April 2019

ASCRS NEWS

Eyeworld journal club
Review of “Visual outcomes after cataract surgery in patients with type 2 diabetes”


by Mohamed Hassan, MD, Kevin Chodnicki, MD, Matthew Starr, MD, and Andrew Barkmeier, MD


Andrew Barkmeier, MD

Ophthalmology residency program director
Mayo Clinic

Cataract surgery in diabetics has always raised questions regarding timing and blood glucose control. I asked the Mayo Clinic residents to review this new Kaiser Permanente study in the current issue of JCRS.

—David F. Chang, MD,
EyeWorld Journal
Club Editor

Performed more than 3 million times every year, cataract extraction is the most common surgical procedure in the U.S., offering most patients favorable outcomes and relatively few complications. Patients with diabetes mellitus are at increased risk of developing cataracts. As of 2015, more than 30 million Americans have been formally diagnosed with diabetes, and an additional 84 million are pre-diabetic.1 Diabetes confers an approximately two-fold increased risk for cataract development overall, with younger patients being even more susceptible.2 As these patients develop visually significant cataracts, it is important to understand both the outcomes and the risks of cataract extraction in the context of diabetes with respect to both perioperative surgical complications and potential worsening of diabetic eye disease.
In this report, Liu et al. analyzed the effect of type 2 diabetes on postoperative best corrected visual acuity (BCVA) in patients undergoing cataract surgery. A 2012 Cochrane review by Buchleitner et al. had previously suggested that surgical outcomes, in general, were no different in patients with tight glycemic control and that tight control may, in fact, increase hypoglycemic episodes; however, its investigation of hospital-based surgery across disparate disciplines did not specifically address ocular surgery.3 This gap in the literature was addressed by Liu et al. in a retrospective review of 102,050 eyes in 65,370 patients 89 years or younger undergoing clear cornea phacoemulsification surgery over a 5-year period within a single, community-based healthcare system. Of these patients, 34% had type 2 diabetes. Notably, the study excluded patients with type 1 diabetes, macular edema, and complex phacoemulsification surgery. The main outcome measures included BCVA postoperatively as well as improvement in BCVA compared to baseline. The authors’ stated hypothesis was that postoperative BCVA improvement would not differ by the severity of retinopathy, duration of diabetes, insulin dependence, or preoperative hemoglobin A1c (HbA1c) level.
Liu et al. found that patients with diabetes and no diabetic retinopathy (DR) were as likely as patients without diabetes to achieve postoperative BCVA of 20/20. In patients with diabetic retinopathy, however, the likelihood of achieving BCVA of 20/20 was significantly lower, with the percentage dropping with each increasing stage of DR. Despite patients with DR not achieving 20/20 as frequently, there was a consistent improvement in BCVA of four lines in all stages of DR, which equaled the average line improvement in those without diabetes. The odds of postoperative BCVA of 20/25 or worse also increased with a longer duration of diabetes and insulin dependence; notably, a higher preoperative HbA1c was not associated with worse postoperative BCVA outcomes. This suggests that in the context of cataract surgery, less emphasis should be placed on the HbA1c value compared to the severity of existing DR.
This study’s most notable strength is its large sample size, analyzing more than 100,000 eyes. Although only one-third of the eyes were from patients with diabetes and only roughly 20% of patients with diabetes had diabetic retinopathy, the large sample size and real-world community practice nature allows conclusions to be drawn that should be generalizable to many practice settings. This study has several implications for patients with diabetic retinopathy who undergo cataract surgery. First, these patients may anticipate a significant benefit in visual acuity after phacoemulsification. Second, poorly controlled diabetics, as determined by HbA1c, need not have their cataract surgery delayed in order to optimize glycemic control, as preoperative HbA1c levels did not affect visual outcomes. Still, these patients must be counseled on the potential limitations in postoperative vision related to their DR, as patients with DR in this study had worse visual acuity outcomes compared to those without diabetes or to those with diabetes but no DR.
The study didn’t include patients with diabetic macular edema (DME) in any analyses. DME remains a leading cause of visual impairment in patients with DR. The visual loss associated with DME is due to the accumulation and exudation of extracellular fluid within the macula secondary to increased vascular impermeability, which can greatly worsen following cataract surgery.4 The prevalence of DME in patients with type 1 diabetes is between 4.2 and 7.9% and in patients with type 2 diabetes is between 1.4 and 12.8%, representing a significant proportion of the DR population.5 The Diabetic Retinopathy Clinical Research Network has two limited reports on the outcomes following cataract surgery in their population of patients. One of these reports analyzed patients without central-involving diabetic macular edema (CI-DME) at the time of cataract surgery and the other enrolled patients with preoperative CI-DME.6,7 In the study examining those eyes without CI-DME, it was reported that any history of treatment for DME prior to treatment increased the risk of developing DME following cataract surgery. The second study was a pilot study examining visual outcomes of 63 eyes with CI-DME that underwent cataract surgery but was discontinued due to slow enrollment. This problem represents a substantial and particularly vulnerable subset of patients undergoing cataract surgery, and we greatly anticipate the findings of the authors’ planned report on patients with DME.
Interestingly, only 41% of diabetic patients had a HbA1c drawn in the 90 days prior to surgery. Given that the HbA1c level was only included if it was measured in that time period, it would have been beneficial to see whether extending the cutoff to 6 months prior to the surgery (and thus increasing the number of patients with preoperative HbA1c) would have impacted any of the associations between preoperative HbA1c and postoperative BCVA. Moreover, 30% of those with severe NPDR and PDR had no postoperative visual acuity up to 1 year following surgery. Given that these two categories of patients represent the most severe DR, it is disappointing that approximately one-third of these patients did not have postoperative outcomes data. The method of measuring postoperative BCVA could also introduce uncertainty. One postoperative BCVA was included and was reported from the date nearest surgery during the interval from 3 weeks to 1 year after cataract extraction. No data was offered regarding the specific postop time the BCVA was taken from in the different groups. In patients with diabetes, who are more prone to postoperative cystoid macular edema (CME), BCVA could have been measured before, during, or after the expected peak of CME.
It is important to note the exclusion of patients with type 1 diabetes. While type 2 diabetes represents 90–95% of all diabetes cases in the U.S., there are several million patients with type 1 diabetes, and providers should be cautious in extrapolating these results when counseling those individuals.1 The authors also elected to exclude complex phacoemulsification cases but did not describe whether patients with diabetes or diabetic retinopathy were more likely to have a complex phacoemulsification and thus be excluded. Previous work has suggested that patients with diabetes can have more iris pigment epithelial changes and miotic pupils, increased corneal epithelial and endothelial fragility, impaired corneal wound healing, higher rates of cystoid macular edema, and increased risk of vitreous hemorrhage.8,9,10 No data was presented regarding the rates of complications, which are extremely important in elective cataract surgery. The general improvement in lines of vision gained in patients with diabetes does not preclude a significant difference in complication rates compared to patients without diabetes.
Regardless of any limitations of this report, it is very useful to know that patients with all grades of DR severity saw an improvement in visual acuity following cataract surgery and that uncontrolled HbA1c levels did not portend poor visual outcomes. This study is an important step toward understanding these complex patients in the context of cataract surgery. Additional research is needed to fully inform timing of cataract surgery, counsel these patients appropriately, and maximize visual outcomes.

