Vitrectomy scatter photocoagulation linked to peripheral thickening in diabetic retinopathy

By Lucy Piper, Senior medwireNews Reporter

Early transient peripheral retinochoroidal thickening following pars plana vitrectomy (PPV) for proliferative diabetic retinopathy (PDR) may be related to intraoperative scatter photocoagulation, suggest researchers.

Their results showed that total peripheral choroidal thickness 3 days after surgery was significantly thicker in 21 patients with PDR who underwent PPV with scatter photocoagulation than in 32 patients who underwent PPV without scatter photocoagulation for an epiretinal membrane.

The patients participated in a comprehensive ophthalmic examination that involved the measurement of intraocular pressure, axial length, slit-lamp and fundus examinations, and optical coherence tomography before surgery and 3 days and 1 and 2 weeks postoperatively. The peripheral retinochoroidal thickness was measured at 5 mm from the limbus in the four quadrants.

Before surgery, patients with PDR had a mean total peripheral thickness, which was the sum of retinochoroidal thickness and the height of choroidal detachment, of 203 µm. This increased significantly to 548 µm at 3 days after surgery.

This 345 µm increase in total peripheral thickness was significantly greater than the 132 µm increase seen in patients with epiretinal membrane, from an average 149 µm before surgery to 281 µm 3 days afterwards.

The increase in total peripheral thickness was only significant 3 days after surgery and not at 1 or 2 weeks, at which times there was also no significant difference between the two patient groups.

Researcher Takeshi Iwase (Nagoya University Hospital, Japan) and colleagues note that choroidal detachment 3 days after surgery was more common among PDR patients, affecting 14 (63.6%) of 22 eyes compared with six (18.7%) of 32 eyes among patients with epiretinal membrane.

They suggest in Investigative Ophthalmology & Visual Science that “the choroidal detachment in the PDR group was not caused by the sclerotomies, but more likely from other surgical procedures such as the intraoperative scatter photocoagulation.”

Indeed, multiple linear regression analysis showed that total peripheral thickness correlated significantly only with the number of laser photocoagulation burns, with this variable also significantly and positively correlated with the increase in total peripheral thickness at 3 days after surgery.

“Thus, our results indicate that a larger number of intraoperative laser burns could cause a greater increase in the overall total peripheral thickness and temporarily reduce the volume of the vitreous”, the researchers explain.

They stress that, although they saw no significant changes in the intraocular pressure of their study participants before and after surgery, reduced vitreous volume could “cause an elevation of the [intraocular pressure] in the early postoperative stage in PDR cases.”

And the researchers add that this would need to be treated for at least a week after vitrectomy, particularly in eyes with silicone oil tamponade, which have previously been reported to be at increased risk of early and late intraocular pressure elevations.

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