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Applied Physics Laboratory

An adequate oxygen supply is essential to the retina and optic nerve head: lack of oxygen can cause vision loss and blindness. Hypoxia of the retina and optic nerve head is an essential factor in the origin of ocular vascular disorders such as diabetic retinopathy, arterial venous occlusion disease, and glaucoma. The development of a non-invasive means of measuring oxygen saturation in the human eye is key in the diagnosis and monitoring of these disorders. A practical system to evaluate retinal blood flow and oxygenation in the retina and optic nerve head using a recent innovation, hyperspectral imaging, is being developed in Dr. Bahram Khoobehi's laboratory.

The hyperspectral imaging device allows measurement - non-invasively and in real time - of reduction and/or elevation in tissue oxygenation. The hyperspectral technique measures spectral changes within the visible and infrared spectra and provides information on the molecular state of hemoglobin. The distinct optical signature of biological materials such as oxy-hemoglobin and deoxy-hemoglobin as a function of their reflectance spectra further enables the determination of their relative concentrations. In recent years, reflectance oximetry has been developed for the non-invasive measurement of oxygen saturation changes in the vessels of the fundus using double, triple, and multiple wavelength reflectance imaging. This system makes it possible to perform in vivo fluorescence confocal microscopy, which can aid not only the diagnosis of infections, but also, perhaps, a new approach to the understanding of basic metabolic changes in vivo and the penetration of fluorescent compounds into single cells in vivo.

There is great potential for clinical application of this innovative technology in the early diagnosis and monitoring of therapy for ocular vascular diseases which can eventually lead to loss of vision. Current research involving retinal blood flow utilizes imaging of fluorescing blood cells to measure the velocity and volume of blood flow in the vessels of the retina. Information gained by this method will aid in the diagnosis and monitoring of blinding eye diseases such as diabetic retinopathy.

 

Saturation map of the optic nerve head. Areas of decreased oxygen saturation correlate with an increase in intra-ocular pressure, such as that observed in glaucoma.