1：Experimental Design and Method Selection:

Observational cross-sectional study design. Cases were categorized based on Early Treatment Diabetic Retinopathy Study (ETDRS) classification into no diabetic retinopathy, non-proliferative diabetic retinopathy, and proliferative diabetic retinopathy groups, with healthy controls. Retinal photoreceptor apoptosis was defined as disruption of the ellipsoid zone (EZ) assessed using spectral-domain optical coherence tomography (SD-OCT). Serum levels of total and ionized calcium were measured using standard protocols. Statistical analyses included Pearson's correlation, univariate linear regression, and binary logistic regression.

2：Sample Selection and Data Sources:

60 consecutive cases with Type 2 diabetes mellitus and 20 healthy controls were included. Exclusion criteria included ocular or systemic diseases affecting retinal vascular pathology, medications or conditions altering calcium levels, previous ophthalmic interventions, low OCT signal strength, and use of mineral supplements or antioxidants.

3：List of Experimental Equipment and Materials:

Zeiss fundus camera FF 450 Plus (Carl Zeiss Meditec AG, Jena, Germany) for digital fundus photography and fluorescein angiography; Spectral domain optical coherence tomography (SD-OCT) [Cirrus HD-OCT Carl Zeiss Meditech, Inc., CA, U.S.A] for macular cube imaging; Autoanalyzer for measuring HbA1c and total calcium; Electrolyte analyzer using ion selective method for ionized calcium; Chemiluminescence microparticle microassay method for vitamin D levels; Blood collection tubes with 3.89% trisodium citrate.

4：89% trisodium citrate. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: Informed consent obtained. Best-corrected visual acuity measured on logMAR scale. Slit lamp biomicroscopy and dilated ophthalmoscopic examination performed. Digital fundus photography and fluorescein angiography done. SD-OCT used to assess EZ disruption, graded as intact, focal disruption, or global disruption. Blood samples drawn by aseptic vein puncture, serum separated, and biochemical parameters measured.

5：Data Analysis Methods:

Data summarized as Mean ± SE. Chi-square test for gender distribution. One-way ANOVA for comparing serum calcium levels between groups. Pearson's correlation for continuous variables. Univariate linear regression with logMAR BCVA as dependent variable. Binary logistic regression with EZ disruption as dependent variable. Analyses performed using SPSS software (window version 21.0).