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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
 
Am J Ophthalmol. Author manuscript; available in PMC 2010 September 1.
Published in final edited form as:
PMCID: PMC2731819
NIHMSID: NIHMS115150

Correlation between Spectral Optical Coherence Tomography and Fundus Autofluorescence at the margins of Geographic Atrophy

Abstract

Purpose

We studied the appearance of margins of Geographic atrophy in high- resolution optical coherence tomography (OCT) images and correlate those changes with fundus autofluorescence imaging.

Design

Retrospective observational case study.

Methods

Patients with geographic atrophy secondary to dry age related macular degeneration (ARMD) were assessed by means of Spectral Domain OCT (Spectralis HRA/OCT; Heidelberg Engineering, Heidelberg, Germany or OTI, Inc, Toronto, Canada) as well as Autofluoresence Imaging (HRA or Spectralis Heidelberg Engineering, Heidelberg, Germany): The outer retinal layer alterations were analyzed in the junctional zone between normal retina and atrophic retina, and correlated with corresponding fundus autofluorescence.

Results

23 eyes of 16 patients aged between 62 years to 96 years were examined. There was a significant association between OCT findings and the fundus autofluorescence findings(r=0.67, p<0.0001). Severe alterations of the outer retinal layers at margins on Spectral OCT correspond significantly to increased autofluorescence; Smooth margins on OCT correspond significantly to normal fundus autofluorescence. (Kappa-0.7348, p<0.0001).

Conclusion

Spectral OCT provides in vivo insight into the pathogenesis of geographic atrophy and its progression. Visualization of reactive changes in the retinal pigment epithelial cells at the junctional zone and correlation with increased fundus autofluorescence; secondary to increased lipofuscin may together serve as determinants of progression of geographic atrophy.

Introduction

Geographic atrophy is responsible for approximately 20% of legal blindness attributable to age related macular degeneration (ARMD) and will become even more prevalent with the growth of the elderly population1 2. The pathophysiologic mechanism of retinal pigment epithelium (RPE) cell atrophy with corresponding atrophy of the choriocapillaries and outer neurosensory retinal layers in this disorder still remain unclear. Several lines of experimental and clinical evidence indicate that lipofuscin accumulation in the lysosomal compartment of RPE cells plays a critical role in the disease process 3 4 5 6. This is supported by in vitro studies. 7

Various studies done in the past using fundus auto fluorescence have shown that lipofuscin laden RPE cells in the junctional zone of geographic atrophy correspond to the band of increased autofluorescence 8 9 10. Optical coherence tomography (OCT) is another way to study tissue morphology in situ and in real time without the need to excise and process specimens. With the advent of spectral domain OCT (SD-OCT) it is now possible to differentiate 11 structural characteristics within the retina including visualization of photoreceptor and pigment epithelial morphology as well as subtle changes associated with disease process11-12. The purpose of our study was to characterize the OCT changes occurring in the junctional zones of geographic atrophy using spectral OCT images and correlate it with the fundus autofluorescence findings.

Methods

We retrospectively examined Spectral OCT scans, fundus autofluorescence images, color fundus photographs and fluorescein angiography images of 16 consecutive patients with geographic atrophy. All studies were performed at the UCSD Jacobs Retina Center and all imaging and clinical examinations were performed within 4 weeks of each other. All patients included in our study underwent a thorough clinical examination with best corrected visual acuity using ETDRS charts, indirect ophthalmoscopy, color fundus photography and fluorescein angiography to confirm the diagnosis of geographic atrophy.

Inclusion Criteria

Eyes with geographic atrophy secondary to dry ARMD were included. Geographic atrophy was defined as one or more discrete areas of loss of RPE measuring 0.5mm or more in greatest linear diameter, with a color change relative to the surrounding RPE and more prominent visualization of the choroidal vessels13. Only eyes with a good quality fundus autofluorescence images were studied.

Exclusion Criteria

Eyes with atrophy of RPE secondary to wet AMD, hereditary retinal diseases and laser photocoagulation were excluded from the study. In addition eyes with pathological myopia, inflammatory choroidopathies, retinal detachment, and ocular trauma or vitreoretinal surgeries were not included in the study.

