Automated detection of clinically significant macular edema by grid scanning optical coherence tomography

Abstract

Objective: To compare the detection of clinically significant diabetic macular edema (DME) by an optical coherence tomography (OCT) grid scanning protocol and biomicroscopic examination.

Design: Retrospective case series.

Participants: Outpatients at the Doheny Eye Institute.

Methods: The clinical and imaging records of a consecutive series of 71 eyes of 40 patients referred for DME who underwent OCT using the both the Macular Grid 5 (MG5) scanning protocol (to allow a more evenly distributed sampling of points in the macula) and the standard Fast Macular Thickness Map (FMTM) pattern were reviewed. An automated algorithm was developed to generate a retinal thickness map using the MG5 data, which was then compared with a normative database to identify presumed areas of retinal edema. Clinically significant macular edema (CSME) was also identified by clinical examination and stereoscopic fundus photographs for comparison with the results of the OCT protocols.

Main outcome measures: Sensitivity and specificity of scanning protocols.

Results: Optical coherence tomograms were inspected visually, and automatically detected retinal boundaries were found to be correct in 69 of 71 MG5 scans and in 65 of 71 FMTM scans. Macular Grid 5 scanning was performed twice in each eye, and the repeatability (pooled standard deviation) of the total area of edema was 0.48 mm2 (coefficient of variation, 6.8%). Sensitivity and specificity of the MG5 for detection of CSME relative to the clinical examination were 89% and 86%, respectively, with kappa being 0.74. Macular Grid 5 and FMTM assessment of foveal CSME also showed good agreement, with kappa being 0.68.

Conclusions: The analysis algorithm for the OCT MG5 grid scan seems to be accurate and repeatable. Automated detection of CSME by the MG5 analysis correlated well with the clinical grading and standard OCT analysis (FMTM). Macular Grid 5 provides more information regarding the perifoveal macula than FMTM and may be of value to clinicians in planning treatment and in future studies of macular edema.

Figures

Figure 1

A, Macular grid 5 (MG5) scan pattern (768 A-scans spiral from center outward; grid spacing, 0.14 mm in central 3 mm and 0.29 mm between 3 and 5 mm). B, Optical coherence tomography (OCT) image of MG5. C, Fast Macular Thickness Map scan pattern (6 radial line scans). D, Six OCT images corresponding to each of the 6 lines.

Figure 2

Gap between A-scan points plotted against distance from the center point (radius) for Fast Macular Thickness Map (FTM) scans and Macular Grid 5 (MG5) scans.

Figure 3

Population average and standard deviation (SD) of retinal thickness map of normal reference. N = nasal; T = temporal.

Figure 4

Segmentation of grid optical coherence tomography image (displayed 2-dimensionally). Upper white line, inner retinal boundary; lower white line, inner segment/outer segment junction. The retinal thickness is defined as the distance between the 2 lines.

Figure 5

Bland–Altman plot of foveal thickness (area-weighted average in the central 1-mm-diameter circle). The solid line is the average difference (or agreement), and the dashed lines are the 95% limits of agreement. A, Comparison between 2 Macular Grid 5 (MG5) scans: average difference, 4.7 μm; standard deviation (SD) of difference, 17.4 μm. B, Comparison between 2 Fast Macular Thickness Map (FMTM) scans: average difference, 0.4 μm; SD difference, 13.5 μm. C, FMTM vs. MG5: average difference, 4.5 μm; SD difference, 18.4 μm.

Figure 6

Case of clinically significant macular edema (CSME) 1 and CSME 2 diagnosed by clinical examination (A, color fundus photograph; B, late fluorescein angiogram frame) and by Macular Grid 5 (C, MG5 thickness map) and Fast Macular Thickness Map (D, FMTM) protocols. The map of edema as identified by the MG5 algorithms is delineated by the white checkered zone in C.

Figure 7

Case of clinically significant macular edema (CSME) 2 but not CSME 1 diagnosed by clinical examination (A, color fundus photograph; B, late fluorescein angiogram frame) and by Macular Grid 5 (C, MG5 thickness map) and Fast Macular Thickness Map (D, FMTM) protocols. The map of edema as identified by the MG5 algorithms is delineated by the white checkered zone in C.

Figure 8

Patient diagnosed to have clinically significant macular edema (CSME) 1 by clinical examination (A, color fundus photograph; B, late fluorescein angiogram frame) but not by Macular Grid 5 (C, MG5 thickness map) or Fast Macular Thickness Map (D, FMTM) protocols. The map of edema as identified by the MG5 algorithms is delineated by the white checkered zone in C. Note that retinal thickening (compared with the normal reference) was present in the central circle of the MG5 map but did not meet the threshold level defined in this study.

Figure 9

Case graded to have clinically significant macular edema (CSME) 2 by Macular Grid 5 (MG5) but not identified by clinical examination. A, Color fundus photograph. B, Late fluorescein angiogram frame. C, Macular Grid 5 thickness map. D, Fast Macular Thickness Map (FMTM). The map of edema as identified by the MG5 algorithms is delineated by the white checkered zone in C. Note that the majority of the areas of retinal thickening were in the outer circle (i.e., >1 disk diameter from the foveal center). Note also the difference in configuration of the areas of retinal thickening in the outer circle between the MG5 map and the FMTM, which relies on more interpolation between data points in the outer zone.

Figure 10

Case graded to have clinically significant macular edema (CSME) 1 by Macular Grid 5 (MG5) and Fast Macular Thickness Map (FMTM) but not identified by clinical examination. A, Color fundus photograph. B, Late fluorescein angiogram frame. C, Macular Grid 5 thickness map. D, FMTM. The map of edema as identified by the MG5 algorithms is delineated by the white checkered zone in C. Note that the retinal thickening inside the central foveal circle is above threshold on the MG5 map, but not as severe as the area of edema just outside the circle. This may explain why the clinician did not judge the edema to be within the foveal zone.