Vision Problems

Astigmatism | Farsightedness | Nearsightedness | Presbyopia | Spots & Floaters


Astigmatism

If you experience a distortion or blurring of images at all distances -- nearby as well as far -- you may have astigmatism. Even if your vision is fairly sharp, headache, fatigue, squinting and eye discomfort or irritation may indicate a slight degree of astigmatism. A thorough eye examination, including tests of near vision, distant vision and vision clarity, can determine if astigmatism is present.

Astigmatism is not a disease nor does it mean that you have "bad eyes." It simply means that you have a variation or disturbance in the shape of your cornea.

Astigmatism is one of a group of eye conditions known as refractive errors. Refractive errors cause a disturbance in the way that light rays are focused within the eye. Astigmatism often occurs with nearsightedness and farsightedness, conditions also resulting from refractive errors.

What causes astigmatism?

Astigmatism usually occurs when the front surface of the eye, the cornea, has an irregular curvature. Normally the cornea is smooth and equally curved in all directions and light entering the cornea is focused equally on all planes, or in all directions. In astigmatism, the front surface of the cornea is curved more in one direction than in the other.

With the cornea's shape more like that of an American football or rugby ball than a basketball, the light hitting the more curved surface comes to a focus before that which enters the eye through the less curved surface. Thus, the light is focused clearly along one plane, but is blurred along the other so only part of anything being looked at can be in focus at any time.

This abnormality may result in vision that is much like looking into a distorted, wavy mirror. The distortion results because of an inability of the eye to focus light rays to a point.

Astigmatism

Why are corneas shaped differently?

Not all corneas are perfectly curved, just as sets of teeth are seldom perfectly aligned. The degree of variation determines whether or not you will need corrective eyewear. If the corneal surface has a high degree of variation in its curvature, light refraction may be impaired to the degree that corrective lenses are needed to help focus light rays better.

The exact reason for differences in corneal shape remains unknown, but the tendency to develop astigmatism is inherited. For that reason, some people are more prone to develop astigmatism than others.

How does astigmatism affect sight?

The clear cornea is situated at the very front surface of the eye and enables light to enter the eyeball. The cornea accomplishes about four-fifths of the refractive work needed for clear vision, bending light rays into a point. The crystalline lens, located behind the cornea, further refines the refractive work begun by the cornea and directs the point of light toward a precise location on the retina, known as the fovea. If light is not focused into a fine point on the fovea, the image that reaches the retina cannot be clearly transmitted to the brain and a blurred image is perceived.

When astigmatism is present, the surface of the cornea is distorted instead of spherical. It is unable to focus light rays entering the eye into the fine point needed for clear vision. At any time, only a small proportion of the rays are focused and the remainder are not, so that the image formed is always blurred. Usually, astigmatism causes blurred vision at all distances.

Who develops astigmatism?

Astigmatism is very common. Some experts believe that almost everyone has some degree of astigmatism, often from birth, which may remain the same throughout life.

Of interest to parents and those who work with children, astigmatism may contribute to poor schoolwork but is often not detected during routine eye screening in schools.

How is it diagnosed?

Astigmatism is diagnosed in the course of a thorough eye examination.

How is it treated?

If the degree of astigmatism is slight and no other problems of refraction, such as nearsightedness or farsightedness, are present, corrective lenses may not be needed. If the degree of astigmatism is great enough to cause eyestrain, headache, or distortion of vision, prescription lenses will be needed for clear and comfortable vision.

The corrective lenses needed when astigmatism is present are called "Toric" lenses and have an additional power element called a cylinder. They have greater light-bending power in one axis or direction than in the others. Precise tests will be made during your eye examination to determine the ideal lens prescription.

Astigmatism may increase slowly over time. Regular eye examinations can help to ensure that proper vision is maintained.

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Farsightedness

Farsightedness

If you can see objects at a distance clearly but have trouble focusing well on objects close up, you may be farsighted.

Farsightedness or long-sightedness is often referred to by its medical names, hypermetropia or hyperopia. Hyperopia causes the eyes to exert extra effort to see close up. After viewing near objects for an extended period, you may experience blurred vision, headaches and eyestrain. Children who are farsighted may find reading difficult.

Hyperopia is not a disease, nor does it mean that you have "bad eyes." It simply means that you have a variation in the shape of your eyeball. The degree of variation will determine whether or not you will need corrective lenses.

What causes farsightedness?

Hyperopia most commonly occurs because the eyeball is too short; that is, shorter from front to back than is normal. In some cases, hyperopia may be caused by the cornea having too little curvature. Exactly why eyeball shape varies is not known, but the tendency for farsightedness is inherited. Other factors may be involved too, but to a lesser degree than heredity.

How does farsightedness affect sight?

Our ability to "see" starts when light enters the eye through the cornea. The shape of the cornea, lens and eyeball help bend (refract) light rays in such a manner that light is focused into a point precisely on the retina.

