Vision Conditions and Disorders

Amblyopia (Lazy Eye)
Diplopia (Double Vision)
Eye Co-ordination
Hyperopia (Farsightedness)
Myopia (Nearsightedness)
Strabismus (Turned Eye)
Vision Therapy
20/20 Vision


What is amblyopia or lazy eye?

Amblyopia is the lack of development of vision in one eye that is not directly caused by any eye health problem. It is not correctable with lenses alone.

Who is likely to develop amblyopia?

Amblyopia is the result of poor early development, and as such, occurs before the age of six. It is estimated that 2-4% of children under the age of six have amblyopia.

What causes amblyopia?

Amblyopia results from a large difference in the prescription between the two eyes or it can occur when strabismus (crossed eyes) is present. It can also occur when something is interfering with the clarity of the various components of the eye. This causes blurred vision in the affected eye. Because the image that is sent to the brain from the affected eye is poor, the brain will ignore this eye. As the brain ignores the eye over time, very few connections are made between the brain and the eye. It is this lack of connections between the brain and the eye that causes the eye to become amblyopic. This is why lenses alone cannot correct the problem.

Is the amblyopic eye blind?

The amblyopic eye is never blind in the sense of being entirely without sight. Amblyopia mostly affects the central vision. Peripheral vision is still almost normal.

What are signs / symptoms of amblyopia?

Most of the time, there are no symptoms of amblyopia. Since only one eye is affected, the other eye usually has reasonably good vision and tends to take over all visual tasks. Unless the good eye is covered, the person will rarely notice the poor vision in the amblyopic eye. Sometimes amblyopia is associated with strabismus (crossed eyes), which may be noted as a sign/symptom.

How is amblyopia diagnosed?

A comprehensive optometric examination can determine the presence of amblyopia. The earlier it is diagnosed, the greater the chance for a complete recovery. That is why it is important to have your child’s vision examined at six months of age, again at age 3 and then regularly thereafter.

How is amblyopia treated?

The most important part of amblyopia therapy involves covering the good eye so that the brain is forced to recognize the amblyopic eye. This will lead to the development of more connections between the brain and the amblyopic eye and improve vision. This is most commonly done by placing a patch in front of the good eye. Patching the stronger eye is necessary to stimulate and strengthen the amblyopic eye. If patching is not tolerated well or is unsuccessful, then prescription eye drops are sometimes used in the good eye as a way to blur its vision temporarily. Corrective lenses may also be necessary.

How will amblyopia affect a person’s lifestyle?

Amblyopia will not interfere with most daily activities. However, some occupations and recreational activities require good vision in both eyes. This may limit someone with amblyopia from these activities. In addition, should the good eye become injured or develop vision problems, a person may have difficulty performing normal activities or may not be able to hold a driver’s license.


What is astigmatism?

Astigmatism occurs when the front surface of your eye (cornea) or the lens inside the eye is slightly irregular in shape, resulting in vision being blurred at all distances. Astigmatism is not a disease, but is actually a vision condition that is quite common.

What causes astigmatism?

When the front of your eye or the lens inside the eye is more oval than round, light does not focus properly on the back of your eye (retina). Astigmatism is caused by small differences in the growth and alignment of the components of the eye. In some cases, it may be hereditary or it may result from such factors as pressure of the eyelids on the cornea.

How common is astigmatism?

Most people have some degree of astigmatism. However, only moderate to highly astigmatic eyes may need corrective lenses.

What are signs/symptoms of astigmatism?

People with severe astigmatism will usually have blurred or distorted vision. Those with mild astigmatism may experience headaches, eyestrain, fatigue or blurred vision at certain distances.

How is astigmatism diagnosed?

A comprehensive eye examination by your Doctor of Optometry will include tests for astigmatism.

Can astigmatism by corrected?

Almost all levels of astigmatism can be optically corrected with properly prescribed and fitted eyeglasses or contact lenses. Laser surgery may be an option for appropriate cases.

Does astigmatism get progressively worse?

Astigmatism may change with time. Regular optometric care can, however, help to insure that proper vision is maintained.

How will astigmatism affect my lifestyle?

You may have to adjust to wearing eyeglasses or contact lenses if you do not wear them now. Other than that, astigmatism probably will not significantly affect your lifestyle at all.

