The Microscope

The operating microscope is the neurosurgeon’s most important tool. It illuminates the operative field, magnifies anatomy, and gives constant visual feedback. Skillful dissection depends on seeing all relevant anatomy and controlling every maneuver, and the microscope empowers us by enhancing sight well beyond the physiologic limit of unaided eyes. However, this unwieldy piece of equipment must be adapted to our individual anatomy and move fluidly with our movements. A finely tuned microscope extends visual perception with imperceptible effort. Therefore, the microscope must be tuned before every case, checking the microscope stand, mouthpiece, oculars, chair, and foot pedals.

The microscope can move fluidly with the neurosurgeon because the counterbalancing stand makes it weightless. Brakes in the stand’s joints hold the microscope’s position, but the microscope floats when the brakes are released. The microscope must be balanced precisely to keep it from drifting, tipping, or feeling heavy. The microscope balances optimally when the stand’s vertical and horizontal beams are at right angles. A stand that overreaches or collapses on itself will drift despite being balanced properly. Therefore, the stand should be positioned beside the patient’s head at an appropriate site and distance to achieve this right angle.

The Mouthpiece

Some who have used the mouthpiece abandon it after a short trial, saying that it is awkward, uncomfortable, and causes gagging. Those who persist in using it find that they can no longer operate without it. The mouthpiece unlocks the microscope’s potential, allowing the neurosurgeon to constantly focus and refocus without using hands, thereby increasing operative pace and efficiency. If the microscope is the tool that enables neurosurgeons to see, then the mouthpiece is the tool that enables them to see clearly. It releases the stand’s vertical brakes to make fine adjustments that bring the operative target into focus. The target depth changes constantly during the dissection, particularly at high magnification, and the microscope must follow. The mouthpiece enables these adjustments to be made with small head movements without having to put down instruments, change the focal length, or interrupt the rhythm of surgery. The head moves naturally to areas of interest, whereas foot movements on the pedals are not a natural way to refocus. The mouthpiece is not meant for major changes in the microscope’s orientation; these movements still require the use of two hands to release all brakes.

The mouthpiece must be carefully fitted with the fixed, upper plate of the mouth switch lying below and in contact with the upper two front teeth. Each neurosurgeon has a unique distance between the interpupillary line and the inferior edge of the front teeth. Another setting adjusts the anterior-posterior position so that it sits comfortably in the mouth. The switch is activated by biting the lower plate with the lower teeth, thereby releasing the stand’s brakes and moving the microscope. The line of sight into the ocular lenses must be maintained with both the biting motion and the head movement to maintain visual feedback; the mouthpiece is not properly set if biting the mouth switch compromises vision. Releasing the mouth switch relocks the microscope into the desired position.

Ocular lenses are adjusted for interpupillary distance, length of the tube, and diopters. An inaccurate interpupillary setting can compromise binocular vision. A tube length that is too long can shadow or constrict the visual field, and one that is too short can rub the nose against the ocular’s bridge. The diopter setting is individualized to avoid visual straining during long procedures.

The Chair

The chair should roll freely in the space under the microscope. Subtle shifts in body position are necessary to align the hands to the surgical field and keep them relaxed. Power cords and cables are routed behind the chair to keep them from getting in the wheel track and limiting the chair’s mobility.

The Foot Pedals

Microsurgery is performed best at high magnification, requiring constant zoom adjustments with the foot pedal while keeping the hands free to dissect. One foot is dedicated to controlling the microscope’s zoom, and the other is dedicated to controlling bipolar cautery. Good chairs have integrated zoom and focus controls that minimize clutter underfoot. Otherwise, the microscope’s foot box is placed at the base of the chair. The mouthpiece minimizes the need for focusing with the foot control. The pedals should be positioned comfortably underfoot to be ready at any time and to relax the legs, which helps keep the body core and hands relaxed.

These adjustments and settings are a prerequisite for any aneurysm operation. Performing the various steps described here becomes routine, and they can be done quickly. When fully adjusted, the microscope is tuned to our bodies and moves fluidly with our movements, which keeps the focus on dissecting and clipping the aneurysm.