Cerebral achromatopsia

A 2005 study examined 92 case studies since 1970 in which cerebral lesions affected color vision.[3] The severity and size of the visual field affected in cerebral achromatopsiacs vary from patient to patient.

The majority of cases in the 2005 study were the result of bilateral lesions in the ventral occipital cortex.[3] It is unknown whether this was the result of bilateral lesions being more likely to produce color-loss symptoms, or if it was a sampling effect of patients with more severe brain trauma more often being admitted for treatment. In many of the cases examined, patients reported only partial loss of color vision. The locations of color vision loss can be restricted to one hemisphere or one quarter of the visual field. The term "hemiachromatopsia" has been used to denote patients who experience loss of color in only one hemisphere of the visual field. However, as applied to achromatopia resulting from brain trauma, the term is incomplete in characterizing the often-complex nature of the vision loss.

In still rarer cases, temporary ischemia of the associated ventral occipital cortex can result in transient achromatopsia. The condition has thus far been characterized only in stroke patients and provides further support for a color processing area.

In one case, a 78-year-old stroke victim had lost the ability to identify color, but was unaware of his deficit until doctors performed color discretion tests.[4] Even when presented with this information, the patient believed he had retained his ability to perceive color even though the world around him appeared grey. He attributed this achromatism to "poor lighting" and it took several weeks for the patient to fully appreciate the extent of his disability. In addition, the characteristic comorbidity of prosopagnosia was present. After two months and frequent sessions with doctors, tests indicated his color had fully returned. The ischemia caused by lesions on the posterior cerebral arteries had subsided and follow up MRI scans indicated that blood flow had once again returned to the VOC.

The most common disorder seen alongside cerebral achromatopsia is prosopagnosia, the inability to recognize or recall faces. In some studies, the comorbidity is seen as high as 72%.[3] This significance has not been overlooked and is a subject of ongoing research. See § Difference from congenital achromatopsia below.

Cerebral achromatopes often have poor spatial acuity.[3]

The most apparent distinguishing characteristic between congenital achromatopsia and cerebral achromatopsia is the sudden onset of color vision loss following a severe head injury or damage to the occipital lobe following a stroke or similar ischemic event.[2] Non-invasive imaging techniques can be the most helpful in determining whether the area of damage following a traumatic event is an correlated with color-vision processing. Simple diagnostic tools can also be used to determine whether a patient is a likely candidate for further testing, as advancing imaging procedures can often prove expensive and unnecessary.

Co-morbid factors can be valuable indicators of the likelihood of cerebral achromatoptsia. One disorder often seen alongside cerebral achromatopsia is prosopagnosia, the inability to recall or recognize faces. The correlation is still the subject of ongoing research, but the most telltale clue in this association is the close proximity of brain lesions seen in prosopagnosics and cerebral achromatopsiacs without prosopagnosia.[3] Figure 1 illustrates overlap of brain lesions compiled from numerous case reports of both disorders. A common area of damage associated with both disorders can be seen in the right occipital lobe.

The most famous instance of cerebral achromatopsia is that of "Jonathan I." immortalized in a case study by Oliver Sacks and Robert Wasserman, and published as "The Case of the Colorblind Painter".[7] The essay tracks Johnathan I.'s experience with cerebral achromatopsia from the point where an injury to his occipital lobe leaves him without the ability to perceive color, through his subsequent struggles to adapt to a black, white and gray world, and finally to his acceptance and even gratitude for his condition. Especially pertinent is the analysis of how cerebral achromatopsia affects his practice as a painter and artist. Descriptions of cerebral achromatopsia's effects on his psychological health and visual perception are especially striking. For instance, in recounting Mr. I.'s descriptions of flesh and foods, the authors write:

Mr. I. could hardly bear the changed appearances of people ("like animated gray statues") any more than he could bear his own changed appearance in the mirror: he shunned social intercourse and found sexual intercourse impossible. He saw people's flesh, his wife's flesh, his own flesh, as an abhorrent gray; "flesh-colored" now appeared "rat-colored" to him. This was so even when he closed his eyes, for his preternaturally vivid ("eidetic") visual imagery was preserved but now without color, and forced on him images, forced him to "see" but see internally with the wrongness of his achromatopsia. He found foods disgusting in their grayish, dead appearance and had to close his eyes to eat. But this did not help very much, for the mental image of a tomato was as black as its appearance.