Alzheimer’s disease (AD) is an age-related progressive neurodegenerative brain disorder that represents the most common type of dementia. It poses a significant diagnostic challenge that requires timely recognition and treatment. Currently, there is no effective therapy for AD; however, certain medications may slow down its progression. The discovery of AD biomarkers, namely, magnetic resonance imaging, positron emission tomography and cerebrospinal fluid molecules (amyloid-β and tau) has advanced our understanding of this disease and has been crucial for identifying early neuropathologic changes prior to clinical changes and cognitive decline. The close interrelationship between the eye and the brain suggests that tears could be an interesting source of biomarkers for AD; however, studies in this area are limited. The identification of biomarkers in tears will enable the development of cost-effective, non-invasive methods of screening, diagnosis and disease monitoring. In order to use tears as a standard method for early and non-invasive diagnosis of AD, future studies need to be conducted on a larger scale.

Diabetic retinopathy (DR) is the most common eye disease complication of diabetes, and hypovitaminosis D is mentioned as one of the risk factors. Vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol) are the best-known forms of vitamin D. Calcitriol (1,25-dihydroxycholecalciferol) is the active form of vitamin D, with the sun being one of its main sources. Vitamin D is synthesized in the skin by exposure to sunlight without protective factors, but care must be taken to avoid the development of sunburn. It not only plays an important role in maintaining healthy bones and immune system but has also been highlighted in numerous studies to have an influence on various diseases, including diabetic retinopathy. A large number of people suffer from vitamin D hypovitaminosis worldwide, and diagnosis is made by measuring the concentration of 25-hydroxyvitamin D (25(OH)D) in serum. Its deficiency can cause numerous diseases and, as such, supplementation is necessary. Clinical studies have proven the effectiveness of vitamin D supplementation in the treatment of diabetic retinopathy, but with a doctor’s recommendation and supervision due to possible negative side effects.

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder of the brain associated with ageing and is the most prevalent form of dementia, affecting an estimated 55 million people worldwide, with projections suggesting this number will exceed 150 million by 2050. With its increasing prevalence, AD represents a significant global health challenge with potentially serious social and economic consequences. Diagnosing AD is particularly challenging as it requires timely recognition. Currently, there is no effective therapy for AD; however, certain medications may help slow its progression. Existing diagnostic methods such as magnetic resonance imaging (MRI), computed tomography (CT), positron emission tomography (PET), and biomarker analysis in cerebrospinal fluid tend to be expensive and invasive, making them impractical for widespread use. Consequently, research into non-invasive biomarkers that enable early detection and screening for AD is a crucial area of contemporary clinical investigation. One promising approach for the early diagnosis of AD may be retinal imaging. As an extension of the central nervous system, the retina offers a distinctive opportunity for non-invasive brain structure and function assessment. Considering their shared embryological origins and the vascular and immunological similarities between the eye and brain, alterations in the retina may indicate pathological changes in the brain, including those specifically related to AD. Studies suggest that structural and vascular changes in the retina, particularly within the neuronal network and blood vessels, may act as markers of cerebral changes caused by AD. These retinal alterations have the potential to act as biomarkers for early diagnosis. Since AD is typically diagnosed only after a significant neuronal loss has occurred, identifying early diagnostic markers could enable timely intervention and help prevent disease progression. Non-invasive retinal imaging techniques, such as optical coherence tomography (OCT) and OCT angiography, provide accessible methods for the early detection of changes linked to AD. This review article focuses on the potential of retinal imaging as a non-invasive biomarker for early diagnosis of AD. Investigating the ageing of the retina and its connections to neurodegenerative processes could significantly enhance the diagnosis, monitoring, and treatment of AD, paving the way for new diagnostic and therapeutic approaches.

Alzheimer’s disease (AD) represents a prominent neurodegenerative disorder (NDD), accounting for the majority of dementia cases worldwide. In addition to memory deficits, individuals with AD also experience alterations in the visual system. As the retina is an extension of the central nervous system (CNS), the loss in retinal ganglion cells manifests clinically as decreased visual acuity, narrowed visual field, and reduced contrast sensitivity. Among the extensively studied retinal disorders, age-related macular degeneration (AMD) shares numerous aging processes and risk factors with NDDs such as cognitive impairment that occurs in AD. Histopathological investigations have revealed similarities in pathological deposits found in the retina and brain of patients with AD and AMD. Cellular aging processes demonstrate similar associations with organelles and signaling pathways in retinal and brain tissues. Despite these similarities, there are distinct genetic backgrounds underlying these diseases. This review comprehensively explores the genetic similarities and differences between AMD and AD. The purpose of this review is to discuss the parallels and differences between AMD and AD in terms of pathophysiology, genetics, and epigenetics.

Background: The prevalence of dry eye disease (DED) is increasing globally, resulting in a variety of eye symptoms characterized by discomfort and visual disturbances. The accurate diagnosis of the disease is often challenging and complex, requiring specialized diagnostic tools. This study aimed to investigate the impact of tear film instability on visual function and to evaluate the value of post-blink blur time (PBBT) as an alternative method for assessing tear film stability. Methods: The study included 62 subjects: 31 with subjective symptoms of DED (Group A) and a control group consisting of 31 healthy participants (Group B). Symptoms were assessed using the standard Schein questionnaire, supplemented with additional questions. PBBT was measured using standard Snellen charts to investigate a potential association between PBBT and tear film dysfunction. Additional clinical assessments included tear film break-up time (TBUT). Results: Statistically significant differences were observed in the average values of PBBT and TBUT between the examined groups. The average PBBT was 8.95 ± 5.38 s in the group with DED and 14.66 ± 10.50 s in the control group, p < 0.001. Group A exhibited an average TBUT of 4.77 ± 2.37 s, while Group B had a TBUT of 7.63 ± 3.25 s, p < 0.001. Additionally, a strong positive correlation was identified between PBBT and TBUT values (r = 0.455; p < 0.001). Conclusions: The research confirms that tear film stability has an important role in the refraction of light and the maintenance of optical quality of vision. PBBT could potentially function as an objective and clinically significant screening test for DED.