B scan is an imaging modality which uses sound energy to capture image of posterior segment. It is a non-invasive procedure used to see the posterior segment in case of opaque media like dense cataract, vitreous haemorrhage, which precludes direct view of posterior segment by ophthalmoscopy. Like OCT, it is a safe investigation entirely free from side effect or complication.
Technique of doing B scan: At first few drops of anesthetic eye drops is given in your eye. B scan can be done in sitting or lying down position after anesthetising your eyes. The ophthalmologist performing ultrasonography takes the ultrasound probe and put some coupling agent usually a jelly like substance upon the probe and put the probe on your eyeball. He will ask you to see in different directions to examine different quadrant of eyeball and take the image on the computer monitor and analyse them.