There have been a few studies evaluating the relationship between retinal thickness changes and glycemic control. Chihara et al.
8 reported that the incidence of RNFL defects is not correlated with the glycosylated hemoglobin level at the time of examination. Likewise, a 3-year follow-up study of retinal thickness alterations in patients with type 2 DM using a retinal thickness analyzer (RTA) found no correlation between changes in retinal thickness and changes in HbA
1c values.
9 In a study using Heidelberg retina tomography (HRT) III, rim area and rim volume measurements were not significantly correlated with HbA
1c levels.
10 Furthermore, a study evaluating the effect of glycemic control on RNFL thickness reported that RNFL measurements following 1-month blood glucose regulation were not significantly different.
11 On the other hand, another study reported that RNFL thickness decreased after 4 months of glycemic control, which was explained by the transient deterioration of diabetic retinopathy following intensive glycemic control.
12 In this study, among a number of parameters evaluated, cube average thickness, average GCIPL, inferonasal GCIPL, inferior GCIPL, and inferotemporal GCIPL thickness parameters measured in the macular area were positively correlated with HbA
1c levels at the time of OCT examination. Retinal changes in DM can be due to a variety of pathways involving several factors. In addition, the severity of diabetic retinopathy, duration of diabetes, type of DM, and glycosylated hemoglobin values can complicate diabetic eyes with different phenotypes. For example, while prolonged duration of poor glycemic control might induce retinal thinning, simultaneous intracellular or extracellular edema can lead to increased retinal thickness. Accordingly, diagnosing glaucoma in eyes of patients with DM using OCT can be challenging.