Learn Together - Seeing Eyes: cataract

Sunday, June 6, 2010

cataract

ANATOMY

EPIDEMIOLOGY
From the age of 40, the proportion of people with cataract doubles with each decade. By their eighties, 80% of people will have some cataract present, including 30% who have had cataract surgery on one or both eyes

VISION OF CATARACT PERSON

Early symptoms include glare and sensitivity to bright light or halos appearing around lights, particularly when driving at night. When severity of cataract increases, vision becomes more blurred and colours become duller and darker.

most common type is nuclear cataract. Others (subcapsular and cortical) least common . the three may form mixed in advanced disease.

RISK FACTORS

The BMES (blue mountain eye study) demonstrated that smoking, heavy alcohol consumption, sunlight exposure and diabetes increased the risk of nuclear cataract. Nutritional factors appeared to reduce the risk. Higher levels of protein, vitamin A (including beta-carotene) and B-group vitamins (thiamin, niacin and riboflavin) in the diet were associated with around a 40% reduction in the frequency of nuclear cataract

TYPES OF CATARACT

NUCLEAR CATARACT

When we develop nuclear cataracts, the nucleus of the eye's lens becomes more curved, which increases the refractive index and causes you to become more nearsighted. Conversely, if you are farsighted, you may notice a temporary improvement in your vision. This condition does not mean your cataract is "cured." The cataract will continue to progress, and this improvement will not last.

CORTICAL CATARACT

The lens cortex does not begin to develop until after birth. The cortex continues to grow as we age, and by the time we reach about 60, 16 percent of the lens is cortex. Cortical production makes the lens more compact and hard, or SCLEROTIC . A cortical cataract often forms in "spokes" around the lens.

Cortical cataract develops in the outer shell of the lens as spokes and wedges and commonly causes increasing glare sensitivity

POSTERIOR SUBCAPSULAR CATARACT

develops at the back of the lens, often in the visual axis, and so affects vision rapidly and severely.

The majority of people needing cataract surgery have some posterior subcapsular cataract present at that time.

Because light converges at the back of the lens (the posterior pole) as it moves through the eye, a posterior subcapsular cataract affects vision even more than other types of cataracts. Anything that causes our pupils to constrict, such as bright light or the convergence of the eyes for reading, makes it very difficult for people with this type of cataract to see. Unlike people with nuclear cataracts, patients with subcapsular cataracts often benefit from the use of dilating drops to keep the pupils large and thus allow more light into the eye.

Posterior subcapsular cataracts can be caused by chronic intraocular inflammation or chronic use of medication such as corticosteroids. Less commonly, this type of cataract may be caused by radiation or trauma.