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Fundus AutoFluorescence 2019

2 CPD in Australia | 1G in New Zealand | 31 March 2019

EXCLUSIVE TO LUXOTTICA

A little history

Fundus autofluorescence (FAF) imaging using a confocal scanning laser ophthalmoscope was first described by von Rückmann et al in 1995. In 2003, Spaide modified a fundus camera to take FAF images and recently near-infrared FAF imaging has been described. Because FAF images do not always correspond to lesions seen using ophthalmoscopy or angiography, FAF represents a new and unique window into disease activity in the posterior retina.

What is FAF?

FAF provides an objective, non-invasive measurement of the metabolic activity of the retinal pigment epithelium. More specifically; FAF provides a topographic map of the distribution lipofuscin and other fluorophores in the outer retina, sub-retinal space and retinal pigment epithelium (RPE).

Fig 1. Comparison of retinal scans of geographic atrophy in AMD

What causes FAF?

1. Lipofuscin (LF)

  • The likely source of FAF is A2-E (N-retinylidene-N-retinylethanol-amine) in LF
  • LF is due to a build up inside the RPE of discarded photoreceptor outer segment membranes
  • LF is an indirect marker of metabolic activity of photoreceptor outer segment turn over and RPE phagocytotic ability.
  • Excessive LF compromises RPE function and contributes to a variety of eye diseases including age-related macular degeneration (AMD), RP and Stargardt's disease.
  • High levels of LF are associated with inflammation, complement system activation and oxidative damage.
  • By the age of 80 years, 20% of the free space within each RPE cell may be occupied by LF.

2. Disease in the inner retina

Disease in the inner retina at the central macula where the FAF signal is usually masked by lutein and zeaxanthin may result in variations in FAF intensities

3. Disease in the outer retina

Disease in the outer retina and subneurosensory space can produce other intrinsic fluorophores

4. RPE atrophy

RPE atrophy can result in collagen and elastin in choroidal blood vessel walls becoming visible.

 

Instrumentation

There are two different technologies used to capture FAF images.

1. FAF imaging first became practical with the widespread use of confocal scanning laser technology.

2. More recently, fundus camera based systems have been developed for FAF imaging. The digital fundus camera technique first described by Spaide employs an excitation filter centered at 580 nm and a barrier filter centered at 695 nm. These wavelengths are shifted toward the red end of the spectrum to avoid unwanted short-wavelength autofluorescence from the crystalline lens.

Second generation FAF filter sets are now available for some fundus camera based systems. The excitation filter has a band-pass range of about 535-585 nm and the barrier filter has a band-pass range of about 605-715 nm. These filters avoid excitation of the crystalline lens and fluorescein, so the instrument can be used immediately after fluorescein angiography.

Despite the disparity in excitation wavelength and barrier filters used in cSLO and fundus camera systems, the techniques obtain results that are quite similar in appearance.

 

Fig 2a. Original FAF Filters 580/695nm, 2b. Camera using "spaide" Filters 535-585/605-715nm, 2c, Spectralis cSLO 488/521nm

Current FAF Devices

1. Heidelberg Engineering Spectralis OCT

This offers BluePeak blue laser autofluorescence technology that is being used in several clinical trials. In particular, the company is using BluePeak to evaluate the potential efficacy of drugs that prevent the onset or enlargement of GA in patients with AMD.

 

Fig 3. Heidelberg Spectralis OCT

2. Optos

The Optos Daytona was first unveiled at the 2011 American Academy of Optometry meeting in Boston. This device incorporates FAF technology into its existing widefield imaging platform in a tabletop design that offer unprecedented views of peripheral changes. Additionally, this device exhibits strong sensitivity in the detection of macular specific diseases, providing results that are in close agreement to those obtained via traditional fundus photography.

Fig 4. Optos Daytona

3. Canon

The Canon CR-2 Plus digital retinal camera is a Non Mydriatic retinal camera with FAF capability. It can take fundus photographs in colour, Red-free, Fluorescein Angiography and Spaide Fundus AutoFluorescence imaging modes.

