This is a machine used prior to cataract surgery to help determine the implant to use during surgery. With cataract surgery, the cloudy cataract lens inside the eye is removed and must be replaced by a new lens implant. These implants come in different prescriptions, just like glasses or contact lenses. To help determine the proper implant prescription, the IOL-Master measures the length of the eye and the curvature of the cornea. This technology has removed much of the operator error with implant calculations (these used to be done by hand and were thus prone to mathematical or transcription errors). The IOL-Master has some limitations with cloudy cataracts and can’t always measure through dense opacities in the lens. If this machine is unable to obtain a good eye measurement, a different (more involved) technique called immersion ultrasound (A-scan) can be used to measure the length of the eye prior to surgery.