Overview of Central Vision Loss
Central vision loss can be devastating – it may be much harder to do everyday activities, such as reading a book, driving a car, or even recognizing faces. Vision loss is usually the result of damage to the eye, either from an injury or from a disease. A number of conditions can cause vision loss, including some of the most common eye conditions in North America today.
Depending on the cause, early detection and treatment may slow the progression. Fortunately, assistive technology exists to help the visually impaired improve their sight enough to lead full and productive lives.
Central vision is the field of view in the center of your vision as you look straight ahead. It is different from peripheral vision, which is what you see to the left and right as you look straight ahead. While central vision only covers about 3 percent of our visual field, it allows us to make important judgments about understanding details about objects in our path and estimating distances.
Changes in the Visual Field
Losing central vision affects visual acuity, which is the ability to discern shapes and details. Those who lose central vision often feel like they are missing fine details or seeing blurred spots in the center part of their visual field. As the disease and the damage it causes progress, the blurred spots will turn into dark or blank spots. Losing central vision is the result of damage to specific tissues and structures within the eye. It can occur alone or along with certain eye conditions, including macular degeneration, glaucoma, and cataracts.
How Central Vision Loss Affects the Eye
The eye is an extremely complex organ. Light carries visual information about the world into the eye. It enters through the clear cornea covering the eye, and passes through the pupil. A lens focuses the light so that it strikes a specific spot on the retina, which is a light-sensitive layer of tissue lining the interior of the back of the eye.
Specialized photoreceptor cells within the retina, known as rods and cones, absorb the light; rods absorb light in low-light conditions, while the cones are responsible for colour and visual acuity. The retina converts the visual information into electrical impulses then sends these signals through the optic nerve to the brain, which translates the impulses into the images we perceive.
Central vision loss is typically the result of damage to the macula, a small area in the middle of the retina that provides sharp, clear central vision. Some diseases affect only the macula, while others damage other parts of the retina too.
Causes of Central Vision Loss
A number of eye diseases can cause central vision loss. Most of these diseases affect the retina or the macula.
Age-Related Macular Degeneration
AMD is the leading cause of severe, permanent vision loss in people over the age of 50. It is a condition that primarily affects older adults and is characterized by degeneration of the macula. In macular degeneration, the macula wears down and becomes thin. As it thins, the macula loses its ability to function well; patients experience reduced central vision in one or both eyes.
Diabetes is an increasingly common condition characterized by high blood sugar levels, which can damage the blood vessels in the retina. Early symptoms of diabetic retinopathy include floaters, blurriness, dark areas of vision, and trouble perceiving colors. As high blood sugar levels continue to damage blood vessels in the retina, diabetic retinopathy can cause central vision loss.
Glaucoma is a group of eye conditions that affect the optic nerve. Glaucoma is usually the result of high pressure inside the eyeball. In the early stages, glaucoma affects peripheral vision, but it can advance further. Glaucoma can lead to significant vision loss in both eyes, and can even lead to blindness.
Cataracts are cloudy areas on the eye’s lens, which cause vision to be cloudy, fuzzy, and sensitive to glare. While cataracts can affect the entire field of vision, they often occur together with macular degeneration and can even mask vision loss symptoms associated with macular degeneration. In fact, patients with severe cataracts can have temporary loss of central vision that gets better after cataract surgery.
Macular edema occurs when pockets of fluid, usually consisting of leakage from damaged blood vessels, develop in the macula. These pockets cause the macula to swell and interfere with the way the macula works. Macular edema distorts vision to be blurry, and colours to look washed out.
Holes and tears can develop in the macula to cause central vision loss. As a macular hole forms, objects in central vision will look blurry, distorted, or wavy. As the macular hole grows, a dark spot or blind area appears in central vision. Macular holes do not affect side vision.
To work properly, the macula must lie flat. Macular pucker occurs when the macula forms creases, bulges, or wrinkles to cause central vision loss. Macular pucker can make things look wavy, or cause a grey or cloudy area in central vision. Blank spots in central vision may develop. Macular puckers do not affect peripheral vision.
Central Vision Loss Diagnosis
A central vision loss test can help an eye doctor determine if a patient has loss of central vision. Eye doctors often use the Amsler Grid, which looks like a piece of graph paper with a dot in the center. The lines of the grid look straight to people with healthy eyes, but look wavy or distorted for those with central vision loss.
Treatment depends largely on the underlying cause. The most common cause is wet AMD which requires anti-VEGF therapy that features a periodic injection of a medication, known as anti-VEGF, into the eye. Treatment for mild cases of diabetic retinopathy includes careful control over blood sugar levels; advanced cases of diabetic retinopathy require laser treatment or surgery. Macular holes can sometimes heal without treatment, but often require surgery to improve central vision. Treatment for macular edema includes steroid medications, while treatment for cataracts and macular pucker require surgery to restore central vision.
Available Assistive Technology for Central Vision Loss
Many successful eSight users live with central vision loss, which makes eSight a popular choice for those with visual impairments and legal blindness.
eSight is a low vision aid that functions by stimulating synaptic activity from the remaining photoreceptor function of the user’s eyes. Using a cutting edge camera, smart algorithms and high resolution screens, the assistive technology can provide the brain with increased visual information to naturally compensate for gaps in the user’s field of view. eSight glasses makes clearer vision possible, resulting in enhanced vision of up to seven lines on a doctor’s eye chart.
David Lee lives with central vision loss caused by AMD, but with eSight, he has been able to resume curling, and even won his curling provincial playdowns.
Although there are other technological options available to enhance vision, eSight is one of the only ones that boasts substantial mobility for its users.