Fig 5. Canon CR2-Plus

4. Topcon

The Topcon TRC-NW8F digital retinal camera is a Non Mydriatic retinal camera with FAF capability. It can take fundus photographs in Colour, Red-free, Fluorescein Angiography and Spaide Fundus AutoFluorescence imaging modes.

Fig 6. Topcon TRC-NW8F

 

Interpreting FAF images

Normal FAF Appearance

FAF identifies the retinal distribution of LF. FAF is highest in the parafoveal area and decreases toward the periphery reflecting rod photoreceptor density and RPE metabolism.

  • The retina in FAF appears as a uniform grey colour.
  • Blood vessels appear dark due to blood absorption
  • The optic nerve head appears dark due to a lack of RPE
  • The fovea has a reduced FAF due to xanthophyll pigment absorbing the signal.

While FAF images look a bit like fluorescein angiography (FA), it is important to remember that FA reveals vascular leakage and FAF shows metabolic activity of the RPE.

Fig 7. FAF Images of a normal central retina

Limitations

There are certain limiting factors for FAF imaging that should be recognized.

  • media opacities decrease contrast in the FAF image and analysis may not be not possible.
  • quantification of FAF images is currently not possible (though likely in the near future).
  • different types of scanning laser ophthalmoscope have different FAF outputs. The lack of reproducibility and consistency between instruments is a major problem in the clinical use of FAF.
  • increased retinal thickness, intraretinal edema, subretinal fluid and motion artifacts make FAF interpretation sometimes difficult.

Decreased FAF is seen when there is

  • atrophy or loss of RPE cells
  • an increase in RPE melanin content
  • absorption from material anterior to the RPE (intraretinal fluid, fibrosis)
    media opacities (cataract)
  • hydroxychloroquine retinopathy
  • chronic central serous retinopathy
  • old choroidal neovascularization in wet AMD

Increased FAF is seen when there is

  • lipofuscin in the RPE from degenerative changes or oxidative injury.
  • Progressing geographic atrophy in dry AMD
  • recent choroidal neovascularization in wet AMD
  • acute central serous retinopathy
  • some retinal tumours
  • cystoid macular edema
  • retinal dystrophies such as
  • retinitis pigmentosa
  • Stargardt’s disease
  • fundus flavimaculatus
  • Bests vitelliform
  • adult vitelliform dystrophy

Variable FAF is seen when there is Drusen

FAF and Drusen

Drusen may have variable FAF characteristics. Some drusen may present with normal FAF, others may have decreased FAF, while large soft foveal drusen can have increased AF. It is possible that the variable FAF in drusen may be related to the RPE being stretched over the drusen.

FAF and early AMD

It has been suggested that peripheral retinal changes may predate posterior pole changes in AMD (Gerson, 2012). FAF may be a useful tool to investigate these early changes, with peripheral and mid-peripheral retina FAF abnormalities occurring in up to 50% of people with early AMD (Domalpally et al, 2014; McCarthy, 2014). These ideas are being investigated in the OPERA (Optos Peripheral Retina AMD) studies.
FAF and dry AMD

Studies have characterized the FAF changes in eyes with dry AMD (Bearelly & Cousins, 2010). Increased FAF was correlated with areas of hyperpigmentation, soft drusen, hard drusen and normal fundus appearance. It was concluded that FAF imaging in dry AMD provides information over and above normal fundus photography methods.

Geographic Atrophy

What is geographic atrophy?

The following section is taken mostly from the excellent AMD review of Schmitz-Valckenberg 2012.
Geographic atrophy (GA) of the RPE is the advanced form of atrophic dry AMD. GA appears as sharply demarcated areas of depigmentation with enhanced visualization of deep choroidal vessels. GA can occur on its own or subsequent to other forms of AMD. GA may vary considerably in appearance from a single atrophic patch to multiple areas of atrophy. In early disease, atrophy is often limited to the parafovea. Over time, the atrophy may enlarge forming a horseshoe configuration and ultimately a ring sparing the fovea. The fovea is usually not involved until late in the disease.

