There are several variations in the extent of Achromatopsia among individual achromats (patients suffering from achromatopsia.) There are “total rod monochromats,” “half rod monochromats,” and “blue cone monochromats.” Total rod monochromats suffer from the most seriously impaired sight of all achromats. Blue cone monochromacy is rarer than rod monochromacy and has completely different inheritance patterns.
Congenital achromatopsia, nonetheless, should not be confused with progressive cone dystrophy or cone/rod dystrophy. Inherited achromatopsia isn't progressive, and it doesn't lead to total blindness. Some physicians refer to this as "fixed cone dystrophy."
Getting Diagnosed with Achromatopsia
Many achromats have erroneously been assigned the medical diagnosis of "congenital nystagmus." Nystagmus (involuntary motion of the eyeballs) is a symptom of achromatopsia, one that is particularly observable during infancy and childhood, but suffering from this symptom isn't necessarily the same as suffering from the medical eye illness called "congenital nystagmus."
Moreover, inherited, congenital achromatopsia shouldn't be confused with cerebral achromatopsia, which is an acquired type of complete colorblindness that can arise from injury, illness, or some other reason. People who suffer from cerebral achromatopsia report that they see a monochromatic image, all in shades of gray or black.
These individuals are capable of seeing gray, since they formerly experienced color vision, making it possible for them to comprehend the absence of color as gray or black. This is in deep contrast to the visual capabilities of congenital, total achromats (i.e., complete rod monochromats), who describe the concept of "gray" as intriguing to them as the idea of any other color.
Patients with cerebral achromatopsia are diagnosed by neurological professionals instead of vision professionals. The loss of color sensing isn't accompanied by severely weakened eyesight, severe light sensitivity, or irregularity in the photoreceptors (nerve cells that sense light) of the retina, as is the case with patients who suffer from congenital, inherited achromatopsia.
Dealing with Achromatopsia
When levels of light increase, the eyesight of individuals with achromatopsia diminishes. In moderately bright interior spaces or outdoors following dawn or just prior to dusk, some achromats adjust to their reduced level of optical functioning without having to wear tinted glasses, by using visual strategies like blinking, squinting, shielding their eyes, or placing themselves favorably in proximity to light sources.
Other people habitually wear medium-tinted glasses in such areas. However, in full sunlight (outdoors) or in extremely bright indoor spaces, just about all achromats use dark tinted glasses to try to function properly with an insufficient amount of eyesight, since their retinas don't possess the photoreceptors required for seeing accurately in such areas.
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References:
Damasio A, Yamada T, et al. "Central achromatopsia: behavioral, anatomic, and physiologic aspects." Neurology. 1980; 30 (10):1064-71.
Lewis, Samuel D., and Mandelbaum, J. "Achromatopsia: Report of Three Cases." Archives of Ophthalmalogy. 1943; 30 (2) :225-231.
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