Several recent studies investigated and reported the vascular density changes of the retinal vasculature and choriocapillaris in diabetic children and adults with DRP or without DRP, and compared them with healthy controls. However, currently there is no available report assessing the microvascular changes in the specific subtype of diabetes of MODY, and any comparison with controls. The current study included not only the clinical diagnosed MODYs, but also molecularly confirmed patients. It is noteworthy to investigate possible specific vascular changes in this specific subgroup of the diabetes or to assess whether the structural components are similar or not to the other types diabetes for controlling and managing the disease effectively.
The structural and flow calculation abilities of the retinal vasculature in the OCTA software might directed researchers to apply OCTA in the diagnose of preclinical DRP, and along with primary care partners to achieve a better clinical and ophthalmological outcome by controlling glycemia, blood pressure and other biochemical components. Across these studies, there is no widely accepted consensus on the vascular densities or perfusion changes of retinal plexus and choriocapillaris according to the recent OCTA studies comparing the non-DRP patients and healthy controls [20, 23–26]. However, patients with non-proliferative DRP or proliferative DRP mostly represented with decreased vessel and perfusion densities and increased FAZ dimensions [23, 25, 27]. In addition to all, Battista et al. concluded that OCTA has come along as an indispensable device for understanding the vascular background in the role of diabetic retinopathy which is not free of limitations such as segmentation errors and/or motion artifacts [28].
A recent meta-analysis scoping 45 of the OCTA studies conducted in the relevant objective, compared diabetic patients with no clinical DRP findings and healthy controls. OCTA results of diabetic patients revealed; decreased VD in superficial and deep capillary plexuses of the macula, increased perimeter of the foveal avascular zone, and reduced VD in radial peripapillary capillaries. Additionally, most of those differences were resulted as nonsignificant (except parafoveal VD of deep capillaries) in type 1 diabetes, while they remained significant in type 2 diabetes according to the subgroup analyses [29].
It is proposed that disruption of vascular arcades around the FAZ area even in the early stages of DRP can be detected by OCTA assessments, and may be differentiated from healthy controls [30]. Significant differences were also resulted in terms of FAZ area and perimetry in patients without DRP [22]. The macular FAZ area, FAZ perimetry, FD and AI values of MODY subjects did not differ significantly from controls in the current study. In addition, the superficial and deep retinal VDs in the MODY group did not change significantly in the study. Those insignificant outcomes may be related to the relatively acceptable or good glycemia control (HbA1c < 7%) of the designated group, young age status, relatively good prognostic nature of the MODY type (GCK, type 2) [31], absence of any systemic comorbidity, and low diabetes duration of the included patients. However, slight but significant increase in the mean CC VD at the parafoveal and perifoveal region was observed in the MODY group (70.8 ± 3.3 vs 69 ± 3.5, and 73.5 ± 2.2 vs 71.3 ± 3.2, respectively). Interestingly, the degree of significance increased with distance from the fovea centre along the periphery of the retina (P = 0.034 vs P = 0.009). Agra CLDM et al. compared the OCTA results between type 2 diabetes and controls with a close objective and methodology to our study, and they reported no difference on the superficial and deep VDs and FAZ area, and resulted slight but significant excess of CC flow area (mm2) resembling our results. They discussed OCTA may not be in the expected position for ensuring an early diagnosis of DRP, and nowadays it cannot replace the clinical funduscopic examinations due to their statistically significant, but clinically insignificant changes [20].
CC, which is a dense vascular network is essential for nutrition and oxygen supply of the outer retinal cells such as photoreceptors and retinal pigment epithelium to maintain normal vision [32]. Previous studies investigated the status of choroid in diabetes and DRP, and there is no widely accepted consensus regarding thickness of choroid. Some of them reported decrease in choroidal thickness even in the absence of DRP in diabetics [33–36], and some of them reported thickening along DRP progression, and also in patients without DRP [37–39]. Of the authors Ferreira et al. concluded that there is a prone to choroidal thickening in those without DRP. In addition, an OCTA study conducted by Ferrara et al. in various stages of diabetes including no DRP, non-proliferative DRP, and proliferative DRP cases concluded that vascular remodelling observed in all types of diabetes was associated to tortuous, beaded irregular choroidal vessels with focal narrowing and dilation [40]. Furthermore, Jo Y. et al found a correlation between increased choroidal thickness and HbA1c levels in diabetics who were hospitalised for control of glycemia [41]. These outcomes suggest that this tissue may be functioning differently in diabetes, and the pattern of influence appears to vary between different phases.
Researchers of the DRCR.net compared the CMT values in diabetic patients who had either minimal or no DRP with healthy controls. They concluded that diabetes without DRP findings is not associated with significant CMT changes which was consistent with the outcomes of the current study in terms of macular thickness [42].
Previous studies suggested that degeneration in neuro-retinal cells can be one of the primary detectable retina abnormalities in diabetes, and can precede microvascular complications. However, until today, the exact mechanism of relationship between retinal neuronopathy and vascular alterations has not been described exhaustively [43, 44].
In conclusion, no significant difference in terms of macular VD assessment between non-retinopathic MODY patients and controls was observed, except VD of CC at the parafovea and perifovea. According to previous various structural and VD of choriocapillaris, there may be sundry demographic, genetic and/or other undetermined factors affecting the choroidal vasculature independent of glycemia or as a contributing factor. Current findings need to be confirmed by prospective and consecutive measurements in larger case series having longer follow-up. Also, the background reasons for the current results can be better understood by further studies conducted in the scope to reveal the probable effects of diabetes in neuro-retinopathy, choroidopathy and/or ocular neuro-vascular innervations. Development in ocular imaging modalities may further characterise the choroidopathy of diabetes in the near future.