Temporal changes in retinal vascular parameters associated with successful panretinal photocoagulation in proliferative diabetic retinopathy: A prospective clinical interventional study

Abstract

Purpose: We aimed to investigate changes in retinal vascular geometry over time after panretinal photocoagulation (PRP) in patients with proliferative diabetic retinopathy (PDR).

Methods: Thirty-seven eyes with PDR were included. Wide-field fluorescein angiography (Optomap, Optos PLC., Dunfermline, Scotland, UK) was used to diagnose PDR at baseline and to assess activity at follow-up month three and six. At each time-point, a trained grader measured retinal vessel geometry on optic disc (OD) centred images using semiautomated software (SIVA, Singapore I Vessel Assessment, National University of Singapore, Singapore) according to a standardized protocol.

Results: At baseline, the mean age and duration of diabetes were 52.8 and 22.3 years, and 65% were male. Mean HbA1c was 69.9 mmol/mol, and blood pressure was 155/84 mmHg. Of the 37 eyes with PDR, eight (22%) eyes had progression at month three and 13 (35%) progressed over six months. Baseline characteristics, including age, sex, duration of diabetes, HbA1c, blood pressure, vessel geometric variables and total amount of laser energy delivered did not differ by progression status. However, compared to patients with progression of PDR, patients with favourable treatment outcome had alterations in the retinal arteriolar structures from baseline to month six (calibre, 154.3 μm versus 159.5 μm, p = 0.04, tortuosity 1.12 versus 1.10, p = 0.04) and in venular structures from baseline to month three (fractal dimension 1.490 versus 1.499, p = 0.04, branching coefficient (BC) 1.32 versus 1.37, p = 0.01).

Conclusion: In patients with PDR, successful PRP leads to alterations in the retinal vascular structure. However, baseline retinal vascular geometry characteristics did not predict treatment outcome.

Keywords: NAVILAS; SIVA; clinical; computer-assisted; humans; panretinal photocoagulation; proliferative diabetic retinopathy; prospective; retinal vessel geometry.

Figure 1

The grid from the semiautomated vessel grading software siva as placed on an optic disc centred 45° fundus image. Arterioles and venules drawn as red and blue lines. Zones A, B and C are located 0.0–0.5, 0.5–1.0 and 1.0–2.0 disc diameters from the edge of the optic disc, respectively. All geometric variables are measured in Zone C.

Figure 2

Definition of the retinal vessel geometric variables. Yellow lines are traced retinal vessels, and blue lines, arrows and titles are drawn to explain the math used to define the geometric variables. D ₀ = parent vessel diameter (μm), D ₁ = diameter of daughter vessel one (μm), D ₂ = diameter of daughter vessel two (μm), θ ₁ = angle between daughter vessel one and imaginary progress of parent vessel if no branching had occurred (degree), θ ₂ = angle between daughter vessel two and imaginary progress of parent vessel if no branching had occurred (degree), L = strait line from branching point to branching point, length diameter ratio = L/D ₀, branching angle = θ ₁₊ θ ₂, branching coefficient = ${(D_1+D_2)}^2/d_0^2$, junctional exponent deviation $\left({(D_0^3-D_1^3-D_2^3)}^{1/3}\right)/D_0$.