If, as in farsightedness, the eyeball is too short, the "point of light" focuses on a location behind the retina, instead of on the correct area of the retina, known as the fovea. As a result, at the point on the retina where a fine point of light should be focused, there is a disk-shaped area of light. Since light is not focused when it hits the retina, vision is blurred. Convex lenses are prescribed to bend light rays more sharply and bring them to focus on the retina.

How is it diagnosed and treated?

Hyperopia is seldom diagnosed in school eye-screening tests, which typically test only the ability to see objects at a distance. A comprehensive eye examination that checks both near and far vision is necessary to diagnose farsightedness. In some cases it may be necessary for the practitioner to use drops during the examination to relax the eye muscles and ensure that the full degree of hyperopia is detected.

This is necessary because the muscles which focus the eye are so accustomed to being used to compensate for the hyperopia that the muscles go into "spasm" and cannot relax without being forced to do so.

Corrective convex lenses (positive powers) are usually prescribed. They bend light rays more sharply and bring them to focus on the retina. If you do not have other vision problems such as astigmatism, you may only need glasses for reading or other tasks performed at a close range.

To determine the best avenue of treatment, questions about your lifestyle, occupation, daily activities and general health status may be asked. For instance, you may be asked whether or not you frequently need near vision. Providing candid, considered answers to the questions will help assure that your corrective lenses contribute to clear sight and general comfort.

A comprehensive eye examination at the recommended intervals will ensure that minor changes in vision are diagnosed and treated so that your vision will remain as clear and comfortable as possible.

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Nearsightedness

Nearsightedness

If you can see objects nearby with no problem, but reading road signs or making out the writing on the board at school is more difficult, you may be near- or shortsighted.

This condition is known as myopia, a term that comes from a Greek word meaning "closed eyes." Myopia is not a disease, nor does it mean that you have "bad eyes." It simply refers to a variation in the shape of your eyeball. The degree of variation determines whether or not you will need corrective eyewear.

What causes nearsightedness?

Myopia most often occurs because the eyeball is too long, rather than the normal, more rounded shape. Another less frequent cause of myopia is that the cornea, the eye's clear outer window, is too curved. There is some evidence that nearsightedness may also be caused by too much close vision work.

How does myopia affect sight?

Our ability to "see" starts when light enters the eye through the cornea. The shape of the cornea, lens and eyeball help bend (refract) light rays in such a manner that light is focused into a point precisely on the retina. In contrast, if you are nearsighted, the light rays from a distant point are focused at a place in front of the retina. As the light will only be focused in that one place, by the time it reaches the retina it will have "defocused" again, forming a blurred image.

Myopia usually occurs between the ages of 8 to 12 years. Since the eyes continue to grow during childhood, nearsightedness almost always occurs before the age of 20. Often the degree of myopia increases as the body grows rapidly, then levels off in adulthood. During the years of rapid growth, frequent changes in prescription eyewear may be needed to maintain clear vision. It is important to bear in mind that the frequent changes in prescription are not making the eyes "weaker". During the growth period that occurs during the teen years the eye is also growing rapidly and hence the degree of blur is also increasing. As the growth cycle slows the prescription changes slow correspondingly.

How is myopia diagnosed and treated?

Myopia is often suspected when a teacher notices a child squinting to see a blackboard or a child performs poorly during a routine eye screening. Further examination will reveal the degree of the problem.

A comprehensive eye examination will detect myopia. Periodic examinations should follow after myopia has been discovered to determine whether the condition is changing, and whether a change in prescriptive eyewear is needed. Eye exams also help to ensure that vision impairments do not interfere with daily activities.

Corrective concave (minus) lenses are prescribed to help focus light more precisely on the retina, where a clear image will be formed.

Depending on the degree of myopia, glasses or contact lenses may be needed all of the time for clear vision. If the degree of impairment is slight, corrective lenses may be needed only for activities that require distance vision, such as driving, watching TV or in sports requiring fine vision.

Nearsightedness in children:

School age children may have vision problems ranging from mild to severe.

When problems are suspected, it is important that the child have a comprehensive eye health examination to determine the nature of the problem and to rule out serious eye diseases. When vision conditions are treated properly, the child will enjoy the best possible sight.

To help a child cope with nearsightedness:

  • Avoid referring to the child's eyes as "bad eyes;" instead tell the child that his or her eyes just bend light differently and corrective lenses are needed to help focus light rays.
  • Ensure that they understand that nearsightedness rarely disappears and that wearing spectacles may be necessary in the long-term, but that this is not a disease.
  • Use illustrations and simple explanations to help the child understand how a differently-shaped eyeball may result in his or her being nearsighted.
  • Make the occasion of selecting new frames for lenses a fun time.
  • Consider contact lenses as an option.
  • Do not restrict the child's activities because of poor vision.
  • Include the child in discussions about his or her eyesight. Encourage the child to verbalize concerns about the adjustment to rapidly changing vision.

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Presbyopia

As baby boomers reach middle age, the question looms large: How to avoid either of two telltale signs of aging -- bifocals or reading glasses?

