Distinguishing Visual Disorders

Currently, nearly 75% of Canadians have a vision disorder that requires corrective lenses. If you are reading this, chances are quite high that you are one of them. Is that the case? If so, there is also a strong chance that your visual disorder is one of the four main types: myopia, hyperopia, astigmatism, or presbyopia. Still true? I knew it! Last question: do you really know what these terms mean? If so, congratulations! If not, keep reading — you will soon see more clearly 🙂

What does normal vision look like?

Those lucky enough not to need vision correction have what could be called “normal” vision. They can distinguish details both at a distance and up close. For distance vision, the eye is neither too long nor too short, and the lens adapts well to the distance being viewed. For near vision, the lens inside the eye accommodates to make light rays converge on the retina in order to see clearly. But what happens when the eye does not get a perfect score? Let’s take a look!

Eye too short? That’s hyperopia!

In hyperopic individuals, light rays meet behind the back of the eye because the eye is too “short.” This makes the image captured by the retina blurry (the retina is a thin membrane at the back of the eye that receives light and transmits information to the brain). Distance vision is generally fairly good, but near vision is difficult. A hyperopic person can, with accommodative effort, achieve relatively clear vision depending on the degree of hyperopia. However, this can cause eye strain and sometimes severe headaches. This visual disorder can appear at any age and often increases over the years. To correct it, a converging lens is prescribed to bring the image forward.

Eye too long? That’s myopia!

People with myopia experience the exact opposite of those with hyperopia: their eye is too long, and light rays cross before reaching the back of the eye. This creates a blurred image, mainly affecting distance vision. Near vision, however, is excellent, because the closer the object is, the farther back the point of convergence moves. Myopia most often appears in early adolescence and tends to stabilize in early adulthood. Since accommodation of the eye is not possible for distance, myopic individuals can hardly do without glasses. To obtain clear vision, a diverging lens is prescribed.

An irregular cornea? That’s astigmatism!

This visual disorder is due to an irregularity of the cornea. The astigmatic eye has two different focal points, which often results in blurred vision. Take the example of a simple cross made of a vertical and a horizontal line: when the eye focuses on one line, the other becomes blurry, and vice versa, which can lead to fatigue and headaches. A person who is myopic or hyperopic can also be astigmatic. In young children, it is crucial to detect this disorder as early as possible, because the brain may tend to favor one eye over the other, which can lead to amblyopia, commonly called “lazy eye.” Note that amblyopia is different from strabismus (crossed eyes) or a phoria.

And as you age, you will develop… presbyopia!

Last but not least: presbyopia. Usually developing after the age of forty, it mainly affects near vision. The length of the eye is no longer the issue; rather, it is a loss of elasticity of the lens. The lens is the eye’s natural lens that bulges to focus on near objects, but with aging, it gradually becomes more rigid and less able to change shape. People with presbyopia tend to hold objects farther away to see them more clearly, but glasses quickly become necessary. Presbyopia usually progresses until the sixties and then often stabilizes. To correct it, a converging lens is prescribed, often multifocal (or progressive), so that the corrective power gradually changes from the top to the bottom of the lens.

Let’s recap…

Did you understand everything? Let’s do a quick summary! Hyperopic: Your eye is too short, so you do not see well up close or experience eye strain, and you need converging lenses. On your prescription, you will see a positive spherical correction, for example +2.50. Myopic: Conversely, you do not see well at a distance because your eye is too long. Your diverging lenses will have a negative spherical correction, such as -4.25. Astigmatic: You may already be myopic or hyperopic, but in addition your vision is always blurry. To correct this, a cylinder with an axis (in degrees) is added to your lenses, for example CYL -0.50 x 90°. Finally, with age, you will not escape presbyopia!

You should now see more clearly the different visual disorders that affect many people.