DIPLOPIA (Double Vision)

If you see two of whatever you are looking at, you may have a condition known as double vision, also referred to as diplopia. Double and blurred vision are often thought to be the same, but they are not. In blurred vision, a single image appears unclear. In double vision, two images are seen at the same time, creating understandable confusion for anyone who has it.

What causes double vision?

There are two possible causes.

  • Failure of both eyes to point at the object being viewed, a condition referred to as “strabismus” or “squint”. In normal vision, both eyes look at the same object. The images seen by the two eyes are fused into a single picture by the brain. If the eyes do not point at the same object, the image seen by each eye is different and cannot be fused. The result is double vision. Why might eyes not point in the same direction? Possibly because of a defect in the muscles which control the movement of the eyes or in the control of these muscles through the nerves and brain.
  • Refractive. Light from an object is split into two images by a defect in the eye’s optical system. Cataracts may cause such a defect. Strabismus is a more common cause of double vision than is refractive defect.

What are its implications?

Double vision can be extremely troubling. The brain acts to alleviate the discomfort by suppressing, or blanking out, one of the images. In young children, if this suppression persists over a continued length of time, it can lead to an impairment of the development of the visual system. The suppressed eye may get to the point where it is unable to see well, no matter how good the spectacle or contact lens correction. Doctors call this condition “amblyopia”. Since it is a result of a defect in the interpretive mechanisms of the eye and brain, it is more difficult to treat than a refractive condition (one having to do with the eye’s ability to bend light).

How is it treated?

Treatment of double vision consists of eye exercises, surgical straightening of the eye or a combination of the two. Therapy is aimed at re-aligning the squinting eye where possible without surgery and re-stimulating the part of the visual pathway to the brain that is not working correctly. If the double vision is due to the presence of cataracts, referral for possible cataract surgery will be undertaken.


What is eye coordination?

Eye coordination is the ability of both eyes to work together as a team. Each of your eyes sees an ever so slightly different image and your brain, by a process called fusion, blends these two images into one three-dimensional picture. Good eye coordination keeps the eyes in proper alignment. A minor misalignment of your eyes can cause symptoms.

What causes poor eye coordination?

Eye coordination is a skill that must be developed. Poor eye coordination results from a lack of adequate vision development or improperly developed eye muscle control. Although rare, an injury, disease, tumor or other trauma can cause poor eye coordination.

How does poor eye coordination affect vision?

Since the images seen by each eye must be virtually the same, a person usually compensates for poor eye muscle control by subconsciously exerting extra effort on the muscles to maintain proper alignment of the eyes. In more severe cases, the muscle cannot adjust the eyes so that the same image is seen and double vision occurs. Since the brain will try to avoid seeing double, it eventually learns to ignore the image sent by one eye. This can result in amblyopia, a serious vision condition commonly known as lazy eye.

What are signs/symptoms of poor eye coordination?

Some signs / symptoms that may indicate poor eye coordination include double vision, headaches, eye and body fatigue, irritability, dizziness and difficulty in reading and concentrating. Children may also display characteristics that may indicate poor eye coordination including covering one eye, head tilting, skipping lines or losing their place while reading, poor sports performance, avoiding tasks that require close work and tiring easily.

How is poor eye coordination diagnosed?

Since poor eye coordination can be difficult to detect, periodic optometric examinations beginning at age 3 are recommended. A comprehensive examination by a Doctor of Optometry will determine the extent, if any, of poor eye coordination.

How is poor eye coordination treated?

Poor eye coordination is often successfully treated through vision therapy, contact lenses and/or other optical aids. If detected early enough, the success rate for achieving proper eye coordination is quite high. In some cases, eye coordination will improve when other vision conditions like nearsightedness or farsightedness are corrected. In some cases, surgery may be necessary.


What are floaters and spots?

Floaters (often called spots) are small, semi-transparent specks or particles within the eye that become noticeable when they fall within the line of sight. They may also appear with flashes of light.

Does everyone have floaters?

Almost everyone sees a few floaters at one time or another. They can occur more frequently and become more noticeable as you grow older. If you notice a sudden change in the number or size of floaters, you should contact your Doctor of Optometry right away, so you can be sure they are not the result of a more serious problem.

