Inclusion criteria for normal control subjects were as follows: age 7–100 years vision correctable to within 20/50 bilaterally intact ocular motility and ability to provide a complete ophthalmological, medical, and neurological history as well as medications/drugs/alcohol consumed within the 24 hours prior to tracking. Written informed consent was obtained from all subjects prior to participation.Ĭontrol subjects were employees, volunteers, visitors, and patients at the investigating institutions. Subjects were recruited in accordance with institutional review board policy. We performed prospective measurement of that ratio in patients with confirmed CN III and VI palsies (positive controls) and in stable, awake neurosurgical patients undergoing procedures for supratentorial and infratentorial mass lesions. Patients with infratentorial lesions or other pathological entities impacting CN VI would be expected to have increased vertical/horizontal eye movement ratios. Patients with supratentorial lesions resulting in uncal mass effect who are assessed with this novel eye-tracking algorithm would be expected to demonstrate decreased vertical/horizontal eye movement relative to normal controls. We then compared the ratio of vertical versus horizontal eye movement for normal subjects to subjects with known pathological conditions of these nerves who were recruited from the ophthalmology and neurosurgery clinics. To test this hypothesis we tracked eye movements in 157 normal control subjects to establish a range for normal eye movement ratios with our algorithm. We hypothesized that our eye-tracking algorithm would detect clinical and subclinical palsies of the abducent and oculomotor nerves. 26 It is known to be susceptible to myriad disorders, including ischemia, diabetes mellitus, trauma, and hydrocephalus. The abducent nerve exits the ventral pontomedullary junction, courses through the prepontine cistern, and travels through the Dorello canal into the cavernous sinus before innervating the lateral rectus muscle of the orbit, lateralizing the pupil. A CN III palsy in the context of trauma or stroke and evidence of radiographic transtentorial herniation may potentially be an indication for neurosurgical intervention. Among other functions, the oculomotor nerve innervates the superior and inferior recti muscles of the orbit, rotating the eyeball up and down. 1 A clinical indicator of transtentorial herniation is palsy of the oculomotor nerve due to compression by the uncus as the nerve courses along the tentorial notch after its exit from the pontomesencephalic junction and prior to its entry into the cavernous sinus. The CN III is classically impacted by supratentorial mass effect, which may lead to transtentorial herniation. Because the method does not entail spatial calibration, it does not compensate for impaired motility and can be used in patients who do not follow commands, such as those with aphasia, patients in a persistent vegetative state, and small children. Our algorithm sets the amount of time that the eye should be moving in any given direction essentially constant and then quantitates the distance that it travels. By using elapsed time analysis, our method should be able to detect impaired ability to move the pupil relative to normal controls. The aperture moves around the monitor periphery at a known rate so that the position of the pupil can be analyzed at any given time based on the time elapsed since the start of the video. We developed a novel algorithm for eye tracking performed while subjects watch a music video playing inside an aperture on a computer monitor. Early detection of subclinical CN palsy in awake patients thus might prove useful for assessment of patients with hydrocephalus, possible shunt malfunction, or traumatic brain injury (TBI). T he cranial nerves (CNs) are known to be susceptible to changes in intracranial pressure (ICP) due to mass effect or hydrocephalus.
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