How You See

The eye functions like a camera. Light rays enter the eye through the cornea (the clear front window), pass through the pupil (the hole in the center of the iris), and then through the lens, finally reaching the retina (the film) at the back of the eye. When light rays land on the retina, they form an upside-down image. The retina converts the image into impulses that travel through the optic nerve to the brain, which converts them into upright visual images.

Vision is clear only if the cornea and lens correctly bend or "refract" the light rays and focus them on the retina. Blurry vision may be due to what is called a "refractive error" --- the failure of the cornea and lens to focus light properly. Prescription eye glasses, contact lenses, and refractive surgery correct or improve refractive errors by focusing light rays closer to, or directly onto, the retina.

More than 90 percent of our knowledge is obtained through our eyes making vision the most valued of the five senses. However, millions of people suffer from diseases, disorders or injuries to the eye. The following section contains information about many eye diseases, vision disorders, and the exceptional services provided by the physicians and scientists of Bascom Palmer Eye Institute.

Eye Protection

Regular eye examinations should provide the basis for maintaining proper eye health as many eye diseases and disorders have no symptoms or early warning signs. However problems or injuries can occur suddenly and unexpectedly.

• Almost all eye injuries can be prevented. Many sports and recreational activities, including tennis, baseball, basketball and racquetball, carry some risk of eye injury. Activities at home such as cooking and gardening, also may present eye injury risk. Use protective eyewear when participating in sports, using chemical cleaners or doing heavy yard work.

• Do not look into a closed container of hot food (especially liquids) immediately after removal from a microwave oven as steam can burn the eyes.

• Do not use eye medication prescribed for someone else.

• Do not use another person's eye make-up and do not apply make-up in a moving vehicle.

• When removing a cork from a bottle, wrap the cork in a towel and direct the bottle away from your face and away from others.

• To minimize eyestrain associated with extensive computer monitor use: blink frequently; change your body, head and eye position often; place reference material as close to the screen as practical to reduce head and eye movements; and minimize glare and reflections from office lighting.

• Be aware of cigarettes or cigars in your hand when around children.

• Keep chemicals, spray cans, adhesives, scissors, knives, forks, keys, pens and pencils away from young children.

If you experience an eye injury, sudden pain, loss of sight, flashing lights, an increase in floaters or other changes in your vision, visit your eye care professional immediately.

Eye Disease Statistics
 

• 80 million people have potentially blinding eye disorders.

• 14 million people have severe visual conditions not correctable by glasses.

• 14 million diabetics risk loss of sight.

• 12 million people have motor sensory diseases such as amblyopia and strabismus.

• 11 million people experience corneal disorders such as herpes and dry eye.

• 10 million people suffer visual loss caused by macular degeneration.

• Age-related macular degeneration (AMD) is the chief cause of blindness among Americans over 50 - and South Florida has the largest concentration of AMD patients over the age of 65.

• 5.5 million people have cataracts that obstruct vision.

• 2.8 million people are colorblind.

• 2.3 million people endure visual losses from inflammatory diseases such as uveitis.

• 2 million people are visually impaired from glaucoma.

• 1 million people are legally blind.

Common Eye Diseases

Amblyopia

Amblyopia is a term used to describe an uncorrectable loss of vision in an eye that appears to be normal.  It’s commonly referred to as “lazy eye” and can occur for a variety of reasons. 

A child’s visual system is fully developed between approximately the ages of 9-11. Until then, children readily adapt to visual problems by suppressing or blocking out the image.  If caught early, the problem can often be corrected and the vision preserved.  However, after about age 11, it is difficult if not impossible to train the brain to use the eye normally. 

Retinal Artery Occlusion

A retinal artery occlusion occurs when the central retinal artery or one of the arteries that branch off of it becomes blocked.  This blockage is typically caused by a tiny embolus (clot) in the blood stream. The occlusion decreases the oxygen supply to the area of the retina nourished by the affected artery, causing permanent vision loss.

In this photograph, the affected area of the retina is the pale, whitish-yellow region (blue arrows) that is normally supplied by the blocked artery (white arrow). The surrounding reddish-orange area is healthy retina tissue.

Astigmatism

Astigmatism means that the cornea is oval like a football instead of spherical like a basketball.  Most astigmatic corneas have two curves – a steeper curve and a flatter curve.  This causes light to focus on more than one point in the eye, resulting in blurred vision at distance or near.  Astigmatism often occurs along with nearsightedness or farsightedness.

Basal Cell Carcinoma

Basal cell carcinoma is a type of skin cancer that occurs most commonly on the face or neck, often near an eyelid or on the nose.  The tumor cells are thought to originate from the basal, or innermost, layer of the skin. 

