Biomedical Engineering Reference
In-Depth Information
MPAF (a.u.)
SHG (a.u.)
(a)
(b)
A1
A2
1.5
1.0
1.0
0.5
0.5
0.0
0.0
0
2
4
6
8
10
0
2
4
6
8
10
t
, day
t
, day
Control
Glycated
FIgurE 12.11
The dependence of autofluorescence (a) and BWSHG (b) signal intensity of bovine cornea. (From
Tseng, J. Y. et al. 2011.
Biomed Opt Express
2(2):218−230. With permission.)
anterior part (100 μm), SHG images reveal similar structures as the tightly interwoven collagen fibers in
both normal and edematous corneas. However, in the posterior region (1000 μm), the BWSHG image of
the edematous cornea becomes similar to the FWSHG image, which indicates the increased back scatter-
ing of the FWSHG signal due to a decrease of corneal transparency.
Comparison of the anterior and posterior of the edematous cornea showed that the reduced struc-
tural alteration in the anterior cornea as compared to that in the posterior region may be due to the
more tightly interwoven collagenous structure in anterior cornea. This study demonstrated the ability
of multiphoton microscopy in recognizing corneal morphology, and the potential of BWSHG signal
characteristic in revealing detailed collagen structure in corneal edema.
12.5 Future in clinical Diagnosis
Cornea is a key organ responsible for vision. Unlike many other organs, the cornea cannot be removed
for histological examination in pathological diagnostics. Therefore, the development of a label-free,
high-resolution imaging modality that is capable of visualizing different corneal structural motifs will
be of significant value in the clinical diagnostics of corneal diseases. In this chapter, we have described
the principles and instrumentation of multiphoton microscopy and provided specific examples of how
nonlinear optical phenomena, such as multiphoton autofluorescence and second harmonic generation,
can be used to visualize the elements of cornea, which is transparent to linear optical sources. Moreover,
we have shown that numerous corneal pathologies, such as corneal edema, keratoconus, physical
trauma, infection keratitis, intraocular pressure-induced structural disorder, and diabetes mellitus-
induced ophthalmological complications, can be imaged and discriminated from normal cornea with-
out extrinsic labeling. With additional development in instrument miniaturization and increased image
acquisition speed, multiphoton microscopy has the potential to be developed into a clinically viable tool
for the diagnostics of corneal pathologies.
