Retinal vascular fractal dimension as a potential marker of treatment outcome in patients with proliferative diabetic retinopathy

Design of study:
Six months prospective, interventional clinical study.

Purpose:
The retinal vascular fractal dimension (FD) is a non-invasive marker of retinal vascular geometry. The purpose of the study was to evaluate FD as a preoperative biomarker for disease activity 6 month after panretinal photocoagulation (PRP) in patients with proliferative diabetic retinopathy (PDR).

Method:
Forty eyes from 38 newly diagnosed patients with PDR were included and followed for 6 months. All patients received standard PRP treatment by a navigated laser (NAVILAS®; OD-OS GmbH, Berlin, Germany) at baseline, with additional treatment at month 3 and 6, if necessary. Wide-field fundus fluorescein angiography (WF-FFA) (Optomap; Optos PLC., Dunfermline, Scotland, UK) was performed for diagnosis at baseline and for disease activity assessment at month 3 and 6. Based on this, patients were categorized with progressing (group 1, n=18) or stabilized (group 2, n=22) disease. FD was measured at baseline and month 6 by a trained grader using the Fractal Analyzer (Singapore Institute Vessel Assessment-Fractal image analysis software, Singapore) and a standardized grading-protocol.

Results:
At baseline, mean age and duration of diabetes were 52±14 years and 21±11 years, respectively, and 75% were male. HbA1c was 68 ±16 mmol/mol, and the mean blood pressure was 183/84 mmHg. Groups 1 and 2 did not differ according to the mean number of laser spots (1581 vs. 1573, p=0.84) or the total laser energy delivered (13.67 joule vs. 13.35 joule, p=0.20).
Patients in groups 1 and 2 did not differ in FD at baseline (1.4044 vs. 1.4063, p=0.89), month 6 (1.4017 vs. 1.4023, p=0.87) or by the difference from baseline to month 6 (-0.0027 vs. -0.0040, p=0.66). Likewise, in both groups, there was no intra-patient difference in FD from baseline to month 6 (group 1 p=0.71, group 2 p=0.62).

Conclusion:
In our cohort, retinal vascular fractal dimension does not seem to be a valid marker for prediction of activity in patients with proliferative diabetic retinopathy 6 months after panretinal photocoagulation.