A 54-year-old patient asked, “Am I at risk for developing glaucoma due to my diabetes?” Here are some evidenced-based insights into what I’ve found to be a common inquiry by patients.

BUILDING THE CASE

In the prospective population-based The Rotterdam Study, having diabetes was not a risk factor for developing open-angle glaucoma.¹ Similarly, The Ocular Hypertension Treatment Study (OHTS) did not show that diabetes was an independent risk factor for glaucoma development in patients who have ocular hypertension. That said, the researchers admit the diagnosis of diabetes was self-reported and not confirmed with blood tests or medication use. Furthermore, patients who have diabetic retinopathy (DR) present were excluded from the study, resulting in an underrepresentation of diabetic patients; thus, leading to the “paradoxical relationship between diabetes mellitus and primary open-angle glaucoma (POAG) in the OHTS.”²

Another issue related to The OHTS results is the possible confounding (and, perhaps, protective) effect of metformin, a common diabetes treatment. More recently, and specific to metformin, Hou et al. shows that it may, indeed, have a protective effect in diabetic patients and glaucoma.³ These findings support a study that reveals slower retinal nerve fiber layer thinning in POAG patients who have diabetes mellitus, if treated with metformin.⁴

Additionally, other retrospective studies show a decreased risk of developing glaucoma among diabetic patients treated with metformin when compared to other oral anti-hyperglycemic drugs for Type 2 diabetics.^5,6

CONNECTION CONFIRMED

On the other hand, the Blue Mountains Eye Study reveals a significant and consistent link between open-angle glaucoma and diabetes.⁷ These findings may be due to the relative elevated risk of increased IOP in diabetic patients who have hypertension, as found in the Barbados Eye Study, and the prevalence of adult-onset diabetes as noted in the Beaver Dam Eye Study.^8,9 At the cellular level, studies show diabetes compromises the neuronal and glial functions/metabolism in the retina, which leads to apoptosis of the retinal neurons, including the retinal ganglion cells (RGC). As a result, this cellular impairment may cause the compromised RGCs to be relatively more susceptible to elevated IOP and glaucoma development.¹⁰ Finally, in their systematic meta-analysis of case-control and population-based cohort studies, Zhou et al. and Zhao et al. show that diabetic individuals had an increased risk of developing POAG.^11,12

Further, the World Glaucoma Association (WGA) concludes, “Diabetes mellitus likely increases the risk for glaucoma onset.”¹³

ANSWERING THE PATIENT

Based on the above studies, and giving the final nod to the WGA, I advised the patient of the strong link between diabetes and glaucoma.

Accordingly, I sent a letter to his primary care provider regarding exam results, with the recommendation of annual exams for diabetes and optic nerve evaluations for glaucoma. OM

References:

1. de Voogd S, Ikram MK, Wolfs RC, et al. Is diabetes mellitus a risk factor for open-angle glaucoma? The Rotterdam Study. Ophthalmology. 2006;113(10):1827–1831.
2. Gordon MO, Beiser JA, Brandt JD, et al. The Ocular Hypertension Treatment Study: baseline factors that predict the onset of primary open-angle glaucoma. Arch Ophthalmol. 2002;120(6):714–720.
3. Hou H, Moghimi S, Baxter SL, Weinreb RN. Is Diabetes Mellitus a Blessing in Disguise for Primary Open-angle Glaucoma? J Glaucoma. 2021;30(1):1-4.
4. Hou H, Shoji T, Zangwill LM, et al. Progression of Primary Open-Angle Glaucoma in Diabetic and Nondiabetic Patients. Am J Ophthalmol.2018;189:1–9.
5. Lin HC, Stein JD, Nan B, et al. Association of Geroprotective Effects of Metformin and Risk of Open-Angle Glaucoma in Persons With Diabetes Mellitus. JAMA Ophthalmol.2015;133(8):915– 923.
6. Maleskic S, Kusturica J, Gusic E, et al. Metformin use associated with protective effects for ocular complications in patients with type 2 diabetes - observational study. Acta Med Acad.2017;46(2):116–23.
7. Mitchell P, Smith W, Chey T, Healey PR. Open-angle glaucoma and diabetes: the Blue Mountains eye study, Australia. Ophthalmology. 1997;104(4):712–718.
8. Hennis A, Wu SY, Nemesure B, Leske MC, Barbados Eye Studies Group Hypertension, diabetes, and longitudinal changes in intraocular pressure. Ophthalmology. 2003;110(5):908–914.
9. Klein BE, Klein R, Jensen SC. Open-angle glaucoma and older-onset diabetes. The Beaver Dam Eye Study. Ophthalmology. 1994;101(7):1173–1177.
10. Nakamura M, Kanamori A, Negi A. Diabetes mellitus as a risk factor for glaucomatous optic neuropathy. Ophthalmologica. 2005;219(1):1–10.
11. Zhou M, Wang W, Huang W, Zhang X. Diabetes mellitus as a risk factor for open-angle glaucoma: a systematic review and meta-analysis. PLoS One. 2014 Aug 19;9(8):e102972.
12. Zhao YX, Chen XW. Diabetes and risk of glaucoma: systematic review and a Meta-analysis of prospective cohort studies. Int J Ophthalmol. 2017;10(9):1430-1435.
13. Weinreb R.N., Garway-Heath D.F., Leung C., Medeiros F.A., Liebmann J.  World Glaucoma Association Consensus Series 10:  Diagnosis of Primary Open Angle Glaucoma.  Kugler Publications. Amsterdam. 2016.

DR. LIFFERTH practices at Grossnickle Eye Center as a consultative optometrist with an emphasis in glaucoma management, and he is a member of the Optometric Glaucoma Society. For additional glaucoma cases, you can also follow Dr. Lifferth on his Instagram account: glaucomaqd. Disclosures: None. Email him at austinlifferth@yahoo.com.