Blepharitis-

Blepharitis is a common inflammatory condition that affects the eyelids.  It usually causes burning, itching and irritation of the lids.  In severe cases, it may also cause styes, irritation and inflammation of the cornea (keratitis) and conjunctiva (conjunctivitis).  Some patients have no symptoms at all. 

Blepharitis is usually a chronic problem that can be controlled with extra attention to lid hygiene.  However, it is sometimes caused by an infection and may require medication. 

Retinal Vein Occlusion

A retinal artery occlusion occurs when the central retinal artery or one of the arteries that branch off of it becomes blocked.  This blockage is typically caused by a tiny embolus (clot) in the blood stream. The occlusion decreases the oxygen supply to the area of the retina nourished by the affected artery, causing permanent vision loss.

In this photograph, the affected area of the retina is the pale, whitish-yellow region (blue arrows) that is normally supplied by the blocked artery (white arrow). The surrounding reddish-orange area is healthy retina tissue.

Cataract

When cataracts are mentioned, people often think of a film that grows on their eyes causing them to see double or blurred images. However, a cataract does not form on the eye, but rather within the eye. Eye without a cataract Eye with a cataract A cataract is a clouding of the natural lens, the part of the eye responsible for focusing light and producing clear, sharp images. The lens is contained in a sealed bag or capsule. As old cells die they become trapped within the capsule. Over time, the cells accumulate causing the lens to cloud, making images look blurred or fuzzy. For most people, cataracts are a natural result of aging. In fact, they are the leading cause of visual loss among adults 55 and older. Eye injuries, certain medications, and diseases such as diabetes and alcoholism have also been known to cause cataracts.      Normal Vision Illustration by Mark Erickson   Illustration by Mark Erickson

Chalazion

A chalazion (stye) is a small lump in the eyelid caused by obstruction of an oil producing or meibomian gland.  Chalazia may occur in the upper or lower lids, causing redness, swelling and soreness in some cases. 

Chemical Burn

It can happen in the blink of an eye.  While pouring liquid drain cleaner down a sink, some of the chemical splashes up in your face, hitting you squarely in the eye.  Chemical injuries don't just happen in the workplace.  Most homes have dozens of everyday products that pose tremendous danger to vision if they contact the eye.  

The severity of the injury is related to whether the chemical is alkali or

Color Blindness

Color blindness may be a hereditary condition or caused by disease of the optic nerve or retina.  Acquired color vision problems only affect the eye with the disease and may become progressively worse over time.  Patients with a color vision defect caused by disease usually have trouble discriminating blues and yellows.   

Inherited color blindness is most common, affects both eyes, and does not worsen over time.  This type is found in about 8% of males and 0.4% of females.  These color problems are linked to the X chromosome and are almost always passed from a mother to her son.  

Color blindness may be partial (affecting only some colors), or complete (affecting all colors).  Complete color blindness is very rare.  Those who are completely color blind often have other serious eye problems as well.

Photoreceptors called cones allow us to appreciate color.  These are concentrated in the very center of the retina and contain three photosensitive pigments:  red, green and blue.  Those with defective color vision have a deficiency or absence in one or more of these pigments.  Those with normal color vision are referred to as trichromats.  People with a deficiency in one of the pigments are called anomalous trichromats (the most common type of color vision problem.)  A dichromat has a complete absence in one cone pigment.   

Conjunctivitis

Conjunctivitis, commonly known as pink eye, is an infection of the conjunctiva (the outer-most layer of the eye that covers the sclera).  The three most common types of conjunctivitis are: viral, allergic, and bacterial.  Each requires different treatments.  With the exception of the allergic type, conjunctivitis is typically contagious. 

Corneal Ulcer

A corneal ulcer forms when the surface of the cornea is damaged or compromised.  Ulcers may be sterile (no infecting organisms) or infectious.  The term infiltrate is also commonly used along with ulcer.   Infiltrate refers to an immune response causing an accumulation of cells or fluid in an area of the body where they don't normally belong.

Whether or not an ulcer is infectious is an important distinction for the physician to make and determines the course of treatment.  Bacterial ulcers tend to be extremely painful and are typically associated with a break in the epithelium, the superficial layer of the cornea.  In some cases, the inflammatory response involves the anterior chamber along with the cornea.  Certain types of bacteria, such as Pseudomonas, are extremely aggressive and can cause severe damage and even blindness within 24-48 hours if left untreated.  

