Non-invasive measurement of corneal hydration.
OBJECTIVE
To investigate the feasibility of a confocal Raman spectroscopic technique for the noncontact assessment of corneal hydration in vivo in two legally blind subjects.


METHODS
A laser beam (632.8 nm; 15 mJ) was maintained on the cornea using a microscope objective lens (25x magnification, NA=0.5, f=10 mm) both for focusing the incident light as well as collecting the Raman backscattered light, in a 180 degrees backscatter configuration. An optical fiber, acting as the confocal pinhole for elimination of light from out-of-focus places, was coupled to a spectrometer that dispersed the collected light onto a sensitive array-detector for rapid spectral data acquisition over a range from 2,890 to 3,590 cm(-1). Raman spectra were recorded from the anterior 100 to 150 microm of the cornea over a period of time before and after topical application of a mild dehydrating solution. The ratio between the amplitudes of the signals at 3,400 cm(-1) (OH-vibrational mode of water) and 2,940 cm(-1) (CH-vibrational mode of proteins) was used as a measure of corneal hydration.


RESULTS
High signal-to-noise ratio (SNR 25) Raman spectra were obtained from the human corneas using 15 mJ of laser light energy. Qualitative changes in the hydration of the anterior-most part of the corneas could be observed as a result of the dehydrating agent.


CONCLUSIONS
Confocal Raman spectroscopy could potentially be applied clinically as a noncontact tool for the assessment of corneal hydration in vivo.
March
W F
WF
Department of Ophthalmology and Visual Sciences, University of Texas Medical Branch at Galveston, 77555-1141, USA.
Bauer
N J
NJ
D000368:Aged; D001834:Body Water / Q000378:metabolism*; D003094:Collagen / Q000378:metabolism; D003315:Cornea / Q000378:metabolism*; D006801:Humans; D018613:Microscopy, Confocal; D013059:Spectrum Analysis, Raman / Q000379:methods
D003094:Collagen