The goal of this observational longitudinal study is to investigates whether tear fluid is a non-invasive source of biomarkers for Alzheimer's disease. The main aim of the study is to evaluate diagnostic accuracy measures (sensitivity and specificity) of tear and retinal biomarkers to discriminate individuals with and without neurodegeneration.

Tear fluid from participants will be collected non-invasively with Schirmer's strips, which is a small paper strip placed in the lower eye lid for a maximum of 5 minutes. Additionally, standard, ultra-wide field and cross-sectional retinal images will be obtained.

Inclusion Criteria (healthy controls):

• Available CSF, PET, CT or MRI data to evaluate the presence/absence of neurodegeneration (preferably within 1 year of inclusion in this study)
• Absence of cognitive complaints or treatment and did not seek help for cognitive complaints in the past
• MMSE score 26-30 at baseline
• Age > 50 years
• Available for follow-up (up to 24 months)
• Written informed consent obtained and documented

Inclusion criteria (patients):

• Available CSF, PET, CT or MRI data to evaluate the presence/absence of neurodegeneration (preferably within 1 year of inclusion in this study)
• Available for follow-up (up to 24 months)
• Written informed consent obtained and documented
• Capable of giving informed consent themselves (MMSE score > 17/30)

Exclusion Criteria (all subjects):

• Ocular conditions that could influence tear biochemical parameters (including eye infection, eye inflammation, eye surgery within the last 28 days or other acute eye conditions)
• Neurological or systemic chronic conditions known to interfere with retinal thickness (e.g., glaucoma, diabetes mellitus)
• Ocular conditions interfering with optical coherence tomography (OCT) quality/retinal thickness: e.g. severe cataract, age-related macular degeneration, and glaucoma

The patients will be selected from the population that visit the memory clinic and are willing to participate in scientific research.