Cone structure imaged with adaptive optics scanning laser ophthalmoscopy in eyes with nonneovascular age-related macular degeneration

Abstract

Purpose: To evaluate cone spacing using adaptive optics scanning laser ophthalmoscopy (AOSLO) in eyes with nonneovascular AMD, and to correlate progression of AOSLO-derived cone measures with standard measures of macular structure.

Methods: Adaptive optics scanning laser ophthalmoscopy images were obtained over 12 to 21 months from seven patients with AMD including four eyes with geographic atrophy (GA) and four eyes with drusen. Adaptive optics scanning laser ophthalmoscopy images were overlaid with color, infrared, and autofluorescence fundus photographs and spectral domain optical coherence tomography (SD-OCT) images to allow direct correlation of cone parameters with macular structure. Cone spacing was measured for each visit in selected regions including areas over drusen (n = 29), at GA margins (n = 14), and regions without drusen or GA (n = 13) and compared with normal, age-similar values.

Results: Adaptive optics scanning laser ophthalmoscopy imaging revealed continuous cone mosaics up to the GA edge and overlying drusen, although reduced cone reflectivity often resulted in hyporeflective AOSLO signals at these locations. Baseline cone spacing measures were normal in 13/13 unaffected regions, 26/28 drusen regions, and 12/14 GA margin regions. Although standard clinical measures showed progression of GA in all study eyes, cone spacing remained within normal ranges in most drusen regions and all GA margin regions.

Conclusions: Adaptive optics scanning laser ophthalmoscopy provides adequate resolution for quantitative measurement of cone spacing at the margin of GA and over drusen in eyes with AMD. Although cone spacing was often normal at baseline and remained normal over time, these regions showed focal areas of decreased cone reflectivity. These findings may provide insight into the pathophysiology of AMD progression. (ClinicalTrials.gov number, NCT00254605).

Keywords: adaptive optics; age-related macular degeneration; cones; scanning laser ophthalmoscopy.

Figures

Figure 1

Clinical images and AOSLO outline. For each study patient, color fundus photograph obtained at baseline is shown with SD-OCT scan superimposed, and area imaged with AOSLO at baseline outlined in black. White horizontal lines represent location of OCT scan. Black dot denotes fixation. Green, yellow, and blue numbers within AOSLO image outline represent locations of ROIs where cone spacing was analyzed in each AOSLO image during the study (Green: intact retinal areas with no drusen or geographic atrophy, yellow: ROIs over drusen, blue: ROIs at the margin of geographic atrophy). White scale bar at lower left corner of each color fundus image: 200 μm.

Figure 2

Morphologic features of AOSLO images from healthy retinal area in an eye with intermediate AMD. Left: color fundus photograph obtained at baseline from the left eye of patient 4 with registered SD-OCT scan. Optical coherence tomography line is indicated in white. Fixation is denoted by black dot. Area surrounding ROI N1 is outlined in blue. Color fundus image shows normal-appearing retinal area and OCT scan shows preserved outer nuclear layer (ONL), photoreceptor IS/OS and RPE layers. Middle: magnified AOSLO image registered on infrared fundus image, showing cones as bright profiles arranged into continuous mosaics. Dark features represent over-riding retinal vessels. Right: magnified AOSLO image of region N1. Scale bar: 15 arc minutes.

Figure 3

Cone spacing measurements in eyes with nonneovascular AMD at retinal regions showing no evidence of drusen or geographic atrophy. Right: cone spacing measures from nonneovascular AMD patients and healthy subjects versus retinal eccentricity. Each ROI was imaged at several follow-up visits, thus, multiple symbols are shown to represent the serial measures of cone spacing obtained from each ROI as listed in the legend on the right. Data from age-matched healthy subjects are plotted as small gray dots. Dark solid line indicates best fit to normal data. Dashed lines: 95% confidence limits of the best fit. Left images: AOSLO images and corresponding SD-OCT scans obtained from healthy retinal regions at baseline and at the last follow-up visit for that patient. Individual cones within mosaics identified in each AOSLO image are denoted by red cross-hairs. White scale bar: 15 arc minutes. Red box on OCT images denotes the area for which a corresponding magnified AOSLO image is shown above. Upper panel: patient 4, left eye, region N2. Cone spacing was measured at different locations of the cone mosaic identified within the same ROI between the visits where cones were unambiguously seen. Spectral domain optical coherence tomography images show normal outer retinal layers at the ROI. Lower panel: patient 6, right eye, location N2. Registered SD-OCT images show normal outer retinal morphology within the ROI that remained unchanged during the study period. Large dark features at the left area of each AOSLO image represents shadowing from a retinal blood vessel. Cone spacing values obtained from all normal regions were normal at baseline and remained within the normal range during the study.

