Vision Related Information

20/20 Vision - What it means

The vision test is a simple and most important component in the eye exam.

In order to compare results, the vision test is always carried out at a standard distance of twenty feet.

Old-fashioned test rooms had to be more than twenty feet in length.

Mirrors are Now used to reflect the image so the test room no longer needs to be long; the image still looks as if it is twenty feet away. Standardised charts are used and eyecare professionals world wide use the same format.

But what do those numbers really mean?

Each line of the eye chart has notation in the form of a fraction that represents your visual acuity.

The numerator is in feet the distance the patient is from the eye test chart.

The denominator represents the distance an eye with normal vision can read the same line.

Understanding the numbers is quite simple,say you can read the 20/40 line, then you're only able to see at 20 feet what a normal eye could see at 40.

If your eyesight is 20/16? You're better than average. You can see from 20 feet an object that a normal eye sees at only 16 feet.

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Astigmatism

Means that the cornea is oval like a rugby ball instead of spherical like a tennis ball..

This causes light to focus on more than one point in the eye, resulting in blurred vision at distance or near.

The condition often occurs along with both nearsightedness or farsightedness.

The symptoms are blurred vision at all distances.

Astigmatism can be corrected with glasses, contact lenses, or surgically.

The most common surgeries used to correct astigmatism are astigmatic keratotomy (procedures that involve placing a microscopic incision on the eye) and LASIK.

These procedures have been developed so as to to reshape the cornea making it spherical or uniformly curved.

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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 and 11.

Until then, children readily adapt to visual problems by suppression or blocking out the image.

If caught early, the problem can be corrected and often the vision is preserved, however, after about the age of 11, it is difficult if not impossible to train the brain to use the eye normally.

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Cataracts

A cataract is a clouding of the eyes natural lens, the part of the eye responsible for focusing light and producing clearly defined, sharp images.

The lens is contained in a sealed bag or capsule as old cells die they become trapped within the capsule.

Over a period of time, the cells accumulate causing the lens to cloud, making images look blurred or hazy.

For most people, cataracts are the natural result of ageing.

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Convergence Insufficiency

This is a condition in which the muscles of the eye responsible for convergence (turning the eyes in) appear to be weaker relative to the muscles responsible for divergence (turning the eyes out).

However, the patient's eyes remain straight in all fields of gaze. This results in strained eyes and the affected patient often complains of headache, eyestrain, blurred vision, or fatigue with continued efforts at near work.

This condition most commonly occurs in teenagers and young adults, though it can occur up through middle age.

Reading glasses or bifocals with base-in prism may be prescribed.

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Longsightedness

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.

Young longsighted people 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 longsightedness often becomes more apparent.

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Shortsightedness or Myopia

Shortsightedness or myopia, occurs when light entering the eye focuses in front of the retina instead of directly on it.

This is caused by a cornea that is steeper, or an eye that is longer, than a normal eye.

Nearsighted people typically see well up close, but have difficulty seeing far away.

This problem is often discovered in school age children who report having trouble seeing the chalkboard.

Near-sightedness usually becomes progressively worse through adolescence and stabilizes in early adulthood and is an inherited problem.