Sterile infiltrates on the other hand, cause little if any pain.  They are often found near the peripheral edge of the cornea and are not necessarily accompanied by a break in the epithelial layer of the cornea.

There are many causes of corneal ulcers.  Contact lens wearers (especially soft) have an increased risk of ulcers if they do not adhere to strict regimens for the cleaning, handling, and disinfection of their lenses and cases.  Soft contact lenses are designed to have very high water content and can easily absorb bacteria and infecting organisms if not cared for properly.  Pseudomonas is a common cause of corneal ulcer seen in those who wear contacts.  

Bacterial ulcers may be associated with diseases that compromise the corneal surface, creating a window of opportunity for organisms to infect the cornea.  Patients with severely dry eyes, difficulty blinking, or are unable to care for themselves, are also at risk.  Other causes of ulcers include:  herpes simplex viral infections, inflammatory diseases, corneal abrasions or injuries, and other systemic diseases.

Dacryocystitis

Dacryocystitis is an infection of the tear sac that lies between the inner corner of the eyelids and the nose. It usually results from blockage of the duct that carries tears from the tear sac to the nose. The blocked duct harbors bacteria and becomes infected. Dacryocystitis may be acute (sudden onset) or chronic (frequently recurs). It may be related to a malformation of the tear duct, injury, eye infection, or trauma. 

This problem is most common in infants because their tear ducts are often underdeveloped and clog easily. Babies often have recurrent episodes of infection; however, in most cases, the problem resolves as the child grows. In adults, the infection may originate from an injury or inflammation of the nasal passages. In many cases, however, the cause is unknown.

Diabetic Retinopathy
 

Diabetes is a disease that occurs when the pancreas does not secrete enough insulin or the body is unable to process it properly.  Insulin is the hormone that regulates the level of sugar (glucose) in the blood.  Diabetes can affect children and adults.  

How does diabetes affect the retina?

Patients with diabetes are more likely to develop eye problems such as cataracts and glaucoma, but the disease’s affect on the retina is the main threat to vision.  Most patients develop diabetic changes in the retina after approximately 20 years.  The effect of diabetes on the eye is called diabetic retinopathy. 

Over time, diabetes affects the circulatory system of the retina.  The earliest phase of the disease is known as background diabetic retinopathy.  In this phase, the arteries in the retina become weakened and leak, forming small, dot-like hemorrhages.  These leaking vessels often lead to swelling or edema in the retina and decreased vision.

The next stage is known as proliferative diabetic retinopathy.  In this stage, circulation problems cause areas of the retina to become oxygen-deprived or ischemic.   New, fragile, vessels develop as the circulatory system attempts to maintain adequate oxygen levels within the retina.  This is called neovascularization.  Unfortunately, these delicate vessels hemorrhage easily.  Blood may leak into the retina and vitreous, causing spots or floaters, along with decreased vision. 

In the later phases of the disease, continued abnormal vessel growth and scar tissue may cause serious problems such as retinal detachment and glaucoma. 

Ptosis

Ptosis (pronounced toe' sis), or drooping of the upper eyelid, may occur for several reasons such as: disease, injury, birth defect, previous eye surgery and age.  In most cases, it is caused by either a weakness of the levator muscle (muscle that raises the lid), or a problem with the nerve that sends messages to the muscle. 

Children born with ptosis may require surgical correction of the lid if it covers the pupil.  In some cases, it may be associated with a crossed or misaligned eye (strabismus).  Left untreated, ptosis may prevent vision from developing properly, resulting in amblyopia, or lazy eye.

Patients with ptosis often have difficult blinking, which may lead to irritation, infection and eyestrain.  If a sudden and obvious lid droop is developed, an ophthalmologist should be consulted immediately.  

Dry Eyes

Dry eye syndrome is one of the most common problems treated by eye physicians.  Over ten million Americans suffer from dry eyes.  It is usually caused by a problem with the quality of the tear film that lubricates the eyes. 

Tears are comprised of three layers.  The mucus layer coats the cornea, the eye’s clear outer window, forming a foundation so the tear film can adhere to the eye.  The middle aqueous layer provides moisture and supplies oxygen and other important nutrients to the cornea.  This layer is made of 98 percent water along with small amounts of salt, proteins and other compounds.  The outer lipid layer is an oily film that seals the tear film on the eye and helps to prevent evaporation.  

Tears are formed in several glands around the eye.  The water layer is produced in the lacrimal gland, located under the upper eyelid.  Several smaller glands in the lids make the oil and mucus layers.  With each blink, the eyelids spread the tears over the eye.  Excess tears flow into two tiny drainage ducts in the corner of the eye by the nose.  These ducts lead to tiny canals that connect to the nasal passage.  The connection between the tear ducts and the nasal passage is the reason that crying causes a runny nose. 