Fig 8. FAF of advanced geographic atrophy (66year old, left eye VA 6/80)

 

Fig 9. Fundus photograph (left) and FAF image (right) of a 78year old patient showing multifocal RPE atrophy with a residual foveal island

There is a high degree of symmetry between fellow eyes in total size of atrophy and atrophy configuration. Papillary atrophy is observed very commonly in eyes with GA and its prevalence in GA is higher compared with age-matched control eyes. Very advanced stages may show huge continuous atrophies including large retinal areas within the temporal arcades, the optic disc and retinal areas nasally to the optic disc.

Fig 10. Composite FAF images of both eyes of a 96 year old patient with advanced GA extending to the macula. Note the symmetry of the atrophy between the two eyes.

 

FAF and the junctional zone in GA

GA represents areas of cell death within the RPE and is a key feature of late stage AMD. An important finding is the presence of increased amounts of LF in areas immediately surrounding GA; the "junctional zone". This is of particular interest because increases in LF may show progression of atrophy. Studies suggest that new atrophic lesions will develop in the hyperautofluorescent areas of the junctional zone of GA (Holz et al, 2007). Clinically we see a white hyperfluorescent ring around a black dead area.

Fig 11. Right eye of a 78 year old patient with age-related macular degeneration. Note the sharp demarcation of the area of atrophy and the increased FAF at the edge of the lesion (junctional zone).

The following patterns of abnormal FAF in the junctional zone of GA have been identified.

Table 1. Patterns of junction zone in GA

Examples of these junctional zone FAF patterns are shown below.

Fig 12. FAF image (B) with a homogeneous background fluorescence (normal pattern). Only small hard drusen are visible in the corresponding fundus photograph (A)

Figure 13. FAF image (B) showing the focal pattern, Fundus photograph (A) of the same eye with multiple har and soft drusen.

Fig 14. The FAF image (B) shows multiple large areas (200um diameter) of increased FAF (patchu pattern) large, soft drusen and or/hyperpigmentation are seen in the fundus photograph (A).

Examples of these junctional zone FAF patterns are shown below.

Fig 15. FAM Study classification of fundus autofluorescence patterns of geographic atrophy in AMD

 

FAF and AMD Progression

A correlation has been found between FAF abnormalities and the rate of progression of GA (Fleckenstein et al 2011).

  • Cases with no junctional zone abnormalities had the slowest progression (0.38 mm2 /yr)
  • Focal abnormalities had intermediate rates of progression (0.81 mm2 / yr)
  • Diffuse abnormalities had the fastest rate of progression (1.77 mm2 / yr)

Fig 16. Geographic atrophy progression over 5 years

 

FAF and Wet AMD

FAF changes in wet AMD have been studied. It has reported that classic choroidal neovascularisation (CNV) formation is associated with decreased FAF possibly because of it blocking the autofluorescence. Occult CNV has a regular or mottled FAF pattern.

Another study found that FAF characteristics depended on the duration of CNV. Recent onset lesions (<1 month) were associated with increased FAF, whereas chronic lesions (>40 month after onset) had decreased FAF. The latter observation may explained by photoreceptor loss and scar formation with increased melanin deposition.

Fig 17. Left eye of a 70 year old patient with choroidal neovascular membrane. Note the decreased FAF associated with the disciform scar formation and haemorrhage and the variably increased FAF surrounding the lesion.

 

FAF appearance with other retinal diseases

Retinal Tumours

The assessment of lipofuscin is an important risk factor in the diagnosis and treatment of choroidal melanocytic lesions. Clinically, lipofuscin is seen as orange-coloured patches over pigmented choroidal melanocytic lesions. FAF imaging can be particularly helpful in these situations to demonstrate lipofuscin.

FIg 18. Choroidal melanoma. A. Fundus Photo, B. Fluorescein angiogram, C. FAF image

 

Plaquenil Retinopathy

Observation and visual fields are the standard clinical tests used to diagnose macular toxicity from excessive Plaquenil use. However, these techniques only detect an advanced disease state. FAF has been proposed as a useful clinical test for early detection of Plaquenil (hydroxychloroquine ) retinopathy. The USA 2011 Plaquenil screening guidelines call for testing using FAF, spectral domain OCT and/or multi-focal electroretinogram testing.