Contact information

Barkmeier: Barkmeier.Andrew@mayo.edu

To view the full abstract online, go to www.jcrsjournal.org and search
“Visual outcomes after cataract surgery in patients with type 2 diabetes.”


References

1. Centers for Disease Control and Prevention. National Diabetes Statistics Report, 2017. Atlanta, GA: Centers for Disease Control and Prevention, US Department of Health and Human Services; 2017.
2. Becker C, et al. Cataract in patients with diabetes mellitus-incidence rates in the UK and risk factors. Eye (Lond). 2018;32:1028–1035.
3. Buchleitner AM, et al. Perioperative glycaemic control for diabetic patients undergoing surgery. Cochrane Database Syst Rev. 2012:CD007315.
4. Das A, et al. Diabetic macular edema: Pathophysiology and novel therapeutic targets. Ophthalmology. 2015;122:1375–94.
5. Lee R, et al. Epidemiology of diabetic retinopathy, diabetic macular edema and related vision loss. Eye Vis (Lond). 2015;2:17.
6. Diabetic Retinopathy Clinical Research Network Authors/Writing Committee, et al. Macular edema after cataract surgery in eyes without preoperative central-involved diabetic macular edema. JAMA Ophthalmol. 2013;131:870–9.
7. Diabetic Retinopathy Clinical Research Network Authors/Writing Committee, et al. Pilot study of individuals with diabetic macular edema undergoing cataract surgery. JAMA Ophthalmol. 2014;132:224–6.
8. Yanoff M, et al. Diabetic lacy vacuolation of iris pigment epithelium; a histopathologic report. Am J Ophthalmol. 1970;69:201–10.
9. Sanchez-Thorin JC. The cornea in diabetes mellitus. Int Ophthalmol Clin. 1998;38:19–36.
10. Javadi MA, Zarei-Ghanavati S. Cataracts in diabetic patients: a review article. J Ophthalmic Vis Res. 2008;3:52–65.

Review of “Visual outcomes after cataract surgery in patients with type 2 diabetes” Review of “Visual outcomes after cataract surgery in patients with type 2 diabetes”
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