An Introduction
“My vision is like an out of focus, over-exposed black and white film. And if it’s a sunny day out there it will be completely over-exposed; I’ll only see white.” - Caitlin Smith, Singer and Songwriter
Achromatopsia is a congenital hereditary condition found in only one birth in every 33,000 to 50,000 births. Thus less than 10,000 Americans may have achromatopsia. There are two basic forms, rod monochromatism and blue cone monochromatism.
Rod Monochromatism, an autosomal recessive condition, is the most common form. Rod monochromatism routinely occurs in both men and women.
Blue Cone Monochromatism, an X-linked recessive condition, is a less common form of incomplete achromatopsia. Blue Cone Monochromatism has an incidence of 1 in 50 to 100,000 births in males and could be as rare as 1 in 10 billion in females.
The movie below presents the experience of an achromat with rod monochromatism.
Patients with both forms of Achromatopsia present with four basic visual problems. Plus, they must deal with social and emotional issues unique to Achromatopsia:
The Problems of Achromatopsia
Day Blindness (Hemeralopia): The first and most significant problem is Hemerlopia or day blindness. This is a severe intolerance to light that can severely impair the patient’s vision. Rather than improve vision, as it does for most of us, light profoundly obscures their vision. We will discuss hemeralopia in detail on this website. If we control the light, we greatly improve the functional vision of achromatopsia patients.
Profound Colorblindness: The second problem is a lack of color vision. This is often a total loss of color vision in Rod Monochromats. Some Rod Monochromats, however, may have incomplete forms and may retain traces of some color vision.
In Blue Cone Monochromats, only visual input from the rod cells and blue cones still function. Thus patients retain the blue channel of color vision. They lack the red and green channels. This does not mean that they see the color blue as most do, but that objects that are blue may be more easily seen.
Reduced Visual Acuity: The third problem is reduced visual acuity related to the loss of cone cells, which normally reside in the center of the retina providing our sharpest vision. The vision of the patient is also constantly affected by the amount of light present. In our examination room with the lights lowered, the patient may read the acuity chart, but be severely hampered when the lights are turned up. If we control the light, the patient’s visual acuity, though still impaired will be functionally improved.
Nystagmus: The fourth element is nystagmus, the rhythmic shaking or movement of the eyes which is often one of the first things that alerts parents that their child‘s vision may be affected. Nystagmus may add to the variation of the vision. Stress is just one of many factors that may affect the speed of the nystagmus and thus clarity.
Emotional and Social Impact: The mechanics of dealing with all of these problems can create a whole set of social problems. The day blindness may cause constant squinting, looking down to avoid light and wearing dark sun lenses inside. All of these impact a person’s interaction with other individuals. It can be especially difficult for a young person.