The goal of this prospective, observational study is to compare in the association of glycemic control and retinal microvascular changes in patients with type 2 diabetes mellitus (T2DM) without diabetic retinopathy (DR).

The main question it aims to answer are:

• Do degenerative changes in retinal microvasculature or nerves depend on glycemic control even before diabetic retinopathy is detected?

Participants will receive an annual routine comprehensive examination including ultra-widefield fundus photography, spectral domain optical coherence tomography (OCT), and swept-source optical coherence tomography angiography (OCTA).

Inclusion Criteria:

• The study included 30-70-year-old patients with T2DM without known DR at baseline who underwent regular screening for DR at the department of ophthalmology.
• Who underwent regular checkups for DR between January 2019 and August 2022 at Dongguk University Ilsan Hospital.
• The controls included patients without DM who presented for regular ophthalmic examination.

Exclusion Criteria:

• patients with a history of retinal or choroidal diseases (i.e., age-related macular degeneration, retinal vein occlusion, uveitis, retinal detachment, and central serous chorioretinopathy), glaucoma, or optic neuropathy
• patients with neurodegenerative diseases, such as Parkinson's disease and dementia.

The study included 30-70-year-old patients with T2DM without known DR at baseline who underwent regular screening for DR at the department of ophthalmology. The controls included patients without DM who presented for regular ophthalmic examination. One eye each of DM patients and controls was included in the study. The eye without significant ocular disease was selected from both eyes; if both eyes were eligible, the right eye was selected. The participants underwent comprehensive ophthalmic examination, including best-corrected visual acuity assessment using the Snellen chart, slit-lamp biomicroscopy, dilated fundus examination, ultra-widefield fundus photography, spectrum-domain OCT, and SS-OCTA. Patients with T2DM were included in the study after a retinal specialist confirmed absence of signs of DR on clinical examination and ultra-wide fundus photography.