MyVisionTest News Archive
Sep 18, 2009
Spectral-domain OCT and fundus autofluorescence in geographic atrophy
A new study that compares images obtained with high-resolution spectral-domain optical coherence tomography (OCT) to those with fundus autofluorescence (FAF) imaging in patients with geographic atrophy finds that severe alterations of the outer retinal layers on spectral-domain OCT correspond significantly to increased autofluorescence.
Geographic atrophy is the end-stage of dry AMD. Geographic atrophy is defined as any sharply delineated round or oval area of hypopigmentation or depigmentation or apparent absence of the retinal pigment epithelium (RPE) in which choroidal vessels are more visible than in the surrounding areas and that must be at least 175 um diameter. However, such a small area may result from the regression of a single drusen. Other proposed dimensions have been wider, varying from 200 um up to 1 mm.
The pathophysiologic mechanism of 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 RPE cells plays a critical role in the disease process.
Geographic atrophy in association with AMD has been shown to enlarge gradually over time. The enlargement rate of geographic atrophy is approximately 2 mm2/year. Studies using FAF have shown that increased FAF patterns at the junctional zone (at the margins of atrophic regions) precede the development and enlargement of preexisting geographic atrophy. It also has been indicated that progression is smaller in eyes with minimal or no FAF alterations at the junctional zone, as opposed to eyes with widespread diffuse changes. Various studies have shown that lipofuscin-laden RPE cells in the junctional zone of geographic atrophy correspond to the band of increased autofluorescence in the junctional zone.
Methods and Results
Patients with geographic atrophy secondary to dry AMD were assessed by means of spectral-domain OCT as well as autofluorescence imaging. The outer retinal layer alterations were analyzed in the junctional zone between normal retina and atrophic retina and were correlated with corresponding FAF.
Twenty-three eyes of 16 patients between 62 and 96 years of age were examined. There was a significant association between OCT findings and the FAF findings. Severe alterations of the outer retinal layers at margins on spectral-domain OCT correspond significantly to increased autofluorescence; smooth margins on OCT correspond significantly to normal FAF.
Discussion and Conclusions
With the advent of the novel, combined high-resolution OCT and SLO system, it has become possible to obtain simultaneous FAF and OCT images, making it easier to find small changes in FAF and to analyze them on OCT. In this study, a statistically significant correlation was found between the pattern of FAF and the type of OCT margin in patients with geographic atrophy secondary to AMD. Two distinct patterns of structural changes at the margins of geographic atrophy were found on spectral-domain OCT corresponding to specific FAF patterns. Those areas showing increased FAF have a corresponding irregular margin on OCT as compared with the second group with no abnormal FAF at the margins and corresponding smooth margin on OCT. These findings are consistent with known histopathologic changes that occur in geographic atrophy.
In summary, the combined OCT and SLO system used in this 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 FAF have shown that progression rates in eyes with increased FAF were significantly higher compared with eyes without FAF abnormalities. FAF is a useful predictor for assessing the progression of geographic atrophy. Because spectral-domain imaging allows visualization of structural changes, it is intriguing to speculate that OCT changes may be a better predictor than autofluorescence of geographic atrophy. This study shows only that these changes are correlated, but does not allow determination of which was the better predictor of clinical progression.
Read more...
Am J Ophthalmol 2009;148:439–444
Tags: dry AMD, OCT, fundus autofluorescence
A new study that compares images obtained with high-resolution spectral-domain optical coherence tomography (OCT) to those with fundus autofluorescence (FAF) imaging in patients with geographic atrophy finds that severe alterations of the outer retinal layers on spectral-domain OCT correspond significantly to increased autofluorescence. Geographic atrophy is the end-stage of dry AMD. Geographic atrophy is defined as any sharply delineated round or oval area of hypopigmentation or depigmentation or apparent absence of the retinal pigment epithelium (RPE) in which choroidal vessels are more visible than in the surrounding areas and that must be at least 175 um diameter. However, such a small area may result from the regression of a single drusen. Other proposed dimensions have been wider, varying from 200 um up to 1 mm.
Geographic atrophy in association with AMD has been shown to enlarge gradually over time. The enlargement rate of geographic atrophy is approximately 2 mm2/year. Studies using FAF have shown that increased FAF patterns at the junctional zone (at the margins of atrophic regions) precede the development and enlargement of preexisting geographic atrophy. It also has been indicated that progression is smaller in eyes with minimal or no FAF alterations at the junctional zone, as opposed to eyes with widespread diffuse changes. Various studies have shown that lipofuscin-laden RPE cells in the junctional zone of geographic atrophy correspond to the band of increased autofluorescence in the junctional zone.
Methods and Results
Patients with geographic atrophy secondary to dry AMD were assessed by means of spectral-domain OCT as well as autofluorescence imaging. The outer retinal layer alterations were analyzed in the junctional zone between normal retina and atrophic retina and were correlated with corresponding FAF.
Twenty-three eyes of 16 patients between 62 and 96 years of age were examined. There was a significant association between OCT findings and the FAF findings. Severe alterations of the outer retinal layers at margins on spectral-domain OCT correspond significantly to increased autofluorescence; smooth margins on OCT correspond significantly to normal FAF.
Discussion and Conclusions
With the advent of the novel, combined high-resolution OCT and SLO system, it has become possible to obtain simultaneous FAF and OCT images, making it easier to find small changes in FAF and to analyze them on OCT. In this study, a statistically significant correlation was found between the pattern of FAF and the type of OCT margin in patients with geographic atrophy secondary to AMD. Two distinct patterns of structural changes at the margins of geographic atrophy were found on spectral-domain OCT corresponding to specific FAF patterns. Those areas showing increased FAF have a corresponding irregular margin on OCT as compared with the second group with no abnormal FAF at the margins and corresponding smooth margin on OCT. These findings are consistent with known histopathologic changes that occur in geographic atrophy. In summary, the combined OCT and SLO system used in this 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 FAF have shown that progression rates in eyes with increased FAF were significantly higher compared with eyes without FAF abnormalities. FAF is a useful predictor for assessing the progression of geographic atrophy. Because spectral-domain imaging allows visualization of structural changes, it is intriguing to speculate that OCT changes may be a better predictor than autofluorescence of geographic atrophy. This study shows only that these changes are correlated, but does not allow determination of which was the better predictor of clinical progression.
Read more...
Am J Ophthalmol 2009;148:439–444
