A handmade eye movement monitor using a piezoelectric device during transsphenoidal surgery

We describe a handmade eye movement monitor featuring a piezoelectric device for use during transsphenoidal surgery (TSS). The sensor consists of a piezoelectric device, condensers, resistors, and several inexpensive parts. Eyeball movements elicited by surgical manipulations during TSS for cavernous sinus tumor are detected by small disc-shaped sensors taped to the eyelids. The responses could be monitored as sharp waves on an electroencephalograph. After we started using this monitor, both the incidence and the severity of cranial nerve injuries during TSS for cavernous sinus tumor decreased. Our device is especially useful at operations to remove functioning pituitary adenomas invading the cavernous sinus and contributes to their favorable endocrine outcomes. None of our patients manifested the postoperative swelling of the eyelids or conjunctival congestion generally seen in patients subjected to the insertion of needle sensors for the acquisition of electromyograms of the extraocular muscles, which is widely used during surgery to identify the cranial nerves responsible for eye movement. Our monitor is less expensive and easier to use than any commercially available sensor devices. As our method does not require the insertion of needle sensors, it is less invasive than electromyography of the extraocular muscles.