Instruments

Spectral OCT images reviewed in the study were obtained using the Spectralis HRA/OCT (Heidelberg Retinal Angiograph, Heidelberg Engineering, Heidelberg, Germany) or Spectral OCT (OTI, Inc, Toronto, Canada.). Spectralis combines high-resolution spectral domain OCT with a scanning laser ophthalmoscope (SLO). The system allows for simultaneous OCT scans with fundus autoflorescence imaging, Infrared imaging, Fluorescein angiography or indocyanine green (ICG) angiography. The instrument uses a broadband 870nm super luminescent diode laser (SLD) for the OCT channel. The retina is scanned at 40,000 A-scans per second, creating highly detailed images of the structure of the retina with an optical depth resolution of 7um. Twenty five OCT scans were averaged to reduce speckle noise. The OTI spectral domain OCT captures pseudo-simultaneous OCT and SLO image pairs and also allowed us to co-localize the spectral domain OCT with retinal lesions and autofluoresence images14 {Mojana F, et al. IOVS 2008; ARVO E-abstract # 260, Brar M, et al. IOVS 2008;ARVO E-abstract # 926}. It uses a modified superluminescent diode with a 40nm bandwidth centered at 830nm wavelength, thus achieving an axial resolution up to 5-7 microns and a transverse one of 16 microns. It has a scanning speed of up to 28,000 A–scans per second. Each B-scan is composed of 512 A-scans and requires 0.182 seconds to acquire. A set of 128 B-scans is acquired covering an area of 8mm × 8mm through the macula. The operator, who manually sweeps the line cursor overlapping the fundus images, chooses the scan orientation in the x-y plane. The fundus images are obtained with a confocal scanning laser ophthalmoscope combined with the OCT system. Fundus autofluorescence images were recorded using Spectralis or a confocal Scanning Laser Ophthalmoscope (HRA2, Germany), the optical and technical principles of which have been described previously 15 16 17. The field size was selected as 30° × 30° at 1,536 × 1,536 pixels. A time sequence of 9-25 frames was captured. The exact number of frames varied between patients and was dependent on media clarity.

Image Selection and Grading

Two reviewers independently graded the fundus autofluorescence and OCT images of each patient and were not aware of the results of one modality when scoring for the other. They reviewed OCT images at the junctional zone between normal retina and atrophic area. Outer retinal layer alterations were studied in the junctional zone and margins of GA lesion were divided into two groups. Horizontal and vertical scans approximately passing through the center of the lesion were chosen and all the four (superior, inferior, nasal, temporal) margins were reviewed and each margin was classified into type 1 or type 2.

Patients in whom margins of GA were found to be smooth with no alterations of the outer retina were classified as type 1 (figure 3) and the other group with severe alterations in the outer retinal layers; irregular margins with or without increased optical reflectivity of the RPE were classified into type 2 (figure 4). Corresponding auto fluorescence at all the four margins was reviewed separately by two independent reviewers and classified again into two types. Type 1 comprise of no abnormal fundus autofluorescence (figure 3) and type 2 (figure 4), for increased autofluorescence at the margins of GA. The Spectralis HRA/OCT allows simultaneous OCT scans and fundus autofluorescence. But for those set of patients who had spectral OCT scans done using OTI, (OCT/SLO, OTI Inc, Toronto, Canada) fundus autofluorescence images were overlaid on the corresponding SLO image considering the vessel as a reference for a correct alignment.

Figure 3
Fundus autofluorescence and spectral OCT images from an 87-year woman with geographic atrophy. Fundus autofluorescence image shows a continuous band of abnormal increased autofluorescence at the margins of geographic atrophy. Corresponding Spectral OCT ...
Figure 4
Fundus autofluorescence and Spectral OCT images with horizontal scans at two different levels in a patient with geographic atrophy. TOP: Spectral OCT shows irregular margins with structural alterations at the outer retina (Black arrow) corresponding to ...

Statistical analysis

Two observers graded the same patient on the four margins of the same lesion. In order to examine if there is a general association between OCT findings and fundus autofluorescence findings, Cochran-Mantel-Haenszel test was performed using observer and patient as the strata.

