Background

The Early Treatment Diabetic Retinopathy Study [1] (ETDRS) showed that focal photocoagulation of “clinically significant” diabetic macular oedema (CSMO) substantially reduced the risk of visual loss. Vascular Endothelial Growth Factor (VEGF) inhibitor drugs have subsequently been shown to have better results for centre involving diabetic macular oedema [2].

Methods

A retrospective analysis of first macular laser treatment was conducted between 01/01/2010 and 31/12/2019 and OCT measurements from the same machine, within 3 months before and 1–12 months after treatment in the Gloucestershire Eye Unit. Eyes were excluded if their central subfield retinal thickness (CRT) was ≥ 400 microns, they had ocular co-pathologies or surgery in the previous 6 months. ETDRS grid areas described by Soliman [3] were used to assess the results of laser treatment (Fig. 1).

Fig. 1: Early treatment diabetic retinopathy study (ETDRS) grid areas.
figure 1

ETDRS grid right eye, ETDRS grid left eye, ETDRS central 1 mm, inner and outer parafoveal rings both eyes.

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Results

Eligible for analysis were 316 eyes from 275 patients with 175 male, 246 T2DM, and median age 63.1 years. A total of 8 consultants treated 198 (62.7%) eyes, 5 specialty doctors treated 101 (32.0%) eyes and 11 trainees treated 17 (5.4%) eyes with 2 consultants treating >50 eyes. The laser machine used was a PASCAL green laser (Topcon UK) for 271 (85.8%) eyes. The median number of burns administered to an eye was 24 (IQR; 15–34). Burn durations of 0.02 or 0.05 s were used for 69.3% of eyes. For 311 (98.4%) eyes the beam diameter was 100 microns.

A total of 253 eyes had Zeiss Cirrus OCT measurements (Table 1), mean baseline CRT 303.6 microns, mean follow-up CRT 305.1 microns and mean difference +1.5 microns (95% CI: −4.8 to +7.7). In only two macular regions did <50% of eyes have a reduction in thickness. A total of 63 eyes had Heidelberg OCT measurements, mean baseline CRT 302.4 microns, mean follow-up CRT 309.4 microns and mean difference +7.0 microns (95% CI: −4.7 to +18.8). In all macular regions >50% of eyes had a reduction in thickness.

Table 1 Macular Thickness estimates for 253 eyes assessed using a Zeiss Cirrus OCT machine and 63 eyes assessed using the Heidelberg OCT machine.
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After VEGF inhibitor injections became available in 2013, only 3 (5.4%) eyes with Heidelberg and 10 (10.5%) eyes with Zeiss OCT measurements received injections within 1 year of laser.

The median baseline and follow up Visual Acuity (VA) were both 0.20 LogMAR.

Discussion

The Diabetic Retinopathy Clinical Research Network (DRCRN) [4] compared two laser techniques in 2007 that had OCT data available on 213 eyes at 12 months post laser. They found, in both treatment groups, a reduction of central retinal thickening, weighted inner zone thickening, and retinal volume with no significant change in visual acuity outcomes.

As the NICE guidelines [5] in England do not recommend treatment until the central subfield retinal thickness (CRT) is ≥400 microns, macular laser treatment was assessed for predominantly non-centre involving diabetic macular oedema.

Macular laser treatment can be effective in reducing retinal thickening in the inner and outer parafoveal zones and in different macular regions with stable VA. Only 5.1% of eyes went on to require injections with VEGF inhibitors within 12 months of the initial laser. This study provides evidence that there is still a place for macular laser treatment in non-centre involving diabetic macular oedema.