What causes floaters?

The inner part of your eye is made up of a clear, jelly-like fluid known as the vitreous. Occasionally, small flecks of protein and other matter become trapped in the vitreous during the formation of the eye before birth and remain in the vitreous body. Floaters and spots may also be caused by the deterioration of the eye fluid or its surrounding parts, or by certain injuries or eye diseases.

What do floaters look like?

Floaters are generally translucent specks of various shapes and sizes. They may also appear as bugs, threadlike strands or cobwebs within the eye. Since they are within the eye, they move as the eye moves and seem to dart away when you try to look at them directly.

Can these floaters cause blindness?

Most floaters are normal and rarely cause blindness. But, floaters can be indications of more serious problems, such as a retinal hole, tear or detachment, and if you see them you should have a comprehensive optometric examination to determine the cause.

How are floaters detected?

As part of a comprehensive eye examination, your Doctor of Optometry will thoroughly evaluate the vitreous and retina of your eyes. Your optometrist uses these instruments to examine the health of the inside of your eyes and may also observe the floaters within your eye. This is often done after the doctor puts special drops in your eyes to make the pupils larger (called dilation) to allow a fuller view of the inside of your eyes.

HYPEROPIA (Farsightedness)

What is farsightedness?

Farsightedness, or hyperopia, as it is medically termed, is a vision condition in which distant objects are usually seen clearly. But close ones are not brought into proper focus.

Why does farsightedness occur?

If the length of your eyeball is too short or the cornea has too little curvature, near objects cannot be brought into a sharp and clearly focused image. Instead of focusing on the retina, light is focused behind the retina. Some theorists believe that farsightedness is hereditary and others believe that it may result from environmental factors.

How does farsightedness affect vision?

If you are farsighted, you involuntarily exert extra effort to maintain clear distance vision and even greater effort to see clearly at close range. This extra effort can cause fatigue, tension and discomfort. If the crystalline lens of the eye cannot bring the object into focus, blurred vision occurs.

How common is farsightedness?

Many people have some degree of farsightedness. The condition is only a problem if it significantly affects a person’s ability to see. It is estimated that over half the people who wear glasses are wearing them because of a focusing problem due to farsightedness or presbyopia, a natural decrease in focusing ability.

What are the signs / symptoms of farsightedness?

Common signs / symptoms of farsightedness include difficulty in concentrating and maintaining a clear focus on near objects, blurred vision, eye strain, fatigue and / or headaches after close work, aching or burning eyes, poor reading ability and general tension.

How is farsightedness detected?

Farsightedness can be effectively diagnosed during a comprehensive optometric examination with your Doctor of Optometry. Common vision screenings, often done in schools, are generally ineffective in detecting farsighted people. This is because these individuals can identify the letters on an eye chart with little difficulty.

How is farsightedness treated?

In mild cases, your eyes may be able to compensate adequately without the need for corrective lenses. In more severe cases, your optometrist may recommend glasses or contact lenses. For appropriate candidates, laser surgery can be considered.

How will farsightedness affect my lifestyle?

If glasses or contact lenses are prescribed, it may take a few days to adjust to them. After that, farsightedness will probably not significantly affect your lifestyle.

MYOPIA (Nearsightedness)

What is nearsightedness?

Nearsightedness, or myopia, as it is medically termed, is a vision condition in which near objects are seen clearly, but distant objects do not come into proper focus.

Why does nearsightedness occur?

When your eyeball is too long or the cornea has too much curvature, light entering the eye is not focused properly. Instead of focusing on the retina, light comes to focus in front of the retina. Some evidence supports the theory that nearsightedness is hereditary. There is some evidence that nearsightedness may also be caused by the stress of too much close vision work.

How common is nearsightedness?

Nearsightedness is a very common vision condition that affects nearly 30 percent of the Canadian population. It normally occurs in school age children. Since the eyes continue to grow during childhood, nearsightedness usually occurs before the individual reaches the age of 20.

Will I have to wear glasses?

You may need glasses part-time or full-time to enable you to see more clearly. If your condition warrants, your Doctor of Optometry will prescribe corrective lenses for you. You may only need them for certain activities, like watching television, going to a movie or driving a car.

Will glasses/contact lenses cure nearsightedness?

