Too strong, too weak or poorly fitted

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.

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.

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.

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.

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.