Relationship between distance-weighted peripheral non-perfusion and diabetic macular edema

Abstract

 

Purpose

 

A new method to weight each pixel of non-perfusion reflecting its respective distance from the fovea was developed in the hopes of improving the correlation between retinal ischemia and the development of diabetic macular edema (DME). In this study, we characterize the relationship between a distance-weighted ischemic area and the extent of DME using ultra-widefield (UWF) angiography.<br /> .

 

Methods

 

40 eyes of 40 patients were enrolled in DAVE trial (NCT01552408) to assess the efficacy and safety of ranibizumab monotherapy compared with ranibizumab plus UWF fluorescein angiography (FA) -guided pan retinal photocoagulation for DME with retinal ischemia. Steered UWF FA images using the Optos 200Tx were submitted to the Doheny Image Reading Center for analysis. Images were montaged and transformed to stereographic projected images for precise quantification using spherical trigonometry. The ischemic index was computed as ratio of non-perfused to total visible retina. In addition, each pixel of non-perfused retina was linearly weighted based on the distance from the fovea and optimized using simulated annealing to produce a weighted ischemic index, which gave more importance to ischemia closer to the posterior pole (i.e. location of edema). Linear and logistic models were constructed to determine the relationship between the baseline extent of DME and various covariates including the weighted and unweighted ischemic indices.

 

Results

 

At baseline, there was no significant correlation between the extent of central macular thickness and macular volume and the unweighted ischemic index (r = 0.077, P = 0.653 and r = 0.071, P = 0.677, respectively). However, after linearly weighting each pixel based on the distance from the fovea, the correlation between the extent of central macular thickness and macular volume at baseline, and ischemic index was improved (though not significant) to r = 0.237, P = 0.147 and r = 0.239, P = 0.129, respectively.

 

Conclusions

 

In this cohort, the severity of DME was not correlated with the extent of peripheral non-perfusion. Although the correlation improved when the ischemic index was linearly weighted to emphasize more central non-perfusion, it did not achieve statistical significance. Consideration of other non-linear weighting functions may strengthen this relationship and should be the target of future studies.