AMD updated - page 85

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Fundus autofluorescence in age-related macular degeneration
Figure 3 - Fresh haemorrhage in the left eye from a patient with choroidal neovascularization secondary to AMD. Fresh haemorrhages typically
appear dark due to blocked fluorescence. (A) Colour fundus and (B) fundus autofluorescence photographs.
A B
be obtained from a quick and minimally invasive explora­
tion with FAF. The decreased FAF intensity may also be
associated with hyperpigmented areas due to the mela­
nin absorption of light(35,39). However, it should be con­
sidered that other fluorophores than LF can be found in
RPE and become more prominent in AMD patients, and
hyperpigmented areas may also cause an increase in the sig-
nal, which is supposed to result from the accumu­lation of
melanolipofuscin.
Other changes in FAF which are not related to RPE defects
may appear in AMD. Fresh haemorrhages typi­cally appear
dark due to blocked fluorescence (Fig. 3). However, these
haemorrhagic areas eventually synthesize substances and
fluorophores, which are observed in the fundus as yellow-
ish areas and in FAF images as increased signals (40) (Fig. 4).
Pigment epithelial and neurosenso­ry detachment and areas
with extracellular fluid accumu­lation associated with exuda-
tive lesions can be observed in FAF as increased or decreased
signal intensity.
Fluid accumulation under pigment epitheliumdetach­ment,
extracellular deposition of material under the RPE (drusen),
and fluid originated from CNV can occur with increased,
normal or decreased FAF intensity. This phe­nomenon is a
consequence of the presence of unknown autofluorescent
molecules other than LF, in the same spectral range than LF.
FAF imaging alone may not distinguish between melano-
lipofuscin from RPE cells migrated into the neu­rosensory
retina and LF within the normal RPE layer. It is always nec-
essary to compare the FAF findings with those from other
techniques such as fundus photograph, reflectance image,
fluorescein angiography or optical co­herence tomography
(OCT)(35, 39).
3.2.1 FAF in early AMD
Early AMD is characterised by the appearance of
lo­calized RPE hypo or hyper pigmentation and drusen.
Drusen are formed by the accumulation of extracellu-
lar deposits in the inner aspects of Bruch’s membrane(3).
De­pending on their size and morphology, they can be
clas­sified as hard or soft drusen. The molecular composi-
tion of drusen is quite complex and has not been com-
pletely elucidated (Fig. 5).
FAF changes in early AMD have already been reported
by several authors(9,21,25,27,33-36,41); all of them concluding
that the changes in ophthalmoscopy and fluorescein
an­giography are not necessarily related with FAF, suggest­
ing that FAF may provide new information regarding the
stages and activity of the disease. Differentiation between
RPE LF and sub-RPE deposits with FAF images in vivo
can be a hard work.
An analysis of the variability of FAF in patients with
early AMD was recently reported by an international
workshop on FAF phenotype in early AMD. Among
their conclusions, a new classification system with eight
different FAF patterns was given(39).
Normal pattern characterized by a homogeneous
back­ground autofluorescence with a gradual fluores-
cence de­crease in the inner macula towards the foveola
(blocked fluorescence caused by yellow macular pig-
ments). FAF may be normal even in the presence of soft
or hard drusen.
Minimal change pattern characterized by a limited and
irregular decrease or increase of background AF, not asso­
ciated to any obvious or important topographic pattern.