Chemistry Reference
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(a)
Age (years)
(b)
Age (years)
FIGURE 6.6
(a) RRS MP measurements of 33 normal eyes for a young group of subjects ranging in age from
21 to 29 years. Note the large (up to ~10-fold) variation of RRS levels that can exist between individuals. Since
the ocular transmission properties in this age group can be assumed to be very similar, the variations can be
assigned to differing MP levels. Subjects with low MP levels may be at higher risk of developing macular
degeneration later in life. (From Ermakov, I.V. et al.,
J. Biomed. Opt
., 10(6), 064028-1, 2005b. With permis-
sion.) (b) RRS measurements of 212 normal eyes as a function of subject age, revealing a statistically signii -
cant decrease of MP concentration with age. Solid circles represent subjects with clear prosthetic intraocular
lenses. Data are not corrected for decrease of ocular transmission with age (see text). (From Gellermann, W.
et al.,
J. Opt. Soc. Am. A
, 19: 1172, 2002. With permission.)
Also, we have noted that patients with unilateral cataracts after trauma or retinal detachment repair
typically have very similar RRS carotenoid levels in the normal and in the pseudophakic eye. Thus,
we have concluded that there is a decline of macular carotenoids that reaches a low steady state just
at the time when the incidence and prevalence of AMD begins to rise dramatically. While this age
effect has been noticed sometimes also in other studies using clinical populations and different MP
detection methods (Sharifzadeh et al. 2006, Nolan et al. 2007), several groups have reported con-
stant, age-independent MP levels. Examples include rel ectance-based population studies in which
respective average MP optical densities of 0.23 (Delori et al. 2001), 0.33 (Berendschot et al. 2002),
and 0.48 (Berendschot and Van Norren 2004) were determined.
6.4 SPATIALLY RESOLVED RESONANCE RAMAN IMAGING
OF MACULAR PIGMENT
MP distributions are often assumed to have strict rotational symmetry, high central pigment lev-
els, and a monotonous decline with increasing eccentricity. However, initial resonance Raman
imaging, RRI, results obtained with excised human eyecups demonstrated intriguing deviations,
clearly revealing the existence of strong signii cant rotational asymmetries, distribution patterns
with central depletions, patterns with widely differing widths between samples, and patterns with
fragmented concentration levels (Gellermann et al. 2002b).
In order to coni rm these new distribution features in the living human retina, we developed the
Raman method for
in vivo
imaging applications (Sharifzadeh et al. 2008). The experimental setup
for this purpose is shown in Figure 6.7. Once the subject achieves head alignment with the help
of a red i xation target, blue light from a solid state 488 nm laser is projected onto the macula as
a ~3.5 mm diameter excitation disk, and two images are recorded with a CCD camera. In the i rst
image, “Raman plus l uorescence image,” the light returned from the retina under 488 nm excitation
is i ltered to transmit only 528 nm light, which is the spectral position,
λ
R
, of the resonance Raman
response of the 1525 cm
−1
carbon-carbon double bond stretch frequency of the MP carotenoids.
Each pixel of this image contains the Raman response of MP as well as the l uorescence components
overlapping the Raman response at this wavelength. In the second image, “l uorescence image,” the
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