Ординатура / Офтальмология / Английские материалы / Atlas of Fundus Autofluorescence Imaging_Holz, Schmitz-Valckenberg, Spaide, Bird_2007
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180 Samantha S. Dandekar, Alan C. Bird
14.2
FAF Findings in Early CNV
The distribution of FAF in patients with different stages of CNV development has been published and compared with fluorescein angiography [5, 7, 16, 23, 26–29]. Eyes with “recent-onset” CNV were found to have patches of “continuous” or “normal” autofluorescence corresponding to areas of hyperfluorescence on the comparative fluorescein angiograms (Fig. 14.2). This implied that RPE viability was preserved at least initially in CNV development. An increased FAF signal surrounding lesions appears to be less common in CNV compared with GA; it could be speculated that RPE lipofuscin may not play such an important role in the development of CNV.
The median visual acuity was found to be greater in the early CNV group, which may suggest that visual outcome is somewhat dependant on RPE preservation. A further finding from the study showed that the abnormal area according to the FAF image was statistically larger than that measured from the fluorescein image, implying that FAF imaging was better able to delineate the edge of CNV lesions [5].
In a subsequent study, intact foveal FAF correlated with visual acuity, size of the lesion, and symptom length, although no individual factor was predictive [24]. Intact FAF was also noted up to 20 months after diagnosis. The integrity of the RPE in the early stages would also support the hypothesis that VEGF and other growth factors are being released from viable RPE in the early stages of the disorder [13, 14].
14.3
FAF Findings in Late-Stage CNV
In the eyes with long-standing CNV, more areas of decreased AF were seen, implying non-viable RPE and lack of photoreceptor outer segment renewal (Fig. 14.3). It is likely that the areas of decreased FAF represent areas of RPE atrophy beneath the CNV scars in the late stages of disease [5].
It has also been shown that areas of increased FAF seen inferior to lesions are thought to be due to a gravitational effect of fluid tracking under the retina, similar to that seen in central serous retinopathy (Fig. 14.3, top row) [15]. Increased FAF signal has also been described around the edge of lesions that are thought to represent proliferation of RPE cells around the CNV (Fig. 14.1) [16].
14.4
FAF Findings in Relation to CNV Classification
The pattern of fluorescence on fluorescein angiography determines the classification of lesions as either classic (early, well-defined hyperfluorescence with late leakage and
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blurring of the margins; see Fig. 14.4) or occult (irregular, stippled hyperfluorescence or late leakage of undetermined source; see Fig. 14.5), based on the macular photo coagulation study definitions [3].
Histopathologic studies have shown that classic complexes have predominantly a subretinal fibrovascular component as opposed to most occult lesions that remain underneath the RPE [15]. This would imply that classic lesions are more likely to be visible on FAF imaging, although this does not always appear to be the case.
14.4.1 Classic CNV
A study by McBain et al. recently compared FAF imaging in classic and occult lesions, demonstrating differences between them [16]. Purely classic lesions showed low or decreased FAF signal at the site of the CNV, with a ring of increased FAF around some lesions (Figs. 14.1 and 14.4). The low signal area was thought to represent blockage of FAF caused by the CNV growing in the subretinal space, rather than direct damage to the RPE layer. It was felt that destruction of the RPE was unlikely, due to the homogeneity of the low signal seen in the images and given that all patients in the study had newly diagnosed CNV. The ring seen around some of the classic lesions was thought to represent proliferation of RPE cells around the CNV. According to Dandekar et al., it was felt that the increased FAF seen in some cases may be related to the phagocyt osis of subretinal debris by macrophages [5].
14.4.2 Occult CNV
In occult lesions, a much more variable pattern of CNV was seen (Fig. 14.5) [5, 16]. This is not surprising given the more heterogeneous nature of such lesions. According to McBain et al., foci of decreased FAF were seen scattered within the lesion (Fig. 14.5, left column for similar appearance). These were felt to be due to small areas of RPE loss or damage caused by the chronic, more indolent lesions growing underneath the RPE. Areas of increased FAF were less frequently associated with the edge of occult lesions compared with predominantly classic lesions.
Other causes of decreased FAF signal in CNV lesions include blood, exudates, and fibrovascular scars (Figs. 14.3 and 14.5) [5]. Here, adjunctive tests such as ocular coherence tomography may help in interpreting FAF images and improving our understanding of the pathogenesis of CNV.
182 Samantha S. Dandekar, Alan C. Bird
14.5
RPE Tears
RPE tears in the presence of AMD have been reported to occur in association with pigment epithelium detachment, either spontaneously or following therapeutic intervention (Fig. 14.6) [10]. FAF imaging may be helpful in establishing the diagnosis by visualization of the affected areas [12, 23]. Areas with RPE loss are characterised by a very low signal because of loss of lipofuscin and are sharply demarcated. The adjacent area with rolled-up RPE is characterised by heterogeneous signal of distinct increased FAF. Thus, the exact location of the tear can be delineated in most cases.
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Fig. 14.1 Colour, fluorescein angiogram, and fundus autofluorescence (FAF) images of two eyes with choroidal neovascularization (CNV). Left column: CNV lesion with a few small exudates superiorly and haemorrhage at the nasal border. Note that blood and exudate appear dark on FAF imaging. The lesion itself, which leaks on fluorescein angiography, appears to be of background FAF intensity, implying an intact retinal pigment epithelium (RPE) layer. Right column: The edge of this subfoveal CNV lesion is seen more clearly on the fluorescein image, but the abnormal area on FAF imaging appears to be larger than that seen on fluorescein angiography [5]. Note the increased FAF around both lesions, thought to be suggestive of proliferation of RPE cells around the CNV [16]
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Fig. 14.2 Colour, fluorescein angiogram, and fundus autofluorescence (FAF) images of two eyes with early-stage choroidal neovascularization (CNV). Left column: Early CNV lesion inferiorly with a small area of geographic atrophy superiorly. Note that the area that fluoresces within the CNV corresponds to an area of “normal” or “background” FAF intensity. The area of decreased auto fluorescence represents an area of atrophy. Right column: The majority of this newly diagnosed CNV lesion corresponds to areas with “normal” FAF intensity, with a band of increased FAF signal adjacent to the area of hyperfluorescence seen on the fluorescein angiogram. The reduced FAF signal around the edge corresponds to blood
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Fig. 14.3 Colour and fundus autofluorescence (FAF) images of three eyes with late-stage choroidal neovascularization (CNV). Top row: Late-stage CNV lesion with an increased FAF signal below the lesion, representing a gravitational effect of fluid tracking beneath the retina. Middle row: Disciform scar secondary to CNV with corresponding areas of decreased FAF, implying retinal pigment epithelium (RPE) cell and photoreceptor loss. Increased autofluorescence signal may represent macrophages or proliferation of RPE cells at the edge of the lesion. Bottom row: End-stage disease with widespread areas of reduced FAF, implying atrophy and RPE loss. Note that areas with pigment migration and melanin deposition also exhibit decreased FAF due to absorption effects