Achromatopsia

The color blindness, achromatopsia or achromatism is a rare color vision disturbance in which no color, but only contrasts ( light and dark ) can be perceived. In the ocular ( or congenital ) achromatopsia is the disturbance of vision in the retina, and therefore in the eye, located in the cerebral ( or acquired ) achromatopsia is a neurological disorder of color perception before.

The term color blindness is often misleading, as colloquially the red-green color blindness is called color blindness. In this disease is, however, merely a color-vision deficiency ( color anomaly ) that approximately 5 % of the population (mostly men ) is present. In the medical - expert's area is usually not distinguish sharply between the disability and the function limitation achromatopsia color-vision deficiency. Both diseases are listed together under the same ICD diagnosis code 53.5 ( color vision defects ), the achromatopsia medically as a complete failure of the color sense with resulting further relevant symptoms (low vision, extreme sensitivity to glare ) is class ID.

Disease

There are three types of color blindness that arise in different ways.

The total color blindness is an autosomal recessive disease of the retina. Women and men are equally affected. The affected people (about 1/100.000 ) may differ only shades of gray and are also known as achromatic lenses, the cause is the achromatopsia. They also suffer from a lack of visual acuity and sensitivity to bright light. There are approximately 3,000 persons with achromatopsia in Germany.

One of achromatopsia like illness is the blue pin - monochromaticity in yet there is a greater Restsichtigkeit in the blue region and the X - linked trait ( locus Xq28 ).

The color blindness can also occur as cerebral achromatopsia, for example after a stroke, traumatic brain injury or other brain lesions. This is therefore an acquired color vision deficiency. The cause is not in the eye as a sense organ itself, but in the disturbed processing of sensory perception " color". Visual acuity is normal as the color sensitive cells function normally and detect the edges and surface separation that occurs in the upstream areas of the brain is intact.

Ocular ( congenital ) achromatopsia

Causes of Color Blindness

The color receptors ( cones) in the retina of the eye allow the color perception of the environment. Of these there are three types of color receptors that absorb and pass the color stimuli. In achromat does none of these types of cones, thus they can not recognize colors.

This vision is also necessary for sharp color vision during the day, so that is not possible photopic vision. Achromatic lenses have only rod receptors, which are designed for scotopic vision. This light and dark receptors allow the normal vision twilight vision because they are sensitive to light than the color receptors. On bright days achromat thereby suffer from an extreme sensitivity to glare. In bright light their chopsticks are overloaded, thus the weak eyesight almost completely back.

The achromatic lens sees only shades of gray between white and black, with particularly deep red appears darker than an intense black. He looks sharp contours. He does not look blurry, not blurred or unfocused. This disease is also called " day blindness ". Located on the site of sharpest vision of the retina ( in the center of the yellow spot, the foveola ) in healthy people only cones and no rods. In achromat located in the "middle " of the retina no functioning sensory receptors. The fact that the center has no function, no quiet fixation can be learned already in the first 8 weeks of life, making it a permanent eye restlessness, nystagmus, comes. So this is a result of poor central visual acuity. Nystagmus is an involuntary and not even perceived by the victim nystagmus.

Clinical symptoms

As a rule, concerned with four symptoms before:

• Nearly complete or total color blindness, since no functional cones are present due to the genetic defect.
• Nystagmus ( nystagmus), as in the yellow spot ( place of sharpest vision in the center of the retina) no functional photoreceptor cells ( see diagram of the retina in healthy subjects and achromatic ), and this defect is to be offset by rapid eye movements exist.
• Hypersensitivity to light: photophobia. Rods are designed for lower light levels ( twilight ). Since no functional cones are present, an inhibition of the rods is not possible with brightness as opposed to non - color-blind people.
• Substantially reduced visual acuity (visual acuity ), since rods are arranged in a lower density in the central visual field.

Diagnostics

• Using a Elektroretinogrammes ( ERG) can be assessed separately in mind the function of the rod receptors ( scotopic vision ) and cones receptors ( color vision ). In this case, flashes of light are projected onto the retina; the reactions of the sensory cells ( rods and cones ) are derived by electrodes.
• By a blood test, it is possible to examine the achromatopsia genes ( see below)

Genetics

• CNGA3 gene ( ACHM2 = Achromatopsia 2 = Rod monochromatism 2): 20-30% of achromatopsia patients have mutations in this gene
• Defect: Cyclic nucleotide - gated cation channel alpha- 3 = alpha- subunit of the cone photo receptor cGMP - gated cation channel
• Episode: complete and incomplete achromatopsia
• Locus: 2q11

• 40-50% of achromatopsia patients have mutations in this gene
• Defect: Cyclic nucleotide gated channel beta subunit beta subunit = of the cGMP - gated cation channel
• Locus: 8q21 - q22

• Defect: cone photo receptor -specific alpha subunit of transducin

Heredity

• A healthy non- gene carriers and
• A healthy gene carriers ( heterozygous )

• 50 % carry the gene (clinically healthy, but carriers )
• 50 % have no achromatopsia gene

• Both carriers of achromatopsia gene ( heterozygous trait carriers)

• 50 % carry the gene (clinically healthy, but carriers )
• 25 % have no achromatopsia gene

• All children wear a achromatopsia gene

• All children wear a achromatopsia gene

Special problems of achromatic

The everyday problems of achromatic lenses are primarily influenced by the high sensitivity to glare. The already low visual acuity is further greatly reduced even at moderate light. A change of lighting conditions often involves also a change of glasses ( adapted tint or cut-off filter ). The inability to distinguish colors, also results in strong color - coded daily difficulties.

Therapy

For the irreversible congenital disorder of the retina therapy is currently not possible.

Specific tools

The tools are divided according to the vision problems into three groups: reduction of glare, compensating for the low visual acuity, color vision compensation for the lack.

• For reducing glare edge filter glasses or tinted contact lenses are required. It also aids such as glasses used with glare protection against lateral incident light or visors. Edge filter glasses need to be changed depending on the light conditions.
• To compensate for the low vision magnifying aids are used. These are optical and electronic magnifiers, monoculars, electronic ( panel ) readers, magnifying glasses or goggles with integrated motion segments.
• Problems due to poor knowledge of colors can be partially reduced by electronic color detection devices.
• A new tool is the Eyeborg that converts using a camera color information in acoustic signals.

Individuals with color blindness

• Nicolas Winding Refn
• Paul Newman