There are so many ways to answer this question.
- They hide your eye bags
- They hide your un-groomed eyebrows
- They make you look smarter
- They help you to see better
Henceforth, this article will focus on point number 4 as this is my area of formal qualification and expertise. Hold on to your seats for a mind numbingly boring yet informative and educational ride.
Let’s start with a “normal” eye, one that doesn’t require any refractive correction in the form of glasses or contact lenses. Such an eye is known as “emmetropic”.
In an emmetropic eye, you want light rays entering the anterior of the eye (in the above diagram the eye is facing towards the left), to be focused by the various elements onto the back of the eye, the retina. It’s when light rays don’t focus on the right spot that things get fuzzy. Whatever state those light rays are in by the time they hit the retina (eg. not in focus) is what you see.
Also known as long-sightedness though I’m not a fan of this terminology as it can be misleading, particularly to poor confused parents of hyperopic children. The name “long-sightedness” also begins to break down as you begin to enter your mid to late 40s and now you can’t see well at near or far.
Hyperopia arises when light rays entering the eye fall behind the retina. Effectively, the focusing strength of the anterior elements of your eyeball is not enough to bend those light rays enough to come together in time once they reach the retina. Another way to think of it is that your eyeball is too short for its focusing power.
What you need here are plus lenses (ie. a plus prescription such as +1.50) that will help to bend those uncooperative light rays so they come together in time when they reach the retina.
The reason parents get confused about this is because with children, they may be hyperopic but still able to see quite clearly and easily at all distances, depending on the degree of their hyperopia. The anatomical lens of the eye (that elongated oval in the diagram) is flexible and able to alter its shape to bring forward or backward the focal point to a certain degree. It does, however, mean that the eye is always working to keep things clear, and in some children this can cause eyestrain, fatigue and an aversion to reading. The closer the viewing object is, the harder the eye has to work to keep it in focus. This physiological focusing system starts to fall apart as presbyopia kicks in (see below).
Also known as short-sightedness, myopia is when light entering the eye falls in front of the retina. This is usually due to the eyeball being too long for the focusing strength of the eye. Myopic patients will often find that while they need glasses or contacts to see at distance, when it comes to reading they can quite easily see clearly without any correction.
Myopia is corrected using a minus prescription (eg. -2.00). High degrees of myopia, classified as over -5.00D, have been associated with an increased risk of eye disease such as retinal tears and detachments, myopic macular degeneration, and glaucoma. A lot of current research is going into what’s being termed “myopia control”.
Greek for “old eyes”, presbyopia strikes around the mid to late 40s (though I know some will be little indignant this age group is considered old). Some people manage to hang on for a bit longer but if you’re human you can expect to succumb to the natural ageing of your eyes at some point.
Presbyopia occurs as the anatomical lens in the eye becomes less flexible with age, to the point where it can no longer adjust itself adequately to bring near objects into focus. You may find yourself holding your reading material further away, you can no longer see the vegetables you’re chopping on the kitchen counter, or to be able to read it becomes necessary to remove your distance spectacles and let your myopic eyes do their thang.
Presbyopia is also the reason why hyperopic patients who had previously enjoyed clear long distance vision find they can no longer see as well at distance or at near – a double whammy, if you will.
Or as many of my patients like to call it, “stigma”. Astigmatism may be in conjunction with both myopia or hyperopia, and if you’re into collecting refractive errors like Pokemon cards, in conjunction with presbyopia as well.
I would draw a diagram for you to demonstrate astigmatism but unfortunately this is where my graphic design skills fail so you’ll just have to read words instead. In most cases, astigmatism arises from the front surface of the eye, the cornea, being more curved along one axis like an Australian Rules football, rather than perfectly round like a soccer ball.
It means light passing through the cornea gets bent to different degrees depending on which axis it entered the eye. It makes for warped images, eyestrain and headaches, and increased glare from street lights and oncoming car lights. Most cases of astigmatism can readily be corrected with spectacle lenses and nowadays quite often in contact lenses too. In a written prescription, the astigmatism is the component that comes after the forward slash, such as (+0.25)/-1.00×180.
It can be a complicated situation, I know. If you had any further questions about refractive error or glasses then feel free to shoot me an email or comment on this post.