Boomers have three contact lens options for correcting the close-up blurred vision that typically begins in middle age; a condition referred to as presbyopia. (One of the three options still calls for reading glasses, but they can be used discreetly.)

The three options are:

  • Bifocal contact lenses
  • Monovision
  • Contact lenses for distance vision with supplementary reading glasses slipped over the contacts for close work

Bifocal Contact Lenses

One of the two main categories of bifocal contact lenses may be suitable for you:

Simultaneous vision

With simultaneous vision bifocals, you look through both the reading and distance portions of the lenses all the time. This means that whenever you look at an object, you see two images of it. One will be clear (from the portion of the lens most matched to the distance at which you are observing). The other will be blurred (from the other portion of the lens). Your brain learns to ignore the blurred image so that you see the other clear image.

Presbyopia

Translating

Translating bifocals are similar in concept to bifocal eyeglass lenses. They have a thicker lower edge, which, when you look down to read, rests on the lower lid. As your eye turns downward to read, it looks through the reading portion in the lower part of the lens. In fact, even though they "translate," a portion of vision through this type of bifocal is of the simultaneous type.

If you wear bifocal contact lenses, they will normally perform optimally in bright conditions. Because bifocal lenses divide the light into two images, each of which will use about half of the available light, you may find that, in dimly lit conditions, seeing is more difficult with bifocal contacts. Driving at night may present more difficulty, for example.

Monovision

Monovision is an option in which one eye is fitted with a lens for seeing things at a distance and the other eye is fitted for seeing close-up. After a period of adjustment, the brain switches to the eye that is giving the clearest image at the time.

While many people successfully use monovision, others find adapting difficult. Mildly blurred vision, dizziness, headaches and a feeling of slight imbalance may last for a few minutes or for several weeks as you adapt. Generally, the longer these symptoms last, the more unlikely it is that you will adapt successfully.

Approximately two-thirds of patients eventually adapt to a monovision correction.

Adjusting to demanding conditions

If you are new to monovision you may benefit from avoiding visually demanding situations at first, and instead to wear their new lenses only in familiar situations. For example, it may be better to be a passenger, rather than a driver, in a car. In fact, you should only drive with monovision correction if you can pass your driver's license eye examination while wearing it.

Coping in special situations

Some people are uncomfortable in situations with low illumination, such as night driving. If that is your concern, ask us about prescribing an additional lens to correct both eyes for distance for those times when sharp distance vision is required.

An alternative is a pair of glasses with additional power in the reading eye so that the combined power of your contacts and the spectacles match your distance prescription.

If you require very sharp near vision, you might want to ask about an additional lens to correct both eyes for close-up work. Or, to occasionally have the clearest vision for critical tasks, you may want to request supplemental glasses to wear over your monovision correction, converting the distance eye to a reading prescription so that you can use both eyes at near distance.

Contacts for distance; Reading glasses for near vision

The final option for correcting presbyopia is this: Wear contact lenses for distance, then slip some reading glasses over them for close-up work.

Perhaps not the perfect answer, this option enables you to avoid the dreaded bifocal glasses. And that can still be a definite plus.

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Spots & Floaters

Do you occasionally see specks or threadlike strands drifting across your field of vision? Then, when you try to look at them, do they seem to dart away? If so, you're seeing what eye care practitioners call spots or floaters.

While almost everyone sees a few spots 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 spots, you should contact us right away so you can be sure they are not the result of a more serious problem.

What are spots or floaters?

Spots are small, semi-transparent or cloudy 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.

The inner part of your eye is made up of a clear, jelly-like fluid known as the vitreous. As time passes the jelly-like fluid gradually becomes more liquid in nature and cells and structural fibres detach and float around in this jelly, resulting in the floaters that we commonly observe.

When flashes of light occur causing spots to become noticeable, it can be a result of the jelly-like vitreous shrinking and pulling on the retina. This tugging action stimulates the retinal receptor cells to "fire," causing the perception of light flashes.

Can these spots cause blindness?

Most spots are normal and rarely cause blindness. But spots can indicate more serious problems. If you notice a change in the number and size of spots, a comprehensive eye examination is in order to determine the cause.

On rare occasions, vitreous detachment can cause small tears or holes in the retina. The damaged part of the retina subsequently does not work properly and a blind or blurred spot in vision results. If untreated, retinal tears or holes can continue to worsen and severe vision loss can result if the retina becomes detached.

How are spots diagnosed?

In a comprehensive eye examination, your eyes will be evaluated with special instruments that allow an examination of the health of the inside of your eyes and possible observation of the spots.

This is often done after special drops are put in your eyes to make the pupils larger (called dilation) to allow a larger view of the inside of your eyes. These procedures provide the relevant information to detect spots.

How are spots treated?

While flashes and floaters are normally not serious or treatable, they can be symptoms or signs of either vitreous or retinal detachment. In either of these cases, treatment with lasers and/or surgical intervention may be necessary to preserve your vision. If you notice a sudden increase or change in the number and type of spots and floaters, contact us immediately.

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