23
QUESTION
WHAT IS FUNDUS AUTOFLUORESCENCE? DO I NEED TO ADD IT TO MY IMAGING OPTIONS?
Amani A. Fawzi, MD
Philipp Roberts, MD, PhD
Fundus autofluorescence (FAF) is an imaging technique that exploits the natural contrast agents in the ocular fundus, which emit light at a longer wavelength, when a particular wavelength is used for excitation. First described by Delori et al,1 FAF has been shown to provide valuable clinical information in a variety of different retinal diseases. Lipofuscin, a fluorophore in the retinal pigment epithelial (RPE) cells, emits a strong autofluorescent signal at a peak wavelength of about 600 to 610 nm when excited with light at a wavelength of around 470 nm (blue light FAF).2 Another approach to imaging lipofuscin fluorescence uses excitation wavelengths of about 515 to 530 nm (green-light), which can be done using specific filters installed in fundus cameras. Green laser is also used in widefield FAF imaging (Optos, Inc).
FAF imaging may also be performed using light at different wavelengths, such as near-infrared autofluorescence (NI-AF). In NI-AF, light at a wavelength of 787 nm is used to excite melanin in the fundus, including choroidal and RPE melanin. The different techniques of autofluorescence imaging are complimentary and show different aspects of the ocular fundus.3,4 In our clinic, FAF imaging is performed as a standard imaging method in many patients who undergo spectral-domain optical coherence tomographic (SD-OCT) imaging or fundus photography. FAF compliments these imaging modalities and, in our experience, adds important and sometimes pathognomonic, information as an en face imaging technique in certain circumstances.
When interpreting an FAF image, it is common practice to comment on the level of fluorescence as iso- (normal), hyper- (bright) or hypoautofluorescence (dark) and on the size and pattern (eg, well-demarcated vs. diffuse vs. mottled) of a specific lesion. Using quantitative FAF, a relatively recent extension of this imaging modality, the fundus emission is normalized to a reference fluorescent target within the machine, which could provide more standardized values to facilitate interpretation and comparisons across patients and within the same patient over time. This approach is currently used to investigate different types of inherited, as well as acquired, macular diseases.
Figure 23-1. FAF image of a healthy eye. Note the hypoautofluorescent disc and blood vessels as well as the hypoautofluorescent area in the fovea.
When 488-nm excitation is used in confocal scanning laser ophthalmoscopy modalities, such as Heidelberg Spectralis (Heidelberg Engineering), the normal FAF image shows a dark hypoautofluorescent disk and dark vessels and a grey to white isoautofluorescent background signal in the macula, except for the fovea. This is specific to 488-nm excitation wavelength where the normal macular pigment absorbs the excitation light, shielding the RPE from exposure to excitation and hence the hypoautofluorescence (Figure 23-1). This characteristic is not present when using green light FAF. Background FAF can vary widely between different patients, even in healthy eyes. Furthermore, FAF imaging itself causes a bleaching effect of the retinal photopigments, which appears as hyperautofluorescence of a previously imaged area. Hence, critical interpretation of FAF imaging is important and careful evaluation of colocalized SD-OCT imaging is advised in cases with ambiguous findings on FAF.
For the following retinal diseases, FAF has proven particularly useful: age-related macular degeneration (AMD), macular dystrophies, inherited retinal disorders, different types of drug toxicity, posterior uveitides, white dot syndromes, neoplastic and paraneoplastic retinal diseases as well as optic disc drusen.
For disorders involving the periphery of the ocular fundus, such as retinitis pigmentosa (RP), widefield imaging is recommended (especially as it uses green light) and is a great way to follow patients.
Age-Related Macular Degeneration
In AMD, FAF imaging is most helpful for evaluating the presence and extent of geographic atrophy (GA). GA is visualized as well-demarcated hypoautofluorescent areas surrounded by regions with varying degrees of hyperautofluorescence (Figure 23-2). Evaluation of foveal involvement is often challenging in patients with GA due to artifactual hypoautofluorescence caused by macular pigment (using 488 nm excitation). Therefore, we suggest ordering SD-OCT in all patients with GA at baseline to unambiguously assess the condition of the fovea. FAF imaging, together with SD-OCT, is used as major outcome variable in randomized multicenter pharmaceutical trials evaluating the efficacy of novel drug treatment for GA. The presence of hyperautofluorescence at the border of GA has been used to characterize different types of GA patterns, of which some have significantly higher rates of progression (eg, diffuse trickling type).5
Figure 23-2. FAF image of the right eye of a patient with GA. The GA area is clearly demarcated as a hypoautofluorescent area, and has a well-defined hyperautofluorescent margin. Grainy hypoautofluorescence can be noted throughout the macula and even outside the arcades, consistent with reticular pseudodrusen.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
