Most of us consider the sense of vision to be among the most important of the senses. Yet we do not appreciate the importance and complexity of vision. It is an integral means of perceiving and interacting with our environment. Like any other sense, a number of different problems can arise that may distort or even totally disable a specific sense. Dim vision is one such case.
How does vision work?
Vision is made possible through a complex process that involves various parts of the eyes and the brain. The process of vision begins when light from the external environment enters our eyes through the cornea. The light then passes through a fluid filled compartment (called the anterior chamber), a lens, and a gel-filled compartment (known as the posterior chamber) before reaching the retina located in the back of the eye.
The lens of the eye focuses the light rays onto the retina, resulting in the formation of a clear image. The retina is a light-sensitive lining that consists of various light receptors. Two types of receptors are found in the human eyes: the rods and the cones. The rods are responsible for perceiving the brightness of the image, whereas the cones are responsible for perceiving the color.
The sharpest image on the retina is formed in a region known as the macula. Visual acuity is the greatest in the center of the macula, a region known as the fovea. When light is perceived by the rods and cones in the retina, nerve impulses are generated. These nerve impulses travel through the optic nerve and reach the visual cortex in the brain, where the nerve signals are deciphered and perception of the visual scene occurs.
Problems within the eyes and the brain lead to a variety of visual disturbances. Improper perception of the brightness of a scene is one such visual disturbance. When we think about vision, we mostly think about clarity, contrast and color in the visual scenes. Visual brightness is not a characteristic we are usually concerned about. In dim vision, the images we see may still be in sharp focus, but the perceived brightness of the scene does not match the actual brightness of the environment.
Causes of Dim Vision
It is important to distinguish between dim vision and other visual disturbances such a blurry vision and double vision. People may mistake blurry vision or double vision for dim vision. However, they are different conditions, and do not involve faulty perception of light intensity.
Dim vision can be caused by many different factors affecting the visual pathway. The causes include obstructions in the light path, problems with the retina and problems affecting the nervous system. When dimming vision arises suddenly and worsens, especially when there is eye pain, then immediate medical attention is necessary.
Read more on eye pain.
Cataract is a very common eye condition that results in dim vision. It is especially common in the elderly, and usually happens after the age of 60 years. However, not all cases of cataract are due to the aging process. Injury to the eyes, eye diseases, and long term use of certain medications (for example, corticosteroids) can also result in cataract.
In cataract, the lens of the eye become cloudy. This is usually a gradual process, and starts affecting the perceived brightness of the scene. The clouding of the lens affects the light path through the eye, preventing much of the light that enters the eye from reaching the retina. The lens gradually becomes opaque and can lead to blindness.
In the early stages of cataract, visual dimness can be corrected by increasing the external lighting or by using eyeglasses. However, when the opacity of the lens interferes with the daily activities, surgery is the best option. Surgical treatment of cataract involves replacing the clouded lens with an artificial lens. This is a safe outpatient procedure with a high success rate.
As mentioned previously, the macular region of the retina is responsible for the visual acuity. Degeneration of the macula leads to loss of visual acuity in the center of the visual field. Age-related changes in the eyes are thought to contribute to the development of macular degeneration. However, the exact cause of macular degeneration is not understood.
There are two types of macular degeneration: wet macular degeneration and dry macular degeneration. In dry macular degeneration, the central region of the retina starts deteriorating. Wet macular degeneration is the less common variety of macular degeneration, and involves leakage of blood and fluid from the retinal blood vessels.
Dry macular degeneration is a possible cause of dim vision. This condition is characterized by a gradual deterioration in the brightness of the vision, especially in the center of the visual field. Dim vision in this condition requires the use of brighter light in order to see things that were previously perceptible under lights of lower intensity. Reading becomes difficult, and eventually even face recognition is impaired.
Stroke refers to destruction of parts of the brain caused by insufficient blood supply. The insufficient blood supply to the brain may occur either due to a blockage of blood flow (technically referred to as ischemia) or leakage of blood (technically referred to as hemorrhage) from the blood vessels. Atherosclerosis and hypertension are the two main causes of stroke. Trauma to the head region and blood vessel malformations could also contribute to stroke.
Depending on the brain region that is deprived of blood supply, a variety of signs and symptoms may occur in stroke. These signs and symptoms are usually one-sided, and include numbness, muscle weakness, tingling sensations, and impaired coordination and balance. In some cases, visual disturbances may also occur. Dim vision is a possible outcome of a stroke.
Treatment of Dim Vision
Appropriate treatment of dull vision can only be determined once the cause of dull vision is diagnosed. Temporary coping mechanisms like increasing ambient lighting and wearing eyeglasses may help in the short term, but the underlying condition needs to be diagnosed and treated in order to resolve the condition completely.
Some of the possible treatment options for dim vision are as follows:
- Dim vision resulting from cataract may require surgical replacement of the damaged lens in the eye. Medication cannot reverse the cloudiness of the lens.
- Dim vision caused by macular degeneration cannot be reversed. However, certain nutrients may help in slowing down the deterioration of vision. Surgery might also be an option.
- Dim vision caused by strokes cannot be reversed once the affected brain tissue dies. Anti-clotting agents and medications to dissolve clots may be helpful in reducing the visual loss during the early stages of stroke.
It is important to note that dim vision is not always reversible. Since the condition may occur gradually over a period of months and years, it is highly recommended to seek early medical attention in case of any visual problems to limit the damage that might otherwise occur.