TL;DR
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Two studies presented at the American Academy of Ophthalmology meeting found associations between higher preoperative hemoglobin A1c and complications after eye surgery. A large VA review linked higher A1c with more cystoid macular edema after cataract surgery, while a separate analysis found a higher five-year infection hazard after glaucoma shunt surgery among patients with A1c above 8.4%. The retrospective findings do not establish that lowering A1c before surgery would prevent either complication.
Two studies presented at the American Academy of Ophthalmology annual meeting linked higher preoperative hemoglobin A1c with complications after eye surgery: cystoid macular edema following cataract surgery and infection after glaucoma tube-shunt surgery. The findings may inform preoperative risk discussions, but the studies were retrospective and do not show that lowering A1c before an operation prevents complications.
In the cataract study, Daniel Fraser, MD, of the University of Minnesota and colleagues reviewed Veterans Affairs Health System records from 2010 to 2022. They identified 6,808 patients who developed postoperative macular edema within six months of surgery and compared them with 121,164 patients who did not. Overall, cystoid macular edema (CME) occurred after 5.3% of cataract surgeries in the analysis.
The rate rose across A1c groups: from 4.2% for preoperative A1c below 6.3% to 6.9% for levels of 8.0% or higher. In adjusted analysis, each 1 percentage-point increase in A1c was associated with a 6% increase in the odds of CME (odds ratio 1.06; 95% confidence interval 1.05-1.08). Pre-existing diabetic retinopathy was a stronger predictor: it was associated with more than three times the odds of CME, and risk rose with retinopathy severity.
A separate analysis by Mohsen Adelpour, MD, of the University of Arkansas for Medical Sciences examined infection after glaucoma tube-shunt surgery using the TriNetX clinical research network. Among matched patients, those with preoperative A1c above 8.4% had a five-year hazard ratio of 1.93 for blebitis or endophthalmitis compared with patients whose A1c was below 7.0%. The intermediate group, with A1c from 7.0% to 8.4%, did not have a statistically significant increase compared with the below-7.0% group.
How A1c May Shape Surgical Risk
The results suggest that A1c may add information to eye-surgery risk assessments, rather than serving as a stand-alone measure. In the cataract analysis, the association persisted alongside the stronger contribution from diabetic retinopathy. For patients and clinicians, that could support more specific conversations about the likelihood of postoperative macular edema, particularly when A1c is high or retinopathy is present.
The glaucoma findings point to a possible association between higher A1c and serious infection, but the estimate is based on a subgroup and has a wide confidence interval. Neither study tested whether changing glucose control before surgery reduces risk. The findings should not be read as evidence that surgery should automatically be delayed at a particular A1c level; decisions require individual clinical judgment.
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Two Studies, Different Eye Surgeries
Cystoid macular edema is swelling in the central retina that can affect vision after cataract surgery. Fraser described pseudophakic CME as the most common vision-threatening complication of the procedure; it occurs in up to 4% of surgically treated eyes in estimates he cited, while the VA analysis reported a 5.3% rate among its study population. These figures come from different contexts and should not be treated as directly interchangeable.
Earlier small, single-center studies had suggested a relationship between A1c and CME, according to Fraser. The VA review examined a much larger group, but Fraser acknowledged that retrospective records cannot establish cause and effect, and that the VA population was heavily weighted toward older white men. The glaucoma analysis addressed another outcome—blebitis or endophthalmitis after shunt surgery—rather than retinal swelling after cataract surgery.
In the glaucoma study, pre-existing myopia was also associated with increased infection risk, with a hazard ratio of 3.58. That association was separate from the A1c comparison, underscoring that surgical outcomes may reflect multiple patient factors.
“The incidence of cystoid macular edema in patients with diabetes was 5.3%, higher than the general population, but it grew to 6.9% in patients with a hemoglobin A1c above 8.”
— Daniel Fraser, MD, University of Minnesota
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Limits of the Risk Estimates
Both analyses were observational and retrospective, so they show associations rather than proving that elevated A1c caused the complications. The cataract study relied on VA records, with the population limitations Fraser described. The reported 6% increase in CME odds for each 1 percentage-point A1c increase is statistically significant, but the study does not establish a threshold at which clinicians should postpone surgery or change treatment.
For glaucoma surgery, the high-A1c group’s hazard ratio had a 95% confidence interval of 1.04 to 3.58, indicating considerable uncertainty about the size of the association. The supplied report does not provide the absolute infection rates for each A1c group. It also does not establish whether improving glucose control changes infection risk. Further details about the glaucoma analysis and its other measured factors are not available in the report.
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Trials Needed to Test Prevention
Fraser called for an interventional study to test whether bringing patients with higher A1c into lower ranges before cataract surgery reduces CME. Until such evidence is available, the meeting findings support discussion of risk, not a proven preventive strategy or a universal cutoff for delaying an operation.
The researchers’ findings may prompt further study of A1c and outcomes after both procedures. Clinicians will need stronger prospective evidence, including absolute risks and assessment of whether changes to preoperative care improve outcomes, before the associations can guide standardized surgical thresholds.
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Key Questions
What complication was linked to higher A1c after cataract surgery?
The VA review found that higher preoperative A1c was associated with a greater incidence of cystoid macular edema, swelling in the central retina, within six months of cataract surgery.
What did the glaucoma shunt study find?
Patients with preoperative A1c above 8.4% had a higher five-year hazard of blebitis or endophthalmitis than those with A1c below 7.0%. The study was retrospective and did not establish that A1c caused the infections.
Does the research show that lowering A1c prevents these complications?
No. The studies identified associations, not the effects of an intervention. Fraser said an interventional study would be needed to determine whether lowering A1c before cataract surgery reduces macular edema risk.
Did the researchers identify an A1c level at which surgery should be delayed?
No specific delay threshold was established. The presenters discussed the findings as relevant to individualized preoperative counseling, not as a universal rule for postponing surgery.
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