The role of community-based screenings for vision-threatening diseases (VTDs) in the detection of cataracts, age-related macular degeneration, diabetic retinopathy, and glaucoma is increasing with the aging of baby boomers, as well as the changing realities of world economies. With unemployment passing the 10% mark in the United States and continuing loss of health insurance, along with increasing prevalences of obesity, hypertension, and poor nutritional habits in both the pediatric and adult populations, the incidence of VTDs is expected to increase. Moreover, VTDs often remain undetected until the late stages of disease, with resultant loss of vision. Fundus autofluorescence (FAF) imaging is a noninvasive procedure that targets the retinal pigment epithelial cells (RPE), among others, and allows the screener to achieve a higher detection rate for changes associated with VTDs in affected subjects. Better detection rates, in turn, translate to more timely triage and clinical referral.
FAF imaging highlights lipofuscin, a biomarker of cellular aging and oxidative cell damage. It forms as an accumulation of lipophilic lysosomal debris from unsaturated fatty acid oxidation.1 Histologic studies in donor eyes have shown increased accumulation of lipofuscin in the RPE with age, poor diet, and in certain retinal diseases.2-4 It is a byproduct of phagocytosed photoreceptor outer segments.5 Lipofuscin buildup compromises RPE function and is involved in the pathogenesis of various retinal disorders.6,7
METHODOLOGY
All subjects who took part in VTD imaging sessions
signed an institutional review board-approved consent
form before their participation. All subjects were previously
evaluated by a board-certified retina specialist and
underwent follow-up examinations. A Canon CX-1
hybrid retinal camera (Canon Inc, Tokyo, Japan) providing
15.1-megapixel resolution (Figure 1), with 45°
nonmydriatic mode (requiring 3.8-mm pupillary dilation)
and 50-degree mydriatic mode, was used for ocular
imaging. The CX-1 allows anterior segment imaging
(cataract detection) by using a plus-diopter setting and
2x function (Figure 2), color retinal imaging (Figures 3
and 4A), red-free imaging (Figure 4B), cobalt blue imaging
for nerve fiber layer assessment, and FAF imaging
(Figure 4C) with an exciter filter (530-580 nm) and a
near infrared barrier filter (640 nm). FAF images were
analyzed for hypoautofluorescence or hyperautofluorescence
as an indicator of lipofuscin accumulation and
retinal health. The CX-1 has fluorescein angiographic
capabilities, but these were not used in our screening
protocol, as we focused on noninvasive procedures only.
DISCUSSION
Fundus autofluorescence provides an index of RPE
lipofuscin8 that can be used for (1) enhancing our
understanding of retinal disease pathogenesis by tracking
temporal changes in lipofuscin deposition and distribution;
(2) determining diagnosis of certain retinal
disorders before detectable functional loss; (3) identifying
risk factors that may affect lipofuscin accumulation
in the fundus; (4) differentiating diseases with similar
lipofuscin signatures; (5) visualizing RPE damage (Figures 5A and B) and subsequent cell migration and
proliferation, such as after laser treatment for diabetic
retinopathy or macular edema;9 and (6) differentiating
choroidal melanocytic lesions and studying the effects
of treatment.10
CONCLUSION
The spectral sensitivity range of FAF was detected in
the area of the RPE and deeper layers.
We have illustrated the usefulness of this technology in diabetic retinopathy, age-related macular degeneration, and ocular trauma. Early detection of VTDs along with lifestyle changes and timely intervention can improve outcomes of certain VTDs such as diabetic retinopathy. In community-based screenings, FAF can improve early detection of VTDs and provide timely referral of patients for treatment of subtle retinal changes that are not well detected with conventional color or red-free retinal imaging.
Bernard Szirth, PhD, is the Director of TeleOphthalmology at the Institute of Ophthalmology and Visual Science at New Jersey Medical School, Newark, New Jersey. Dr. Szirth reports that he is an ophthalmic consultant for Canon Medical Systems. He can be reached at Szirthgone@aol.com.
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