253
membrane and choroid immediately adjacent space can
be obtained, but the remainder of the choroid is beyond
the capabilities of the instrument. To study this layer,
Spaide developed a system consisting of an approximat-
ing scanner to the eye for multiple inverted images that
then are processed to obtain a higher quality image in
which the choroid can be seen in greater depth. Several
diseases have been studied using this technique. This
technique may be relevant for studying wet AMD asso-
ciated with RPE detachment and especially in occult
CNV, which often cannot be visualized conventional
OCT.
40,41,73-76
New Prototypes: High-Speed Resolution Ultrahigh
OCT
SD instruments reach axial resolutions close to 5 microns
using a source that emits light at a certain wavelength
and detection system based on the Fourier principle.
To obtain even higher resolutions, several groups have
designed devices that vary primarily based on the light
source. A group at Tufts Medical Center, Boston, devel-
oped a prototype that uses a broadband laser superlumi-
nescent diode combined with a Fourier detection system
that can achieve axial resolutions up to 3.5 microns and
allows precise analysis of the outer retinal layers, such
as the photoreceptors layer, the RPE, and Bruch’s mem-
brane.
77
The investigators have published several studies
highlighting the importance of these strata in the patho-
genesis of dry AMD, the ability for early detection of
intraretinal and subretinal fluid, and the status of the
photoreceptors before and after ranibizumab treatment
in a series of patients with wet AMD.
4,66,78,79
RPE Study of Polarization-Sensitive OCT
SD instruments identify external retinal structures but
provide limited information on the region of the RPE,
making it possible to assess only the status based on
hyper-reflectivity. To explore differences in the reflectiv-
ity of the RPE in the various AMD subtypes, an OCT
prototype has been designed that incorporates a receiver
capable of obtaining measurements of intensity and
polarization at each point of study. In a study conducted
in 44 patients with drusen, GA, disciform scarring, and
neovascular forms, the authors described the different
patterns of involvement of the RPE and suggested future
uses of the device to assess the status, progression, and
even disease prognosis.
80
OPTICAL COHERENCE TOMOGRAPHY IN AGE-RELATED MACULAR DEGENERATION
