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.