How Do Glasses Work? Understanding Refraction

Eyeglasses are an indispensable accessory for so many people, as they help those with refractive errors and other vision problems see clearly.

Vision problems are commonly caused by a refractive error, which is an eye condition that occurs when your eye keeps light from focusing correctly on your retina. The retina is the light-sensitive tissue at the back of your eye that receives and organizes visual information. 

Continue reading to learn more about how glasses use the power of refraction to correct vision problems with your local eyecarecenter.

Changing the shape of the glass allows us to focus the light on the correct part of your retina, which is located at the back of the eye. There are different types of refractive errors that have varying prescription lens shapes. Continue reading to learn more about each of the four refractive errors.

Myopia

If the eye is too long, the image ends up focused in front of the retina instead of directly on it. This is known as myopia, or nearsightedness, and causes objects to appear fuzzy when seen from far away.

Hyperopia

If the image ends up focused behind the retina, then things seen up close are out of focus. This is known as hyperopia, or farsightedness. 

Astigmatism

When the clear dome of the eye called the cornea is an uneven shape, there can be more than one focal point, causing images to appear blurry. This is called astigmatism.

Presbyopia

Presbyopia is a refractive error caused by the eye’s natural aging process. As the eye ages, the natural lens in your eye will get worse at correctly focusing the light on your retina. It can make seeing up close difficult and affect everyday tasks such as reading.

The Evolution of Glasses

Abbas ibn Firnas’ Reading Stone

Centuries ago, humans discovered we could use glass to refract light and magnify small print. Abbas ibn Firnas is believed to have discovered and created the first reading stone in the 9th century, which was a small piece of glass that magnified text. This invention led to the discovery of reshaping light to aid in vision, allowing us to eventually correct common refractive errors.

Glassblowers Create The First Eyeglass Lenses During the Renaissance Era

The earliest type of eyeglass lenses were created by glassblowers in the 13th century. These discovered that they could change the direction of light by forming the glass into different shapes. The glassblowers then realized that changing the direction of the light could help those experiencing problems with their vision. The first to use these lenses were monks. They were commonly held like a magnifying glass or wore resting on the nose. Frames like the ones we know today didn’t make an appearance until the Renaissance era. These frames were fashioned with arms that fit behind the ears and made from readily available materials such as wood or bone.

What Eyeglasses Can Treat Today

Glasses today come in a variety of forms. The different types of lenses can correct various types of refractive errors and vision problems.  

Nearsightedness

This condition means you have difficulties seeing objects that are far away. These lenses are thicker at the edges and thinner in the middle. This lens shape can also be called concave lenses.

Farsightedness

If you can see clearly far away, but have difficulties seeing up close, you may be farsighted. These lenses are commonly referred to as convex lenses. They are designed thicker in the middle and thinner on the ends of the lens.

Astigmatism

Cylindrical lenses, which have an asymmetrical thickness, are prescribed for astigmatism. An astigmatism is caused by the cornea being irregularly shaped, often resembling a basketball.

Presbyopia

There are a variety of options available for those needing vision correction due to presbyopia. In addition to traditional bifocal lenses, those with presbyopia can opt for trifocal lenses. Trifocal lenses have a third optical power for intermediate distances. Trifocal or bifocal lenses can also be created as progressive lenses, which have a smoother transition between the optical powers.