Biomedical Engineering Reference
In-Depth Information
simultaneously measures multiple wavelengths of reflected light
across a spectrum, hence the name spectral-domain. SD-OCT is
100 times faster than TD-OCT and acquires 40,000 A-scans per
second. The increased speed and number of scans translate into
higher resolution.
Specular microscopy provides in vivo, noninvasive imaging of the
corneal endothelial cells [
86
,
138
]. It can be performed using a
contact or non-contact method. Once visualized, the corneal endo-
thelial cells can be evaluated with regard to cell morphology and can
be quantified as to the number of cells per mm [
2
]. Normal corneal
endothelial cells are regular in arrangement and hexagonal in shape.
Cells are evaluated for cell density, pleomorphism, and polymegeth-
ism. As cell counts vary by age of the animal and region of the
cornea these variables must be standardized using animals of the
same age and examining the axial cornea. Animals must be sedated
or anesthetized to obtain an accurate image and automated systems
are available that simplify the technique. Guidelines for specular
microscopy in human FDA clinical trials have been established and
these can be used as a guideline for preclinical study design [
138
].
3.8 Specular
Microscopy
In vivo confocal microscopy is a noninvasive method for the micro-
scopic imaging of the living tissues that allows optical sectioning of
almost any material with increased axial and lateral spatial resolu-
tion and better image contrast [
86
,
139
,
140
]. It allows in vivo,
noninvasive, real-time images of the eye at magnifications (630
3.9 Confocal
Microscopy
)
which allow resolution of anatomical detail at the cellular level
[
139
]. Three-dimensional confocal microscopy of the eye has also
been described [
141
,
142
]. Confocal microscopy has been used to
image the cornea of various laboratory species including rabbits,
rats, and mice [
143
]. Its use has also been described in dogs, cat,
birds, guinea pigs, and horses [
144
-
148
]. Confocal microscopy can
provide detailed imaging of the corneal architecture at the cellular
level of each corneal epithelial cell layer, the epithelial basement
membrane, corneal stroma including nerve fibers and keratocytes,
Descemet's membrane, and endothelium [
86
]. While confocal
microscopy is most commonly used in the clinical arena
[
149
-
153
], its use may be indicated to evaluate the cornea and
corneal thickness in contact lens studies, to evaluate the stromal
keratocytes or corneal endothelium for toxicity, or to monitor
wound healing [
86
,
144
].
Confocal scanning laser ophthalmoscopy (cSLO) is an ophthalmic
imaging technology that uses laser light instead of a bright flash of
white light to illuminate the retina en face [
154
]. The advantages of
using cSLO over traditional fundus photography include improved
image quality, small depth of focus, suppression of scattered light,
patient comfort through less bright light, 3D imaging capability,
3.10 Confocal
Scanning Laser
Ophthalmoscopy
