Development of a Fiber-Optic Optical Coherence Tomography Probe for Intraocular Use.

PURPOSE: To evaluate the performance of a newly developed 23-G optical coherence tomography (OCT) probe in animal and human eyes. METHODS: The probe is a side-imaging OCT device with a scanning beam set 43° to the optical axis and a working distance of 1.5 to 2.0 mm. The performance of the OCT probe was tested during vitrectomy in porcine cadaver eyes and rabbit eyes in situ. Optical coherence tomography images of a normal retina, retinal break, optic disc, pars plicata of the ciliary body, and intraoperative surgical manipulations were recorded. The probe was also tested in a pilot study of clinical cases; intraoperative real-time OCT imaging was performed in three patients, including a 56-year-old woman with an epiretinal membrane. RESULTS: The OCT probe was able to delineate intraocular tissues, including the posterior retina, and even the most peripheral pars plicata in animal eyes. The OCT probe also successfully delineated intraoperative surgical maneuvers such as membrane peeling and the minute structures of the vortex veins, ora serrata, and vitreous incarceration in the scleral incision from the trocar with sufficient resolution in the patients. There were no complications resulting from its use. CONCLUSIONS: The ability of this new 23-G OCT probe to obtain images of intraoperative manipulations from the most peripheral tissues in animal and patient eyes suggests that it could enable surgeons to make better decisions during the course of intraocular surgery.

Detection and prediction of drowsiness by reflexive eye movements.

A reliable predictor of drowsiness using objective measures is desirable for machine and vehicle operations in which human errors may cause fatal accidents. We have evaluated the Vestibulo-Ocular Reflex (VOR) as a possible predictor of drowsiness. The VOR is a compensatory eye movement that stabilizes retinal image during head motion, and is inevitably induced by vibration in a car running on the road. We employed an uneventful driving simulation (DS) featuring vibration stimulation to induce both drowsiness and VOR in healthy human subjects. VOR performance was characterized by its gain and variability, and evaluated in relation to the subjects' drowsiness. A significant decrease in VOR gain and increase in variability accompanied subjective sleepiness, with the changes occurring before subjects became aware of sleepiness. From this finding, we developed a reliable method (88.9% accuracy) to predict oncoming sleepiness using changes in VOR performance as a cue.

Characterization of iris pattern stretches and application to the measurement of roll axis eye movements.

Eye movements are utilized in many scientific studies as a probe that reflects the neural representation of 3 dimensional extrapersonal space. This study proposes a method to accurately measure the roll component of eye movements under the conditions in which the pupil diameter changes. Generally, the iris pattern matching between a reference and a test iris image is performed to estimate roll angle of the test image. However, iris patterns are subject to change when the pupil size changes, thus resulting in less accurate roll angle estimation if the pupil sizes in the test and reference images are different. We characterized non-uniform iris pattern contraction/expansion caused by pupil dilation/constriction, and developed an algorithm to convert an iris pattern with an arbitrary pupil size into that with the same pupil size as the reference iris pattern. It was demonstrated that the proposed method improved the accuracy of the measurement of roll eye movement by up to 76.9%.

The pupil as a possible premonitor of drowsiness.

Prediction of drowsiness based on an objective measure is demanded in machine and vehicle operations in which human errors may cause fatal accidents. Currently we focused on the pupil of the eye which is controlled by the autonomic nervous system, and easily observable non-invasively from the outside of the body. We employed uneventful driving simulation to induce drowsiness of human subjects, and an anti-saccade task to evaluate their cognitive and motor performance. First we confirmed that pupil diameter fluctuates with large amplitude at low frequencies when the subject is aware of his/her drowsiness as reported previously. During this period, the latency of anti-saccade initiation was elongated and varied. We then found that prior to this fluctuation, pupil diameter decreases gradually in most subjects, and they were not aware of sleepiness during this period. We conclude that this monotonic gradual miosis can be a reliable premonitor of drowsiness.

Comparative physiology of postnatal developments of cardiopulmonary reflex.

We analyzed and compared the frequency components of the heart rate variability in human neonate, rat, white chicken, turtle, and frog during the developments. Frequency analysis with autocorrelation-FFT method was applied to the heart rate and respiration waves to calculate the respiration induced frequency component in the power spectra. The comparative analysis of the cardiopulmonary reflex in human and rat neonates resulted in a similar developmental progress. In case of human immature neonate, respiration induced frequency component in the heart rate variability was negligible at day-old 0, and significantly increased at postnatal 1 month. The rat neonates also showed no or negligible respiration induced components until days 8 and it became significant approximately postnatal 1 month. The white chicken also indicated negligible respiration induced component before and a few days after hatching, and became significant after 38 days-old (17 days post hatching). However the frog and the turtle indicated no clear response in entire periods of the development even in adult. The results strongly suggested that gravity may be a possible essential factor of the appearance of the post natal development of the cardiopulmonary reflex.