Unit 5: Essential Amino Acids and Miscellaneous Topics
1. Essential Amino Acids
Amino acids are the building blocks of proteins. Out of the 20 amino acids required for human growth and metabolism, 9 are termed essential amino acids because the human body cannot synthesize them and they must be obtained from the diet. These amino acids play a vital role in physiological development, immune responses, tissue repair, neurotransmission, and maintaining ocular health.
List of Essential Amino Acids
- Histidine
- Isoleucine
- Leucine
- Lysine
- Methionine
- Phenylalanine
- Threonine
- Tryptophan
- Valine
Functions of Essential Amino Acids
- Histidine: Required for growth, tissue repair, and maintaining the myelin sheath. It is also essential in the production of histamine, an immune system mediator.
- Isoleucine: A branched-chain amino acid that helps in muscle metabolism and energy production, especially during physical stress.
- Leucine: Promotes protein synthesis and muscle repair. It also regulates blood sugar levels and supports growth hormone production.
- Lysine: Crucial for calcium absorption, collagen formation, and antibody production. It plays a role in corneal health and healing.
- Methionine: Acts as a sulfur donor and helps in detoxification. It is also a precursor for cysteine and taurine, which are vital for the retina.
- Phenylalanine: Precursor to dopamine, norepinephrine, and epinephrine. It supports mental alertness and mood regulation.
- Threonine: Important for forming proteins, collagen, elastin, and maintaining the mucosal lining of the eye and gastrointestinal tract.
- Tryptophan: Precursor to serotonin and melatonin, which influence sleep, mood, and pain perception. It also supports ocular nervous function.
- Valine: Stimulates muscle regeneration and energy production. It also aids in cognitive functions and stress resistance.
Sources of Essential Amino Acids
High biological value proteins such as:
- Eggs
- Milk and dairy products
- Meat, poultry, and fish
- Soybeans
- Quinoa
- Legumes and pulses (in combinations)
Essential Amino Acids and Eye Health
Essential amino acids support multiple aspects of ocular health. Lysine is required for collagen production and corneal repair. Methionine and its derivatives protect retinal tissue through antioxidant effects. Tryptophan supports neurotransmitter balance crucial for visual processing. Deficiency in essential amino acids may lead to delayed healing of ocular tissues, reduced visual performance, and compromised immunity, which increases susceptibility to eye infections.
Clinical Relevance in Optometry
- Delayed wound healing post eye surgeries in protein-deficient individuals.
- Corneal thinning and dryness due to lack of structural proteins and collagen.
- Altered neurotransmitter function affecting visual perception and ocular movement control.
- Increased risk of keratoconjunctivitis due to compromised immunity.
2. Miscellaneous Topics
2.1 Measles and Associated Eye Disorders
Measles (Rubeola) is a highly contagious viral infection caused by the paramyxovirus. Though primarily a systemic infection characterized by fever, cough, and skin rash, measles has significant ocular complications, especially in undernourished children or those with Vitamin A deficiency. The infection spreads through respiratory droplets and typically affects children below 5 years of age, especially in developing nations.
Ocular Manifestations of Measles
- Conjunctivitis: One of the earliest signs. The eyes become red, watery, and sensitive to light.
- Photophobia: Sensitivity to light due to inflamed conjunctiva and cornea.
- Corneal Ulcers: Secondary bacterial infection or vitamin A deficiency can lead to ulceration, which if untreated, may cause corneal scarring.
- Keratitis: Inflammation of the cornea, often bilateral, causing blurred vision and discomfort.
- Xerophthalmia: Vitamin A deficiency may be worsened during measles, resulting in dry eyes and Bitot’s spots.
- Blindness: In severe cases, especially in malnourished children, measles can cause permanent vision loss due to corneal damage or optic neuritis.
Role of Nutrition in Measles-Associated Ocular Complications
Nutrition plays a crucial preventive and therapeutic role in measles-related eye conditions. Measles increases metabolic demands and reduces nutrient absorption, especially Vitamin A, making supplementation essential during and after infection.
- Vitamin A Supplementation: WHO recommends two doses of high-dose Vitamin A for children with measles to prevent ocular complications and reduce mortality.
- Protein-Energy Nutrition: Ensures proper immune function and tissue repair, especially in undernourished children.
Optometrist’s Role
Optometrists should recognize early ocular signs of measles and refer cases for immediate medical and nutritional intervention. Educating caregivers about measles vaccination, hygiene, and nutrition can significantly reduce complications.
2.2 Low Birth Weight (LBW)
Low Birth Weight is defined as a birth weight of less than 2500 grams (5.5 pounds), regardless of gestational age. LBW may be due to premature birth (before 37 weeks of gestation) or intrauterine growth restriction (IUGR). According to WHO, more than 20 million infants worldwide are born with LBW each year, a major concern in public health, especially in low- and middle-income countries.
Causes of Low Birth Weight
- Maternal malnutrition during pregnancy
- Teenage pregnancy
- Multiple pregnancies (twins/triplets)
- Infections during pregnancy (e.g., malaria, UTIs)
- Maternal smoking, alcohol, or substance abuse
- Poor prenatal care
Nutritional Consequences of LBW
Low birth weight infants have increased nutritional demands due to rapid catch-up growth, but reduced reserves and immature digestive systems. This leads to a higher risk of:
- Protein-energy malnutrition
- Micronutrient deficiencies (especially iron, calcium, and Vitamin A)
- Growth retardation
- Neurodevelopmental delays
- Delayed visual maturation
Ocular Implications of LBW
- Retinopathy of Prematurity (ROP): One of the most serious consequences, especially in preterm LBW infants who require oxygen therapy. Abnormal blood vessel growth in the retina may lead to retinal detachment and blindness if untreated.
- Delayed Visual Development: LBW infants may have immature visual pathways and increased risk of amblyopia, strabismus, and refractive errors.
- Optic Nerve Hypoplasia: Associated with poor intrauterine growth and metabolic insults during gestation.
Management and Prevention
- Antenatal care: Nutritional counseling, iron-folic acid supplementation, calcium intake, and infection screening for pregnant women.
- Postnatal nutrition: Exclusive breastfeeding for the first 6 months, with fortified milk or supplements as advised.
- Screening: All LBW and preterm infants should undergo routine vision screening for early detection of ROP or visual delays.
Role of Optometrists
Optometrists should be aware of the ocular risks in LBW children and participate in early vision screening programs. They must also educate parents about the need for timely eye checkups, especially in infants with a history of prematurity or neonatal care.
Conclusion
Unit 5 of Nutrition focuses on critical aspects that have both systemic and ocular health implications. Essential amino acids are foundational to human development, immune function, and ocular tissue repair. A deficiency in any of these can lead to visual dysfunction, delayed healing, and growth failure. Similarly, understanding the ocular complications of systemic conditions like measles and low birth weight is crucial for comprehensive care in optometry. A preventive approach that integrates nutrition with eye care practices can greatly improve outcomes in vulnerable populations.
