Korean J Ophthalmol.  2019 Oct;33(5):399-405. 10.3341/kjo.2019.0049.

New Method of Quantitative Analysis of Hard Exudate Using Optical Coherence Tomography: Application in Diabetic Macular Edema

• Kim HR
• Yoon CK
• Kim HW
• Pak KY

• KMID: 2459520
• DOI: http://doi.org/10.3341/kjo.2019.0049

Abstract

PURPOSE
In the present study, the volume of hard exudates (HEs) was quantitatively measured using optical coherence tomography (OCT) and the agreement and correlation with area of HEs in fundus photography were analyzed.
METHODS
The medical records of patients with diabetic macular edema who underwent focal laser treatment and were followed up more than 3 months were retrospectively evaluated. An automated customized program designed for measuring HE volume was used. The HEs in each OCT B-scan binary image were measured using 512 × 128 pixels, 6 mm × 6 mm OCT cube scans. The volume was measured by summing the segmented HEs in each 128 B-scan image. The area was measured in 6 mm x 6 mm fundus photography. The volume and area were measured before and 3 months after the treatment. The agreement of increase and decrease in HEs, and the correlation of volume and area of HEs were analyzed.
RESULTS
A total of 35 patients (39 eyes) were included in the study. The volume was significantly reduced from 0.07978 to 0.02565 mm³ at 3 months (p < 0.001). The area was also significantly reduced from 15.35 to 8.60 mm² at 3 months (p < 0.001). The volume was decreased in 34 eyes and increased in 5 eyes. The area was decreased in 37 eyes and increased in 2 eyes. A significant correlation between volume and area was found (p < 0.001) as well as agreement between increase and decrease in volume and area.
CONCLUSIONS
In the 3-dimensional quantitative volumetric analysis, the volume and area of HEs were correlated and the direction of increase and decrease was concordant. Considering the distribution of HEs in multiple layers of the retina, volumetric analysis could be considered a substitute for the analysis of HE area.

Keyword

Focal laser; Hard exudates; Macular edema; Volume analysis

MeSH Terms

Exudates and Transudates*
Humans
Macular Edema*
Medical Records
Methods*
Photography
Retina
Retrospective Studies
Tomography, Optical Coherence*

Figure

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  Fig. 1 Volumetric analysis of hard exudates. (A) Optical coherence tomography B-scan image before binarization. (B) Binary image of optical coherence tomography B-scan. (C) Summation of each 128 binary image to calculate the volume of hard exudates.

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  Fig. 2 Area analysis of hard exudates. (A) Fundus photography before binarization. (B) Binary image of fundus photograph. (C) Measurement of area within 6 × 6 mm image.

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  Fig. 3 Scatter plot between the volume and area of hard exudates.

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  Fig. 4 Representative case of discrepancy between the volume and area of hard exudates. Color fundus photographs before (A) and after (B) the focal laser show decreased area of hard exudates. In the cross-sectional optical coherent tomography and optical coherent tomography binary images of the same location (sky-blue arrows), hard exudates (yellow arrows) were increased in the outer retina after focal laser (D,F) compared with baseline (C,E).

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  Fig. 5 Representative case of discrepancy between the volume and area of hard exudates. (A) In fundus photography, presence of hard exudates is not obvious (arrow). (B) On optical coherence tomography, hyperref lective materials (arrows), suspected as hard exudates, are visible in horizontal (top) and vertical (bottom) scans.

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