Ever since optical coherence tomography (OCT) became popular in the early 2000s, it’s been the reigning champion as THE top piece of medical optometry equipment to have in our offices.
It’s fast, non-invasive, and useful in many ocular conditions. Plus, it’s got so much color! (Nothing personal, visual field, but chunky pixels are soooo 20th century.)
Fundus autofluorescence (FAF) is another non-invasive retinal imaging tool that is starting to become very popular among colleagues. It is used to determine the health of the retina by evaluating the presence and/or absence of certain fluorophores within the retina. Fluorophores are molecules in our bodies that when “excited” by a certain wavelength, will emit a certain wavelength in return. Think of it as “communicating” with them with the use of specific wavelengths and FAF is the “eye-phone” . . .
Lipofuscin is the dominant fluorophore in the retina, specifically in the RPE cells. Other fluorophores include melanin and rhodopsin.
Hyper- and Hypo-autofluorescence
Retinal lesions that produce hyper-autofluorescence can indicate too much lipofuscin in the RPE cells, window defects due to loss of the RPE, or a pocket of accumulated subretinal fluid such as Best’s Disease.
Hypo-autofluorescence occurs when there are decreased or absent lipofuscin. A perfect example would be geographic atrophy in AMD because there are no RPE cells at all. Another reason for hypo-autofluorescence is due to a blocked view of the RPE cells by certain objects such as hemorrhages and fibrotic materials.
Fundus autofluorescence can be captured by fundus cameras, confocal scanning laser ophthalmoscopes (cSLO), and ultra-wide field systems. Each of these systems are used differently and can yield a certain FAF imagery. For example, FAF with a fundus camera can be used to evaluate CNV and CSRs. FAF with cSLO can be used to quantify the macular pigment density. With ultra-wide field systems, hence the name, we can now evaluate conditions in the periphery in which previous systems were unable to accomplish.
Here are five conditions that you should be utilizing FAF for:
Fundus autofluorescence (FAF) can be used clinically to provide insightful information about the functional health of the retina along with diagnosis. Here are my top 5 conditions for which FAF should be utilized in clinic:
1) Macular Degeneration
While current popular imaging systems like the fundus camera and OCT can help detect and monitor early dry AMD, utilizing FAF may reveal a more underlying widespread disease. It also provides insightful information to assess the risk and rate of progression. For example, areas of hypo-autofluorescence indicates RPE cell absence/death which can be a sign of early geographic atrophy (GA) and/or indication of choroidal neovascularization. Furthermore, certain FAF patterns of GA have been developed and are used to assist in determining visual prognosis. Drusen and drusenoid pigment epithelial detachments produce hyper-autofluorescence lesions which also are risk factors of disease progression.
Characteristic FAF patterns in patients with GA allows us to predict which patients may undergo rapid vision loss, thus allowing us to prepare an optimal management protocol.
2) Macular Dystrophies
Dystrophies such as Best’s and Stargardts can be hard to diagnose during early phases of the disease process, especially when the fundus appears “normal” and patient has decreased vision. This is when FAF can be utilized to determine the functional health of the retina.
During the early stages of the disease, focal hyper-autofluorescence occurs due to increased degeneration of the photoreceptors which then causes an increased accumulation of lipofuscin in the RPE cells. As the disease progresses, the once hyper-autofluorescent lesions become hypo-autofluorescent due to RPE atrophy.
You can be certain of Stargardt’s disease when FAF shows macular hypo-autofluorescence surrounded by hyper-autofluorescent specks with peripapillary sparing. For Best’s disease, the “egg-yolk” appearance in the macula will hyper-autofluoresce due to lipofuscin accumulation in the subretinal space. Stargardts, Best’s vitelliform, and other macular dystrophies have certain characteristic FAF patterns which can aid in diagnosis and proper management.
3) Central Serous Chorioretinopathy (CSR)
Central serous chorioretinopathy (CSR) occurs commonly in our practices and optical coherence tomography has been the go-to diagnostic piece of equipment. Using FAF can help us evaluate the extent of the damage. As fluid-containing lipofuscin leaks from the RPE and into the subretinal space, serous retinal detachments can be seen in FAF imagery as hyper-autofluorescent. As the disease progresses without management, the once hyper-autofluorescent lesions becomes hypo-autofluorescent due to atrophy of the RPE cells. Chronic CSR has a distinct FAF pattern of vertically descending tract of hypo-autofluorescence due to the gravity-driven subretinal fluid.
4) Retinitis Pigmentosa
Pairing the FAF imaging technology with electroretinography (ERG) and other diagnostic equipment further enhances our ability to diagnose and manage patients with retinitis pigmentosa (RP). Interestingly, FAF can reveal a hyper-autofluorescent parafoveal ring (Robson-Holder Ring) that may not be visible on a typical fundus examination. The borders of this ring is an important clinical clue because it delineates dysfunctional retina (outside) from the functional retina (inside) which can be measured via visual field testing.
The autofluorescent ring’s (AF ring) area decreases as the disease progresses due to rods beings affected first. Therefore, the bigger the ring, the “healthier” the retina and vice-versa. It can be compared to glaucoma, as the disease progresses, the visual fields constricts and eventually “zips” shut leading to total blindness. That can be said with the AF ring.
Utilizing FAF imaging technology in RP patients allows us understand and estimate the prognosis of this serious condition. Thus, we can help manage their quality of life a bit better.
Other retinal conditions share this similar AF ring which may lead us to believe they share a common pathogenesis and a step forward in understanding these sight-threatening conditions.
5) White Dot Syndromes (WDS)
This rare group of chorioretinopathies share similar clinical appearances due to the inflammatory events of the retina, RPE, and choroid leading to multifocal, yellow-white lesions throughout the fundus. Yet not all forms of WDS produce these yellow-white lesions and it can be difficult to observe on fundus examination, hence the ability to detect this can be a bit tricky. The utilization of FAF imaging technology allows these difficult and faint lesions to be easily appreciated, especially during its early onset. Generally, hyper-autofluorescent lesions indicates active inflammation or window defects whereas hypo-autofluorescent lesions point to the later phases like chorioretinal atrophy and/or scarring.
A fundus photo and FAF image of same patient with Multiple Evanescent White Dot Syndrome. Multiple ill-defined spots of hyper-autofluorescent in FAF can be easily seen.
A fundus photo and FAF of same patient with Birdshot Chorioretinopathy. Scattered areas of hypo-autofluorescent lesions in FAF indicating RPE atrophy.
Indocyanine green angiography continues to be test of choice for patients with possible WDS due to its ability to detect lesions pretty well. Though the FAF is not as sensitive as the ICG angiography, it is a great substitute because its ease of administration and its non-invasive nature. In my 6 years of practice, I would not be surprised that I have missed these elusive WDS because of how clinically obvious they present on FAF compared to the naked eye. Makes you wonder, eh?
Fundus autofluorescence is becoming increasingly popular among practitioners due to its ease of administration and non-invasive nature. Just like other diagnostic equipment, the FAF has its pros and cons. Since the FAF imaging technology evaluates the functional health of the RPE and photoreceptor layer, it can be a great supplemental option when paired with the OCT and/or visual field. Furthermore, it can reveal a wider spread of damage in which a fundus photo can not accomplish. This is extremely important when it comes to proper management during the early phase of the disease.
Certain ocular conditions that once were thought different are now in question due to their common FAF patterns. This could be a step towards better understanding of the conditions leading to proper interventions.