a form of biometry, taking measurements of the eye, and is here being done prior to cataract surgery and the insertion of an IOL (intraocular lens). This non-contact, non-invasive test measures eye length and surface curvature. The results are displayed at left, with the positioning of the peripheral spots displayed here used to determine when to take the measurements by pushing the joystick button.