Causes and symptoms
There are many types of cataracts. Most are caused by a change in the chemical composition of the lens resulting in a loss of lens transparency. These changes can be caused by aging, eye injuries, certain diseases and conditions of the eye and body, and hereditary or birth defects.
The normal process of aging may cause the lens to harden and turn cloudy. These are called senile cataracts and are the most common type. They can occur as early as age 40. The most common types of senile acquired cataracts include nuclear sclerotic cataracts, cortical cataracts and posterior subcapsular cataracts. Nuclear sclerotic cataracts are characterized by a centrally located lens discoloration (yellow-brown) caused by deterioration of the older fiber cells near the centre of the lens. Posterior subcapsular cataracts are characterized by opacities at the posterior surface of the lens and tend to be the most visually debilitating due to their central location on the lens. Cortical cataracts are caused by swelling and liquefaction of the younger, more exterior cortical fiber cells. This type of cataract is characterized by radial linear opacities along the outer edge of the lens.
Children as well as adults can develop cataracts. When cataracts appear in children, they are sometimes inherited or they can be caused by an infection or inflammation during pregnancy which affects the unborn baby. This latter type of cataract is called congenital, meaning present at birth.
Eye injuries can cause cataracts in people of any age. A hard blow, puncture, cut, intense heat or chemical burn can damage the lens and result in what is called a traumatic cataract.
Certain infections, drugs, or diseases of the eye such as diabetes can also cause the lens to cloud and form a secondary cataract.
Depending on the size and location of the cloudy areas in a lens, a person may or may not be aware that a cataract is developing. If the cataract is located on the outer edge of the lens, no change in vision may be noticed. If the cloudiness is located near the center of the lens, it usually interferes with clear sight. Common symptoms experienced with developing cataracts include blurred or doubled vision, sensitivity to light and glare which may make driving difficult, less vivid perception of color, and frequent eyeglass prescription changes.
As the cataract grows worse, stronger glasses no longer improve sight. It may help to hold objects nearer to the eye for reading and close-up work. The pupiI, which normally appears black, may undergo noticeable color changes and appear to be yellowish or white.
Detection and diagnosis
Usually cataracts cannot be viewed from the outside of the eye without proper instruments. If blurred vision or other symptoms are noticed, an eye doctor should be visited as soon as possible for a comprehensive medical eye examination.
An eye doctor examines the eye with a variety of instruments to determine the type, size and location of the cataract.
The interior of the eye is also viewed after dilation to determine if there are any other eye disorders contributing to the blurred vision.
When cataracts cause enough loss of sight to interfere with a person's work, hobbies or lifestyle, it is probably time to remove them. Depending on individual needs, the patient and the eye doctor decide together when removal is necessary.
Surgery, which can be performed under general or local anesthesia and often on an out-patient basis, is the only effective way to remove the cloudy lens from the eye. Cataracts cannot be removed with a laser (an intense beam of light energy). Ophthalmologic laser surgery can, however, be used later to open part of the lens membrane (capsule) if it becomes cloudy after cataract surgery. Though rapidly changing technology and ongoing research has improved the treatment of cataracts in recent years, eye drops, ointments, pills, special diets or eye exercises have not been proven to dissolve or reduce a cataract.
Fortunately, cataract surgery is highly successful and over 90% of patients who undergo surgery regain useful vision. It is important to understand that complications during or after surgery can occur. As with any surgery, a good result cannot be guaranteed.
Once the cloudy, natural lens of the eye is removed, the patient needs a substitute lens to focus the eye. Medical advances have provided new ways to restore vision after the lens is removed:
- Intraocular lenses (IOLs)--permanent lenses implanted inside the eye during the cataract surgery. A new generation of intraocular lenses include the aspherical intraocular lenses. The aspheric IOLs have negative spherical abberations which may balance or counteract the positive spherical aberrations found on the cornea and lead to a neutralization of total spherical abberations in the eye. These aspheric IOLs could provide improved contrast sensitivity and visual acuity over traditional spherical IOLs.
- Cataract glasses--thinner and lighter than they used to be but still thicker than most ordinary glasses;
- Hard or soft contact lenses--these can be worn all day but are taken out at night;
- Special extended-wear soft contact lenses--appropriate for longer wear.
Although the intraocular lens is by far the most popular choice, there are advantages and disadvantages to each type of lens replacement. An eye doctor helps the patient decide which lens or combination of lenses is best suited to their lifestyle and eye health.
Loss of sight is largely preventable
If you notice any cataract symptoms, consult an eye doctor as soon as possible. Since cataracts most often form as a result of aging, individuals over the age of 40 with a family history of cataracts should have their eyes checked periodically.
There is no known preventive measure for cataracts, but modern cataract surgery is highly effective and permanent vision loss is usually preventable. Once diagnosed, mild cataracts can be watched to see if they progress. If vision loss due to a cataract is interfering with your daily activities, there is usually no reason to delay surgical treatment. Fortunately, a cataract patient no longer needs to become nearly blind before cataracts can be removed.
If you have any additional questions or would like further information, call the Toronto Eye Clinic for a consultation with one of the doctors.