Improving retinal health - clinical applications

April 1, 2010

FAF imaging is a powerful and versatile tool that can be used to diagnose and monitor a number of retinal diseases, most of which are still largely under-diagnosed and therefore under-treated.

FAF imaging is a powerful and versatile tool that can be used to quickly and non-invasively diagnose and monitor a number of retinal diseases, most of which are still largely under-diagnosed and therefore under-treated. For example, wet AMD is the leading cause of legal blindness in people over 50 years of age in the western world, affecting around 500 000 people worldwide each year.1 This figure might, however, be significantly higher, with further research indicating that between 55 and 70% of AMD sufferers are undiagnosed.2 This clearly indicates an inadequacy in current screening and referral methods and, as such, a certain level of responsibility lies with the general ophthalmologist to reduce the number of undiagnosed cases of AMD and other debilitating retinal diseases.

FAF imaging has traditionally been regarded as a tool for experienced retinal specialists only; however, this perception is beginning to change as general ophthalmologists are becoming aware of the increasing importance of their role in the ongoing monitoring of their patients' retina health. Early identification is critical in most retina diseases and regular and accurate retina health checks, particularly in high-risk patients, could help minimise future damage and even prevent blindness.

cSLO technology, for the acquisition of FAF images, offers general ophthalmologists a reliable tool for the diagnosis and ongoing monitoring of retina conditions; it can be easily integrated into a clinic and has a simple, well established, standardised protocol. No patient preparation or particular environmental conditions are necessary and the technology provides quick, detailed and reliable scans of the retina.

With the increasing prevalence of retina diseases, largely owing to the aging population and lifestyle factors, general ophthalmologists are under increasing pressure to ensure that their screening methods are clear and accurate to avoid misdiagnoses and poor referrals. Rising prevalence rates and the availability of novel treatments will also continue to add a great deal of strain onto retina clinics, most of which are already operating above capacity. As more therapeutics are made available, the general ophthalmologist will be increasingly relied upon to be involved in the ongoing monitoring of patients and to track treatment progress. As such, the use of cSLO technology by general ophthalmologists is expected to increase as more demands are placed upon them to diagnose and refer early and to work alongside retina specialists in the ongoing treatment of their retina disease patients.

Wet AMD

Much attention has been focused in recent years on the wet or exudative form of AMD, because of the high prevalence of the disease, which is estimated, on average, to exceed 500 new cases per million population in western Europe each year.3,4 Although much more is known about the pathophysiology of wet AMD than the dry form of the disease, and therapeutic interventions exist with a growing number in the pipeline, the number of undiagnosed patients remains unacceptably high.

Wet AMD is characterised by choroidal neocascularisation (CNV), which develops between Bruch's membrane, RPE and the photoreceptor layer. In studies, it has been shown that all types of CNV are associated with normal, increased, or decreased focal RPE autofluorescence.5.6 Thus RPE dysfunction has been shown to play a role in the pathogenesis of wet AMD. These studies have also shown an association between FAF pattern and the duration of neovascularisation and visual function, suggesting that FAF imaging may be important in identifying and monitoring CNV secondary to AMD.

In these patients, FAF shows patches of 'continuous' or 'normal' autofluorescence implying that RPE viability is preserved, at least initially, in CNV development.7 This corresponds with areas of hyperfluorescence on comparative fluorescein angiograms. By contrast, eyes with long-standing CNV typically exhibit more areas of decreased signal, which could be explained by the photoreceptor loss and scar formation with increased melanin deposition that is often seen with CNV progression. Importantly, abnormal FAF intensities visible in eyes with CNV often extend beyond the edge of a lesion defined by fluorescein angiography, which indicates a more widespread disease process, over and above that witnessed on conventional angiograms. It has been speculated that this observation may reflect the proliferation of RPE cells around the CNV.8

The classification of CNV, as classic or occult, is also possible with FAF imaging; a report by Spital and co-workers found that focal areas of decreased FAF are more prevalent in classical CNV in comparison to larger occult CNVs.9

Although the role of the areas with increased FAF intensities due to RPE dysfunction in wet AMD remains unclear, findings from many studies that have shown clear evidence of disease using FAF imaging, underscores its value in the diagnosis and monitoring of wet AMD.