CATARACTS: A Leading Cause of Preventable Blindness

Epidemiology Cataracts are the leading cause of

blindness in the world More than 1.3 million cataract

procedures are performed in the U.S. each year

Visual disability associated with cataracts account for 8 million physician office visits each year

Cataract is the leading cause of blindness in those 40 years or older in the United States

History The earliest reference to cataracts can

be found in Hindu writings from the 5th century BC

The word Cataract comes from the Greek word meaning “Waterfall”

Until the mid 1700’s, it was thought that cataract was formed by opaque material flowing, like a waterfall into the eye

Lens The human lens is

a naturally clear structure located behind the iris and supported by the zonules

The lens is avascular-It does not have a vascular supply

Structure The basic lens

consists of a central nucleus surrounded by the cortex contained within the lens capsule

Optics When light passes

through the pupil, it is focused by the lens to produce clear, sharp images on the retina, the light-sensitive membrane on the back of the eye that functions like the film of a camera

Optics When this

arrangement is disturbed in any way, the transparency is lost

This results in scattering of light, blurring, and blocking of the image

Structure The lens is made mostly of water and protein

fibers The protein fibers are arranged in a precise

manner that makes the lens clear and allows light to pass through without interference

With aging, the composition of the lens undergoes changes and the structure of the protein fibers breaks down

Some of the fibers begin to clump together, clouding areas of the lens, and leading to the loss of transparency

This loss of transparency, or opacity formation is called Cataract

Clouding of the lens is a normal part of aging

About half of Americans older than 65 have some degree of clouding of the lens

According to one study, after age 75, 39% of men, and 46% percent of women in the U.S. have visually significant cataracts

Cataracts produce a gradual, painless, progressive loss of vision, and many patients are unaware of vision problems

Generally do not cause pain, or abnormal tearing

But as the clouding progresses, the cataract eventually interferes with your vision

Commonly affect distance vision Cause problems with glare In the early stages, stronger

lighting and eyeglasses can help deal with the vision problems

If impaired vision jeopardizes your normal lifestyle, you might need surgery

Patients often describe trying to look through a fogged-up window

Clouded vision can make it more difficult to drive a car, read, or see details

Symptoms

Blurred vision Increasing difficulty with vision at

night Glare, especially at night Halos around lights The need for brighter light for reading Double vision in a single eye Fading or yellowing of colors

Due to increase of yellow-brown pigment in the lens, color perception also is affected

These may also be symptoms of other eye conditions, therefore it is important to see your ophthalmologist annually, or if there is a persistent change in vision

Pain, redness, discharge, or irritation in the eye are usually not signs or symptoms of a cataract, but may be signs and symptoms of other eye disorders

Hypermature Cataract A cataract isn't

dangerous to the eye unless the cataract becomes completely white, a condition known as an overripe (hypermature) cataract

This can cause inflammation, eye pain and headache

A hypermature cataract is extremely rare and needs removal

Types of Cataract The lens consists of

three layers The outer layer is a

thin, clear membrane It surrounds a soft,

clear material (cortex) The hard center of the

lens is the nucleus A cataract can form in

any part of the lens

Nuclear Cataract Occurs in the center of the lens In its early stages, the patient may

become more nearsighted or even experience a temporary improvement in reading vision

This so-called “second sight” disappears as the lens gradually turns yellow and begins to cloud the vision

Seeing in dim light and driving at night may be especially troublesome

Cortical Cataract Begins as whitish, wedge-shaped

streaks on the outer edge of the lens cortex

As it slowly progresses, the streaks extend to the center and interfere with light passing through the nucleus

Both distance and near vision can be impaired

Patients also have problems with glare and loss of contrast

Subcapsular Cataract Starts as a small, opaque area just under

the capsule shell, usually at the back of the lens, right in the path of light on its way to the retina

This type of cataract may occur in both eyes but tends to be more advanced in one eye than the other

Often interferes with reading vision, reduces your vision in bright light and causes glare or halos around lights at night

Etiology Why age-related changes happen to the

lens is not known One possibility is damage caused by

unstable molecules known as free radicals

Smoking and exposure to UV light are two sources of free radicals

General wear and tear on the lens over the years also may cause the changes in protein fibers

Etiology Age-related changes in the lens are not the only

cause of cataracts Some infants are born with cataracts or develop

them during childhood Such cataracts may be the result of the mother

having contracted rubella during pregnancy Metabolic disorders

Congenital Cataracts Responsible for nearly 10% of all visual

loss in children worldwide Approximately 0.03% of newborns have

some form of congenital cataract Most are not associated with additional

developmental problems Around one fifth of these patients have

a family history of congenital cataract but in up to half of all cases there is no family history

