Raman Spectroscopy of Ocular Tissue - Emerging Raman Applications and Techniques in Biomedical and Pharmaceutical Fields - page 282

could play a key role in the development of opacities or cataracts, which are
widespread visual impairments affecting the elderly population. Motivated by
these questions, Yu and East [3] and Schachar and Solin [4] applied Raman
spectroscopy to ocular protein research for the first time in the 1970s. Working
with excised bovine eyes, Yu and East [3] first generated isolated protein
fractions from a gel filtration chromatography column. Based on the order in
which the lens proteins eluted from the column, they could distinguish several
protein fractions with high molecular weight ( -crystallins), and

also a fraction consisting of lower molecular weight materials (peptides, amino
acids, etc.). For all fractions they could detect distinct Raman responses, and
subsequently were able to assign them to the Raman features they observed
for intact lenses.
An example of a lens Raman spectrum for a young, non-cataractous, ex-
cised human eye lens, which is nearly identical to the bovine lens in all its
Raman features, is shown in Fig. 12.2, which is reproduced from Bertoluzza
et al. [5]. Based on the earlier assignment results [3] the spectrum is charac-
terized by broad and strong scattering responses from water OH stretching
modes near 3390 cm − 1 , strong aliphatic CH and CH 2 stretching modes of
protein components near 2900 cm − 1 , weaker modes of sulfhydryl (S-H) pro-
tein subgroups in the 2500-2800 cm − 1 region, and a large number of distinct
protein component modes in the 500-1700 cm − 1 region.
The latter include the amide I and amide III bands near 1672 and
1240 cm − 1 , respectively, which are characteristic for the peptide CONH groups
(the 1672 cm − 1 line originates from the C=O stretch vibration and the lines in
the 1240 cm − 1 region from C-N stretching and N-H in-plane bending modes).
Furthermore, there are well-resolved lines from the aromatic amino acids
phenylalanine (Phe) at 1004 cm − 1 , tryptophan (Try) at 760 cm − 1 , and ty-
rosine (Tyr), the latter having several modes in the 600-900 cm − 1 region. The
spectral region between 1800 and 2500 cm − 1 does not reveal any appreciable
Raman response.

α -, β -, and γ

Fig. 12.2. InvitroRamanspectrumofthenucleusofa23-year-oldhumanin-
tact lens, showing Raman responses from protein components and water in the
500-4000 cm − 1 region. Adapted from [5]