Eye Health and Diseases

Learn about the eye’s anatomy and common eye diseases — including causes, symptoms, and options for prevention and treatment.
 

Good eye health and eye care are important to protect your sight, prevent common eye diseases and treat eye problems early.

The best way to maintain your best vision is by living an overall healthy lifestyle. This includes protecting your eyes from the sun’s ultraviolet radiation, not smoking, eating a healthy diet, getting plenty of physical activity, and having regular, comprehensive dilated eye exams. Check out our Comprehensive Dilated Eye Exam page to learn more about this sight-saving exam.

Here, take a tour of the eye to learn how the eye works. Find out about common eye conditions, as well as causes, risk factors, symptoms, detection and treatment options, and current research.

Tour of the Eye

How Does the Eye Work?

The eye is an organ with several parts. These parts work together to perform the eye’s primary function: to detect light. This section features information about these parts and how they can impact vision.

 

Eyelids

The eyelids protect the eye. Glands in the eyelid secrete oil, water, and other substances, which are spread in an even layer across the surface of the eye, forming the “tear film,” when the eyelids blink. When the glands are unhealthy, the tear film is missing components, and the eye may feel dry and scratchy or have excess tearing. Treatments for this condition include using warm compresses and lubricant eye drops (artificial tears). It is best to use eye drops that are not labeled as “taking the red out.”

Illustration of parts of the eye, indicating position of the upper, lower, and third eyelids

 

Sclera

The white, outer part of the eyeball is called the sclera. It protects the eye.

Illustration of parts of the eye, indicating position of the sclera.

 

Cornea

The cornea is the clear outer part at the front of the eye. It does most of the eye’s focusing. The cornea’s inner layer of cells continuously pumps water out of the cornea. If those cells are damaged, the cornea will become swollen and cloudy, and a corneal transplant or other surgery is needed to restore clear vision. Corneal transplants usually are successful because the cornea has no blood vessels. There is a constant need for organ donors to provide corneas.

Illustration of parts of the eye, indicating position of the cornea

 

Iris

The iris is the ring-shaped, colored part of the eye behind the cornea. It regulates how much light enters the eye.

Illustration of parts of the eye, indicating position of the iris

 

Pupil

The pupil is the opening at the center of the iris. The iris’ muscles change the iris’ width, which changes the pupil’s size. That is how the iris controls how much light can enter the eye.

Illustration of parts of the eye, indicating position of the pupil

 

Lens

The lens helps to focus light onto the retina at the back of the eye. A cloudy lens is called a “cataract.” Cataract surgery can be done when a person notices that his or her vision is inadequate to do whatever he or she likes to or must do. The surgeon makes a tiny incision and inserts a long, thin instrument that breaks up the cloudy lens with ultrasound waves and suctions the pieces out of the eye. A clear, plastic lens is then placed in the eye. The incision is so small that stitches usually are not needed.

Illustration of parts of the eye, indicating position of the lens

 

Vitreous Gel

The vitreous is a clear gel that fills the inside of the eye behind the lens and helps maintain the round shape of the eye.

Illustration of parts of the eye, indicating position of the vitreous gel

 
 

Retina

The retina is a light-sensitive tissue that lines the back of the eye. It converts light into electrical impulses that are sent to the brain through the optic nerve. Many eye diseases affect the retina and thus cause poor vision. Diabetes can cause the growth of abnormal blood vessels on the retina’s surface. These can leak and bleed, and over time they may contract and detach the retina from the back of the eye. Diabetes also can cause swelling of the retina. These problems are treated most quickly and most effectively when caught early. So, everyone with diabetes should have a comprehensive dilated eye exam once a year. The best way to prevent vision problems from diabetes is to keep the blood sugar at a healthy level.

Illustration of parts of the eye, indicating position of the retina

 

Macula

The macula is a small area of the retina at the center of the back of the eye. It provides central vision. At the center of the macula is the fovea, which allows you to see details sharply. Age-related macular degeneration (AMD) affects the macula. There are two forms: dry and wet. In the wet form, abnormal blood vessels grow beneath the retina. They can leak blood and other substances, and resultant scarring causes loss of central vision. In the dry form, the macula thins and deposits of fat combined with protein (called “drusen”) occur beneath the retina. Dry AMD can become wet AMD, but not vice versa. Both forms of AMD can cause loss of central vision, but wet AMD causes more rapid loss of vision.

Illustration of parts of the eye, indicating position of the macula

 

Optic Nerve

The optic nerve is a cable of nerve fibers that connects your eye to your brain. The nerve communicates input for the retina to the brain, which tells you what you are seeing. Glaucoma is a group of eye diseases that damage the optic nerve. This damage is irreversible and progresses unless the glaucoma is treated. Treatment does not restore vision lost from glaucoma. Rather, it prevents further damage from occurring, so catching glaucoma early and maintaining treatment for it is important.

