Corneal and Retinal Neuronal Degeneration in Early Stages of Diabetic Retinopathy

Abstract

PURPOSE. To examine the neuronal structural integrity of cornea and retina as markers for neuronal degeneration in nonproliferative diabetic retinopathy (NPDR).METHODS. Participants were recruited from the broader Brisbane community, Queensland, Australia. Two hundred forty-one participants (187 with diabetes and 54 nondiabetic controls) were examined. Diabetic retinopathy (DR) was graded according to the Early Treatment Diabetic Retinopathy Study (ETDRS) scale. Corneal nerve fiber length (CNFL), corneal nerve branch density (CNBD), corneal nerve fiber tortuosity (CNFT), full retinal thickness, retinal nerve fiber layer (RNFL), ganglion cell complex (GCC), focal (FLV) and global loss volumes (GLV), hemoglobin A 1c (HbA 1c ), nephropathy, neuropathy, and cardiovascular measures were examined.RESULTS. The central zone (P ¼ 0.174), parafoveal thickness (P ¼ 0.090), perifovea (P ¼ 0.592), RNFL (P ¼ 0.866), GCC (P ¼ 0.798), and GCC GLV (P ¼ 0.338) did not differ significantly between the groups. In comparison to the control group, those with very mild NPDR and those with mild NPDR had significantly higher focal loss in GCC volume (P ¼ 0.036). CNFL was significantly lower in those with mild NPDR (P ¼ 0.004) in comparison to the control group and those with no DR. The CNBD (P ¼ 0.094) and CNFT (P ¼ 0.458) did not differ between the groups.CONCLUSIONS. Both corneal and retinal neuronal degeneration may occur in early stages of diabetic retinopathy. Further studies are required to examine these potential markers for neuronal degeneration in the absence of clinical signs of DR.

Longitudinal Changes in Corneal Cell and Nerve Fiber Morphology in Young Patients with Type 1 Diabetes with and without Diabetic Retinopathy: A 2-Year Follow-up Study

“…14 This is the first longitudinal study in young adolescents with T1DM and it shows no significant change in epithelial, stromal, and endothelial cell densities over 2 years. With regard to early nerve fiber alterations, previous studies have shown a reduction in corneal and retinal nerve fiber parameters prior to the development of retinopathy 13,27 and a relatively greater reduction in CNFL in patients with T1DM compared to T2DM. 28 In the present study over 2 years, there was a significant decrease in the distal branches (CNBD and CNTBD) in young patients with T1DM without DR and a reduction in more proximal nerves (CNFD) in patients with DR.…”

<p>Stereopsis in Early Diabetic Retinopathy</p>

“…Considering that larger ganglion cells in the retina might have been further damaged than the small ganglion cell, the presence of two parallel magnocellular and parvocellular pathways of processing for depth perception is supported. The extensive evidence regarding the thickness reduction in the ganglion cell layer and the retinal nerve fiber layer in the early stages of DR [2][3][4][5][6][8][9][10]29,[31][32][33] further supports the parallel pathways of depth perception. Our findings also do not rule out the serial model of processing.…”

“…Recent OCT findings revealed that pockets of ganglion cell volume loss have been observed in patients with very mild NPDR compared with the non-diabetic group. 29 However the type of the cell in these pockets were not clear. There is also evidence that retrograde axonal transport is impaired for large and medium retinal ganglion cell types in diabetic rats.…”

Diabetic corneal neuropathy: clinical perspectives

“…The appearance of neuronal damage in early stages of diabetes has been demonstrated in laboratory studies, 4 – 7 and the findings have been described clinically in a study by Srinivasan et al, who examined the neuronal structural integrity of the cornea and retina as markers for neuronal degeneration in non-proliferative diabetic retinopathy. 36 They assessed the corneal nerve fiber length (CNFL), corneal nerve branch density (CNBD), and the corneal nerve fiber tortuosity (CNFT), and reported that shorter CNFLs were significantly associated with the severity of the nonproliferative diabetic retinopathy, CNBD, and CNFT. According to Srinivasan et al, CNFL may be a better marker, than CNBD and CNFT, for detecting corneal neuronal degeneration in patients with mild nonproliferative diabetic retinopathy, compared with controls and those with diabetes but without retinopathy.…”

“…According to Srinivasan et al, CNFL may be a better marker, than CNBD and CNFT, for detecting corneal neuronal degeneration in patients with mild nonproliferative diabetic retinopathy, compared with controls and those with diabetes but without retinopathy. 36 …”