THE PARAOPTOMETRIC: DIFFERENTIATING THE TYPES OF CATARACTS AND HOW THEY AFFECT VISUAL ACUITY

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The rate of progression of a cataract can vary from person to person and eye to eye. 
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The types of cataract diagnosed depend on which part of the lens is affected.
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Cataracts are one of the most common causes of vision loss in the elderly. 

Tips for optometric assistants and technicians on how to improve their instrumentation skills.

Many patients coming into an ECP’s office have misconceptions regarding cataracts. They may think that the cataract is an actual “film” covering the outside of their eye, or that by using their eyes, it will make the cataract worse. Some patients also think cataracts can be reversed by doing exercises or taking vitamins.

SIGNS AND SYMPTOMS
The effect on vision depends on the location and the degree of clouding of the cataract. If the cataract is located in the lens periphery, the vision may not be as affected in the same way as when the cataract is located centrally. The rate of progression of a cataract can vary from person to person and eye to eye. Some of the signs and symptoms of cataracts are very subtle and may not affect daily living. The most common symptoms include cloudy, blurry, dimmed, or yellowed vision; increased difficulty seeing at night; sensitivity to light and glare; frequent changes in glasses or contact lens prescriptions; and/or double vision.

HOW LIGHT ENTERS THE EYE

The light rays entering the eye pass through the cornea, the anterior chamber, and pupil before encountering the lens. As light strikes the lens, it is refracted and comes to a focal point on the retina. From there, the light rays are transmitted into an electrical impulse and travel through the optic nerve and ultimately end at the visual cortex, where it is processed.

The lens of the eye is made up of mostly water and protein. The proteins are arranged in a precise way, which allow light to pass through the lens and maintain its clarity. As a result of the natural human body aging process, the protein material of the lens chemically changes, and the proteins begin to clump together. This clumping results in the clouding and discoloration of the lens.

As new cells form on the outside of the lens, the older cells are pushed closer together and become more compacted, which cause the lens to gradually lose its transparency and develop opacities. Since light rays require clear media to pass through on its way to the retina, any loss of clarity will affect the amount of light being transferred to the retina.

As a result, the images projected onto the retina are blurred and the vision is foggy. Also, as the lens becomes more compacted, the zonule fibers that are attached to the periphery of the lens become less effective. These fibers contract and relax to allow the lens to become thicker and rounder and thus change focus from distance to near. The loss of the ability to change the shape of the lens (accommodation) will affect the person’s ability to change focus from distance to near. This process is known as presbyopia.

The types of cataract diagnosed depend on which part of the lens is thus affected: nucleus, cortex, or posterior sub-capsular. Patients developing cataracts may develop one kind or a combination.

TYPES OF CATARATS

Nuclear Sclerotic Cataract: This type of cataract affects the center of the lens. It causes the patient to become more nearsighted. In addition, the lenses changes color ranging from yellow to brown as the lens becomes denser and clouds the vision. Patients may also experience difficulty distinguishing different shades of color.

Cortical Cataract: The cortical cataract first affects the lens periphery by forming white streaks along the edge of the lens cortex. The streaks gradually progress toward the center of the lens and block light, causing glare in bright sunlight.

Posterior Subcapsular: This type of cataract affects the posterior surface of the lens and will start as a small opacity on the back of the lens. This opacity can block the path of the light on its way to the retina. Patients will often complain of difficulty reading, glare, and halos around lights at night.

Congenital Cataract: A congenital cataract occurs when an infant is born with a cataract. This can be a result of the mother contracting an infection during gestation. A congenital cataract may also develop during childhood. Congenital cataract may be very slow in development and may not always affect the vision.

Traumatic Cataract: Usually this occurs because of blunt trauma to the eye, which can cause the lens fibers to swell, become white, and restrict vision. Such types of trauma may cause water to enter the lens, resulting in swelling. The opacification of the lens decreases the amount of light hitting the retina.

RISK FACTORS
Cataracts are one of the most common causes of vision loss in the elderly. It is not painful, but can impact the day-to-day activities of a person and limit independence. There are several risk factors that are known to cause cataracts, including the following.

Age: As the body ages, the lens gradual clouds, hardens, and yellows over time. Changes in the water content of the lens fibers can cause wedge-shaped streaks on the lens. This causes light that enters the eye to scatter, and creates problems with blurred vision, depth perception, and contrast.

Smoking: Excessive cigarette smoking can double the risk of development of nuclear and posterior subcapsular cataracts, and may double the risk of developing cataracts. Smokers are more at risk for developing cataracts located in the nucleus of the lens.

Drug Use: Medications such as corticosteroids have been shown to cause cataract development. Drugs like beta blockers and ACE inhibitors may also increase the risk of cataract formation.

Diabetes: Elevated blood glucose levels causes swelling of the lens and thereby affects vision. Diabetic patients are more likely to develop cortical cataracts. Patients with diabetes are known to develop cataracts at an earlier age than those who are diabetes-free.

Excessive drinking: Chronic heavy drinkers are at high risk for development of cataracts.

Excessive sunlight exposure: Having a deep suntan is not only bad for your skin, but also your eyes. Exposure to low-level UVB radiation from sunlight increases the risk for cataracts and can cause cataracts to form in the lens nucleus. People who are exposed to sunlight for prolonged periods of time are at risk. These people include those who live in the equatorial region, work outdoors, and who have significant sun exposure at a young age.

Exposure to Radiation: Cancer radiation and X-rays exposure can cause cataracts. UV light emitted by the sun is partially filtered by the earth’s atmosphere and the rays that reach the earth can lead to cataract formation. Microwave radiation can affect the lens proteins which can lead to cataracts.

Family History: Cataracts tend to run in families.

Obesity: Obese persons have increased risk of developing cataracts, but there has been some debate as to the relationship between cataract and obesity.

High Blood Pressure: Research has shown that persons with high blood pressure are at greater risk of cataract formation that someone with normal blood pressures. Therefore, people with high blood pressure should be monitor their pressure, and watch their diet in order to control their blood pressure.

Ethnicity: African-Americans have almost twice the risk of developing cataracts as caucasians. The reason could be related to the link with diabetes, and African-Americans are more prevalent to development of diabetes than caucasians.

Janet Hunter is president of Eye Source LL and specializes in ophthalmic technician training.

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