optometrist

What Are Optical Illusions?

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An optical illusion is something that deceives the eye by appearing to be other than it is. They use patterns, colour and light to create the deception.

We have five main senses – sight, hearing, taste, touch and smell – however most information we receive from the world around us comes via our eyes. This might make sight the most important of all the senses, although let us not underestimate our ability hear a cow moo, touch a feather, smell a beautiful rose or taste an hot apple pie.

Vision depends on our eyes to see and on our brain to convert what we see into images.

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When we look at an optical illusion we may think are we seeing things? Are our eyes deceiving us?

An illusion is proof that we don’t always see what we think we do because of the way our brain interprets the image, we are looking at something that confuses our brain.

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To demonstrate, I particularly like this quote from on http://www.archimedes-lab.org:

Unfortunately (or fortunately?), seeing isn’t some kind of direct perception of reality. Atcually, our bairns are cnostanlty itnerperting, corrceting and gviing srtuctrues to the viusal ipnut form our eeys.

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A mirage and a rainbow are not illusions, they are known as optical phenomena. They are events you can see as a result of light from the sun or moon interacting with the atmosphere, clouds, water and dust.

by John Owens – http://www.john@ezidlabels.comhttp://www.ezidlabels.com

What is low vision?

I have read two definitions:

  • “Low vision is the term used to refer to a visual impairment that is not correctable through surgery, pharmaceuticals, glasses or contact lenses. It is often characterised by partial sight, such as blurred vision, blind spots or tunnel vision. Low vision can impact people of all ages, but is primarily associated with older adults.”and,
  • “Low vision is ‘not enough vision to do whatever it is you need to do’, which can vary from person to person”.

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Your vision can deteriorate with age; however, vision loss does not have to be an accepted part of growing old. A yearly eye examination by an optometrist or vision specialist can identify potential vision problems before they occur. In my case a simple trip to the optometrist to organise a new pair of reading glasses revealed the fact I have Age Related Macular Degeneration. I still needed the new reading glasses, and I was given a referral to an eye specialist who is now treating my macular disease.

Because of this early diagnosis the specialist has told me “I will have very useful vision for a long time”. I am now 63 and a bit so ‘a long time’ sounds like very good news to me.
Some of the more common causes of low vision include:

Age Related Macular Degeneration (AMD): AMD is the leading cause of vision loss, for example in the USA it accounts for nearly 50% of all low vision cases. It is caused when the macular breaks down which can cause the loss of central vision, please see this link for more information about AMD.

Glaucoma: is the second major cause of low vision and it can occur without warning. For more info about glaucoma please use this link.

Diabetic Retinopathy: Diabetic retinopathy affects blood vessels in the retina at the back of the eye. It is a major cause of blindness and it is the most common cause of vision loss among people with diabetes.

Cataracts: Most of the eye’s lens is made of water and protein, and the protein is arranged in an exact way to keep the lens clear. As we grow older some of the protein may clump together creating a cataract. Over time, it may grow larger and cloud more of the lens, making it harder to see.

Vision is also an important factor in maintaining balance. Since 2011 In the USA the rate of life-threatening injuries after a fall since has nearly doubled when compared to the previous decade.

It is a shock when you discover your vision loss cannot be reversed, however please remember it can be treated. So, organise the professional help that will provide you with the strategies and treatments to keep you active and safe. Also, why not have a look at the low vision aids we have created to assist in some of your most common daily activities, you will find everything you need here: www.ezidlabels.com.

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by John Owens – john@ezidlabels.comwww.ezidlabels.com

 

Who Created The Eye Test Chart?

The eye test chart was designed by Herman Snellen (1834 – 1908) in 1862. Herman was a Dutch ophthalmologist and he developed the chart as an aid to measure an individual’s vision.

Snellen earned his medical degree at Utrecht University in the Netherlands in 1858. He specialised in ophthalmology after completing his degree and in 1877 was appointed a professor of ophthalmology at the University. His research was based on causes of low vision including glaucoma and astigmatism (a fault in the shape of the eye’s lens).

Other versions of eye test charts had been developed previously however these charts were never standardised. They used fonts of different sizes and shapes and did not necessarily provide an accurate assessment of a person’s real vision.

The British Army placed a large order for the Snellen chart in 1863, and from there it quickly became the global standard for almost 100 years. It is also the standard on which all more recent eye test chart systems are based.

Snellens’ innovation was to use specially designed characters, known as optotypes, instead of an existing, standard font. The Snellen optotype was based on a 5 x 5 grid and this grid was used to create a limited character set of 9 – 10 letters. The lines were a standard thickness and letters were all the same shape.

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This allowed the chart to be reproduced easily and provide accurate results wherever it was used.

The Snellen chart normally includes eleven lines of block letters. The first line comprises a single large letter, usually the letter E. Each of the following lines have increasing numbers of letters, each progressively smaller in size.

The Snellen eye test determines the visual acuity (clarity of vision) of an individual based on which is the smallest row of letters they can read.

With the traditional Snellen eye chart, the individual who can read the row of letters fourth from the bottom of the chart at 20 feet has 20/20 vision. The next three lines provide a measurement of 20/15, 20/10 and 20/5 vision. Not many individuals have 20/10 or better however many animals do, especially birds of prey, which may have an acuity of 20/5 or even better.

Testing with the Snellen eye chart helps reveal visual problems and symptoms of other medical conditions. However it is only one component of a complete eye examination.

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Images courtesy Wikipedia

by John Owens – john@ezidlabels.com   – www.ezidlabels.com