Evaluation of retinal neurodegeneration in patients with type 2 diabetes mellitus (DM2) without diabetic retinopathy or with mild non proliferative diabetic retinopathy

Retinal complications in diabetes mellitus (DM) patients were typically considered part of a vascular process. However, recent studies suggest that ocular degeneration in DM might be caused by 2 different conditions: vasculopathy and neuropathy . For some authors, neuropathy observed in the retina of DM patients might be a part of an underlying polyneuropathy ; for others, however, neuropathic changes might precede microvascular alterations .

Axons of retinal ganglion cells compose the retinal nerve fiber layer (RNFL) in the retina and then form the optic nerve connecting the eyeball and brain. Retinal nerve fiber layer (RNFL) loss is recognized as an important neurodegenerative sign in glaucoma. Thinning of the RNFL has also been found in multiple sclerosis, Parkinson's disease and Alzheimer's disease, indicating neurodegeneration of the retina. If RNFL thinning is significant in diabetic patients with preclinical diabetic retinopathy, evaluation of peripapillary RNFL thickness would be very important, because early detection and treatment of diabetic retinopathy is critical to reduce the risk of blindness Optical coherence tomography (OCT) has been introduced into clinical practice as the most noninvasive and objective method to visualize the retina, showing an amount of detail that resembles histological specimens. Initially, OCT was applied to detect complications of DR (edema macular or epiretinal membrane). Later on, it allowed quantitative and qualitative measurements of retinal thickness and segmentation of all intraretinal layers. OCT might detect early retinal neurodegenerative changes, and thus help define which diabetic patients may be at risk to develop DR.

Inclusion Criteria:

• All patients with confirmed type 2 DM diagnosis of at least 6 months
• Best-corrected visual acuity (BCVA) of 6/12 or higher (using a Snellen chart) in each eye
• Intraocular pressure (by applanation) less than 21 mmHg.
• Healthy controls had no record nor evidence of ocular or neurologic disease of any kind; their BCVA is > 6/9 based on the Snellen scale.

Exclusion Criteria:

• presence or past history of moderate or severe non proliferative diabetic retinopathy or proliferative diabetic retinopathy , confirmed by indirect funduscopy or retinography images.
• presence of significant refractive errors (≥5 diopters of spherical equivalent refraction or 3 diopters of astigmatism)
• intraocular pressure ≥21 mmHg
• media opacifications
• concomitant ocular diseases, including history of glaucoma or retinal pathology
• systemic conditions that could affect the visual system, including neurodegenerative disorders such as Parkinson's disease, multiple sclerosis, or dementia.

40 eyes of patients with DM2 and without any signs of diabetic retinopathy or with mild non proliferative diabetic retinopathy and 40 eyes of healthy controls