Imaging Critical to Determine Retinal Neurodegenerative Changes in Gestational and Type 2 Diabetes

Decreased ganglion cell layer (GCL) thickness might just be the first retinal neurodegenerative sign of gestational diabetes mellitus (GDM) or type 2 diabetes (DM2), according to research published in the Canadian Journal of Ophthalmology. The study solidified the critical role swept-source (SS) optical coherence tomography (OCT) with deep range imaging (DRI) can potentially play in detecting early retinal alterations associated with GDM and DM2. 

Early detection is important because the sooner retinal neurodegeneration is diagnosed (ideally before diabetic retinopathy (DR) develops), the sooner preventive measures can be taken to avoid the development of potentially serious ophthalmic complications, the investigators explain.

Researchers compared the central macular, subfoveal choroidal thickness, retinal nerve fibre layer (RNFL), and GCL thicknesses in pregnant individuals with GDM, nonpregnant females with diabetes, and healthy nonpregnant females. To do so, they used SS-OCT and gathered detailed information from their retinal and choroidal layers.

A total of 58 people participated in the study — 20 newly diagnosed with GDM, 18 nonpregnant females with a history of DM2 without DR, and 20 nonpregnant females without diabetes to serve as the control group. All groups had similar ages, best-corrected visual acuity, and intraocular pressures. 

The mean central macular thicknesses in the GDM, DM2, and control groups were approximately 215.3 µm, 220.58 µm, and 230.03 µm, respectively (P =.002). This shows significant reductions in the GDM and DM2 groups compared with the control group, but no significant difference between the GDM and DM2 groups. The RNFLs were slightly thinner in the study groups, but only in the inferior zones, according to the research  (P =.058). However, significantly lower values were observed across the thicknesses of all GCLs . No significant differences were noted in the subfoveal choroidal thicknesses of any group.

“Our results indicate that neurodegeneration of the ganglion cells, especially in the GCL, might occur in the early stages of DM2, but axonal loss, especially in the RNFL, may not be simultaneously present. This might be attributed to earlier alterations of ganglion cells in the GCL than in the RNFL, which underlines the importance of examining the GCL along with the RNFL in DM2 and GDM,” the study shows.

This study confirms prior findings that suggest patients with DM without DR experience decreased macular thicknesses. The research speculates that this might be due to a decrease in perifoveal capillary blood flow before a CMT increase. “Like our study, a previous study found significantly lower CMT values in healthy pregnant and GDM groups than in a healthy nonpregnant group and observed no significant difference between the GDM and the healthy pregnant group,” the report shows. 

Researchers noted the study’s small sample size, cross-sectional design, and lack of simultaneous examination of dynamic vascular changes as limitations.

The team suggests that practitioners utilize SS-OCT with DRI technology for patients with GDM and DM2, even if they are not diagnosed with DR, so that early retinal alterations can be detected. 

Reference

Akpolat C, Kurt M, Evliyaoglu F, Yilmaz M,Ordulu F. Analysis of retinal neurodegeneration in gestational and type 2 diabetes using swept-source optical coherence tomography. Can J Ophthalmol. Published online October 14, 2020. doi: 10.1016/j.jcjo.2020.09.017