How Does Achromatopsia Affect Eyesight?

Affecting one in 33,000 people in the United States, including men, women and children of all ages, achromatopsia, also known as rod monochromacy, is an inherited medical condition that causes varying degrees of visual impairment, including visual acuity loss, colorblindness and severe light sensitivity. As achromatopsia is characterized by an almost complete lack of cone cell function in the eyes, those with faulty achromats, or the acrhomatic lenses in the eyes, tend suffer from "day blindness."

Inheritance

• As an inherited condition, achromatopsia only occurs when a certain recessive gene, labeled as CNGA3 or CNGB3, is passed on to the child by both parents. This gene is associated with color and vision abilities.

Visual Acuity

• Achromatopsia is characterized by a nonprogressive loss of central vision. Visual acuity usually depends on the type of achromatopsia the person has and the brightness of the environment he is in. People with complete achromatopsia, that is visual acuity of 20/200 or more, are often considered legally blind. Those with incomplete achromatopsia have slightly more working cone cells and therefore tend to have better visual acuity, from 20/60 to 20/100.

Nystagmus

• Characterized by a shaking of the eyes, nystagmus is a condition seen mostly in children with significant visual impairment. Many people with achromatopsia also suffer from this condition. People with nystagmus often tilt their heads in order to adjust to the shaking and improve their visual acuity. Nystagmus can get worse when the person is stressed or tired.

Light Sensitivity

• The human eye uses two visual systems in order to see normally. The photopic system uses the cone cells to see color, detail, and to see in bright light. For those with achromatopsia, this system is not working properly, so their eyes are forced to resort to the second system, called the scotopic system. This system uses the rod cells in the eye, which work best in low light and at night. When someone with this condition goes into a brightly lit area, inside or outside, the scotopic system goes to work trying to provide appropriate vision, but because rod cells are sensitive to light, it quickly "blinds" the person. For this reason, many with achromatopsia are photophobic, or fearful of bright lights, and use very dark sunglasses to help them see.

Visual Aids

• Those with achromatopsia usually need to resort to visual aids to use their eyes to the fullest. Dark sunglasses help block out bright light, making it easier to see when outside or in brightly lit rooms. Due to decreased visual acuity, those with this condition often use special magnification devices, labels, large-print books, and computers with a larger font.