Prediction of changing cerebral blood flow by use of the conjunctival oxygen tension/arterial oxygen tension index

Orthogonal polarization spectral imaging of conjunctival microcirculation

PURPOSE

Orthogonal polarization spectral (OPS) imaging is an optical imaging technique that uses a handheld microscope and green polarized light to visualize the red blood cells in the microcirculation of organ surfaces. The purpose of this study was to evaluate whether OPS imaging can be used for the functional and morphological evaluation of microcirculation in the conjunctiva.

METHODS

To accomplish the aforementioned purpose, 21 eyes of 21 volunteer patients were examined. OPS images of the vasculature of the inferior conjunctiva and the nasal part of the bulbar conjunctiva were taken from each eye. The images were subsequently analyzed using a computer, and the following parameters were assessed: red blood cell velocity, blood vessel diameter, and functional capillary density. In addition, distinct qualitative aspects of the conjunctival microvasculature were characterized.

RESULTS

OPS imaging facilitated both the observation of red blood cells that were flowing through conjunctival vessels on a white background, and the measurement of other quantitative and qualitative microvascular parameters. Significant differences between several measures of the inferior and nasal bulbar conjunctival microcirculations were found, including differences in the configurations of the vessel segments, the number of vessel segments, the number of bifurcations, the mean diffusion distance, and the functional capillary density.

CONCLUSIONS

OPS imaging can be used to measure the diameters of microvessels, functional capillary density, and other parameters. Significant differences between the microcirculations of the inferior conjunctiva and the nasal bulbar conjunctiva were found, which indicates the necessity of using a standardized approach to examine the conjunctival vasculature. OPS imaging is suitable for both the functional and morphological evaluation of the conjunctival microcirculation.

Continuous oxygen monitoring of the conjunctiva in neonates

OBJECTIVE

To report the first use of a noninvasive conjunctival oxygen monitor in neonates. We wished to investigate if measuring the partial pressure of oxygen directly from the conjunctiva could track hyperoxia and hypoxia as well as, or better than, pulse oximetry. This has the potential to reflect brain oxygenation while yielding important systemic information.

STUDY DESIGN

Criteria standard.

SETTING

Tertiary care hospital neonatal intensive care unit.

PATIENTS

Ten newborns monitored with pulse oximetry.

INTERVENTION

The conjunctival oxygen monitor was studied for effectiveness and safety and compared to pulse oximetry.

RESULTS

The device remained on the eyes up to 120 minutes. The correlation coefficient between conjunctival oxygen tension and pulse oximetry was significant for all readings (p<0.001) and for pulse oximetry measurements below 100% (p=0.024). One infant developed eyelid edema, which subsided when the device was removed and one sustained a small corneal abrasion that healed overnight.

CONCLUSION

This initial pilot report suggests that the conjunctival oxygen monitor is effective and relatively safe in neonates. The device holds promise to indicate a tissue oxygen reading, which may provide neonatologists with more information about systemic oxygenation.