In addition to lubricating the eye, tears are also produced as a reflex response to outside stimulus such as an injury or emotion.  However, reflex tears do little to soothe a dry eye, which is why someone with watery eyes may still complain of irritation. 

Dry eye syndrome has many causes.  One of the most common reasons for dryness is simply the normal aging process.  As we grow older, our bodies produce less oil – 60% less at age 65 then at age 18.  This is more pronounced in women, who tend to have drier skin then men.  The oil deficiency also affects the tear film.  Without as much oil to seal the watery layer, the tear film evaporates much faster, leaving dry areas on the cornea.

Many other factors, such as hot, dry or windy climates, high altitudes, air-conditioning and cigarette smoke also cause dry eyes.  Many people also find their eyes become irritated when reading or working on a computer.  Stopping periodically to rest and blink keeps the eyes more comfortable. 

Contact lens wearers may also suffer from dryness because the contacts absorb the tear film, causing proteins to form on the surface of the lens.  Certain medications, thyroid conditions, vitamin A deficiency, and diseases such as Parkinson’s and Sjogren’s can also cause dryness.  Women frequently experience problems with dry eyes as they enter menopause because of hormonal changes.  

Entropion

Entropion, an eyelid that turns inward, is a problem that typically affects the lower lid.  It usually stems from a muscle spasm; however, it can also be caused by scarring from trauma or inflammation from certain diseases that involve the eyelids. 

When the eyelid turns inward, the lashes rub against the eye, resulting in irritation, scratchiness, tearing and redness.  Surgery is often required to correct the problem. 

Signs and Symptoms

• Tearing

• Burning

• Irritation

• Sandy, gritty feeling

• Red eye
   

Farsightedness or hyperopia, occurs when light entering the eye focuses behind the retina, instead of directly on it.  This is caused by a cornea that is flatter, or an eye that is shorter, than a normal eye.  Farsighted people usually have trouble seeing up close, but may also have difficulty seeing far away as well. 

  
Illustration by Mark Erickson

Young people with mild to moderate hyperopia are often able to see clearly because their natural lens can adjust, or accommodate to increase the eye’s focusing ability.  However, as the eye gradually loses the ability to accommodate (beginning at about 40 years of age), blurred vision from hyperopia often becomes more apparent.

Foreign Body

Anyone who has felt as if there was a grain of sand in his or her eye  has probably had a foreign body.  Foreign bodies might be superficial, or in more serious injuries, they may penetrate the eye.  Fortunately, the cornea has such an incredible reflex tearing system that most superficial foreign bodies are naturally flushed out with our natural tears.  But if the object is more deeply embedded, medical attention is required.  

Illustration by Mark Erickson

This photo-illustration shows a foreign body in the iris tissue.  The patieint was hammering a nail (without wearing eye protection) and was struck in the eye by a chip from the nail.  Note how the nail chip tore the iris.
 

Glaucoma is a disease caused by increased intraocular pressure (IOP) resulting either from a malformation or malfunction of the eye’s drainage structures.  Left untreated, an elevated IOP causes irreversible damage the optic nerve and retinal fibers resulting in a progressive, permanent loss of vision.  However, early detection and treatment can slow, or even halt the progression of the disease. 

What causes glaucoma?

The eye constantly produces aqueous, the clear fluid that fills the anterior chamber (the space between the cornea and iris).  The aqueous filters out of the anterior chamber through a complex drainage system.  The delicate balance between the production and drainage of aqueous determines the eye’s intraocular pressure (IOP). Most people’s IOPs fall between 8 and 21.  However, some eyes can tolerate higher pressures than others. That’s why it may be normal for one person to have a higher pressure than another. 

Common types of glaucoma

Open Angle

Open angle (also called chronic open angle or primary open angle) is the most common type of glaucoma.  With this type, even though the anterior structures of the eye appear normal, aqueous fluid builds within the anterior chamber, causing the IOP to become elevated.  Left untreated, this may result in permanent damage of the optic nerve and retina.  Eye drops are generally prescribed to lower the eye pressure.  In some cases, surgery is performed if the IOP cannot be adequately controlled with medical therapy.  

Acute Angle Closure

Only about 10% of the population with glaucoma has this type.  Acute angle closure occurs because of an abnormality of the structures in the front of the eye.  In most of these cases, the space between the iris and cornea is more narrow than normal, leaving a smaller channel for the aqueous to pass through.  If the flow of aqueous becomes completely blocked, the IOP rises sharply, causing a sudden angle closure attack.

