Frequently Asked Questions

Frequently Asked Questions

What is Vitamin A deficiency?
Vitamin A is an essential element which keeps the retina healthy. Vitamin A deficiency is a lack of vitamin A in humans. It is common in poorer countries but rarely seen in more developed countries. Night blindness is one of the first sign of vitamin A deficiency. Xerophthalmia, keratomalacia, and complete blindness can also occur. Vitamin A Deficiency is the leading cause of avoidable blindness amongst children. It is estimated that between 250,000 – 500,000 vitamin A deficient children coming blind every year, with half of them dying within 12 months of losing their sight. Night blindness caused by Vitamin A Deficiency is due to Malnutrition. Before structural changes in retina, supplementation with vitamin A or eating foods rich in Vitamin A, may help reduce symptoms. Vitamin A was found to slow the progression of Retinitis Pigmentosa. Vitamin A in humans is primarily obtained by conversion of beta-carotene, a pigment found in fruits and vegetables. Zinc is necessary to transport vitamin A from the liver to the retina, so zinc supplementation may help improve night vision.
WHAT IS NIGHT BLINDNESS?

Night Blindness (Nyctalopia) is a type of vision impairment. People with night blindness experience poor vision at night or in dimly lit environments. Although the term “night blindness” implies that you cannot see at night. Patients of night blindness may just have more difficulty seeing and / or driving at night.

Patients of night blindness try to finish their work before the sun sets. If something is left for them to do, they do it next day.

If someone has night blindness, he has consistent difficulties in seeing at night, but will be able to see normally during the day or when an adequate amount of light is present. He will not be able to see objects in the dark that are easily visible to others, and his eyes may need more time to adjust after he goes from a brightly lit space into a dark space, such as a movie theatre.

Causes And Symptoms Of Night Blindness: Several different conditions and diseases can cause night blindness. The causes of night blindness fall into two categories: treatable and non-treatable.

Treatable causes:

-Vitamin A deficiency: Night blindness is commonly caused by a deficiency in vitamin A, in fact, it is one of the first indicators of vitamin A deficiency.

-Cataracts: This condition is characterized by a cloudiness of the lens.

-Nearsightedness: Use of certain drugs

-Liver conditions: Reduced night vision can be linked to poor liver functioning, due to a variety of conditions, which impairs vitamin A metabolism.

 -Macular degeneration: Degeneration of the macula retina, a specialized region of the retina, can cause night blindness.

-Xerophthalmia: This condition is characterized by dryness of the conjunctiva (the membrane that covers the eyelids and exposed surface of the eye) and cornea, light sensitivity, and night blindness. It is caused by vitamin A deficiency. Xerophthalmia rarely occurs in countries with adequate supplies of milk products. -Zinc deficiency: Zinc is a mineral that is necessary for vitamin A to improve vision.

Non-treatable Causes:

-Birth defects

-Retinitis pigmentosa

WHAT IS RETINITIS PIGMENTOSA?
Retinitis Pigmentosa (RP) refers to a group of inherited diseases causing retinal degeneration. The cell-rich retina lines the back inside wall of the eye. It is responsible for capturing images from the visual field. People with RP experience a gradual decline in their vision because photoreceptor cells (rods and cones) die. Forms of RP and related diseases include Usher syndrome, Leber’s congenital amaurosis, rod-cone disease, Bardet-Biedl syndrome, and Refsum disease, among others. SIGNS AND SYMPTOMS People may experience one or more of the following symptoms:
  • Night blindness or nyctalopia
  • Tunnel vision (no peripheral vision)
  • Peripheral vision (no central vision)
  • Latticework vision
  • Aversion to glare
  • Slow adjustment from dark to light environments and vice versa
  • Blurring of vision
  • Poor colour separation
  • Extreme tiredness
Symptoms depend on whether rods or cones are initially involved. In most forms of RP, rods are affected first. Because rods are concentrated in the outer portions of the retina and are triggered by dim light, their degeneration affects peripheral and night vision. When the more centrally located cones – responsible for color and sharp vision – become involved, the loss is in colour perception and central vision. Night blindness is one of the earliest and most frequent symptoms of RP. People with mainly cone degeneration however first experience decreased central vision and ability to discriminate color.   RP is typically diagnosed in adolescents and young adults. It is a progressive disorder. The rate of progression and degree of visual loss varies from person to person. Most people with RP are legally blind by age 40, with a central visual field of less than 20 degrees in diameter. In families with X-linked RP, males are more often and more severely affected; females carry the genetic trait and experience vision loss less frequently.
HOW IS RP INHERITED?

An estimated 100,000 people in the U.S. have RP, mainly caused by gene mutations (variations) inherited from one or both parents. Mutated genes give the wrong instruction to photoreceptor cells, telling them to make an incorrect protein, or too little or too much protein. (Cells need the proper amount of particular proteins in order to function properly). Many different gene mutations exist in RP. In Usher syndrome, for example, at least 14disease-causing genes have been identified.

Genetic mutations can be passed from parent to offspring through one of three genetic inheritance patterns – autosomal recessive, autosomal dominant, or X-linked.

In autosomal recessive RP, both parents carry one copy of the mutated gene but have no symptoms themselves. Children have a 25 percent chance of being affected by inheriting a mutated copy from each parent.

In autosomal dominant RP, usually is affected and is the only parent with a mutated gene. A child has a 50 percent chance of being affected by inheriting the mutated gene from that parent.

In families with X-linked RP, the mother carries the mutated gene, and her sons have 50 percent chance to being affected. Daughters are carries and aren’t usually affected. However, some daughters are affected, but with milder symptoms.

If a family member is diagnosed with RP, it is strongly advised that other members of the family also have an eye exam by a physician who is specially trained to detect and treat retinal degenerative disorders. Discussing inheritance patterns and family planning with a genetic counselor can also be useful.

ARETHERE ANY OTHER RELATED DISEASES?
Other inherited diseases share some of the clinical symptoms or RP. The most common in Usher syndrome, where hearing and vision are both affected. Other related syndromes being studied through FFB funding include Best disease, choroideremia, gyrate-atrophy, and Stargardt disease.