Introduction
Modifying and optimizing daily dietary habits can prevent or alter the progression of various ocular diseases, namely cataracts, age-related macular degeneration (AMD), diabetic retinopathy, glaucoma, and dry eye syndrome. This review study focuses on the first three conditions, as they represent the leading causes of blindness and have well-documented associations with dietary patterns.

Methods
This was a review study. Relevant literature was retrieved by searching various keywords, such as cataract, AMD, type 2 diabetes, diabetic retinopathy, and diet in PubMed and MEDLINE databases for articles published between 2010 and 2023. The most pertinent studies were selected, translated into Persian where necessary, and analyzed for this review.

Results 

Cataract
Cataracts are the leading cause of blindness worldwide, affecting approximately 95 million individuals. Recent studies suggest that nutrition may significantly influence cataract formation and progression [1]. While cataractogenesis is a multifactorial process, oxidative damage is a primary contributor. Oxidative stress occurs when there is an imbalance between reactive oxygen species (ROS) production and cellular antioxidant defense mechanisms. Recognized oxidative risk factors include smoking, ultraviolet-B (UV-B) radiation exposure, and diabetes [2، 3].
Plant-based diets, rich in antioxidant compounds, have the potential to protect cells from chronic oxidative damage [4-6]. On average, plant-derived foods contain 64 times more antioxidants than animal-based products [7]. Furthermore, high-temperature cooking of animal products generates heterocyclic amines (HCAs), which have been linked to cataract formation [8]. Diets rich in fruits, vegetables, whole grains, nuts, and legumes that minimize animal product consumption are beneficial for cataract prevention.

AMD
AMD is the most common cause of blindness in developed countries, accounting for over 90% of blindness cases. Its incidence is rising in developing nations as well. Multiple studies have demonstrated a strong correlation between dietary patterns and AMD risk [13]. Three key pathophysiological mechanisms suggest dietary influence on AMD development.
Macular pigments: Macular pigments, including lutein, zeaxanthin, and meso-zeaxanthin, play a critical role in protecting the retina and macula from oxidative damage caused by short-wavelength light (blue light) [14]. These pigments are entirely derived from dietary sources and are most abundant in dark green leafy vegetables, including kale and spinach, as well as yellow-orange fruits and other vegetables [15]. The selective uptake of xanthophylls by retinal cells and their high concentration in the retina highlight their importance in retinal health [16، 17].
Inflammation: Chronic inflammation is a well-recognized factor in AMD pathogenesis. Drusen, the hallmark pathological feature of AMD, contains inflammatory components such as fibrinogen, vitronectin, and C-reactive protein (CRP) [20, 21]. CRP is a low-grade inflammatory marker associated with chronic conditions, such as cardiovascular disease, type 2 diabetes, and certain malignancies. Aging-associated alterations in the balance of pro-inflammatory and anti-inflammatory cytokines contribute to a persistent low-grade inflammatory state, increasing the risk of AMD. Recent systematic reviews and meta-analyses indicate that vegan and vegetarian diets are associated with lower CRP levels (mean differences of -0.54 mg/L, P<0.0001, and -0.25 mg/L, P=0.05, respectively) compared to conventional diets in both healthy and diseased populations. However, further research is needed to establish dietary interventions for AMD prevention [21].
Oxidative damage: Aging leads to a decline in the efficiency of endogenous antioxidant defense systems and an increase in oxidative burden. Consequently, dietary intake of exogenous antioxidants is essential for ocular aging support. Retinal tissue is highly susceptible to oxidative stress due to prolonged light exposure, high oxygen consumption, and the subsequent generation of free oxygen radicals, which adversely affect retinal polyunsaturated fatty acids [23]. Oxidative stress also contributes to AMD pathogenesis via angiogenesis and inflammation [24]. Oxidative damage to the retinal pigment epithelium may trigger apoptotic cell death, exacerbating AMD progression [25]. Furthermore, chronic oxidative stress promotes the accumulation of drusen proteins in the retina [26].

Type 2 diabetic retinopathy
Globally, an estimated 438 million individuals are affected by type 2 diabetes, reflecting a 49% increase since 1990 [31]. Diabetic microvascular and macrovascular complications significantly impact mortality rates and quality of life. Lifestyle and dietary modifications play a crucial role in preventing and managing type 2 diabetes to preserve vision and overall health.

Pathophysiological considerations
Hyperglycemia is a recognized driver of cellular damage, primarily via metabolic pathways, such as the polyol pathway, non-enzymatic glycation of proteins, hexosamine flux, and protein kinase C activation. Dietary interventions targeting these pathways can reduce inflammatory and oxidative stress markers.
Non-enzymatic glycation of proteins is a critical contributor to advanced glycation end-product (AGE) formation, which plays a key role in the pathophysiology of diabetic retinopathy. Although AGEs are naturally occurring, excessive accumulation is pathogenic. Animal-derived products, particularly beef and cheese, contain the highest AGE concentrations, followed by pork, poultry, fish, and eggs. Cooking methods involving high temperatures, such as grilling, frying, and roasting, accelerate AGE formation. By contrast, plant-based foods, even after cooking, contain minimal AGE levels [37].

Conclusion
Substantial evidence supports the role of Mediterranean and plant-based diets, rich in fruits, vegetables, legumes, whole grains, and nuts, in reducing the risk of vision loss associated with cataracts, AMD, and diabetic retinopathy. These dietary patterns may also offer protection against other ocular conditions with underlying pathogenic mechanisms involving chronic oxidative stress, inflammation, or macular pigment alterations. However, most existing research in this domain is observational. Further longitudinal, randomized controlled trials are required to establish definitive causal links between dietary patterns and ocular diseases.

Ethical Considerations

Compliance with ethical guidelines
There were no ethical considerations to be considered in this research.

Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors.

Authors' contributions
Conceptualization, study design, supervision, review and editing: Ebrahim Azaryapour; Project administration, technical, or material support: Hassan Behboudi; Writing the original draft: All authors.

Conflicts of interest
The authors declared no conflict of interest.
 

References