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Correlation of precise area of peripheral non-perfusion with the ischemic index in retinal vein occlusion

Session Details

Session Title: Vascular Diseases II

Session Date/Time: Friday 27/09/2013 | 11:00-12:30

Paper Time: 11:40

Venue: Hall F (Level 2)

First Author: S.Sadda USA

Co Author(s):    C. Tan   M. Chew   J. Van Hemert   D. Bell     

Abstract Details

Purpose:

Identification of peripheral retinal non-perfusion, facilitated by the availability of ultra-widefield (UWF) imaging systems, has become important in the management of eyes with retinal vein occlusion. Because of non-linear distortion at the periphery of UWF images, investigators have quantified the severity or extent of non-perfusion as a percentage of the total visible retina (an ischemic index). Recent advances in software, however, have now permitted anatomically correct areas of non-perfusion to be calculated in mm2. In this study we compare the new corrected measures of non-perfusion with the ischemic index.

Setting:

Medical Center Ophthalmology Associates, San Antonio, Texas, USA and the Doheny Image Reading Center (DIRC), Los Angeles, CA, USA.

Methods:

Thirty two patients with branch or central retinal vein occlusion from the practice of a single retina specialist were recruited for standardized UWF (up to 200 degrees) fluorescein angiographic (FA) using an Optos 200Tx. Uncorrected raw images were exported from the device and sent to the DIRC for analysis by a masked, certified reading center grader. Using validated planimetric reading center grading software, the grader manually outlined all areas of capillary non-perfusion as well as the total area of visible retina in order to calculate an ischemic index (percentage of visible retina that was non-perfused). The manually annotated images were then converted using a proprietary “stereographic projection” method in order to compensate for the peripheral distortion or stretching of the peripheral retina. Based on the manufacturer provided scale (pixel/mm), the precise areas (in mm2) of perfused and non-perfused retina (in the visible field) were calculated. Both the corrected area of non-perfusion and the corrected non-perfusion percentage were compared with previously generated ischemic index.

Results:

Of the 32 eyes, the precise areas of peripheral non-perfusion ranged from 0 mm2 to 365.4 mm2 with a mean of 95.1 mm2. The corrected non-perfusion percentage ranged from 0% to 52.9%, with a mean of 13.5%. The uncorrected ischemic index ranged from 0% to 67.7%, with a mean of 14.8%. Both the corrected area of non-perfusion and the corrected percent non-perfusion correlated with the uncorrected ischemic index (R=0.978, p<0.001), but the difference in non-perfusion percentage between corrected and uncorrected metrics was as high as 14.8%. A higher percentage of non-perfusion was associated with the presence of persistent edema (P<0.001). Following anti-vascular endothelial growth factor (VEGF) treatment, the area of non-perfusion was noted to decrease in 68.8% of cases, with a mean area of reversible non-perfusion of 16.3 mm2 and a maximum of 145.6 mm2.

Conclusions:

Software advances have now allowed for correction of peripheral distortion and the calculation of lesion areas in correct physical units (i.e. mm2), on ultra-widefield images. Eyes with retinal vein occlusions can show large areas of peripheral non-perfusion which seem to correlate positively with the severity of associated macular edema. Despite the extensive nature of the non-perfusion, some portion of the non-perfused areas appear to be reversible with anti-VEGF therapy.

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