Previous vitrectomy does not reduce risk of diabetic macular edema after cataract surgery

This retrospective review evaluated the effect of previous vitrectomy on the incidence of macular edema after cataract surgery in diabetic eyes. The results indicate that previous vitrectomy does not appear to lessen the rate of macular edema after cataract surgery, which was 30 percent by six months in this study. The authors also found that cataract formation is common after vitrectomy in diabetic eyes, while the risk of postcataract surgery macular edema is substantial and more likely in eyes with prior clinically significant macular edema (CSME).

I doubt that many diabetic pars plana vitrectomies are done without being warranted. However, it is interesting that the presence or absence of vitreous doesn't play a role in diabetic macular edema (DME), providing more evidence that it develops due to a different mechanism than does standard cystoid macular edema.

The authors retrospectively reviewed medical records for patients with diabetes who underwent vitrectomy at one eye institute during a 10-year period. They included 70 patients (90 phakic eyes) in the study. Postvitrectomy macular edema increased initially but then leveled off at 28 percent by four years after surgery. The cumulative proportion of eyes requiring cataract surgery after vitrectomy climbed steadily, reaching 40 percent at four years and 60 percent at eight years. Of those eyes that underwent vitrectomy and subsequent cataract surgery, the incidence of postvitrectomy macular edema was 6 percent at six months and of postcataract surgery macular edema was 30 percent at six months (P < 0.02) and 48 percent at four years (P < 0.02). Previous CSME predicted the development of postcataract surgery macular edema (P < 0.04).

The authors conclude that the dramatic increase in the incidence of macular edema, along with its timing, strongly suggests that cataract surgery was the precipitating cause. They say that their results suggest that factors independent of the vitreous, such as inflammation, are mainly involved in the pathogenesis of postcataract surgery macular edema in diabetic eyes.

The authors conclude that cataract formation and the risk of postcataract surgery macular edema should be considered when assessing the long-term benefits of vitrectomy in patients with diabetes. They say that since eyes with pre-existing CSME appear to be at greater risk of developing postcataract surgery macular edema, they may benefit from closer monitoring and prophylaxis.