The agreement of ratings by each observer based on two instruments was measured by calculating the Kappa within each observer. The agreement was also measured and tested between the two observers. In addition, correlation among the four margins of each eye on both OCT and fundus autofluorescence was analyzed using Spearman correlation test. All tests were two tailed and p<0.05 was considered statistically significant (SAS software v 9.2, Cary, North Carolina).

Results

23 eyes of 16 patients (9 women, 7 men) aged between 62 to 96 years with unifocal or multifocal geographic atrophy due to dry AMD were included in the study. We examined 4 margins per eye, if both eyes were included in the study i.e. 8 margins per patient. There was a good agreement between two observers in terms of grading the lesions on OCT (kappa = 0.8644, p< 0.0001) and fundus autofluorescence image (kappa = 0.9762, p< 0.0001).

After adjustment (using Cochran-Mantel-Haenszel test) of inter-observer and intra patient there was a significant association between OCT findings and the fundus autofluorescence findings (r=0.67, p<0.0001) OCT seen changes in the junctional zone including outer retinal layer alterations were found to correlate well with increased fundus autofluorescence and smooth margins with no structural changes were appreciated at points correlating to areas with normal fundus autofluoresence (kappa-0.7348, p,0.0001)(Table 1). In most cases with increased fundus autofluorescence at the margin there was a corresponding structural alteration at the outer retina (93.64%) (Figure 3,,55).

Figure 5
Simultaneous fundus autofluorescence and Spectral OCT image from Spectralis (HRA + OCT) in a patient with geographic atrophy: Fundus autofluorescence image shows diffusely increased FAF(arrowhead) and corresponding horizontal scan on Spectral OCT shows ...
Table 1
Correlation between Spectral OCT and Fundus autofluorescence at the margins of Geographic atrophy in 23 eyes (92 margins)*.

Highly reflective material at the level of RPE and irregularities found in the junctional zone, are possibly caused by RPE hypertrophy and /or phagocytosed melanin by RPE /macrophages18, 19. In the lesions showing no abnormalities in autofluoresence, the smooth OCT margins suggest no abnormal accumulation of lipofuscin and thus no changes in the RPE cells (78.38%) (Figure 2). We also statistically analyzed the correlation between fundus autofluorescence and the type of OCT margin by randomly picking up one margin (temporal) per eye per patient. Kappa value was 0.7089, p<0.0002. In addition to this, there was found to be a correlation although not strong among four margins of each eye on OCT and fundus autofluorescence (Table 2).

Figure 2
Fundus autofluorescence and Spectral OCT images from a 74 year old man with geographic atrophy. Fundus autofluorescence image showed no abnormal increased auto fluorescence at the margins. Horizontal scan on OCT showed atrophic outer retina with loss ...
Table 2
Correlation of four margins of each eye with geographic atrophy on Spectral OCT and fundus autofluorescence.

Discussion

Geographic atrophy is defined as any sharply delineated round or oval area of hypopigmentation or depigmentation or apparent absence of the RPE, in which choroidal vessels are more visible than in the surrounding areas and which must be at least 175μm in diameter20 However, since such a small area could result from the regression of a single drusen, other proposed dimensions have been wider, varying from 200 μm21, 500μm13, 700 um22 to 1mm23. We studied eyes with geographic atrophy at least 500μm in its greatest linear diameter as was done in the recent past by other study groups 24.

With the advent of novel combined high resolution OCT-SLO system it has become possible to get simultaneous fundus autofluorescence / OCT images making it easier to find small changes in fundus autofluorescence and analyze them on OCT25. In our study, we have shown that there is a statistically significant correlation between pattern of fundus autofluorescence and type of OCT margin in patients of geographic atrophy secondary to AMD. In our cross-sectional analysis we identified two distinct patterns of structural changes at the margins of geographic atrophy on spectral OCT corresponding to specific fundus autofluorescence patterns. Those areas showing increased fundus autofluorescence have a corresponding irregular margin on OCT as compared to the second group with no abnormal fundus autofluorescence at the margins and corresponding smooth margin on OCT.

