92
higher compared to eyes without FAF abnormalities and
“focal” FAF pattern. Another interesting finding of this
study was the identification of eyes with extremely rapid
progression of the atrophy, showing distinct FAF features
of atrophy that had not been previously reported. The
authors introduced the term “diffuse trickling” for a pat
tern associated with a significantly faster enlargement
of atrophy. Areas with increased FAF and consequently
higher concentrations of RPE LF precede the develop
ment of new areas of GA or the enlargement of the pre
existing atrophic areas.
The phenotypic features of FAF abnormalities may play
a stronger influence on the progression of atrophy than
any other previously reported risk factors such as smok
ing, arterial hypertension or diabetes. The different rates
of enlargement of atrophy may be related to heterogene
ity at a cellular and molecular level in the disease. The
high degree of symmetry in GA suggests that genetic
determinants may be involved, rather than nonspecific
aging changes.
3.2.2.2 Choroidal neovascularization
Choroidal neovascularization is considered to cause
almost 90% of the cases of severe visual loss related to
AMD
(50)
. CNV is usually studied by fluorescein angiog
raphy and OCT to assess the extent, location and
nature of the lesion
(51)
. Fluorescein angiography shows
changes in retinal vascularization, but does not reveal
how deeply RPE is affected. FAF imaging shows RPE
damage, with the advantage that is a non invasive test,
less time consuming than angiography.
Several studies have reported that CNV may show
irregular FAF alternating areas of increased, normal and
decreased fluorescence intensity
(20,34-37)
. (Fig. 14). Areas
of abnormal FAF extend beyond the edge of the angio-
graphically defined lesion. As in other exudative retinal
diseases such as central serous chorioretinopathy, areas
of increased FAF next to CNV are frequently found
inferior to the leaking areas in fluorescein angiography.
The hypothesis was that they might represent areas with
subretinal fluid and that their location was influenced
by gravity. Other fluids may typically decrease FAF, as
occurs with haemorrhages and exudates. Decreased FAF
is caused by blocked fluorescence. It is usually necessary
to compare the results of FAF with colour photographs.
Recent research has examined early CNV in FAF
(36, 52, 53)
,
reporting that early CNV lesions tend to show normal
FAF in areas that were hyperfluorescent in fluorescein
angiography, whereas eyes with a history of one month
or more since CNV was diagnosed, showed decreased
FAF in areas of previous fluorescein leakage
(52)
. These
data suggest that RPE affected by the CNV may still be
viable in the early stages of the disease (Fig. 15).
These studies have also reported that areas with previ
ously high levels of FAF may show decreased FAF six
months later
(36)
. These changes may be secondary to
photoreceptor loss, RPE atrophy, replacement of nor-
mal phenotypes of RPE cells with scar, and increased
melanin deposition. These findings may have therapeu-
tic implications and clarify long-term visual prognosis.
For example, a person with an active CNV on fluores-
cein angiography, and normal FAF, may show a much
better outcome than another with an abnormal basal
FAF.
Data comparing FAF findings in occult and classic
CNV are limited. Spital et al. reported that classic CNV
usually shows more focal areas of decreased FAF than
occult CNV
(34)
. These findings have been confirmed by
McBain et al.
(54)
who guessed that low FAF at the site
of the CNV are related to blocked fluorescence induced
by the presence of CNV in the subretinal space, rather
than to severe damage to the RPE.
A more recent study did not find significant differences
in FAF patterns in early classic and occult CNV second
ary to AMD
(53)
(Fig. 16). A continuous preserved auto-
fluorescence pattern was observed in the central macula
in most of the cases. These findings suggest that neovas-
cular complexes, regardless if classic or occult, would be
external to the RPE in most cases.
Additional studies with a higher number of patients
and longer monitoring are required to verify with these
changes in patients with CNV (Fig. 17).
3.2.2.3 Pigment epitelial detachment (PED)
PED can show different FAF patterns
(11,16,31,55)
. FAF can
provide complementary information to that of fundus
colour photograph and fluorescein angiography. In
most of the cases, a moderately and diffusely increased
FAF can be found, surrounded by a clearly defined
ring with decreased fluorescence
(34,35,55)
. Occasionally,
intermediate or even decreased FAF can be found that
may not correspond to the atrophic RPE or to fibrovas-
cular scars. These changes in the FAF could correspond
to different stages in the PED evolution
(16)
.
The findings in FAF should be compared with those
in fluorescein angiography. We should bear in mind
that areas with increased FAF do not always correspond
to increased or decreased LF. Besides, the presence of