Eyeglasses or contact lenses optically correct the problem by altering the way the light images enter your eyes, but they do not cure nearsightedness. At present there are no proven cures for nearsightedness. Surgical procedures such as LASIK and / or ocular implants may eliminate your need for glasses.

How is nearsightedness diagnosed?

Nearsighted people will often have trouble seeing the chalkboard, the movie screen, the television set or other distant objects. When your optometrist gives you a comprehensive eye examination, it will include a test for nearsightedness.

How will nearsightedness affect my lifestyle?

If glasses or contact lenses are prescribed, it may take up to 2 weeks to adjust to seeing clearly with them. Some nearsighted people may find that they are restricted from some occupations e.g. police officer or fire fighter, due to their nearsightedness. In these cases, laser surgery may be useful for some people. Contact lenses are very helpful for correcting nearsightedness and are ideal for people with more active lifestyles.


What is presbyopia?

Presbyopia is a vision condition in which the crystalline lens of your eye loses its flexibility. This results in difficulty in focusing on close objects.

What causes presbyopia?

The lens in your eye continues to grow and produces more and more cells. Eventually the lens loses most of its elasticity and therefore, loses most of its focusing ability.

At what age does presbyopia occur?

It varies from person to person. Although presbyopia may seem to develop suddenly, the actual decline takes place over the course of many years. Presbyopia usually becomes apparent to people in their early to mid-forties.

What are signs/symptoms of presbyopia?

Some signs/symptoms of presbyopia include the tendency to hold reading materials at arms length, blurred vision at normal reading distance and eye fatigue along with headaches when attempting to do close work.

Can presbyopia be prevented?

Unfortunately not. Presbyopia is a natural part of the aging process.

How is presbyopia diagnosed?

A comprehensive eye examination by a Doctor of Optometry will include testing the quality of your near vision. This will determine the extent, if any, of presbyopia.

How is presbyopia treated?

To compensate for presbyopia, Doctors of Optometry prescribe reading glasses, bifocals, trifocals or contact lenses. Since presbyopia can complicate other common vision conditions like nearsightedness, farsightedness and astigmatism, your optometrist will perform other tests to determine the specific lenses that will allow you to see clearly. Laser surgery can be used to provide “monovision” for patients. By doing this, one eye is corrected for distance vision and one eye is corrected for near vision. This can also be done with contact lenses. Monovision does not work well for all people. People who require good distance visual acuity with both eyes, such as pilots or police officers, may not be suitable candidates for monovision. Your optometrist can discuss monovision with you to help determine if this is the right option for you.

Will I have to wear glasses all the time?

This will depend on a number of factors, including any other vision conditions you have. You may only need your glasses for reading, sewing or other close work. However, you may find that wearing your glasses all the time is more beneficial and convenient for your vision needs.

Can I still wear contact lenses?

You will likely be able to wear contact lenses part time or full time, depending upon your prescription and your daily visual needs. Your Doctor of Optometry will tell you about your options and help you decide what is best for you.

Why are frequent lens changes necessary after 40?

The effects of presbyopia constantly change the ability of the crystalline lens to focus properly. As a result, approximately every 2-3 years, changes in your eyewear are necessary to maintain correct vision between ages 40-60.

STRABISMUS (Turned Eyes)

What is strabismus?

Strabismus, more commonly known as crossed-eyes, is a vision condition in which your eyes are not properly aligned with each other. For a variety of reasons, one or both of your eyes turn in, out, up or down.

What causes strabismus?

Coordination of your eyes and their ability to work together as a team develops in your first six years. Failure of your eyes (or more precisely, your eye muscles) to adjust properly can lead to crossed-eyes. Strabismus may also have a tendency to be hereditary.

Who is affected by strabismus?

Children under 6 are the ones most affected by crossed-eyes, but this often first appears between birth and age 21 months. It is estimated that five percent of all children have some type or degree of strabismus. Although rare, strabismus sometimes begins in adulthood, but this is usually the result of a stroke, tumor or other vascular disease.

Will a child outgrow strabismus?

This is a common misconception. A child will not outgrow crossed-eyes. In fact, the condition may get worse without treatment.

What are the effects of strabismus?

