Tegaderm and Visual Evoked Potentials

Corneal injury is the most frequent ocular complication during general anesthesia as the patient does not have the ability to blink or keep their eyes completely closed. Lagophthalmos is defined as the inability to close the eyelids completely. Blinking covers the eye with a thin layer of tear fluid, thereby promoting a moist environment necessary for the cells of the exterior part of the eye. The tears also flush out foreign bodies and wash them away. This is crucial to maintain lubrication and proper eye health. If this process is impaired, as in lagophthalmos, the eye can suffer abrasions and infections. Lagophthalmos leads to corneal drying and ulceration. Several strategies are widely used to try and prevent corneal abrasions, although there is a paucity of recent studies to support one method over another. If a patient is to receive general anesthesia the common practice is to lubricate the eyes and tape them closed.

One of the ways to prevent lagophthalmos is to use tegaderm. A tegaderm is a thin transparent barrier customarily used to protect wounds and catheter sites. The tegaderm has several advantages including breathability and conformity to skin. In the operating room it is place over the patients' eyelids to keep the eyes closed and prevent injury.

During surgical removal of a pituitary adenoma, conduction in the anterior visual pathways is monitored by continuous recording of visual evoked potentials (VEP). The VEP tests the function of the visual pathway from the retina to the occipital cortex. It measures the conduction of the visual pathways from the optic nerve, optic chiasm, and optic radiations to the occipital cortex. This method is performed by the application of special goggles over the eyes. These goggles placed over the tegaderm are noninvasive and have an embedded flashing diode for delivery of visual stimuli. Changes of the occipital EEG (as recorded intraoperatively on a computer program by a neurophysiology technician) can be observed under stimulation of light in attempt to localize structures or possible damage of those structures in the primary visual pathway. This is helpful to the neurosurgeon who aims to avoid compression and injury to the optic nerve.

These goggles have been used routinely over years for visual pathway monitoring during pituitary tumor resection. Nevertheless there is a question if the application of tegaderm affects VEP monitoring. By measuring visual evoked potentials before and after tegaderm placement, we hope to determine if there is a change in evoked potential data due to placement of tegaderm. On other words, we will be able to identify if tegaderm placement affects visual evoked potential data reliability.

Experimental Plan:

The investigators will approach all patients over the age of 18 undergoing transsphenoidal pituitary tumor resection with visual evoke potential monitoring.The plan is to include 40 patients here at University Hospital. If patients are agreeable all subjects will have their VEP measured before and after routine tegaderm application. Visual evoked potential monitoring will be conducted as routinely done by the neurophysiology technician. Data will be collected from neurophysiologist report and then analyzed for latency and amplitude before and after tegaderm application. As a matter of routine, the full monitoring report becomes a component of the patient's medical record.