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Author: samgrotsky

Have you ever thought about how vision works? Seeing is an incredible gift made possible by a system in which the eye and the brain process visual information from the outside world. If any step of that process does not function properly, vision will be impaired.Eye works

Similar to a camera, the eye transmits light from the world around us into an image that we can perceive. Certain parts of the eye even function like the different parts of a camera such as the shutter, the lens and film (if we can hearken back to the days when we used film in cameras). Here is a quick breakdown of the fascinating way our eyes and brain enable us to see and experience the world around us:

The Vision Process

Light reflected from an object in our field of view is gathered by the cornea which is essentially the clear “window” to our eye. The cornea then refracts the light rays through the pupil (the center of the iris where light enters the eye). The iris, which like the shutter of a camera will enlarge and shrink based on how much light is coming in, then passes the image onto the crystalline lens. Just like a camera lens, the lens in the eye focuses the light rays, projecting them to a point at the back of the eye called the retina, where the image will appear upside down. The retina contains a thin layer of color-sensitive cells called rods and cones that perceive color.

From the retina, the visual signals travel to the brain via the optic nerve. The brain receives information from both eyes and must then converge the images (and flip them right side up) to get a complete picture.

Vision Problems

A breakdown in vision can happen at any point in this process. From the muscles that control the eyes, to the parts within the eye, to the pathway to the brain. Sometimes vision impairment is due to technical problems with the eye receiving the information and passing the signal on, such as convergence insufficiency (inability to coordinate the eyes to converge on one point), myopia (nearsightedness) or cataracts (clouding of the lens).

Other times, the eyes might work perfectly, but there is a problem with the brain interpreting the signals it receives. In these cases we can’t “see” in the traditional sense, because our brains aren’t able to properly “read’ the signals or we don’t know what we are looking at. This is the case for some learning disorders that are caused by the visual processes in the brain such as dyslexia.

As you can see, vision is quite a complicated process. A simple vision exam isn’t always able to determine vision problems, especially in children which is why it is so important to have regular comprehensive eye exams, to measure the health of the eye and all of its parts.

As an optometrist, I always get many people asking me what is color vision deficiency? Well, color vision deficiency is a condition that deprives an individual the ability to distinguish certain color shades. In some severe cases, the patient might not be able to see colors at all.

Many people refer to this condition as color blindness. However, I have only had very few patients who are completely colorblind. People suffering from color vision deficiency are able to see colors; the problem is that they have difficulty differentiating between blues and yellows or specific shades of greens and reds. For those who are completely colorblind, all things they see look black, white or grey. Although a color deficiency will not inhibit your ability to see or function, it may determine which jobs you are less suited to perform. Most color deficient individuals are not painters, electricians or pilots.

What is the cause of color vision deficiency?

Although injury and certain diseases can cause color vision deficiency, it is mainly an inherited condition. It is commonly passed from mother to son through an X-linked recessive gene. Some of the diseases that might lead to color vision deficiency include: leukemia, diabetes, Parkinson’s disease, multiple sclerosis, sickle cell anemia, Alzheimer’s disease, macular degeneration and glaucoma. Other causes include aging, exposure to certain chemicals and some types of medications.

How is color vision deficiency inherited?

Once I diagnose a patient with color vision deficiency, I always ask them whether anyone in their family suffers from this condition. This is because most cases of color vision deficiency are usually inherited. Some of you might be wondering how this condition can be inherited. Well, it all goes back to the genetic makeup of human beings.

The red-green and blue cone monochromacy color vision defects are inherited from the X-linked recessive gene. Mutations in OPNILW and OPNIMW genes which are contained in the X chromosome are what cause color vision deficiency.

Red-green color vision defects occur in the event of genetic changes in the OPNILW and OPNIMW genes. This leads to the production of abnormal opsin pigments or an absence of M or L cones thus affecting red-green vision. These changes also lead to the production of premature or defective S cones. Impaired S cones alter the perception of the blue color and make it difficult for a person to differentiate between dark blue and black or shades of blue and green.

Blue cone monochromacy occurs when the genetic changes in OPNILW and OPNIMW genes prevent the normal functioning of L and M cones. Only the S cones function normally. The result is poor color vision and reduced visual acuity.

Why are men more prone to color vision deficiency than women?

As I had explained earlier, color vision defects are inherited through the X-linked recessive pattern. The X chromosome is one of the two sex chromosomes in human beings. Males have only one X chromosome therefore, it only takes one genetic change in each cell to cause color vision defects. Females have two X chromosomes therefore, for them to get a color vision defect, a genetic change should occur on both chromosomes. Color vision defects are usually passed on from mother to son. Fathers cannot pass on this condition to their sons since they cannot pass their X-linked traits.