Andrew A. Dahl, MD, is a board-certified ophthalmologist. Dr. Dahl's educational background includes a BA with Honors and Distinction from Wesleyan University, Middletown, CT, and an MD from Cornell University, where he was selected for Alpha Omega Alpha, the national medical honor society. He had an internal medical internship at the New York Hospital/Cornell Medical Center.
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
Cataracts can be classified by anatomical location within the lens, degree of
clouding of the lens, or by the cause of the cataract.
The lens of the human eye is shaped similar to an M&M's candy. It has a front
(anterior) part and a back (posterior) part. The central portion of the lens is
called the lens nucleus, and the outer portion is called the lens capsule.
Between the inner nucleus and the outer capsule is a portion of the lens called
the cortex. Clouding of the lens can occur only in the nucleus, in which case
the term nuclear cataract or nuclear sclerosis is used. If the clouding occurs
in the lens cortex only, the cataract is termed a cortical cataract. If the loss
of clarity of the lens is primarily in the capsule, the term subcapsular
cataract is used. The location of the clouding can also be defined as being
anterior or posterior, central, or peripheral. Often the clouding of the lens may
affect multiple portions of the lens. The most common type of cataract that is
related to age is sometimes termed a senile cataract. This type of cataract
primarily involves the nucleus of the lens. Cataracts that develop in the
posterior subcapsular area (in the rear region of the lens capsule) are more
common in a younger age group.
Any degree of loss of the normal transparency of the lens is called a
cataract. The more cloudy the, lens the more advanced the degree of cataract. A
cataract may be mild, moderate, or severe. It may be early or advanced. If the
lens is totally opaque it is termed a "mature" cataract. Any cataract that is
not opaque is therefore termed an "immature" cataract. Most mature cataracts are
white in color.
What are causes of cataracts?
The lens is made of mostly water and protein. The protein is arranged in a
specific way that keeps the lens clear and allows light to pass through it to
focus a clear image onto the retinal surface. As we age, some of the protein may
clump together and start to cloud a small area of the lens. This is our
understanding of the cause of an age-related cataract. Over time, the cataract
may become more dense or cloud more of the lens, making it more difficult to see
through. A cataract is not a growth or tumor.
There are many causes of non age-related cataracts or secondary cataracts.
Secondary cataracts are a result of similar changes to the protein of the lens,
also resulting in visual blurring or visual loss.
Blunt or penetrating injury to the eye may cause secondary cataracts, either
immediately after the injury or some weeks to years afterward. A cataract
following an injury may appear and then not increase in density (be stationary)
or be progressive. Eye surgery for other conditions can also cause cataracts.
Excessive exposure to ionizing radiation (X-ray), infrared radiation (as in
glass blowers), or ultraviolet radiation cause secondary cataracts.
Diabetes is associated with the development of secondary cataracts.
Inflammatory disease of the eye, such as iritis or uveitis, may cause or
accelerate the development of cataract in the involved eye.
There are many genetic illnesses that are associated with the development of
secondary cataracts. These include myotonic dystrophy, galactosemia,
homocystinuria, Wilson's disease and
Down syndrome, plus many others.
Congenital infections with herpes simplex,
rubella, toxoplasmosis,
syphilis, and
cytomegalic inclusion disease may also result in cataracts.
There are many medications which, when taken over a long period of time, can
cause secondary cataracts. The most common of these are oral corticosteroids,
such as prednisone, which are used for a wide variety of medical conditions.
The term "congenital cataract" is used when a baby is born with any clouding
of the lens. This may be present in one or both eyes, be stationary or be
progressive. Causes include genetic disorders or intrauterine developmental
disorders, both often associated with other physical abnormalities of the baby.
Patients who develop cataracts in both eyes at an early age often have family
members who have also developed cataracts prematurely, implying a genetic cause,
even in the absence of a recognized underlying disease.
Diabetes mellitus is a chronic condition characterized by high levels of sugar (glucose) in the blood. The two types of diabetes are referred to as type 1 (insulin dependent) and type 2 (non-insulin dependent). Symptoms of diabetes include increased urine output, thirst, hunger, and fatigue. Treatment of diabetes depends on the type.
Retinal detachment is the separation of the retina from its attachments to the underlying eye tissue. Symptoms of retinal detachment include flashing lights and floaters. Highly nearsighted young adults and those who've had cataract surgery are at higher risk for retinal detachment.