Geographic atrophy in association with AMD has been shown to gradually enlarge over time26, 13, 21. Recent study done by Sunness et al using stereo color fundus photographs has reported the median overall enlargement rate of geographic atrophy to be 2.1mm2/year24. Further studies using fundus autofluorescence have shown that increased fundus autofluorescence patterns at the junctional zone precede the development and enlargement of preexisting geographic atrophy9. It has also been indicated that progression is smaller in eyes with minimal or no fundus autofluorescence alterations at the junctional zone as opposed to eyes with widespread diffuse changes27.

Our study using spectral OCT provides in vivo insight into the morphological alterations at the margins of geographic atrophy. Findings in our study correlate well with the histopathological studies performed in the past 7. In those studies, lipofuscin and melanolipofuscin-filled RPE cells were observed in the junctional zone between the atrophic and the normal retina. In the zone of severe degeneration towards the atrophic region, RPE cells were found to become increasingly abnormal in shape and cell drop out was evident. Close to the edge of the atrophic area large hyper-pigmented RPE cells were observed to be shed into the subretinal space. Many of those cells contained large membrane bound bodies filled with fused lipofuscin and the subsequent increased autofluorescence granules in these cells is not only the result of autophagy and outer segment phagocytosis but also of engulfment of cellular debris, including spent RPE cells. In our study outer retinal changes seen on Spectral OCT might suggest abnormal hypertrophic and damaged RPE cells with increased lipofuscin correlating to increased auto fluorescence on fundus autofluorescence image as well.

In summary, combined OCT-SLO system used in our study allows detection of small structural changes at the margins of geographic atrophy. Currently there is no gold standard predictor of vision loss in geographic atrophy, but large studies using fundus autofluorescence has shown that progression rates in eyes with increased fundus autofluorescence were significantly higher compared to eyes without fundus autofluorescence abnormalities 9 27. Fundus autofluorescence is a useful predictor for assessing the progression of geographic atrophy but spectral OCT gives us a low power in vivo insight into the structural changes at the junctional zone. Since spectral domain imaging allows visualization of the pathological structural changes it is intriguing to speculate that OCT changes might be a better predictor than autofluorescence of geographic atrophy prediction. Our study only shows that the two changes are correlated but does not allow determination of which was the better predictor of clinical progression. The ability to anatomically classify the margins of geographic atrophy on Spectral OCT might serve as a prognostic determinant of geographic atrophy progression together with fundus autofluorescence. Future longitudinal studies may further contribute to understand the progression of geographic atrophy.

Figure 1
Normal retina as imaged by HRA + OCT (SPECTRALIS). Arrows: Different outer retinal layers as imaged by spectralis. External limiting membrane (ELM), IS/OS (inner segment outer segment junction) and RPE (retinal pigment epithelium layer. Inset; Magnified ...

Acknowledgments

A. Funding/Support: None.

B. Financial Disclosures: This study was supported by the Research to Prevent Blindness (RPB), New York, New York the Department National Eye Institute (NIH-NEI) Grant No. EY16323 (Dr Bartsch), and the National Institutes of Health (NIH) Grant No. EY07366 (Dr Freeman). Dr Freeman is the recipient of an RPB Physician Scientist award. Dr Bartsch has received discounted products and specialized software from OTI, Inc.

D. Statement about conformity with Author information: The University of California San Diego Institutional Review Board approval was obtained to conduct this study. Informed consent for research was obtained from the patients and the study is in accordance with Health Insurance Portability and Accountability Act.

E. Other Acknowledgements: None.

Biography

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Manpreet Brar, MD, graduated from Govt. Medical College, Chandigarh, India. She completed her residency at the Dept. of Ophthalmology, Christian Medical College, Ludhiana, India in December 2004 and is presently undergoing a retina fellowship at Jacobs Retina Center, Shiley eye Center, University of California San Diego, USA.

Footnotes

C. Contributions to the authors: Involved in design of study (W.R.F., M.B., I.K.); collection and management of data (M.B, I.K., F.M., R.Y.); interpretation of data (I.K., L.C., W.R.F, M.B.); preparation of manuscript (M.B., N.N. D.U.B); and approval of final manuscript (W.R.F., S.O).

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