Some patients in the “severe nonproliferative” stage of diabetic retinopathy can stave off intravitreal injections or vitreoretinal surgery by undergoing panretinal photocoagulation (PRP), which delivers laser heat to address vessel abnormalities. However, a new study suggests that the procedure itself may cause a decrease in the macular pigment optical density (MPOD). The Clinical and Experimental Optometry study shows that patients experienced reduced MPOD in proportion with the laser energy applied.

“Clinicians should note the possibilities of the indirect effect of vibration wave in the vitreous caused by PRP treatment or the direct impact of the thermal stress of laser application,” the researchers said. “As a result, it has been observed in this study that a significant decrease occurs in MPOD values after laser applications due to the effects of PRP, whether direct or indirect.”

The researchers examined 36 eyes of 36 subjects with severe nonproliferative diabetic retinopathy without macular involvement. The laser treatments were applied at baseline, 1 month, 2 months, and 3 months for participants who clinically required it. They also monitored the subjects at each visit, measuring their MPOD and retinal thicknesses.


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Although the participants received PRP treatments to the non-macular retina, MPOD decreased in both the foveal and pericentral regions in participants who showed no previous macular findings. “Considering this result, one of the critical findings of the study is that the MPOD decreased in the pericentral and foveal regions and correlated with the total laser energy applied,” the study authors said. 

Although diabetic retinopathy itself can contribute to this process, the study authors also concluded that the average central macular thickness and foveal thickness values increase significantly at 6months, making it “more likely that the increase is due to increased permeability from vascular structures and secondary inflammation.”

The mean macular pigment optical density reduction in the fovea over the 6 months was 0.02 (±0.02 logarithmic units; P <.001).

Study findings indicated that the correlations between changes in central macular pigment, foveal thickness, and MPOD after laser treatment may be specifically indicative of increased oxidative stress in the macula, however, further studies are needed.

Reference

Dogan M, Kutluksaman B. Macular pigment optical density after panretinal photocoagulation. Clin Exp Optom. Published online August 31, 2020. doi: 10.1111/cxo.13126