What Are Optical Illusions?


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.


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.


To demonstrate, I particularly like this quote from on

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.


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.com

The Braille Alphabet

Louis Simon Braille (1809 – 1852) was born in Coupvray, France, the fourth child and only son of Simon-René Braille, a saddle and horse tack maker, and his wife Monique.


When Braille was three years old, he injured one of his eyes while playing with his father’s leather making tools. This resulted in both his eyes becoming infected, and by the time Braille was five, he was completely blind. Although there were few options for blind children his parents wanted Braille to be educated, first at the local village school then via a scholarship to attend the National Institute for Blind Youth in Paris.

This was the first school of its kind to educate blind students using a combination of oral instruction and raised-print books developed by the school’s founder. Braille did well at his studies and became an accomplished musician. And the crude raised-print books gave Braille the idea that a tactile alphabet would allow blind people to read and write.

In 1821, a retired soldier named Charles Barbier visited the school to share his invention called sonography. This was a complicated code used by soldiers to write and decode messages at night, using a system of twelve raised dots, without having to use a light. The army decided the system was too complicated, however Barbier thought the system might assist blind people.

Braille and some of the other students recognised the possibilities of sonography and over the next three years Braille worked to develop a much simpler system using six dots lined up in two columns of three dots each.


Braille became an apprentice teacher at the school when he was 19 and in 1837 the school published the first book in braille. However, the school did not adopt the system. Nonetheless, by 1850, when tuberculosis forced Louis Braille to retire from teaching, his six-dot method was on its way to widespread acceptance.

Louis Braille died of his illness on January 6, 1852, in Paris, at the age of 43. Today, in most languages, braille is the standard form of communication used by blind people.

“Access to communication in the widest sense is access to knowledge, and that is vitally important for us if we are not to go on being despised or patronised by condescending sighted people. We do not need pity, nor do we need to be reminded that we are vulnerable. We must be treated as equals – and communication is the way we can bring this about.” Louis Braille 1841.

See the EZiD braille label here.

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.


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.


Images courtesy Wikipedia

by John Owens –   –

A Short History of Contact Lenses


Some believe that the sketches made by the artist and scientist Leonardo da Vinci about 1508 were intended to indicate contact lenses. He experimented by dissecting eyes and developing his own theories about eyes and how they work. His ideas were at odds with his peers when he correctly concluded that vision is a result of the eye receiving rays of light.  


Drawing by Leonardo da Vinci

In 1636 Frenchman René Descartes (1596 – 1650) arrived at the innovative idea of corneal lenses by placing a tube full of water over the cornea to correct a person’s vision. His idea was that this would theoretically lengthen the eye’s axis and therefore increase the size of the image. The practical problem with this idea was that the tube would have been too thick to allow blinking.


Drawing by René Descartes

The first contact lenses to have been worn were invented by the German Ophthalmologist Adolf Gaston Eugen Fick (1852 – 1937) around 1888. Fick was one of the first to actually experiment with contact lenses. They were made from heavy brown glass and he tested them on rabbits first, then himself and a group of volunteers. Fick’s lens was large, unwieldy, and could only be worn for a couple of hours at a time.

The others experimenting with contact lenses at the same time were German glassblower F.A. Muller, an optician from Paris called Edouard Kalt, and August Müller (1864 – 1949), a medical student from Germany who corrected his own severe myopia with a more convenient glass-blown scleral contact lens of his own manufacture in 1888. However his lenses were difficult to fit, painful to wear, and the eye had to be anaesthetised before fitting the lens.

The lenses developed by these men were called Glass Scleral lenses as they were designed to cover the entire corneal surface and rest on the white, or sclera, of the eye. They were the standard form of contact lens until the invention of Perspex and Plexiglass in the 1930s. These plastics made it possible to produce lightweight, transparent contact lenses that were easy to manufacture, unbreakable and scratch resistant which quickly made glass contact lenses obsolete. However they were still scleral lenses covering the entire eye and could only be worn for a few hours per day.

The first “corneal” lenses were developed in 1948 by an English optical technician called Kevin Touhy. Apparently in the process of sanding down a plastic lens the lens broke leaving only the portion that covered the cornea intact. So he sanded off the sharp edges and fitted the lens to his own eye. He discovered that the lens still worked and stayed in place even if he blinked. His ‘invention’ was the forerunner of the lens technologies that exist today.


by John Owens –

What is Glaucoma?


Glaucoma is a complicated disease in which the optic nerve at the back of the eye is damaged which leads to progressive, irreversible vision loss. Glaucoma is one of the leading causes of blindness.

There are two main types of glaucoma: primary open angle glaucoma and acute angle closure glaucoma.

The most common form is primary open angle glaucoma. This is often associated with an increase in eye pressure. Eye pressure refers to the tissue pressure within the human eye and is typically caused by the continual drainage and production of aqueous humour.


The aqueous humour is the watery fluid between the cornea and the lens. It maintains the pressure needed to inflate the eye and provides nutrition for the central cornea and lens as they do not have their own blood supply. It circulates from behind the iris into drainage channels between the iris and the cornea. If it cannot drain away correctly, then there can be a fluid build-up leading to a rise in eye pressure and ultimately damage to the optic nerve.

