This is the technology where sound waves are bounced off internal organs in order to examine human anatomy. Ultrasound is classically used in the examination of pregnant women, but the technology has some utility in ophthalmology as well. We use ultrasound to measure the length of the eyeball prior to cataract surgery. This measurement is called an A-scan ultrasound. Ultrasound is also useful for examining the eye in cases of vitreous hemorrhage – this is bleeding inside the eye that would otherwise block our view of the retina. We also use ultrasound to examine someone with an extremely dense cataract when our view is blocked by the cloudy lens. The ultrasound technology allows us to check for retinal detachments and other problems inside the eye before we subject someone to eye surgery.