In the case of a newborn infant, a cataract causes the immature visual system to be deprived of the stimulation needed for normal development

If left untreated, permanent visual loss may occur

Unilateral cataracts are more likely to cause visual loss because of the competition between the two eyes

If the cataract is small there may be only slight blurring of vision with near normal visual development

If the cataract is larger, or located more posteriorly, it can effect visual development

In some cases this can lead to permanent amblyopia (lazy eye)

Without adequate stimulation central vision can be permanently effected

Outcome is very much dependent on the type of cataract

Some congenital cataracts impair visual development only to a small degree and may never require surgery

If the cataract is only in one eye, there is a strong tendency for the child to prefer the healthy eye The eye affected by the cataract rarely

achieves normal vision, therefore removal of the cataract is indicated

Etiology of Pediatric Cataracts Hereditary

Autosomal dominant form most common Genetic and Metabolic Diseases

Down syndrome Marfan’s syndrome Myotonic Dystrophy

Maternal Infections Rubella, Syphilis, Toxoplasmosis,

Varicella

Ocular Anomalies Aniridia-Absence of iris at birth

Toxic Corticosteroids, Radiation

Trauma

Risk Factors In Adults Exposure to sunlight (UV light) Smoking Diabetes Trauma (blunt or penetrating) Family history of cataracts Corticosteroid therapy Radiation exposure Electrical injury Myotonic dystrophy Uveitis- Ocular inflammation

Risk Factors Everyone is at risk of developing

cataracts simply because age is the single greatest risk factor

By age 65 about half of all Americans have developed some degree of lens clouding

Cataracts develop sooner in diabetic patients than in non-diabetic patients

This is caused by shifts in the glucose, electrolyte, and water balance within the lens

Fluctuating vision and rapid shift to near sightedness are symptoms of diabetes

Clinical Findings The most

common objective finding associated with cataracts is decreased visual acuity

This is measured with an office wall chart or near-vision card

Visual Acuity Acuity refers to the sharpness of vision

or how clearly you see an object In this test, your eye doctor checks to

see how well you read letters from across the room

Eyes are tested one at a time, while the other eye is covered.

Using the chart with progressively smaller letters from top to bottom, to determine the level of vision

Refraction This is performed

by your doctor to see if the decrease in vision is simply due for need for new glasses, or if there is another process at work that accounts for the decrease in visual acuity

                                                           

Slit Lamp Exam (SLE) SLE allows the

ophthalmologist to see the structures of the eye under magnification

The microscope is called a slit lamp because it uses an intense slit of light to illuminate your cornea, iris, and lens

These structures are viewed in small sections to detect any small abnormalities

Dilated Exam Dilating drops are

placed in the eyes to dilate the pupils wide and provide a better view to the back of the eyes

It allows the ophthalmologist to examine the lens for signs of a cataract and, if needed, determine how dense the clouding is

Dilated Exam It also allows for

examination of the retina and the optic nerve.

Dilating drops usually keep your pupils open for a few hours before their effect gradually wears off

                     

When pupils are dilated, patients will have difficulty focusing on close objects

With your pupils open this wide, sunglasses are helpful on a sunny day, and you may need a driver to drive you home

Other Causes of painless Vision Loss Cataract Retinal detachment Macular degeneration Diabetes mellitus Glaucoma Retinal artery occlusion

Retinal detachment is often accompanied by floaters, flashes of light, and loss of peripheral vision, which is often described as a gray curtain or shade covering all or part of the visual field

Risk factors include a history of previous ocular trauma, nearsightedness, retinal detachment in the fellow eye, or a family history of retinal detachment

Macular degeneration usually causes a slow, progressive loss of central vision

Symptoms of acute vision loss and distortion result from leakage from abnormal subretinal vessels

Patients should be referred to a retina specialist immediately

Diabetic retinopathy may also contribute to vision loss

Findings include dot-and-blot hemorrhages, microaneurysms, dilated and tortuous vessels, and neovascularization of the disk and retina

Cataracts often obscure the fundus, making assessment of diabetic retinopathy difficult

Open-angle glaucoma produces slow, painless visual field loss that usually begins peripherally

Optic nerve damage and subsequent loss of peripheral vision occur at normal as well as elevated intraocular pressures

With progressive optic nerve damage and visual field loss, central vision is the last to be affected

Cataracts are the most treatable cause of decreased vision in the United States

For most patients, observation and frequent eyeglass prescription changes are sufficient

When activities of daily living, such as driving, reading, working, and self-care are affected surgery should be discussed

Cataract Surgery should be considered when changes in eyeglasses no longer help, quality of life is jeopardized, and cataract removal is likely to have an impact on vision