Night Blindness

Night Blindness: Overview

Alternative Names: Nyctalopia.

Night blindness is the inability or reduced ability to see in dim light or darkness.  It also refers to the condition in which the time it takes for the eyes to adapt to darkness is prolonged. Light travels through the cornea and lens and lands on the retina at the back of the eye.  The retina is composed of photoreceptors – specialized nerve cells which convert light rays into electrical signals and transmit them to the brain, which then creates an image.

There are two types of photoreceptors, rods and cones.  There are some 3 million cones and 100 million rods in each eye.  Rods see only black and white, but cones see colors.  Rods also enable the eyes to detect motion and provide peripheral vision.  Rods are responsible for vision in dim light and cones are responsible for vision in bright light.  The rods are spread throughout the retina, but the cones are only in the center of the retina.

Vision in dim light or darkness is blurry because of the connections between the photoreceptors and the nerve cells which are linked to the brain.  Each rod must share this connection to the brain with several other rods so the brain does not know exactly which rod produced the signal.  Vision in bright light is sharp because each cone has its own connection to the brain so the brain can determine exactly where on the retina the signal originated.

Another feature of rods is that they must adapt to darkness.  This is best exemplified by walking into a dark movie theater.  At first, one can see very little.  With time, vision improves and one is able to discern objects.  Ultimately, one can see moderately well.  This dark adaptation process occurs because of the chemical nature of rhodopsin.  Rhodopsin is decomposed in bright light, making the rods nonfunctional.  In darkness, rhodopsin is regenerated faster than it can be decomposed.  Full dark adaptation takes about 15-30 minutes and, when complete, increases light sensitivity by about 100,000 times.

Persons who experience night blindness should not drive during the evening or at night.

Causes and Development

Night blindness is a symptom of several different diseases or conditions, sometimes caused by unlikely diseases or medications.  All of the possible causes of night blindness are associated with the way in which the eye receives light rays.

Diagnosis and Tests

Night blindness can be diagnosed and treated by an ophthalmologist, a physician who specializes in eye disorders.  Opticians can only dispense eye glasses but optometrists may be able to diagnose and treat vision problems.

Diagnosis begins with a detailed medical history regarding the night blindness.  Questions include: severity of night blindness, when night blindness began and whether it occurred gradually or suddenly.  An eye examination is performed and a slit lamp examination – in which a narrow beam of intense light is used to examine the internal components of the eye – may also be performed.  Additional testing may be performed based upon the results of these standard tests.

Seek medical attention if...

Changes in vision should never be taken lightly.  Because night blindness can be a symptom of a serious disease, an ophthalmologist should be consulted before a person embarks on self treatment.

Signs, symptoms & indicators of Night Blindness:

Symptoms - Head - Eyes/Ocular

Risk factors for Night Blindness:

Aging

Cataracts increases risk of Night Blindness Cataracts

Cataracts, characterized by cloudiness of the lens, can cause night blindness.

Nutrients

Zinc Requirement often increases risk of Night Blindness Zinc Requirement

Zinc is required in order to transport vitamin A from the liver to the retina and thus zinc supplementation, especially in those who are deficient, should help improve night vision.

Vitamin A Requirement often increases risk of Night Blindness Vitamin A Requirement

Night blindness is commonly caused by a deficiency in vitamin A.  It is considered one of the first indicators of vitamin A deficiency.

Organ Health

Retinitis Pigmentosa increases risk of Night Blindness Retinitis Pigmentosa

Retinitis pigmentosa results in visual rods being destroyed early in the course of disease, resulting in night blindness.  Night blindness in children may be an early indicator of retinitis pigmentosa.

Liver Detoxification / Support Requirement may increase risk of Night Blindness Liver Detoxification / Support Requirement

Reduced night vision can be linked to a variety of conditions caused by impaired liver function which in turn reduces vitamin A metabolism.

Night Blindness suggests the following may be present:

Organ Health

Night Blindness may suggest Retinitis Pigmentosa Retinitis Pigmentosa

Retinitis pigmentosa results in visual rods being destroyed early in the course of disease, resulting in night blindness.  Night blindness in children may be an early indicator of retinitis pigmentosa.

KEY

Weak or unproven link: may increase risk of; may suggest
Weak or unproven link:
may increase risk of; may suggest
Strong or generally accepted link: often increases risk of
Strong or generally accepted link:
often increases risk of
Definite or direct link: is a sign or symptom of; increases risk of
Definite or direct link:
is a sign or symptom of; increases risk of