Being one of the most fascinating aspects of the human body, the human eye is a sense organ that allows vision to occur. The eye behaves in many ways like a camera – we ‘see’ when the lens of our eye starts to focus on an object, whereby the image is then transmitted to the light-sensitive membrane at the back of our eye known as the retina. We now know that neurological impulses are carried from the retina to various parts of the brain. The visual association cortex – which is a disproportionately large area of the brain – then pieces together what we ultimately perceive as a visual scene.

  • Understanding our eyes in historyarrow

    Ancient Greek studies had two main schools of thought about how the human eye ‘sees’. One of them described how rays would be emitted from our eyes, bouncing off objects and the movement of the rays would then allow us to see. Aristotle and his followers believed that something entered our eyes and presented us somehow with a representation of an object – therefore this idea was not so far from what we understand today.

    It was Leonardo da Vinci however who first began to grasp the wonderful optical nature of the human eye.

    Now, can you not see that the eye embraces the beauty of the whole world? He draws the cosmos, he advises all the human arts and corrects them, he moves humanity to the diverse parts of the world. This is the king of mathematics, whose knowledge is certain; he has measured the distance and size of the stars; he has found the proper place for the elements; he has predicted the future by means of the stars’ course; he has begotten architecture, perspective, and divine painting.” (Manuscript from the Vatican Library, MS Urb. Lat. 1270.)

    Leonardo was fascinated by eyes and this was represented in his sketches and paintings. He believed that the eyes were the gateway to the soul and even examined a skull at one point to see if he could fathom how the eyes could see.

    It was not until around the 17th century that the real mechanisms of the eye truly began to be understood. For example, at this point, it was deduced that the retina (the light-sensitive layer of tissue lining the inner surface of the eye) was responsible for transmitting nerve impulses to the brain via the optic nerve. Johannes Kepler from Germany and René Descartes from France were two well-known physicists of the time that made great strides in understanding how our eyes work.

    It was, in fact, Descartes, in an experiment involving an eye from an ox, who determined that an image was being inverted after being focused on to the retina by the lens of the eye. It was Thomas Young, however, at the beginning of the 19th century, who correctly described how the lens focuses images onto the retina. He also was able to demonstrate astigmatism where an improperly curved cornea cannot focus light correctly on to the retina.

  • Understanding our eyes todayarrow

    This leads us on to today’s understanding of our eyes. Light is reflected off objects and projected onto our retina by the lens. The retina then detects this light and sends impulses along the optic nerve to our brain where the end result is decoded into what we know as vision.

    Perfect vision (known as emmetropia) is achieved when the lens at the front of the eye projects light rays onto the back of the eye (the retina) in sharp focus, helping us to see images clearly. However, just as with a camera, if the lens is not adjusted properly these images can appear blurred. The extent of this blurring is known as refractive error, consisting of short sight, long sight, and astigmatism.

    Other conditions include presbyopia (a condition related to age, where the eye beings to lose its ability to focus on near objects) and of course cataracts.

How does the Eye Test chart work?

We often measure the standard of vision achieved with or without glasses using the familiar eye test (Snellen) chart, which is viewed from a distance of 6 metres (20 feet).

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What is short-sightedness?

Short-sightedness is a very common cause of reduced vision affecting 1 in 4 people in the UK where distant objects appear blurred and close objects are clearly visible.

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What is long-sightedness?

Long-sightedness is a common cause of reduced vision affecting 1 in 4 people in the UK. If you are long-sighted you will see objects in the distance clearly but your near vision will be blurred.

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What is astigmatism?

The term ‘astigmatism’ is a very common type of refractive error, but in general, only 1 in 4 people with moderate to high levels need treatment.

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What is Presbyopia?

Presbyopia (From the Greek for ‘old eyes’ – unfortunately!) is the age-related condition characterised by the need to wear reading glasses later in life, usually from mid-40s onwards.

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What is ‘perfect’ vision?

Many people refer to ‘perfect’ vision as ‘6/6’ or ‘20/20’ (US notation measured in feet), but this is not strictly true - these terms refer to ‘average’ vision. So what is 'perfect'?

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What is ‘Cataract’?

A cataract exists when the natural crystalline lens of the eye becomes cloudy or opaque over time, leading to blurring and a gradual loss of visual clarity. Fortunately, it is easily treated by surgery.

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"I'm seeing disco lights?”

It is very common for people to notice dark or semi-transparent dots or squiggly lines in their vision from time to time. So what are they?

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Are screens ruining my eyes?

With so many of us spending hours glued to a computer screen, tablet or smartphone each day, it’s not surprising that we get asked this question time and time again.

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Why are my eyes so scratchy and dry?

It is usually caused by ‘dry eye’ where the eye surface dries and becomes inflamed. It is a common condition affecting 1 in 4 people in the UK.

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Why do flowers make my eyes so miserable?

Hayfever is a common allergy that affects 1 in 5 people at some point in their lives. It is caused by a reaction to pollen, a fine powder released by trees, flowers, grasses and weeds.

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