Over 75% of Australians need prescription glasses to focus their eyes. But what is it about prescription glasses and the lens that can somehow correct their blurred vision? How do prescription glasses use refraction of light to their wearer’s advantage? To understand this, we have to go into their history and the science of light refraction.
What is light refraction?
Light Refraction refers to how light bends when entering a medium where it’s speed is different. These light rays change direction when reflected off of a surface, travel through a medium which composition is changing or moves from one transparent medium to another. This can be easily observed when putting a pencil into a glass cup of water, and observing from the outside. The pencil appears to enter at one direction and is displayed in a different view from where it was put it. This is the work of light refraction.
How do our eyes see?
In order for our eyes to see, light must be shown unto the pupil and the cornea (the curved outer surface of the eye). These both curve and shrink received images to be focused onto the retina (in the back of the eye). The images that the retina receives, is what the brain sees. Perfect vision occurs when the pupil and cornea perfectly adjusts any incoming light to focus clearly on the back of the retina. However, if the incoming light is not properly adjusted and is focused onto the front of the retina, your ability to see distance will be faltered, causing what is known as being nearsighted. Likewise, if the incoming light is not properly adjusted, and is focused behind the retina, that is known as being farsighted.
Creation of prescription glasses and how they correct eyesight
By the 13th century, glassblowers from Italy discovered prescription glasses by determining that different glass lenses could be constructed to alter and correct eyesight by using light refraction. This was done by creating lenses of different thicknesses which would alter the eye’s focus, in order to correct vision problems. The first of these lenses was concave-shaped lenses, which had a thick perimeter and a thin centre. This shape moved the eye’s focus back towards the retina in order to correct nearsightedness. The second lenses were convexly shaped, with a thick centre, which moved the eye’s focus forward to correct farsightedness. The final lenses were of cylindrical shape. The thickness/thinness of the lenses was asymmetrical, in order to correct astigmatism. As technologies advanced, these lenses were plastic frames, and thus, the prescription glasses were born.
Glasses in modern times
The 20th century ushered in the age of prescription glasses, through fashion accessories and the development of strong plastic lenses, thanks to the Industrial Revolution. The range of prescription glasses became very broad, with spectacles having different colours, shapes and sizes. Likewise, the use of sun spectacles for protection against the Sun’s harmful UV rays and the sunlight glare became extremely popular. In addition to this, prescription sun spectacles too became very popular amongst the populace, specifically with athletes, those involved in sports and outdoor-oriented enthusiasts. This allowed a wider demographic, as it allowed people to enjoy the outdoors whilst also being able to see correctly, and doing it in style.
The history of prescription glasses is long, and the science behind them is fascinating. We are lucky in these modern times to have access to such prescription glasses and their range of styles and variety, not only correcting our eyesight but also keeping us in fashion.