Grip strength is associated with retinal and choroidal thickness in type 2 diabetes mellitus patients without retinopathy

Objective To determine the relationship between grip strength and retinal or choroidal thickness in Chinese patients with type 2 diabetes mellitus. Design Observational study-cross-sectional design. Setting and Participants The study was conducted among diabetes patients without retinopathy registered in the community health system in Guangzhou, China. Measures Grip strength was measured twice for each hand with a dynamometer in kilograms (kg). The retinal and choroidal thickness in macular Early Treatment Diabetic Retinopathy Study (ETDRS) sectors were measured by commercial swept-source optical coherence tomography (SS-OCT; DRI OCT-2 Triton; Topcon, Tokyo, Japan). Results A total of 1,029 patients were included in the study. Both retinal thickness and choroidal thickness increased with the higher quartile of grip strength. Regression analyses indicated that the average retinal and choroidal thickness increased by 0.14 μm (95%CI: 0.03-0.25 μm, P=0.011) and 0.57 μm (95%CI: 0.03-1.11 μm, P=0.037) for each additional kg of grip strength following adjustment for age and gender. Further adjustments were made for axial length, HbA1c, length of time the patient had diabetes, insulin usage, height, weight and systolic and diastolic blood pressure, which resulted in an average retinal and choroidal thickness increase of 0.13 μm (95%CI: 0.02-0.24 μm, P=0.024) and 0.65 μm (95%CI: 0.13-1.16 μm, P=0.013) for each additional kg of grip strength. Consistent results were obtained in the analyses in ETDRS 9 sectors. Conclusion Greater hand grip strength was found to be significantly associated with thicker retinal and choroidal layers in diabetic patients. Grip strength may provide a useful indicator of retinal health in diabetic patients. Further studies are needed to determine directionality and causality, and to examine whether improving muscle strength has a positive effect on retinal and choroidal thickness. Article summary Strengths and limitations of this study Grip strength is an indicator of upper limb muscle function and tension, and it is one of the important indicators of aging in the human population. This is one of the few studies to examined the relationship between grip strength and retinal thickness and choroidal thickness in a large sample size of patients with diabetes mellitus. Greater hand grip strength was found to be significantly associated with thicker retinal and choroidal thickness in diabetic patients, and grip strength may provide an easily-administered marker of retinal health in diabetic patients. Causal inferences could not be inferred due to the cross-sectional design of the study. The dynamic changes in grip strength and their impact on retinal and choroidal thickness are warranted to be explored in longitudinal studies.