Children with strabismus may initially have double vision. This occurs because both eyes are not focusing on the same object. In an attempt to avoid double vision, the brain will eventually disregard the image from one eye. In time, the ignored eye will become unable to function normally and will become largely unused. This may result in the development of lazy eye (amblyopia).

How is strabismus diagnosed?

Parents may be the first to notice a slight wandering of one or both of a child’s eyes. A comprehensive vision examination by a Doctor of Optometry is recommended by the age of three, as parents often will not notice it. The examination can determine if strabismus is present.

How is strabismus treated?

Treatment for strabismus can include eyeglasses (regular or bifocal), prisms, vision therapy, and in some cases, surgery. Strabismus can be corrected with excellent results if detected and treated early.


What is a vision therapy?

Vision therapy is an individualized treatment program prescribed to improve conditions like crossed-eyes (strabismus) or lazy eye (amblyopia) and to help you learn, relearn or reinforce specific vision skills. Such skills include eye movement control, focusing control, eye coordination and teamwork of the two eyes.

How does vision therapy work?

Like many of our skills, visual skills are developed. Since they are developed, they can generally be improved via proper therapy. In vision therapy, the optometrist prescribes individually appropriate visual tasks / exercises to be practised regularly. Repetition of these tasks enhances vision by coordinating, strengthening and improving eye movement, focusing ability and by straightening the eye alignment.

How successful is vision therapy?

Vision therapy has proven to be an effective treatment for many problems that cannot be treated with eyeglasses or contact lenses alone. It can help people see more clearly, efficiently and comfortably. Success, however, is not guaranteed. Much of the improvement depends on the patient’s willingness to follow the optometrist’s instructions. For patients who do so, significant progress toward more efficient and comfortable vision usually results.

What are some vision therapy procedures?

In addition to the use of lenses, prisms and filters, there are many different procedures that can be used in vision therapy. Some, using stereo-viewers or video games, may seem like child’s play. More sophisticated equipment and instrument are also used to increase the eye’s ability to see and the brain’s ability to understand the visual information.

How long does vision therapy take?

The length of time required for completion of vision therapy program, including the number of visits per week, the length of each visit and the amount of out-of-office therapy, varies. This is dependent upon the type of vision problem(s), how long the condition has existed, the motivation of the patient and the level of improvement desired. A typical program may take from a few weeks to several months.

How will vision therapy affect my lifestyle?

Depending upon your vision condition, therapy can have a profound effect on your lifestyle. By undergoing vision therapy, you may find yourself looking at life in a whole new way. Your Doctor of Optometry can provide you with more specific information about how vision therapy can help improve your vision.

20/20 VISION

What does 20/20 vision mean?

20/20 vision is a term used to express normal visual acuity (the clarity or sharpness of vision) measured at a distance of 20 feet. If you have 20/20 vision, you can see clearly at 20 feet what should normally be seen at that distance. If you have 20/100 vision, it means that you must be as close as 20 feet to see what a person with normal vision can see at 100 feet.

Does 20/20 mean perfect vision?

No. 20/20 vision only indicates the sharpness or clarity of vision at a distance. There are other important vision skills, among them peripheral awareness or side vision, eye coordination, depth perception, focusing ability and color vision that contribute to your overall vision ability.

Is 15/15 vision better than 20/20?

No. 15/15 means normal sharpness of vision at 15 feet just as 20/20 indicates normal acuity at 20 feet. Most optometrists in Canada use 20 feet as the standard to express sharpness of vision.

Why do some people have less than 20/20 vision?

Visual acuity is affected by many factors. Less than optimum clarity may result from vision conditions like nearsightedness, farsightedness, or astigmatism, or from eye diseases.

Will clarity of vision vary with distance?

Some people can see well at a distance, but are unable to bring nearer objects into focus. This condition can be caused by farsightedness or presbyopia (a loss of focusing ability). Others can see items that are close, but cannot see those far away. This condition may be caused by nearsightedness.

If my vision is less than optimum, what can I do?

A comprehensive eye examination by a Doctor of Optometry should identify those causes, if any, that are affecting your ability to see well. In most cases, your optometrist can prescribe glasses, contact lenses or a vision therapy program that will help improve your vision. If the reduced vision is due to an eye disease, the use of ocular medication or other treatment may be needed.


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