Novel measurement technique of retinal vessel caliber using fundus photographs obtained from optical coherence tomography

Abstract

 

Purpose

 

Measurement of retinal vessel caliber has been previously performed on color fundus photographs using the Interactive Vessel Analysis (IVAN) software. In this cross-sectional study, we compared and assessed the correlation between manual measurements on confocal scanning laser ophthalmoscopy (cSLO) fundus images and the IVAN technique.

 

Methods

 

A total of 36 eyes (36 subjects) were included in the study: 11 subjects with no known ocular or systemic diseases, 13 with non-neovascular age-related macular degeneration (AMD), and 12 with systemic hypertension without any known ocular diseases. 30˚ optic disc-centered fundus photos (Field 1M) were obtained by cSLO (Heidelberg Spectralis®) using multicolor imaging mode. Color fundus photographs of the same eyes were also acquired using Carl Zeiss FF450 fundus camera. IVAN was used to measure retinal vessel caliber from the color fundus photos, whereas measurement tool of the Heidelberg Eye Explorer (HEYEX v5.2) was independently used to measure manually the retinal vessel calibers from the cSLO images (Figure). All measurements were taken in an area of 0.5 to 1 disc diameter from the margin of optic disc for both color photos and cSLO images. Central retinal arteriolar equivalents (CRAE) and central retinal venular equivalents (CRVE) were calculated using a standardized formula for both image modalities. Correlation between the CRAE and CRVE values obtained by the two methods was analyzed using the Pearson correlation coefficient.

 

Results

 

The mean age was 32, 59, and 73 years for the normal, hypertensive and non-neovascular AMD groups, respectively. The mean difference for CRAE between IVAN and cSLO method ranged from 19.1 to 22.7 µm. Mean differences for CRVE between the two methods ranged from 19.6 to 21.6 µm. There was a strong correlation between IVAN and cSLO for CRAE and CRVE measurement across the three groups (Table).

 

Conclusions

 

Measurement of retinal vessel caliber using Heyex measurement tool on cSLO fundus images may provide an alternative method to the standard IVAN software. The Heyex technique requires less image processing and is less time consuming. The cSLO images can also be obtained without the need for mydriasis.  

 

A: Fundus photograph processed by IVAN, B: Multicolor cSLO image processed by HEYEX. Zone 1: 0 to 0.5 disc diameter from optic disc margin, Zone 2: 0.5 to 1.0 disc diameter from optic disc margin