Cataract surgery may raise diabetic macular oedema risk

Cataract surgery increases the risk of diabetic macular oedema (DMO), medical records from the United Kingdom suggest. An analysis of 4,850 eyes showed that the rate of DMO requiring treatment spiked about 4 months after the surgery.

“There may be, therefore, an argument for providing a further OCT-based assessment, whether in the community or in the hospital eye clinic, at around 4 months post-operatively to screen for the development of DMO, and to provide the opportunity for early treatment,” wrote Professor Alastair K Denniston from the University Hospitals Birmingham NHS Foundation Trust in Birmingham, UK and colleagues.

They published their finding in the British Journal of Ophthalmology.

Cataract surgery increases levels of inflammatory mediators such as prostaglandins, thromboxane A, nitric acid and various cytokines as well as vascular endothelial growth factor (VEGF). But previous efforts to examine the relationship of DMO to cataract surgery have reached conflicting conclusions, the authors write.

These studies had small numbers of patients. To obtain data on a larger sample, Professor Denniston and colleagues analysed records from 19 centres using the same electronic medical records system (Medisoft Ophthalmology, Medisoft, Leeds, UK). Each site is the only National Health Service (NHS) provider of DMO care to their local population, and few patients change providers or get private care, they found.

This system includes a nationally-defined minimum dataset for diabetic retinopathy (DR) that mandates recording of the minimum clinical signs necessary to automatically calculate a precise proxy-ETDRS/International Clinical Grading System retinopathy and maculopathy grade following each consultation.

The researchers looked at eyes undergoing cataract surgery from patients with diabetes, with retinopathy grades recorded in the 2 years pre-surgery and post-surgery, and who had not developed DMO requiring treatment prior to surgery.

They found 1,719 eyes with no apparent DR, 1,034 with mild non-proliferative DR (NPDR), 1,527 with moderate NPDR, 165 with severe NPDR and 405 with proliferative DR.

Risk

They determined that 2.9% of these 4,850 eyes developed DMO that required treatment within the year prior to surgery and 3.1% required treatment in the year prior to that. By contrast, 5.3% needed treatment for DMO in the year after surgery and 4.8% in the year after that.

The need for DMO treatment peaked in the 3-6 months after surgery, and the cumulative risk rose from 6.2% in the first 24 months after surgery to 14.7% in the 48 months after surgery.

The risk of needing DMO treatment was associated with the pre-operative grade of retinopathy. In the first year after surgery, the risk was 1% in those with no DR prior to surgery, 5.4% in those with mild NPDR, 10% in those with mild NPDR, 13.1% in those with severe NPDR and 4.9% in those with proliferative DR.

“Our findings provide additional data to suggest that there is a real increase in treatment-requiring DMO after cataract surgery,” write Professor Denniston and colleagues.

They note that the finding conflicts with Early Treatment of Diabetic Retinopathy Study (ETDRS) Report 25 (Arch Ophthalmol 1999;117:1600–6), which did not show an association between cataract surgery and clinically significant macular oedema.

But they note that cataract surgery has changed since this study was conducted, with the widespread adoption of phacoemulsification and “advances in the care of diabetic eye diseases”. Also, they note that the ETDRS patients had a high proportion of patients with more advanced retinopathy.

A more recent prospective study looking at unilateral cataract surgery in 132 eyes with the fellow eye acting as a control documented a 6.1% rate of clinically significant macular oedema in the treated eye vs. 4.5% in the fellow eye within the first 6 months (J Cataract Refract Surg 2006;32:1438–44).

Professor Denniston and colleagues point out that they measured “treatment-requiring DMO” rather than clinically significant oedema, a classification they deemed to be less subjective.

“We would recommend that assessment prior to cataract surgery for any patient with diabetes should include a record of [diabetic retinopathy] severity status and a macular OCT of both eyes, while recognising that the lens opacities may limit assessment in some eyes,” the authors concluded.

They suggested increased monitoring of patients with mild DR after surgery.