Illustration of parts of the eye, indicating position of the optic nerve

Diseases and Conditions

Learn about different types of diseases that commonly affect the eye. Gain a better understanding of signs to look for, factors that can put you at risk, and ways to prevent and treat these conditions.

 

Amblyopia icon

Amblyopia and Strabismus

Amblyopia, commonly known as “lazy eye,” affects approximately 2 to 3 out of every 100 children. Vision in one of the eyes is reduced because the eye and the brain are not working together correctly. One of amblyopia’s most common precursors is strabismus — otherwise known as “crossed eyes” or “turned eye” — in which an individual’s eyes do not line up in the same direction when focusing on an object.

What is Amblyopia?

Amblyopia (“lazy eye”), is decreased vision in one or both eyes due to abnormal vision development in infancy or childhood, causing the brain not to receive normal stimulation from one or both eyes. The eye itself may look normal, but it is not being used normally because the brain is favoring the other eye. The reason it is often called “lazy eye” is because one eye is not being used as much as the other eye.

Without early detection and correction, a child faces a permanent loss of vision in the affected eye.

Treatments are generally most successful when they are done early in life, due to the plasticity of a child’s visual system. At a young age, vision connections from the eyes to the brain are still developing and can, therefore, be corrected. As a child ages, the connections are solidified and cannot be changed. Consequently, all children in the region must be screened by a trained professional using a medical screening model.

Long-term Consequences of Untreated Amblyopia:

  • Permanent vision loss, including loss of depth perception and peripheral vision, may occur in the affected eye if not treated properly.
  • Increased risk of permanent damage to the unaffected eye due to higher usage and exposure.

Causes and Risk Factors:

  • Refractive errors like nearsightedness, farsightedness, and astigmatism. Treatment with prescription eyeglasses or contact lenses can correct these issues.
  • Strabismus (a turned or crossed eye), can cause the affected eye to not work like the straight eye. An eye can drift vertically, or to either side.
  • Children with born congenital cataract are at higher risk for amblyopia. A cataract can cause cloudiness in the lens of an eye, which will cause images to look blurry. This is rarer in babies and children, but still possible.

Symptoms

It can be challenging to spot a child with amblyopia. Depth perception can be an issue. You may also notice your child squinting more, shutting one eye, or tilting their head. Regular (at least annual) vision screenings for young children (ages 1–5) are essential for early detection and treatment.

Treatment

Unless treated in early childhood, amblyopia usually persists into adulthood and will continue to worsen in the affected eye. It is the most common cause of monocular (one- eye) visual impairment among children and young and middle-aged adults. The good news is that early treatment works well and usually prevents long-term vision problems.

If there is an underlying condition, doctors may recommend:

  • Glasses or contacts (for kids with refractive error)
  • Surgery (for kids with cataract)

Then, the doctor will want to “re-train” the brain to use the weaker eye. Like with exercise, the more the eye is used, the stronger it gets. These treatments include:

  • Wearing an eye patch on the stronger eye. This forces your child to use the weaker eye. The length of time child needs to wear the eye patch can vary, and this can be a stressful time for some children. You must be a positive support for your child in helping them comply with the doctor’s instructions.
  • Applying special eye drops in the stronger eye. These eye drops (atropine) temporarily blur a child’s near vision in the stronger eye, forcing the brain to use the weaker eye.

Both of these options can be effective, and treatment length may range from a few weeks to many months. Working with your pediatric ophthalmologist is best to decide which is best for your circumstance.

What is Strabismus?

Strabismus is the medical term used when the two eyes do not look in the same direction at the same time. Also called “crossed eyes” or “turned eye,” the condition occurs in approximately 2 to 4% of the population.

There are three common types of strabismus:

  1. Crossed eyes (Esotropia). A child may be born with this condition, or they may develop it within a few months of birth or around two years of age.
  2. Walleye, or divergent eyes (Exotropia). A child may be born with this condition, or it may develop later.
  3. Vertical strabismus. The eyes are out of alignment vertically.

Long-term Consequences of Untreated Strabismus:

  • Reduction of vision (amblyopia) in the turned eye. Reduced vision may occur in one eye, especially under certain circumstances, such as late treatment.
  • Defective binocular vision. The eyes must be straight for the brain to be able to combine what the two eyes see into a single image. This enables accurate vision and stereopsis (3-D vision), which is used to judge depth.

Causes and Risk Factors:

  • Family history. Most commonly, a tendency to have some type of strabismus is inherited.
  • Farsightedness. Sometimes, the condition is due to the eyes being far-sighted and requiring corrective eyeglasses.
  • Muscle abnormality. The muscles in the eyes may not be working correctly, which can cause strabismus.
  • Another eye problem. Very rarely, strabismus may be secondary to a severe abnormality inside the eye, such as a cataract or tumor.

