Phaco surgery may still pose risk for progression of diabetic retinopathy

Cataract surgery may promote progression of retinal pathology secondary to diabetes, although the exact mechanism of action remains unclear.

Phacoemulsification surgery is less destructive to the ocular structure than older cataract extraction techniques, although it may still carry a risk of promoting progression of underlying diabetic retinopathy.

Published studies have estimated that as many as 38% of patients may exhibit signs of progression in their diabetic retinopathy (DR) after extracapsular cataract extraction surgery. However, little evidence exists on whether phaco surgery carries a similar risk for patients with diabetes.

In a sampling of 190 patients with diabetes undergoing cataract surgery employing phaco, researchers at the University of Sydney in Australia, in a study based at Westmead Hospital, noted progression of retinopathy with one or more steps on the ETDRS scale in 28.2% of pseudophakic eyes compared with 13.8% of phakic eyes. An analysis of eyes undergoing phaco compared with unoperated fellow eyes of the same patients revealed a similar pattern.

“In this surgical cohort of patients with diabetes, we found that those undergoing phacoemulsification showed nearly a doubling of the progression rates for DR 12 months after surgery. This increased progression rate was lower than previously reported DR progression rates using older cataract techniques,” the study authors wrote.

The results should reinforce the importance of preoperative measures to mitigate the risk of DR progression in patients undergoing cataract surgery, according to Jie Jin Wang, MMed, PhD, a chief investigator and corresponding author of the study.

“Current practice includes aggressive preoperative laser treatment to adequately control DR and diabetic macular edema in order to reduce the risk of DR progression in patients with significant DR who are undergoing cataract surgery,” Dr. Wang told Ocular Surgery News in an e-mail interview. “This practice has been in place for a long time but still needs to be emphasized.”

Increased risk

Several aspects of the study point to a link between phaco surgery — and cataract surgery in general — and progression of DR. The study analyzed outcomes of 190 patients with diabetes from a pool of 1,994 patients undergoing cataract surgery at the hospital. Of these, 56 patients had already undergone cataract surgery at the time of enrollment.

“After adjusting for age, sex, duration of diabetes and baseline HbA1c level, pseudophakic eyes had significantly higher odds of presenting with DR,” according to the study.

After the 56 pseudophakic eyes were excluded from the analysis, 22 eyes (28.2%) of study eyes that underwent surgery shortly after enrollment and 12 control eyes (20%) that were unoperated at baseline showed progression of their DR in the 12 months after surgery. However, when eyes that subsequently underwent phaco surgery during the 12-month follow-up were excluded — leaving eyes that remained unoperated for the full 12 months — only 13.8% of these eyes had progression of DR.

There were 45 eyes in the study that had only unilateral phaco surgery during the 12 months of the study. In this subsample, 35.6% of pseudophakic eyes and 20% of phakic fellow eyes had progression of DR.

Only 32 patients enrolled in the study had previous laser treatment for DR, and these eyes were excluded from analysis of DR progression.

“The current indications for laser treatment of DR include advanced stages of DR (proliferative DR, advanced non-proliferative DR and macular edema),” Dr. Wang said. “The DR progression that we reported in this article included only mild to moderate non-proliferative DR stages, all prior to the stages at which laser treatment is usually requested.”

Effect of phaco surgery

The study design attempted to isolate the effect of phaco on progression of DR. First, unlike previous studies, eyes that remained unoperated for the entire follow-up were used as a comparator, thus eliminating any potential bias between operated and non-operated eyes in the two comparison groups, Dr. Wang said.

Secondly, the subgroup analysis in 45 patients with unilateral surgery showed a difference in DR progression that supports the findings in the wider sample. The comparison with fellow eyes of the same patients also mitigates potential interpersonal differences in diabetes control, which may affect DR progression, and limits the potential confounding effects on the study findings.

Cataract is a known complication of diabetes; however, this cannot explain the differences in DR progression between the operated and non-operated fellow eye of the same patient, given that diabetes equally affects both eyes, he said.

“Although these findings should not argue against performing cataract surgery in older people with diabetes, it is important for clinicians to recognize this residual risk and to take appropriate precautions (good preoperative control of diabetes and DR and closer monitoring for at-risk eyes after surgery),” according to the study. – by Bryan Bechtel

Reference:

• Hong T, Mitchell P, de Loryn T, et al. Develop-ment and progression of diabetic retinopathy 12 months after phacoemulsification cataract surgery. Ophthalmology. 2009;116(8):1510-1514.

• Jie Jin Wang, MMed, PhD, can be reached at the Centre for Vision Research, Department of Ophthalmology, University of Sydney, Westmead Hospital, Hawkesbury Road, Westmead, New South Wales, Australia, 2145; e-mail: jiejin_wang@wmi.usyd.edu.au.