Patients aged 50 years or more with GA secondary to dry ARMD have been included into this prospective cross-sectional study. Inclusion criteria included clear media to allow FAF imaging and a total area of GA larger than 0.5 mm2. Only one eye of each patient was included in the study. If both eyes qualified for the study, the eye with the better visual acuity (VA) was used. Exclusion criteria included any history of retinal surgery, laser photocoagulation, or other retinal diseases in the study eye, including diabetic retinopathy or hereditary retinal dystrophies, and refractive error of more than 3 D. Fluorescein angiography was performed only if there were funduscopic signs indicative of exudative ARMD in addition to GA. Such eyes were excluded from the study. All subjects underwent FAF, infrared (IR), and simultaneous spectral OCT (Spectralis HRA+OCT; Heidelberg Engineering, Heidelberg, Germany) imaging. In addition, we performed a comprehensive ocular examination with best-corrected visual acuity (BCVA) using Early Treatment Diabetic Retinopathy Study (ETDRS) charts, binocular ophthalmoscopy color fundus photography (FF 450 plus; Carl Zeiss Meditec, Jena, Germany), and fluorescein angiography using the Heidelberg Retina Angiograph (HRA, Heidelberg Engineering). In addition, ARMD risk factors (e.g., sex, family history, and status of smoking) were assessed with a standardized questionnaire.
The Spectralis HRA+OCT combines high-resolution spectral domain OCT with an SLO. The system allows for simultaneous OCT scans with FAF imaging, infrared imaging, blue light reflectance imaging, fluorescein angiography, or indocyanine green (ICG) angiography. The instrument uses broadband 870-nm super luminescent diode (SLD) for the OCT channel. The retina is scanned at 40,000 A-scans per second, crating highly detailed images of the structure of the retina. The OCT optical depth resolution is 7 μm, the digital depth resolution, 3.5 μm. The combination of high-resolution scanning laser retinal images and spectral domain OCT allows for real-time tracking of eye movements and real-time averaging of scanning laser images and OCT scans, reducing speckle noise of the OCT images. Twenty-five OCT scans were averaged to reduce speckle noise by a factor five.
Before examination, the pupil of the study eye was dilated with drops containing 0.5% tropicamide and 2.5% phenylephrine. We obtained two spectral OCT scans in cross-hair fashion centered on the fovea. Thereafter, combined FAF images and spectral OCT images were recorded.
The spectral OCT images were graded as follows: The integrity of the retinal layers was analyzed in the areas with apparently normal retina, the junctional zone between the normal retina and the geographic atrophy, and within the atrophic area. Especially, the presence and integrity of the external limiting membrane (ELM), the photoreceptor inner segment (IS), the outer segment (OS), and the retinal pigment epithelium (RPE) was assessed. The presence of a third hyperreflective layer just above the RPE and the below the IS/OS complex was noted. In addition, integrity of the inner retinal layers, foveal depression, and presence of intraretinal fluid accumulation were evaluated
(Fig. 1) .
FAF images were classified according to Holz et al.
15 as follows: group 1, GA without any abnormal FAF outside the area of atrophy; group 2, GA with a
continuous band at the margin with variable peripheral extension; group 3, GA with a
diffusely increased FAF at the entire posterior pole; and group 4, GA surrounded from
small focal spots of increased FAF in the junctional zone.
All images were assessed by two independent graders from the Bern Photographic Reading Center (BPRC) in blinded fashion. In case of discrepancies between the two observers, the differences were discussed, and a third observer was asked to arbitrate.
The research adhered to the tenets of the Declaration of Helsinki and was approved by the Institutional Review Board. Informed consent was obtained from each subject after explanation of the nature and possible risks of the study.