A Family Doctor's Tale -NIGHT BLINDNESS

DOC I HAVE Night Blindness

Night Blindness is defective vision in conditions of lowered illumination.

The main causes of Night Blindness is classified into 2 :

1.Congenital Night Blindness:
This is a simple congenital defect of:
a.dominant trait
b.recessive trait
c.recessive sex linked trait

2.Acquired Night Blindness:
This pathological state occurs when the rod function of the retina cells are depressed:
a.Vitamin A deficiency - prolonged deficiency can affect marked degenerative changes in the rods, then cones and subsequently in the neuronal layers of the retina


Causes of Vitamin A deficiency:
inadequate dietary intake
impaired absorption in celiac disease, tropical sprue or liver cirrhosis

b.retinitis pigmentosa - a degenerative disease of the retina affecting the cones and rods starting in the equatorial region and then spreading to the macular region

c.liver disease not associated with vitamin deficiency

d.rare mucopolysaccharidase deficiencies

e.Refsum disease

f.Choroideremia:
progressive atrophy of the choroid -very rare

g.Neuronal ceroid lipofuscinosis

h.Abetalipoproteinuria
Diffuse Night Blindness is inflammation in all areas of the uvea.

Night Blindness affects both eyes and are more common in the elderly:

Symptoms of night blindness:
1.inability to see well at dusk

2.worse after long phases in bright sunlight

Diagnosis of night blindness:
1.History, physical examination and family history eliminates the rarer causes of night blindness.

2.measurement of Vitamin A or carotene levels

3.An early clinical sign of Vitamin A deficiency is conjunctival prexerosis associated with triangular areas of keratinised epithelium at the temporal limbus .

These are called Bitot's spots.

Treatment of night blindness:
1.Most genetic causes of night blindness cannot be cured

2.Vitamin A deficiency:
high doses of Vitamin A of 50,000 to 100,000 units per day up to 14 days.
Longer treatment may cause Vitamin A toxicity and damage the liver.

3.Maintenance dose of 2500 units of Vitamin A(or 750mg) is recommended daily.

Prognosis of night blindness:
depends on the cause -no cure for genetic causes

Poor when due to secondary causes

Excellent in early treatment of Vitamin A deficiency

Prevention of night blindness:
1.knowledge of family history

2. avoid prolonged bright lights

3.Take natural forms of Vitamin A such as carotene in carrots, tomatoes, papaya and other vegetables and natural vitamin A in fish liver oils, liver and meat.