Systemic Protein Deficiency and Its Role in Dry Eye Pathophysiology: A Bioclinical perspective

Nayla Altom Mohamed Ismail, M. Optom

PhD Candidate, AL-Neelain University, Sudan, Africa

 

Did You Know Your Tears Tell the Story of Your Health?

Tears are far more than salty drops that slide down the cheeks; they are a sophisticated biological shield, silently protecting and nourishing the eyes while reflecting the health of the entire body. In fact, tears are an essential secretion that preserves the integrity of the ocular surface, visual clarity, and overall eye comfort. ⁽¹⁾

The protective film is structured in three layers.

• Aqueous Layer – Provides hydration
• Mucin Layer – Ensures adhesion to the eye surface ⁽²⁾
• Lipid Layer – Prevents tear evaporation

Figure 1: Layers of Tear Film

These layers are enriched with electrolytes and crucial proteins, acting as silent guardians of ocular health. The most notable among them include:

• Lysozyme – A natural germ-killer
• Lactoferrin – An anti-inflammatory agent
• Lipocalin – Stabilises the tear film
• Secretory IgA – A key immune defence component ⁽²⁾

These proteins do not just protect the eyes; they also regulate osmotic balance, prevent inflammation, and maintain tear stability.

This delicate system can collapse due to systemic diseases like Diabetes, Lupus, or Sjögren’s Syndrome, leading to chronic, painful dry eyes — more than just a local issue, it is a warning signal from within. ⁽³⁾

The Biochemical and Functional Profile of Tear Film Proteins

1. The Protein-Rich Layer: Aqueous Layer

• Location: Middle layer of the tear film, accounting for ~90% of its total thickness.
• Source: Secreted by the main and accessory lacrimal glands.
• Protein Concentration: Contains the highest percentage of tear proteins, compared to the lipid and mucin layers. ⁽⁴⁾

2. Bio-chemical Composition of Tear Film

Component	Approximate %	Description
Water	~98%	Main solvent and carrier.
Proteins	~1–2%	Enzymes, immune molecules, stabilising factors.
Electrolytes	~0.9%	Sodium, potassium, chloride.
Other Nutrients	Trace	Glucose, oxygen – nourish the cornea.

Table 1: Chemical Composition of Tear Film (Approximate Percentages) ⁽⁵⁾

3. Major Tear Proteins and Their Functions

Protein	% of Total Proteins	Function	Deficiency Consequence
Lysozyme	20–40%	Antibacterial, lyses microbial walls	Increased infection risk
Lactoferrin	10–20%	Binds iron, anti-inflammatory, and immune support	Reduced microbial protection
Lipocalin	15–25%	Stabilises lipid layer, transports lipids	Tear film instability, dry eye
Secretory IgA	5–10%	Neutralises pathogens, mucosal immunity	Frequent conjunctival infections
Albumin	~5%	Osmotic balance, scavenges free radicals	Oxidative stress and inflammatory imbalance

Table 2: Major Tear Proteins and Their Functions ⁽⁵⁾

4. Normal Protein Concentration in Tears

Total Protein Level: ~6–10 mg/mL under normal conditions.
Altered Levels: Protein imbalance affects tear health: dryness, inflammation, allergic signs. ⁽⁶⁾

5. Factors Influencing Tear Protein Concentration

i) Age, Systemic Health, Environmental Factors. ⁽⁷⁾

ii) Systemic Diseases Affecting Tear Proteins and Dry Eye

• Sjögren’s Syndrome: Autoimmune disease attacking exocrine glands including lacrimal and salivary glands. ⁽⁷⁾
• Other Autoimmune Diseases (e.g., Lupus, Rheumatoid Arthritis): Chronic inflammation affecting lacrimal glands. ⁽⁷⁾
• Diabetes Mellitus: Chronic hyperglycemia → microvascular damage → reduced lacrimal gland perfusion. ⁽⁸⁾
• Vitamin A Deficiency: Vitamin A is essential for producing mucin proteins in the innermost tear layer. ⁽⁹⁾
• Thyroid Disorders: Hyper- or hypothyroidism affects metabolic protein regulation.
• Chronic Liver and Kidney Disease: Toxin accumulation → disrupted synthesis of essential proteins (e.g., albumin). ⁽¹⁰⁾
• Genetic Diseases (e.g., Cystic Fibrosis): CFTR mutations → impaired ion channels → thick secretions. ⁽¹⁰⁾
• Drug Side Effects: Antihistamines, antidepressants, chemotherapy.

Disease	Affected Proteins	Impact on Tear Film
Sjögren’s Syndrome	Lysozyme, Lactoferrin	Aqueous layer deficiency → dry eye
Diabetes Mellitus	Albumin, Enzymes	Impaired secretion → tear deficiency
Vitamin A Deficiency	Mucin	Mucin layer disruption → evaporation
Thyroid Disorders	Membrane-related proteins	Proptosis → rapid evaporation

Table 3: Protein Tear Impact

Integrated Therapy

• Treat underlying causes: Control systemic/ocular diseases (e.g., autoimmune disorders) to reduce inflammation.
• Artificial tears: Restore tear film balance and relieve dryness.
• Nutritional support: Use Vitamin A and Omega-3 to enhance tear quality.
• Systemic factors: Manage diabetes or thyroid disorders that affect tear proteins. ⁽¹¹⁾

Conclusion

Every tear that falls from eyes carries a hidden story about body health. Dry eyes might not just be caused by screens or dry weather; it can be a silent warning from your body about something deeper, like an autoimmune disorder, a vitamin deficiency, or poor nutrition. ⁽¹²⁾

Therefore, do not ignore your dry eyes — they might be trying to tell you something important! True eye care starts from within, through nutrition, immunity, and even emotional well-being. With today’s medical advances, analysing tear proteins has become a smart tool that can reveal surprising health insights.

Let your eyes guide you and listen closely to what your tears are trying to say.

Get screened, stay protected, and never ignore the silent story that your tears may be telling.

 

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