Cone Rod Dystrophy

Overview

Cone Rod Dystrophy (CRD) is an umbrella disorder that encompasses more than 30 variants of inherited diseases. CRD exclusively denotes diseases that affect the eye’s cones and rods (cells that gather light).

Light carries visual information from the world and enters the eye through the pupil, which then strikes the light-sensitive tissue lining at the back of the eye. This tissue is called the retina. The retina converts information from the light into electrical pulses, which are sent to the brain by the optic nerve. Once the light signals have arrived at the brain, we can perceive vision. 

People affected by CRD will gradually lose their vision as the retina begins to deteriorate. Eventually, this leads to partial or legal blindness. 

Cone Rod Dystrophy can also be referred to as: 

• Retinal Cone-Rod Dystrophy
• Tapetoretinal Degeneration
• Cone-Rod Degeneration
• Cone-Rod Retinal Dystrophy
• CORD
• Progressive Cone Retinal Dystrophy
• Sensory Retinal Dystrophy
• Stargardt Disease

The International Classification of Diseases (ICD) code for CRD is H35.53. This code is used for diagnoses on medical records and for insurance reimbursement purposes.

Function of Rods and Cones

The retina contains rods and cones, which work to help you see and process information from the world. Rods and cones are known as photoreceptors cells, which, through light exposure, are stimulated to absorb light. 

Rods work at very low light levels—they are the cells you use for night vision. However, rods do not help you see color; this is why you cannot see color at night. The human eye has about 100 million rod cells. As their name implies, rod cells are rod-shaped (long and skinny). 

Cone cells, by comparison, are cone-shaped (tapered at one end). The human eye has about 3 million cone cells; most of these are in the fovea, which is a small pit at the back of the eye that helps you see the sharpness and detail of images. It takes a significantly greater amount of light to activate a cone cell compared to a rod cell. Cone cells help you to see colors through three types of cones: blue, green, and red.

These unique photoreceptor cells also facilitate other forms of vision. For example, rods allow for peripheral vision to the far left and right of your field of view, while cones enable central vision and help you see details and colors in your field of view.

Deterioration of Rods and Cones

Cone Rod Dystrophy is an inherited condition, which means it develops due to genetic mutations passed down from parents to their children. These mutations cause the retina cones and rods to degenerate, resulting in decreased sharpness in vision, increased sensitivity to light, impaired color vision, blind spots in the center of the visual field, and partial loss of peripheral vision. 

Cones typically break down before rods, meaning that sensitivity to light and loss of color are usually the first symptoms of CRD. 

At later stages of deterioration, night blindness can occur, making reading and other close-up work difficult, including actions that require the use of peripheral visual fields. The deterioration can be severe enough to limit a person’s ability to walk or drive safely.

Can Rods And Cones Regenerate If Damaged?

Currently, scientists are unable to regenerate rods and cones in human eyes. There are studies currently in progress that aim to stimulate human photoreceptor cells to regenerate, along with other breakthroughs in genetics, bionics and stem-cell therapy. Further research and testing will need to be done before determining if rod and cone regeneration is possible in humans; however, there is hope that new developments in medical gene therapy will see future regeneration possibilities.

Cone Rod Dystrophy vs. Retinitis Pigmentosa

Retinitis Pigmentosa (RP) is a form of CRD where the retina’s rods begin to degenerate before the cones do. This is in contrast to types of Cone Rod Dystrophy, where the cone is first to degenerate. 

People with Retinitis Pigmentosa can start developing it as early as childhood, and may become legally blind by adulthood. Due to the rods being affected first, many people with RP will notice their inability to adjust to dark or shadowed light or lose their peripheral vision as their first symptoms.

It is important to note that despite RP affecting the rods first, in the later stages of the disease, cones may also become affected. This can make it harder to see details and for your eyes to process light, reducing overall vision.

What Do People with Cone Rod Dystrophy See?

People with Cone Rod Dystrophy, where the cones are usually the first to degenerate, usually begin to experience reduced sharpness in vision (visual acuity) and a heightened sensitivity to light (photophobia). This can be followed by blind spots (scotomas) in the center of vision, impaired color vision (dyschromatopsia), loss of peripheral vision, and eventually, loss of vision at night.

Prevalence of Diabetic Retinopathy

Cone Rod Dystrophies occur in 1 out of 30,000-40,000 people. While this makes a  relatively rare genetic disease, CRD still affects a vast amount of people in North America and around the world. Parents who already know that a family member has Cone Rod Dystrophy should bring their kids in for examination by an ophthalmologist, according to a report from FamilyConnect.

Causes

Cone Rod Dystrophy is a genetic disorder caused by mutations of over 30 genes. Mutations in these genes problematize the proper function and structure of the photoreceptors.About 20 of these genes are inherited through an autosomal recessive CRD (meaning that both parents need to pass on a recessive mutated gene), while the other ten are inherited through an autosomal dominant pattern (meaning that only one parent needs to pass on the mutation, as it is dominant). The autosomal recessive pattern accounts for 30-60% of cases among people with CRD disorders, according to Medline.

Treatment

There are several treatments for Cone Rod Dystrophy that can help people to improve their vision. While studies are underway investigating potential solutions, no cure has been identified. It is suggested that people with CRD consult a vision specialist to learn about how to prevent further loss of vision and available tools to compensate for decreased vision.  Tools may include assistive devices, and the support of family, support groups, eSight Together, and health care practitioners.

The following describes treatment options available to help people with CRD manage their condition:

Cone Rod Dystrophy Gene Therapy

Gene therapy is a promising treatment method for Cone Rod Dystrophy but is not yet approved for use. Scientists are working through clinical trials to discover how gene and stem cell therapy could help stop the progression or reverse the damage of CRD. Ideally, gene therapy could help millions of people worldwide with impaired vision from CRD to restore vision loss.

Nutritional Supplements and Vitamins for CRD

The use of supplements and vitamins may help to support the function of photoreceptor cells. It is always best to speak with your ophthalmologist to determine what supplements or vitamins could be best for your or your child’s specific CDR disorder. Nutrients such as taurine, vitamin C, and Omega 3 fatty acids can help support retina health. Always consult a medical professional before starting any supplement or vitamin regime.

Ayurvedic Treatment for Cone Rod Dystrophy

There are many anecdotal claims that ayurvedic treatment can be helpful for CRD; however, they have yet to be scientifically proven. Advice from Ayurvedic practitioners may be helpful for overall eye health and slowing progression through promoting a healthy lifestyle and diet. That said, it is important to consult with your health care practitioner before undertaking an ayurvedic regime. This is to be sure there are no contraindications, especially to other medications being taken.

Low Vision Apps To Assist With CRD

Among the products available to individuals with low vision are mobile applications. Make sure that your smartphone’s operating system is up-to-date before downloading low vision apps to ensure that they will work properly on your device. An overview of what makes for a good low vision app is available at iAccessibility.

Of course, you can make adjustments to your phone without the help of an app, such as changing the contrast or using an assistant that responds to your verbal commands and reads text to you from the screen.