Two Types Part II: Achromatopsia layout

  • Cerebral Achromatopsia: Ask Dr. Green
  • Detecting Cerebral Achromatopsia
  • Specific Region Affected
  • Hemiachromatopsia
  • Transient Achromatopsia

    • Cerebral Achromatopsia: In a nut shell Ask Dr. Greene.

    What are the symptoms?

           Screening tests help detect colorblindness; however earlier symptoms include an apparent difficulty learning some or all of the colors.

    Is it contagious?

           No

    How long does it last?

           This is generally a lifelong condition.

    How is it diagnosed?

           Colorblindness is usually tested at children's four-year physicals. The doctor asks them to identify a red and a green line on the eye chart. If any question remains, more precise visual testing can determine the exact nature of the problem.

    How is it treated?

           There is no known way to restore color vision in those who have hereditary colorblindness. By being aware of their condition, we can help our children learn other ways to distinguish between red and green -- the position of traffic lights, for instance. In addition, we can decorate their worlds, and wrap their presents, in the millions of nuances of color that are still available to them.

    How can it be prevented?

           There is no practical way to prevent color blindness.



    Cerebral achromatopsia is acquired typically through trauma or illness and it is very rare. The injury causes a disruption in either the neural pathways between the eye and the brain or in the specific areas where the signals are perceived as color. Since brain damage is rarely confined to specific regions, it is very possible that other functions related to color perception may be affected, such as object recognition (agnosia) or inability to name colors appropriately (color anomia).

    People with cerebral achromatopsia do not have any defects with the cones in their eyes. Unlike congenital colorblindness, they can see objects as gray because prior to the trauma or illness, they understood what color was.

    People with cerebral achromatopsia are perfectly aware of their visual experiences; however, they are unable to imagine or remember colors. They see the world like a big black and white television where everything is a shade of gray. They cannot chromatically order or discriminate hue but they can distinguish color contrast like a normal person.



    Below is a picture illustrating what a person with brain damage to both sides, bilateral, achromatopsia would see compared to a person with normal vision.

    Detecting cerebral achromatopsia

    Eye specialists cannot detect cerebral achromatopsia since it is not a problem with the eye itself. Primarily a neurologist diagnoses it because the impairment is in the part of the brain that detects color. Bilateral achromatopsia is due to damage that involves both the left and right visual fields in the back of the brain.

    Specific Region Affected

    Cerebral achromatopsia is due to damage to the occipitotemporal junction that contains color perception information. This area, involves two areas, or lobes, of your brain. The lobe in the very back of your brain is the occipital lobe. The lobe begins at your temples and extends back along the side of the head to the occipital lobe. The occipitotemporal is in between the occipital lobe and temporal lobe.

    The primary visual cortex in the occipital lobe interprets the signals that come from the eye. Within the occipitotemporal junction, the color remembering and imaging center is located in the V4-lingual and fusiform gyri (bumps on the brain). Below are two pictures that illustrate the different parts of the brain. The part of the brain closest to you in yellow picture is the back of the head, where the visual cortex is. The second photo is a side view of the relative areas of the head that relate to specific functions.



    Hemiachromatopsia

    It is possible to have only one side brain damage, commonly called one-sided partial colorblindness (unilateral hemiachromatopsia). If the damage, or lesion, is confined to one hemisphere, then the visual field contralateral to the injury would experience the damage.

    The two graphics below illustrate what a person who has hemiachromatopsia would see.



    Transient Achromatopsia

    This type of achromatopsia is caused by temporary constriction of a blood vessel in the brain. People who experience this rare vascular insufficiency where oxygen in the blood cannot get to the part of the brain responsible for recognizing color may experience temporary loss of color vision. This is caused in people who have strokes and the effects are very similar to those with cerebral achromatopsia except it is typically temporary.