Symptoms

It can be challenging to spot a child with strabismus. The most common symptom a parent may notice is the misalignment of one or both of their child’s eyes. The child likely does not realize that one or both of their eyes are misaligned. You may notice your child bumping into things more than usual because depth perception can be an issue. You may also see your child squinting more, shutting one eye, or tilting their head. Regular (at least annual) vision screenings for young children (ages 1–5) are essential for early detection and treatment.

Treatment

Treatment aims to restore functional vision in each eye individually, as well as good binocular vision—the earlier the treatment, the better the chances of positive outcomes for the child. If treatment is delayed, vision may not be restored. This permanent vision loss can be prevented with early detection and treatment. Do not delay if your child has strabismus. Seek professional advice from your family doctor.

Treatment usually includes:

  • Patching. Patching the eye that is always straight to bring the vision up to normal in the turned eye.
  • Prescription eyeglasses. Eyeglasses may be used, particularly for eyes that are out of focus.
  • Eye drops. Special eye drops (phospholine iodide) may also help straighten the eyes.
  • Surgery. Surgery on the eye muscles is sometimes necessary.

Mitigating the Effects of Strabismus and Amblyopia

Amblyopia and strabismus can both lead to irreversible vision loss in children. The best way to prevent this is through early detection and treatment of these diseases. The American Academy of Ophthalmology and the American Association for Pediatric Ophthalmology and Strabismus offer age-specific recommendations for childhood eye screening:

  • Newborn: An ophthalmologist, pediatrician, family doctor, or another trained health professional should examine a newborn baby’s eyes.
  • Infant: A second screening for eye health should be done by an ophthalmologist, pediatrician, family doctor, or another trained health professional at a well-child exam between six months and the first birthday.
  • Preschool-Age:Between the ages of 3 and 3½, a child’s vision and eye alignment should be assessed by a pediatrician, family doctor, ophthalmologist, optometrist, or person trained in vision assessment of preschool children.
  • Visual acuity should be tested as soon as the child is old enough to cooperate with an eye exam using an eye chart.
  • School-age: Upon entering school, or whenever a problem is suspected, children’s eyes should be screened for visual acuity and alignment by a pediatrician, family doctor, ophthalmologist, optometrist, orthoptist or person trained in vision assessment of school-aged children, such as a school nurse.

However, if you or your child notices problems with his or her vision, visit an eye doctor immediately.

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Cataract icon

Cataracts

What is a Cataract?

A cataract is a clouding of the eyeÆs lens that affects vision. Most cataracts are related to aging. Cataracts are incredibly prevalent; by age 80, more than half of all Americans either have a cataract or have had cataract surgery.

Causes

The eye’s lens has proteins in it that will begin breaking down and clumping together as we age. This creates the clouding, which worsens over time. A cataract can occur in either one eye or both eyes. It cannot spread from one eye to the other.

Symptoms

Your eye doctor will check for cataracts during a dilated eye exam. However, you may notice signs of cataracts before an exam. If you experience any of the following, be sure to mention them to your doctor. Symptoms include:

  • Cloudy or blurry vision
  • Fading of colors
  • Poor night vision
  • The appearance of halos around lights or lights appear too bright

Treatment

Cataracts are removed surgically. Surgery may not be recommended in the early stages, but when the cataract begins to affect your quality of life significantly, surgery will be necessary.

Cataract surgery is one of the safest surgeries available. The surgeon makes a tiny incision and inserts a long, thin instrument that breaks up the cloudy lens with ultrasound waves and suctions the pieces out of the eye. A clear plastic lens is then placed in the eye. The incision is so small that stitches are usually not needed. This lens can also be specialized based on your eyeglasses prescription, which can further improve your eyesight.

How can I slow or prevent cataracts?

  • Wear sunglasses with UV protection and a hat outside
  • Quit smoking if you are a smoker
  • Eat a healthy diet including fruits and vegetables
  • Have regular comprehensive dilated eye exams

Other Types of Cataract

While most cataracts are related to aging, there are other types:

  • Secondary cataract. Cataracts that form after surgery for other eye problems, such as glaucoma. Cataracts can also develop in people who have other health problems, such as diabetes or conditions that are treated with prolonged steroid use.
  • Traumatic cataract. Cataracts can develop after an eye injury, sometimes years later.
  • Congenital cataract. Some individuals are born with cataracts or develop them in childhood, often in both eyes. These cataracts may be so small that they do not affect vision. If they do, the lenses may need to be removed.
  • Radiation cataract. Cataracts can develop after radiation exposure.

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