Cataracts can occur in any age group for different reasons but most of the time it is seen in older adults due to age-related changes in the lens of the eye. It is also linked to conditions like high blood pressure (hypertension) and diabetes, which are common chronic conditions that are more often seen in older adults.
Almost 1 in 5 Americans over 40 years of age have a cataract in either eye but most people do not notice it until much later in life. This type of age-related cataract can be corrected with surgery, which has a 95% success rate but can recur when predisposing conditions like high blood pressure and diabetes are not properly treated and managed.
How Do Cataracts Affect Sight?
To understand how cataracts affect sight, it is important to first understand the functions of the different parts of the eye. Light enters the eye through the transparent cornea and then the amount of light passing into the inner eye is controlled by the iris. The light then passes through the lens of the eye. The lens is a transparent structure that focuses light on the most sensitive part of the retina.
The muscles that hold up the lens can contract and relax to change the shape of the lens to some degree. It bends the light rays (refraction) to sharply focus an image. This focused light stimulates receptors at the back of the eye and signals are sent to the brain. These signals are then decoded into images. The perception of this light is what we refer to as the sense of vision, or sight.
Cataracts are a problem with the lens of the eye. It may affect one lens or both lenses, which means that the vision in either one eye or both eyes may be affected. In a cataract, the lens becomes cloudy over time due to age-related changes in the lens structure. This blocks and scatters light that is passing through the lens. It affects the focusing of light on the retina which ultimately affects vision.
Read more on cataracts.
Most cataracts develop slowly and progress gradually over years and decades. It causes a gradual loss of vision and can eventually result in blindness in the affected eye or eyes. Cataracts are one of the main causes of blindness throughout the world but most of the time it can be fully corrected with surgery. Less commonly, cataracts may arise due to trauma to the eye or it may be present from birth (congenital).
How to Spot Cataracts
The signs and symptoms of cataracts are usually not evident in the early stages. Many people may be diagnosed with cataracts during routine eye examinations despite not having any noticeable impairment in vision. This is due to the the fact that the clouding only occurs in one part of the lens or is very minor to significantly impair the passage of light. However, as the clouding becomes more extensive then symptoms start to become more evident and severe.
Apart from the presence of the signs and symptoms discussed below, various diagnostic tests should be conducted to confirm a cataract. This is includes a visual acuity test, retinal examination and split lamp eye examination. The visual acuity test is able to determine the ability of a person to see at varying distances. The retinal and split lamp examinations allows the doctor to view the structures in the eye.
Cloudy, Blurred and Double Vision
With less light passing through the lens, vision gradually becomes dimmer. This may be described as foggy or cloudy vision. The dimming is more evident in dull lighting but vision may also be affects with very bright lights. The dimming vision may not always be obvious. Instead a person may notice that brighter light is required for activities like reading or doing fine work.
Blurred vision is another common sign of cataracts. The changes in the lens affects its ability to sharply focus light. This blurring may only affects near or far vision, depending on the type of cataract. Double vision (diplopia) is another impairment of eyesight that may occur with a cataract. This is usually monocular diplopia where the double vision involves only one eye. The double vision does not resolve by covering the unaffected eye.
Read more blurred and cloudy vision.
Glare and Halos
Glare is another disturbance in normal vision that people with cataracts may notice. However, glare is not uncommon with many types of eye and vision conditions. The glare may be described as a sensitivity to light specifically in brightly lit environments and with lighting that was otherwise tolerable in the past.
The sunlight when outdoors may be unbearable to some people and there is a need to use protective eyewear. Others may experience more of a problem at night, such as with oncoming vehicle headlights as well as street lights. This can affect the ability to drive at night. Halos may also be seen around lights, especially brighter lights.
Color perception may also be affected with cataracts. A person may find that colors are duller or have faded from previous recollections, or hues do not appear as intense as others describe. Colors may eventually appear to be tinged with yellow or a light brown. As the condition progresses, a person with cataracts may find it difficult to distinguish between similar colors, like different shades of blue or between blue and purple.
Even when other characteristic symptoms of cataracts like cloudy vision or duller color perception is not as obvious, people with cataracts may instead notice worsening of eyesight. The prescription for spectacles or contact lenses may be rapidly changing at a time in life when most people find their vision stabilizing if there were pre-existing refractive errors, such as nearsightedness or farsightedness.
A sign of cataracts that some people experience is improved vision which may seem contradictory to the other typical cataract symptoms. In these cases, a person may find that their near vision improves. This uncharateristic improvement in eyesight, which is also referred to as second sight, is due to the changes in the lens focusing light more effectively. The improvement is temporary and gradually disappears as the cataract worsense.