Understanding Vision

Too strong, too weak or poorly fitted

What can the wrong spectacle lenses do to your eyes?

20 May 2019

Various complaints can be traced back to tired eyes

A lot of spectacle wearers know the feeling: sooner or later, your glasses are too weak, and your eyes have to work harder than usual. Incorrectly fitted glasses can also force your eyes to work overtime. The results aren't pleasant. But do spectacle lenses that are too strong, too weak or otherwise 'wrong' really cause long-term damage to our eyes? Do inadequately corrected vision problems necessarily hurt your eyes? And what happens if our eyes are forced to put in extra effort, such as when reading in poor light? BETTER VISION provides an overview.

  • Too strong, too weak or poorly fitted: what can the wrong spectacle lenses do to your eyes?

Have you ever asked yourself if the wrong spectacle lenses can damage your eyes? This isn't an easy question to answer. Glasses that don't provide optimum correction certainly negatively impact a person's vision and quality of life, but there are few cases where this leads to long-term, irreversible damage. While inadequately corrected myopia can actually make the wearer even more short-sighted, there are no reports of this happening with long-sightedness. Nevertheless, the eye must still do more, sometimes very difficult work to achieve clear vision. The reason: undercorrecting or overcorrecting means the lens does not provide optimum support. For someone with age-related vision loss known as presbyopia, improperly fitted spectacle lenses can make them feel ill, such as when climbing the stairs, because their field of vision blurs.

The visual system is extremely flexible: it 'learns' to correctly focus at different distances and adjusts a person's vision to the particular situation as well as possible – depending on any visual defects.

You often see people squint when they can no longer clearly read the words on their mobile phone, or they assume an uncomfortable posture to compensate for a vision problem that has yet to be suitably corrected. All this can easily be avoided with an individualised pair of glasses.

How do incorrectly fitted glasses affect the wearer?

The causes of most complaints from spectacle wearers prove harmless and aren't permanent, meaning the problems disappear as soon as the person enjoys optimum vision again. A typical symptom of incorrectly fitted spectacle lenses is the inability to see clearly while wearing glasses. This results in tired eyes as the visual system has to work significantly harder to achieve a clear image. Overcorrection means the glasses are too strong for the wearer, while undercorrection means they are too weak. For many spectacle wearers, this can lead to eyestrain as well as headaches, neck pain and nausea. Cheap, ready-to-wear spectacle lenses that have not been fitted often have this effect. Needless to say, it makes perfect sense to opt for 'off-the-shelf' lenses under exceptional circumstances or in an emergency. However, since these have not been at all adjusted to the wearer's eyes, stressed eyes and the accompanying side effect may result. In this case, we recommend visiting your optician or ophthalmologist as they can perform an eye test to determine whether you have a visual impairment, or if your current glasses still provide optimum correction.

Can the wrong pair of progressive glasses damage your eyes?

The initial onset of age-related vision loss (called pre-presbyopia, usually starting in a person's mid-30s to mid-40s) requires a switch from single vision lenses or contact lenses to multifocal, i.e. progressive lenses. There are two reasons a lot of people have difficulty with this change. First, they believe that progressive lenses are just something older people wear; and second, switching forces the wearer to 'relearn' how to see. Progressive lenses require vertical eye movements, because the vision zones in the lenses for near, intermediate and distance vision are arranged one one above the other. Without glasses or when just wearing single vision lenses, we mainly move our eyes and head horizontally.

When switching to progressive lenses due to presbyopia, there are two basic pieces of advice to follow: the earlier you start, the easier the adaptation, because it's less taxing to start with 'light' progressive lenses, and the visual system is more capable of learning how to see with these new lenses. In addition, glasses for presbyopia should always be customised for the particular wearer – the vision zones found in 'off-the-shelf' lenses do not provide optimum visibility.

Glasses with progressive lenses that have not been properly fitted cause excessive eyestrain, and the resulting symptoms are not only distracting, but can even affect the wearer's health. In addition to unclear vision, the symptoms include dizziness, headaches, tiredness or nausea, such as when climbing the stairs, because the visual field blurs. But having different vision fields in the progressive lens – for near, intermediate and distance vision – perfectly matched to the wearer's vision profile both improves spontaneous wearer tolerance and is also a major determining factor of how well a person can see with their new progressive glasses. Keep in mind that progressive lenses only reach their full potential when the position of the spectacle frames and the lenses are precisely matched to the wearer's face, eyes and lifestyle. The different vision zones in the lens require precise lens centration. You should visit your optician and recalculate your vision profile if you suspect you're wearing the 'wrong' spectacle lenses, i.e. if the near zone power is too weak for reading, or if it's difficult to see clearly when performing challenging tasks like driving.

Children need a good pair of glasses

Children need a good pair of glasses

Children's eyes are still developing and undergoing numerous changes: a visual acuity of around 50 percent in the first year of life generally jumps to 100 percent once they've reached the age of three. Spatial vision is completely evolved by the time a child is nine years old, while their field of vision continues to develop until they're about 12. Even then, this development process is not yet complete, because a person's eyes continue to grow until they become an adult. Thus it's important to have your child's vision tested frequently. An ophthalmologist, optometrist or a specialist optician should check regularly if the spectacle lenses still have the right prescription as this can change quickly, especially with children. Protecting children's eyes from harmful UV radiation is also an absolute must, and kids' glasses must meet certain other criteria, like exceptional robustness.

Glasses that are not optimally fitted can impact the eyes of both children and adults who are short-sighted or long-sighted. While an improperly fitted pair of glasses doesn't damage a child's eyes, it can hinder their vision from fully developing. Happily, a perfectly fitted pair of children's glasses can have the opposite effect: it helps foster optimum vision. For children with a form of short-sightedness particularly prevalent in Asia called progressing myopia,  special lenses can help  alter the progression of the refractive error. A pair of glasses can also assist in the prevention of visual problems resulting from certain types of squinting. For this reason, babies and small children should have their eyes checked regularly by an ophthalmologist so that they can start receiving any necessary treatment as quickly as possible. You will find more information on the different types of squinting and the accompanying treatment  options here.

Does reading in poor light or by candlelight damage your eyes?

Young woman wearing a warm pullover is using tablet PC

People often used to say that reading in poor light, such as by candlelight, would damage your eyes. As with other urban myths like "if you cross your eyes, they'll stick", there is no scientific foundation for this assertion. Still, in poor light or with the wrong spectacle lenses, the eye has to work harder to achieve good vision. In addition to exhausting the eye muscles prematurely and temporarily limiting a person's vision, no damaging effects have been identified.

The greatest risk to the health of our eyes comes from natural light emitted by the sun. The UV radiation found in sunlight poses both short-term and long-term risks if you don't adequately protect your eyes. For complete protection, sunglass lenses with an enhanced UV filter or clear spectacle lenses with high-quality UV protection are a must.

To sum up: there's no evidence that incorrectly or poorly fitted spectacle lenses can permanently damage a person's eyes. Moreover, as far as anyone knows, reading in poor light or using brightly illuminated screens is mostly just unpleasant rather than damaging. Since children's eyes are still developing, any visual defects should always be optimally corrected. And everyone should protect their eyes from harmful UV radiation.

When it comes to 'bad vision', our eyes can take a lot of abuse. Nevertheless, a well-fitted pair of glasses not only prevents the side effects of uncorrected visual defects, but also increases wearer comfort and improves a person's quality of life.

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