Eye pressure is usually shown as millimetres of mercury (mm Hg). The standard eye pressure should measure less than 21 mm Hg. Ocular hypertension occurs when the eye pressure increases. Vision damage occurs very slowly and the first signs may be the loss of some parts of the visual field, most commonly the peripheral, or side vision.

Acute angle closure glaucoma occurs when the drainage system becomes completely blocked and the fluid pressure rises quickly as more fluid continues to be made. The usual symptoms are sudden and severe eye pain, a red eye and blurred, haloed or decreased vision. The sufferer may feel sick and vomit and it can rapidly lead to blindness in the affected eye if not treated promptly.

Glaucoma can affect young children also; it is called congenital, paediatric or infantile glaucoma. It is usually diagnosed within the first year of life. Symptoms include enlarged eyes, cloudiness of the cornea and sensitivity to light.

Glaucoma can be treated with eye drops, pills, laser surgery, traditional surgery or a combination of these methods. All are intended to decrease eye pressure and, thereby, protect the optic nerve. The goal of any treatment is to prevent loss of vision, as vision loss from glaucoma is irreversible. The good news is that glaucoma can be managed if detected early, and with medical and/or surgical treatment, most people with glaucoma will not lose their sight.


John Owens –

Who are the real Three Blind Mice? – part 2



EZiD’s version of the Three Blind Mice

The rhyme as we know it was published in 1842 by James Orchard Halliwell. Some years later (maybe around 1900) an illustrated children’s book by John W. Ivimey with the title The Complete Version of Ye Three Blind Mice was also published, here is the link to the book. And the famous words are:

Three blind mice. Three blind mice.
See how they run. See how they run.
They all ran after the farmer’s wife,
Who cut off their tails with a carving knife,
Did you ever see such a sight in your life,
As three blind mice?

This version turns the mice into mischievous characters who seek adventure, eventually being taken in by a farmer whose wife chases them from the house and into a bramble bush, which blinds them. Soon after, their tails are removed by the farmers’ wife using a modern translation of lines from the original verse. The story ends with them using a tonic to grow new tails and recover their eyesight, learning a trade (making wood chips, according to one illustration in Ivimey’s book), buying a house and living happily ever after.

While the words to the rhyme have not been changed since Halliwell’s book was published, the tune has been used and adapted by a number of composers. Even James Bond has had an impact on the rhyme as the soundtrack for the 1962 film Dr. No features “Kingston Calypso”, a calypso version of “Three Blind Mice” with new lyrics that reference the three villainous characters in the film. And the Three Stooges used a jazz interpretation of Three Blind Mice as the theme song for their comedic short films.
The rhyme has even found its way into sport. Basketball and hockey have three referees and the term “Three Blind Mice” is sometimes used as a derogatory expression for their poor performance.


John Owens –

A Short History of Bifocals and Multifocals


Multifocal eyeglass lenses contain two or more lens powers to help you see objects at all distances if you lose the ability to naturally change the focus of your eyes due to age. This condition is called Presbyopia and it is caused by the hardening of the lens of the eye. This causes the eye, when looking at close objects, to focus light behind the retina instead of on the retina.


Presbyopia occurs from age 40 and everyone is affected to some degree. Many people complain their arms have ‘become too short’ because they cannot hold reading material in a comfortable position. Other symptoms include eyestrain, blurred vision when looking at one object up close then another object further away, and difficulty reading small print.

Bifocal and multifocal lenses provide clear vision at all distances. Bifocals have two prescriptions in the same lens and multifocal have a range of powers; distance, intermediate and near vision. Your pupil alternates between the powers as your gaze moves up or down. The top part of the lens is for distance vision and the bottom part for near vision.


The invention of bifocals has long been credited to Benjamin Franklin (1705 – 1790) the American politician, statesman and diplomat. He was also an inventor so this may be true or it could be a myth. He was certainly one of the first to wear bifocals. Franklin was involved in the optical business before he left America. He imported spectacles and records of his advertisements in newspapers still exist. From the mid 1750s to the mid 1770s he spent much of his time in London and it was during this time that he was first said to have invented bifocals.

It is likely that London opticians were making ‘split lenses’ also known as ‘divided lenses’ for artists including Benjamin West (1738 – 1820) and Sir Joshua Reynolds (1723 – 1792). Both these men were in London at the same time as Benjamin Franklin and both of them have also been named as the inventor of bifocals.

There is also one recorded example of bifocal use in the animal world, Thermonectus marmoratus. This is a species of diving beetle also known as the sunburst diving beetle and the spotted diving beetle. These beetles live in ponds and lakes in Southern California, Arizona, New Mexico, Texas and Mexico. If their water source dries up they fly to a new one. Adult male beetles are about ½” or 1cm in length and females are slightly bigger. They are unique because they have, within their principal eyes, two retinas and two separate focal planes so they can switch their vision from close to distance when they are searching for food.


Thermonectus marmoratus – the Diving Beetle

John Owens