Raman Spectroscopy of Ocular Tissue - Emerging Raman Applications and Techniques in Biomedical and Pharmaceutical Fields - page 286

Fig. 12.4. Raman spectra of excised rabbit cornea. Adapted from [13]

type I collagen fibers. Furthermore, it was found that corneal collagen has a
relatively large amount of phenylalanine amino acid content.
Bauer et al. [14] and Erckens et al. [15] used confocal Raman spectroscopy
to investigate the corneal hydration status and drug-induced changes of the
living rabbit cornea. Their confocality approach allowed them to monitor
changes along the axis of the cornea. To determine the corneal hydration
status, they determined the ratios of the Raman intensities of the water OH
stretch mode at 3390 cm − 1 and the protein CH stretch mode at 2945 cm − 1 ,
respectively. The studies demonstrated an increased gradient of corneal water
content from the anterior to the posterior region [14].
Manipulations of the hydration are possible with a topically applied dehy-
drating agent, such as Muro 128 R

, an ointment usually used to treat corneal
edema [15]. Representative results of this study are shown in Fig. 12.5, which
displays a series of average Raman spectra obtained for successive axial lo-
cations of normal rabbit corneas and the same corneas after treatment with
the drug. A comparison shows a decrease of about 30% of the OH/CH ra-
tio between the untreated and treated cases. As future applications of their
method the authors [14] envision the monitoring of healing processes following
photorefractive keratectomy, the monitoring of corneal grafts, and studies of
the effects of contact lenses on the cornea. Regarding pharmacokinetic appli-
cations, it may be possible in the future to study open questions such as the