The goal of this observational study is to learn about the interaction between the eyes, brain, and kidneys in adult patients with Chronic Kidney Disease (CKD). The main question it aims to answer is:

Do changes in the brain's network connectivity and the retina's blood vessels correlate with cognitive decline and kidney function in CKD patients? Participants with CKD who are already undergoing clinical care will complete cognitive tests and questionnaires, have non-invasive MRI scans of their brain and kidneys, and undergo non-invasive eye imaging (OCT/OCTA) of their retinas.

This is a prospective, single-center, observational cohort study designed to investigate the multi-system interactions among the eyes, brain, and kidneys in patients with Chronic Kidney Disease (CKD) stages 1-5. The study integrates multimodal imaging, clinical laboratory tests, and neuropsychological assessments to establish a comprehensive "eye-brain-kidney" evaluation framework.

Study Design and Procedures:

The study plans to enroll CKD patients from Beijing Friendship Hospital, Capital Medical University, between December 2025 and December 2028. All enrolled participants will undergo comprehensive evaluations at two time points: baseline and a 3-year follow-up. Baseline assessments include: medical history collection, neuropsychological scale evaluations (Montreal Cognitive Assessment, Symbol-Digit Modalities Test, Digit Span Test, Hospital Anxiety and Depression Scale), blood tests (complete blood count, biochemistry, and specific biomarkers such as Tau protein and β2-microglobulin), multimodal brain magnetic resonance imaging (MRI), multiparametric kidney MRI, and ocular optical coherence tomography (OCT). The above assessments will be repeated at the 3-year follow-up to observe longitudinal changes in all parameters.

Assessment Methods and Technical Parameters:

1. Brain MRI: A 3.0T MRI scanner will be used to acquire multiple sequences including 3D T1-weighted structural imaging, resting-state functional MRI, arterial spin labeling perfusion imaging, diffusion tensor imaging, quantitative susceptibility mapping, and amide proton transfer-chemical exchange saturation transfer imaging. These will be used to analyze brain structure, perfusion, functional connectivity, and metabolic changes.
2. Kidney MRI: A 3.0T MRI scanner will be used with sequences such as intravoxel incoherent motion, arterial spin labeling, and T1 mapping to quantitatively assess renal microcirculation perfusion, tissue diffusion characteristics, and the degree of fibrosis.
3. Ocular Imaging: Optical coherence tomography and angiography will be used to obtain quantitative parameters including retinal nerve fiber layer thickness, macular structure, choroidal thickness, and vessel density in the superficial and deep retinal capillary plexuses.
4. Clinical and Cognitive Assessments: In addition to standardized scales, remaining serum and plasma samples from participants will be preserved for subsequent biomarker analysis.

Quality Control and Data Management:

A comprehensive quality control plan has been developed and implemented for this study:

Data Acquisition QC: Standardized scanning protocols and fixed procedures are used for imaging data acquisition, including the use of specialized earplugs and head fixation pads to reduce noise and motion artifacts. Criteria for data re-acquisition or exclusion are established for subjects with excessive head motion or inability to cooperate.

Data Management: Prospective data collection utilizes unified, standardized questionnaires performed by trained research personnel with simultaneous double verification. All data will be anonymized and stored in an encrypted, dedicated database with strict tiered access control to ensure data security and privacy.

Process and Ethical Oversight: The study protocol, informed consent forms, and other documents have been reviewed and approved by the hospital's Life Ethics Committee. A participant follow-up safeguard mechanism has been established, including follow-up reminders, emergency plans for clinical changes, and documentation of loss to follow-up. The study guarantees participants the right to withdraw unconditionally at any time, with their legitimate rights and interests fully protected.

Sample Size and Statistical Analysis:

The sample size was calculated based on between-group comparisons of the primary outcome measure (MoCA score). Using a one-way ANOVA, with α=0.05, power of 80%, and an effect size f=0.10, the minimum required sample size was calculated to be 1200. Considering a 15% attrition rate, the final planned enrollment is 1500 participants.

Statistical analysis will be performed using SPSS 26.0 and SPM12 software. Continuous data will be described using mean ± standard deviation or median based on normality test results. Between-group comparisons will use ANOVA or non-parametric tests according to data distribution. For multimodal imaging data, voxel-wise between-group comparisons will be conducted, controlling for covariates such as age and sex, with cluster-level FDR correction. Correlation analyses will use Pearson or Spearman correlation, with Bonferroni correction for multiple comparisons. The significance level is set at p < 0.05.

Inclusion Criteria:

1. Aged 18-70 years.
2. Patients clinically diagnosed with CKD stages 1-5.
3. No contraindications for MRI examination (e.g., cardiac pacemaker, claustrophobia, cochlear implant, hearing aid, coronary stents implanted before 2015) and able to complete the MRI scan.

Exclusion Criteria:

1. Patients with recent or prior cerebral hemorrhage or cerebral infarction.
2. History of epileptic seizures or psychiatric disorders.
3. Patients with claustrophobia.
4. Pregnant or lactating patients.
5. Presence of other central nervous system diseases (e.g., tumor, trauma).
6. Unstable angina, congestive heart failure (NYHA class III or IV), or acute myocardial infarction.
7. Any systemic or other diseases deemed unsuitable for clinical trial participation.

The study population will consist of a prospective cohort of adult patients with Chronic Kidney Disease (CKD) recruited from a single clinical center. All participants will be selected from patients attending the Department of Nephrology and other relevant clinics at Beijing Friendship Hospital, Capital Medical University. The primary eligibility criteria include an age range of 18 to 70 years and a clinical diagnosis of CKD at any stage (1 through 5). Key exclusions are applied to ensure patient safety and specificity of the observational findings, primarily concerning conditions that contraindicate MRI procedures or represent significant, unstable comorbid systemic, cardiovascular, or neuropsychiatric diseases. A total of 1500 participants meeting these criteria are planned to be enrolled. Each participant will undergo a comprehensive baseline assessment and a follow-up evaluation at 3 years.