While patients with open angle glaucoma don’t typically have symptoms, those with angle closure glaucoma may experience severe eye pain accompanied by nausea, blurred vision, rainbows around lights, and a red eye. This problem is an emergency and should be treated by an ophthalmologist immediately. If left untreated, severe and permanent loss of vision will occur in a matter of days.

Secondary Glaucoma

This type occurs as a result of another disease or problem within the eye such as: inflammation, trauma, previous surgery, diabetes, tumor, and certain medications.  For this type, both the glaucoma and the underlying problem must be treated.

Congenital

This is a rare type of glaucoma that is generally seen in infants. In most cases, surgery is required.
 

Iritis is an inflammatory problem of the iris, the colored part of the eye.  It often occurs for unknown reasons, but it may be linked to certain diseases affecting the body, infections, previous eye surgery, or injury.

Iritis may affect one or both eyes.  It is sometimes a chronic, recurring condition.

Nevus-A nevus is typically a flat, benign, pigmented area that may appear inside the eye or on its surface.  Nevi commonly appear on the choroid (the layer just behind the retina), the iris, and the conjunctiva.  Nevi are similar to freckles, and don’t typically change or grow. 

Ectropion

Patients with ectropion have a sagging lower eyelid that leaves the eye exposed and dry.  It is caused by a lack of tone of the delicate muscles that hold the lid taut against the eye.  Excessive tearing is a common with ectropion, but wiping the tears away only causes the lid to sag more.  Ectropion is most common among people over the age of 60.  

Signs and Symptoms

• Irritation

• Burning

• Gritty, sandy feeling

• Excessive tearing

• Red, irritated eyelid

Pterygium
 

terygium is a raised, wedge-shaped growth of the conjunctiva.  It is most common among those who live in tropical climates or spend a lot of time in the sun.  Symptoms may include irritation, redness, and tearing.  Pterygiums are nourished by tiny capillaries that supply blood to the tissue.  For some, the growth remains dormant; however, in other cases it grows over the central cornea and affects the vision.  As the pterygium develops, it may alter the shape of the cornea, causing astigmatism.  If the pterygium invades the central cornea, it is removed surgically.  

Since pterygiums are most commonly caused by sun exposure, protecting the eyes from sun, dust and wind is recommended.  Instilling artificial tears liberally is also helpful to decrease irritation.  In some cases, steroid drops are prescribed to reduce inflammation.

Retinal Tear

Retinal tears commonly occur when there is traction on the retina by the vitreous gel inside the eye.  In a child’s eye, the vitreous has an egg-white consistency and is firmly attached to certain areas of the retina.  Over time, the vitreous gradually becomes thinner, more liquid and separates from the retina.  This is known as a posterior vitreous detachment (PVD).

PVDs are typically harmless and cause floaters in the eye; but in some cases, the traction on the retina may create a tear.  Retinal tears frequently lead to detachments as fluids seep underneath the retina, causing it to separate and detach.

Retinal Detachment

A retinal detachment occurs when the retina’s sensory and pigment layers separate.   Because it can cause devastating damage to the vision if left untreated, retinal detachment is considered an ocular emergency that requires immediate medical attention and surgery.  It is a problem that occurs most frequently in the middle-aged and elderly. 

There are three types of retinal detachments.  The most common type occurs when there is a break in the sensory layer of the retina, and fluid seeps underneath, causing the layers of the retina to separate.  Those who are very nearsighted, have undergone eye surgery, or have experienced a serious eye injury are at greater risk for this type of detachment.  Nearsighted people are more susceptible because their eyes are longer than average from front to back, causing the retina to be thinner and more fragile. 

The second most common type occurs when strands of vitreous or scar tissue create traction on the retina, pulling it loose.  Patients with diabetes are more likely to experience this type.

The third type happens when fluid collects underneath the layers of the retina, causing it to separate from the back wall of the eye.  This type usually occurs in conjunction with another disease affecting the eye that causes swelling or bleeding.
 

Retinal vein occlusion occurs when the circulation of a retinal vein becomes obstructed by an adjacent blood vessel, causing hemorrhages in the retina.  Swelling and ischemia (lack of oxygen) of the retina as well as glaucoma are fairly common complications. 

The visual symptoms can vary in severity from one person to the next, and are dependent on whether the central retinal vein or a branch retinal vein is involved.  Patients who experience a branch vein occlusion often notice a gradual improvement in their vision as the hemorrhage resolves.  Recovery from a central vein occlusion is much less likely since it affects the macula. 

This problem appears equally in males and females and is more common after the age of 60.