New Chromaticity Diagram

(The loss of normal 3-D vision)

based on



Last Update 01 Apr 09     Rhodonine and Activa are trademarks


There must be a distinct line between the medical and academic aspects of syndromes as serious as astereopsis. This material should not be considered medical advice. Subjects aware of this syndrome should speak with their doctor.

Students subject to rote testing based on the content of their textbooks are encouraged to review the Cautions Page before proceeding. Others may find the material controversial. However, the results speak for themselves.


This is a preliminary report for purposes of documentation.

A recent case was brought to my attention by DX. DX reports smeared out colors and double images under normal daylight conditions, with or without (clear)corrective lenses. She also reported broadband type snowy vision. The condition is apparently not sufficiently debilitating to prevent her from driving. Recently, DX was examined by an Irlen Institute practitioner and received a pair of very dark glasses. In evaluating these glasses, she found they were too dark to wear indoors and under low light level conditions.

In wearing the Irlen glasses outdoors, her observations were interesting. By reducing the light level reaching the retina sufficiently, her eyes did converge and she perceived three dimensional imagery for the first time. The light level at the retina was still high enough to support color vision.

The presence of poor color constancy, loss of resolution and loss of stereopsis suggests DX has a mild form of achromatopsia. She does not report photophobia but her vision is marginally better under mesotopic conditions compared to photopic conditions. Under normal daylight conditions, she encounters saturation within the sensory neurons like most achromatops. This causes a corruption of the color difference channels leading to her loss of color constancy. The corruption is not sufficient to cause complete saturation in the color channels. It is sufficient to prevent the vergence channels working properly. This signaling error results in a loss of stereopsis, and may lead to nystagmus. In her case, the nystagmus has not been great enough to come to the attention of clinicians. However, it is present as indicated by the double vision.

The density of the Irlen provided lenses is sufficient to reduce the effective light level at the retina from photopic to mesotopic. Under this condition, the saturation in the sensory neurons is avoided and her vision is much improved. She noted the color of the sky returned to blue from a washed out white, and the double vision was replaced by stereoptic vision.

The source of this problem can be traced using the material on the achromatopsia page. That material and the presence of broadband snowy vision suggests the adaptation amplifiers are operating at maximum gain at virtually all light levels. It may also be that the negative internal feedback associated with these amplifiers is reduced from normal. Only more detailed clinical evaluation can differentiate between these conditions.

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Primary references:

Elements of the following papers were used in formulating this page. However, not all of the ideas presented in these papers are supported here. This is particularly true of the statements made in the introductory paragraphs of these papers.

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An extensive list of references are provided in the appropriate Chapters of PROCESSES IN BIOLOGICAL VISION. The website for this material is given above.