Many of us put more value to our sense of vision than to other senses like smell or taste. And the first sign of a visual disturbance triggers anxiety and stress. But vision problems are not uncommon in the modern world. Refractive errors like myopia (shortsightedness) are commonplace these days and can be easily corrected. It is unlikely to lead to serious disturbances in vision even in the long term. However, not every visual disorder is as easily treated. Sometimes blurred vision is an early symptom of a more serious eye disorder that can eventually lead to blindness.
Eye strain is probably one of the most common causes of blurred vision. With the widespread use of computers, long hours watching TV and playing video games, eye strain is seen more often these days. But it can also occur with reading for long hours, staring at any fixed object for periods of time or doing fine work in poor lighting. Even bright light exposure like with sunlight can cause eyestrain. A dull ache, watery and red eyes as well as a tired feeling in the eyes and eyelids are common symptoms. Blurring of the vision is more likely to occur with more severe eyestrain. It is usually short lived and a few hours of resting the eye.
Refractive errors of the eye are the most common vision problems. Blurred vision is the earliest and usually the only permanent symptom. A refractive error simply means that the eye cannot bend light rays as it normally would. Therefore a clear image cannot be focused on the light-sensitive area of the eyeball. It is easily treated with spectacles or contact lenses and these days refractive eye surgery like LASIK and PRK can completely eliminate these problems. The main refractive errors are myopia (shortsightedness), hyperopia (farsightedness), presbyopia (age-related) and astigmatism. Blurring of the vision is usually gradual in all these conditions.
Cataracts are another relatively common eye problem. The hallmark sign is cloudy vision but blurring also occurs. A cataract is where the normally clear lens of the eye becomes cloudy and discolored. It is a gradual occurrence. The clouding obstructs the passage of light through the lens. Cataracts are mainly a problem for older people. However, there are different types of cataracts and some can even be present from birth. Apart from age-related changes, cataracts may also be caused by an injury to the eye, lifestyle factors (cigarette smoking, alcohol consumption, poor nutrition and excessive sunlight exposure), infections and systemic diseases like diabetes mellitus.
Glaucoma is another eye problem that is relatively common. There are several different types of glaucoma but it is mainly associated with an increase of pressure within the eye (intra-ocular pressure). This damages the optic nerve that carries signals from the eye to the brain. Usually the changes in vision are gradual and progressive but sometimes it can be intermittent. Eye pain is another common symptom of glaucoma which differentiates it from the eye conditions mentioned above. Glaucoma is also more likely to occur in the elderly but can also occur with eye injury, diabetes mellitus, tumors, chronic corticosteroid use, certain systemic disorders and eye problems like uveitis.
Nerve and Brain Problems
Signals generated in the eye when light strikes the retina are carried by the optic nerve to the brain. Here the brain deciphers these signals and forms images that we perceive as vision. Problems with the optic nerve and/or brain can therefore also cause vision problems even if the eye is otherwise healthy. Compression of the optic nerve or inflammation of the nerve (optic neuritis) are some of the possible causes. It is usually gradual. Brain-related conditions can also cause visual disturbances. Traumatic brain injury, brain tumors or a stroke are some possibilities. With trauma and a stroke the visual disturbances are usually sudden whereas with tumors it is generally more gradual in nature.
The retina is the innermost layer of the wall of the eye. It is laden with light-sensitive receptors. When stimulated by light these receptors produce electrical signals that travel as nerve impulses to the brain. Problems with the retina will be experienced as vision problems. One common problem with the retina that often occurs after impact to the head is retinal detachment. Here the retinal layer tears away from the underlying layers that normally supply it with blood. Retinitis pigmentosa is another retinal problem but rather rare. It is an inherited disorder where there is an abnormality with the light-sensitive receptors and dark deposits in the retinal layer. It often results in blindness.
Macular degeneration is another retinal problem that is worth considering on its own. The macula sits at the center of the retina. At the center of the macula is the fovea which is responsible for the clearest vision. There are two types of macular degeneration – dry and wet. Both are chronic eye conditions. Dry macular degeneration is where there is deterioration of the tissue of the macula. Wet macular degeneration is where fluid and blood from vessels in the area leaks out into the macula tissue. Central vision gradually decreases and there may be clearly defined blurred spots in the field of vision. Both types tend to worsen over time with the wet variety starting suddenly and worsening rapidly.
Uveitis and iritis
The uvea is the middle layer of the eye. The iris is the pigmented part of the eye around the pupils which is a part of the uvea. When these structures are inflamed it is known as uveitis and iritis respectively. Inflammation may be due to an infection, injury or with certain systemic conditions like autoimmune disorders. Blurred vision is a common symptom and usually there is some degree of discomfort or even eye pain. These conditions can be acute, where the symptoms are intense and develop suddenly, or chronic where it persists for long periods of time.
Headaches and migraines
Blurred vision is a common symptom with severe headaches and migraines. However, the headaches may not be the cause of blurred vision sometimes. Rather both the vision disturbances and head pain may be due to the same cause, like with eyestrain. In some instances there is no explanation for blurring with a headache although it is usually mild and short lived. Blurred vision is common with migraines. It may sometimes precede the onset of the actual head pain and here the blurring is part of the aura. But not all migraines are preceded by an aura.
Poisoning and Toxins
Some chemicals can cause blurring of the vision. Common toxins like alcohol can cause blurred vision particularly when consumed in excess or with alcohol poisoning. Usually the blurring resolves as the alcohol is metabolized and removed from the symptom. But blurring of the vision can also be a sign of more serious poisoning and toxin exposure. It may be accompanied by other symptoms like nausea and vomiting. Sometimes the blurred vision can culminate in blindness which may be permanent even if the poisoning is treated successfully and a person does not die. For example, blurred vision and even blindness can occur with drinking large quantities of methanol, another type of alcohol.