Fig 19. Plaquenil retinopathy. 63 year old female. 25 years Plaquenil use for arthritis. 7 months history of metamorphopsia. VA 6/9. A. Fundus photo B. Fluorescein angiogram C. FAF

 

Central Serous Retinopathy

Acute central serous retinopathy (CSR) shows an increased FAF in the active stages corresponding to increased metabolic activity of the RPE and decreased FAF in chronic stages indicating reduced metabolic activity of the RPE because of photoreceptor cell loss.

 

Fig 20. Multifocal central serous retinopathy

 

Diabetic Retinopathy

Cystoid macular edema (CME) is a common feature in a number of choroidal and retinal disorders. FAF shows a can be used as a rapid and non-invasive technique to study this disease.

Fig 21. Foveal FAF patterns in diabetic CME: normal FAF (left); single-spot FAF (centre); multiple-spot FAF (right).

 

Hereditary Dystrophies

Retinitis Pigmentosa

Loss of peripheral FAF corresponds with the photoreceptor loss in RP. Adjacent areas of surviving retina can show increased FAF in the absence of other ophthalmic abnormalities. Macular edema, present in some RP cases, manifests initially as increased FAF. Chronic macular edema, in contrast, may result in a loss of photoreceptors and a decrease in FAF.

Right eye of a 42 year old patient with retinitis pigmentosa. VA 6/6. Note the parafoveal ring of increased FAF and decreased FAF outside the vascular arcades

Stargardt's disease

Macular dystrophies such as Stargardt’s disease, fundus flavimaculatus and Bests / vitelliform dystrophy are associated with focal increased FA. Focal increases tend to increase with time and eventually give way to focally decreased FAF and RPE atrophy.

Fig 23.This patient presented with Stargardt’s macular dystrophy (FAF left, colour fundus right). The FAF image illustrates the extent of macular disease more clearly.

 


 

References

  • Bearelly S & Cousins SW. Fundus autofluorescence imaging in age-related macular degeneration and geographic atrophy. Adv Exp Med Biol. 2010;664:395-402.
  • Bindewald A et al. Classification of fundus autofluorescence patterns in early age-related macular disease. Invest Ophthalmol Vis Sci. 2005;46:3309-3314
  • Domalpathy A, Danis RP, Chew E et al. Ultra Wide Field Autofluorescence Imaging in Age Related Macular Degeneration- Optos Peripheral Retina (OPERA) Age Related Eye Disease Study 2(AREDS2) Ancillary Study. ARVO Abstracts 2014.
  • Fleckenstein M et al. Progression of age-related geographic atrophy: role of the fellow eye. Invest Ophthalmol Vis Sci. 2011 Aug 22;52:6552-7.
  • Gerson JD. The clinical utility of fundus autofluorescence imaging. Supplement to April 2012 Review of Optometry. www.revoptom.com
  • Gomes NL et al. A comparison of fundus autofluorescence and retinal structure in patients with Stargardt disease. Invest Ophthalmol Vis Sci.2009;50:3953-3959
  • Gündüz K et al. Fundus autofluorescence if choroidal melanocytotic lesions ans the effect of treatment. Trans Am Ophthalmol Soc 2007;105:172-179
  • Holz FG et al. FAM Study Group. Progression of geographic atrophy and impact of fundus autofluorescence patterns in age-related macular degeneration. Am J Ophthalmol 2007;143:463-72.
  • Lindblad AS et al. Age-Related Eye Disease Study Research Group. Change in area of geographic atrophy in the Age-Related Eye Disease Study: AREDS report number 26. Arch Ophthalmol. 2009;127:1168-74.
  • McCarthy CE. 2014. Two AREDS2 ancillary studies presented at ARVO. http://optometrytimes.modernmedicine.com
  • Schmitz-Valckenberg S et al. Fundus autofluorescence imaging: review and perspectives. Retina 2008;28:385-409.





' ...FAF provides a topographic map of the distribution lipofuscin and other fluorophores in the outer retina, sub-retinal space and retinal pigment epithelium... '