Alcoholism is a disease that includes alcohol craving and continued drinking despite repeated alcohol-related problems, such as losing a job or getting into trouble with the law.
Glaucoma is a common eye condition in which the fluid pressure inside the eye rises because of slowed fluid drainage from the eye. If untreated, glaucoma may damage the optic nerve and other parts of the eye, causing the loss of vision or even blindness.
Eye floaters are deposits or condensation that forms in the eye's vitreous humor. These deposits cast shadows on the retina, and as the eye moves, the deposits shift position, making it appear as though the shadows are moving or floating.
Smoking is an addiction. More than 430,000 deaths occur each year in the U.S. from smoking related illnesses. Secondhand smoke or "passive smoke" also harm family members, coworkers, and others around smokers. There are a number of techniques available to assist people who want to quit smoking.
Many common eye disorders resolve without treatment and some may be managed with over-the-counter (OTC) products. It's important to visit a physician or ophthalmologist is the problem involves the eyeball itself or the condition hasn't improved after 72 hours of use of an eye-care OTC product.
Uveitis is inflammation of the eye. Symptoms include blurred vision, eye pain, eye redness, and floating spots before the eyes. Treatment may involve prescription eyedrops, antibiotics, and wearing dark glasses.
Sunburn is caused by overexposure to UV radiation from the sun. UV rays can also damage the eyes. Repeated overexposure to UV rays also increases the risk for scarring, freckles, wrinkles, and dry skin. Symptoms of sunburn include painful, red, tender, and hot skin. The skin may blister, swell, and peel. Sun poisoning (severe sunburn) include nausea, fever, chills, rapid pulse, dizziness and more. Treatment for sunburn depends upon the severity. Sun protection and sunscreen for an individual's skin type is recommended to decrease the chance of sunburn.
Blindness is the state of being sightless. Causes of blindness include macular degeneration, stroke, cataract, glaucoma, infection and trauma. Symptoms and signs may include eye pain, eye discharge, or the cornea or pupil turning white. Treatment of blindness depends upon the cause of the blindness.
Age-related macular degeneration (AMD) is a disease that gradually destroys the central vision. In people over 60, AMD is a leading cause of vision loss. Wet AMD occurs when abnormal blood vessels behind the retina start to grow under the macula, leaking blood and fluid and causing rapid vision loss. In dry AMD, light-sensitive cells slowly break down in the macula, resulting in gradual vision loss. Pain is not associated with either form of AMD.
Retinitis pigmentosa (RP) is a genetic condition that causes retinal degeneration and eventual vision loss. Symptoms include night blindness and tunnel vision. Visual field testing and electrophysiological testing are essential in diagnosing RP. Though there is no cure for RP, vitamin A therapy and an omega-3-rich diet may be recommended for patients to slow disease progression.
Diabetes and eye problems are generally caused by high blood sugar levels over an extended period of time. Types of eye problems in a person with diabetes include glaucoma, cataracts, and retinopathy. Examples of symptoms include blurred vision, headaches, eye aches, pain, halos around lights, loss of vision, watering eyes. Treatment for eye problems in people with diabetes depend on the type of eye problem. Prevention of eye problems include reducing blood pressure, cholesterol levels, quitting smoking, and maintaining proper blood glucose levels.
Double vision (diplopia) is a symptom that my indicate Graves' disease, myasthenia gravis, stroke, multiple sclerosis, Guillain-Barre syndrome, diabetes, cataracts, aneurysm, brain tumor, or migraine. Symptoms and signs include eye pain, droopy eyelids, nausea, headache, and a cross-eyed appearance. Treatment of double vision depends upon the underlying cause.
eye. Read about symptoms, signs, diagnosis, treatment, and prognosis.
Coats' disease is a rare eye condition that typically progresses to vision loss or blindness in one eye. Gradual vision loss is usually the first symptom, followed by a cloudy white or yellow pupil due to the presence of a cataract. Treatment focuses on limiting the blood vessel progression and may involve cryotherapy or laser photocoagulation.
Nonprescription eyeglasses are available over the counter (OTC) and are typically used by people who can no longer read fine print. OTC trifocals are helpful for those who require multiple distances or focal lengths for near and intermediate tasks. OTC sunglasses should offer 100% protection from the sun's UVA and UVB rays. OTC magnifying glasses are useful for viewing tiny objects or fine print.
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