Figure 4

Morphologic features of AOSLO images from retinal areas over drusen in eyes with nonneovascular AMD. AOSLO images from region D12 of patient 7 obtained at baseline and after 21 months of follow up are registered with Heidelberg SD-OCT scans. The exact OCT scan location is indicated by the white line. The green and orange boxes indicate areas of the magnified AOSLO images shown in green and orange insets, respectively. Scale bar: 15 arc minutes.

Figure 5

Adaptive optics scanning laser ophthalmoscopy images from regions over drusen at which cone spacing values were marginally increased at baseline compared with normal. Shown are two ROIs from the right eye of patient 6 (D3, D5). For each ROI, the corresponding SD-OCT and magnified AOSLO images are shown in the upper and lower panels, respectively (region D3: Light blue; region D5: Light green). Box on OCT cross-section image denotes the exact location of the ROI analyzed. Scale bar on AOSLO images: 15 arc minutes.

Figure 6

Cone spacing measurements in eyes with nonneovascular AMD at regions over drusen. Left images: AOSLO images and corresponding SD-OCT scans obtained from ROIs over drusen at baseline and at the last follow-up visit. Individual cones within mosaics identified in each AOSLO image are labeled by red cross-hairs. Red bars on OCT images denote the area for which a magnified AOSLO image is shown above. Upper panel: patient 7, right eye, location drusen 4. Spectral domain optical coherence tomography images show increased lateral extent and height of the druse at 21 months versus baseline. Cone spacing values obtained from this region were normal at baseline and remained within the normal range during the study. Lower panel: patient 5, left eye, location drusen 3. Registered SD-OCT images show stable drusen morphology in this ROI during the study period. Cone spacing values from this region were normal throughout the study period. Upper right: cone spacing measures from eyes with nonneovascular AMD and age-similar, visually healthy control subjects versus retinal eccentricity. Data from control subjects are plotted as small gray dots. Dark solid line indicates best fit to normal data. Dashed lines: 95% confidence limits of the best fit. Each ROI was imaged at several time points and multiple data-points are shown for each ROI to represent the serial spacing measures obtained during the study. Lower right: change in cone spacing measured at baseline and at each study visit for each ROI. All spacing values from all drusen ROIs remained within the normal range during the study period.

Figure 7

Morphologic features of AOSLO images in retinal areas adjacent to geographic atrophy margins. Left column: AOSLO images from ROI GA2 from the left eye of patient 2 at baseline and after 12 months of follow up are registered with infrared fundus images and SD-OCT scans. White lines indicate the location of the OCT sections, which skim the edges of the GA regions. The green and dark blue boxes (left) indicate areas of magnified AOSLO images shown in green and dark blue insets in the right column, respectively. Areas of reduced cone reflectivity seen as hyporeflective AOSLO signal around the margin of geographic atrophy correspond with hyporeflectivity of the IS/OS layer in the SD-OCT images (asterisks). Scale bar: 15 arc minutes.

Figure 8

Cone spacing measurements in eyes with nonneovascular AMD near margins of geographic atrophy. For each study eye, images obtained from regions of interest at the margins of geographic atrophy at baseline and at the last follow-up visit, including color fundus photograph and infrared fundus image, are shown. Locations of ROIs identified at the margins of GA are denoted on each infrared image. A magnified AOSLO image from one ROI is shown on the right of each panel. On each magnified AOSLO image, individual cones identified are denoted with red cross-hairs. White scale bar on color fundus photographs: 200 μm. Black scale bar on AOSLO images: 15 arc minutes. Upper left panel: patient 1, right eye. Upper right panel: patient 1, left eye. Lower right panel: patient 2, left eye. Lower right panel: patient 3, left eye. Lower left: Cone spacing measures from eyes with nonneovascular AMD and age-similar visually healthy control subjects versus retinal eccentricity. Data from the control subjects are plotted as small gray dots. Dark solid line indicates best fit to normal data. Dashed lines: 95% confidence limits of the best fit. Patient 3 shows mildly increased cone spacing to the near-normal level at locations GA4 and GA5, but all other GA regions derived normal or near-normal cone spacing measures throughout the entire study period. Lower right: Cone spacing measures from all ROIs identified at GA margin versus follow-up time.

Figure 9

Proposed simplified model to explain loss of visibility of cones at the edge of advancing GA. Cones and RPE cells in regions without GA (left side of illustration and registered SD-OCT image) are closely packed, have near normal spacing and are easily imaged owing to their inherent wave-guiding properties. Closer to the GA, the RPE cell health is compromised, resulting in subsequent loss of cone wave-guiding properties, even though the cones are still present. Finally, the RPE cells along with their corresponding cones die to form a region of GA. Cones at the edge of GA are still present, but because their wave-guiding properties are compromised they are less visible in OCT and AOSLO images. Rods are not shown in this simplified model but their loss is assumed to take place through a similar mechanism.