An optical instrument comprising adjustable magnifying lenses that greatly enlarge a small object under study – for example, an insect, blood cells, or bacteria. Some microscopes use electron beams to magnify minute objects such as chromosomes, crystals, or even large molecules. Optical microscopes are also used for MICROSURGERY when the area being operated on is otherwise inaccessible: for example, in eye and inner ear surgery; for the removal of tumours from the brain or spinal cord; and for resuturing damaged blood vessels and nerves.