Optics in simple language
Astigmatism: There’s no need to worry if you have an astigmatism, over 95% of the population has one. It simply means that your eye is a little rugby ball in shape instead of football. This is corrected for in both distance and near vision and can be built into all lenses so it doesn’t reduce your options. This is called your ‘cyl’ on your prescription print out, just to add to the confusion.
Presbyopia: This is a fancy word for meaning you need glasses for near work. Once we reach our forties, our ability to focus on closer objects reduces, requiring correction for near vision. This is very natural, occurring as our lens in our eye thickens, making it harder for it to bend and therefore for us to focus. You may just need a simple pair of reading glasses, but you also have varifocals and office lenses available to you.
Long sight – Hypermetropia: The image of a distant object is focused behind the retina, because the eye may be too short or the refractive mechanism is too weak. Long-sighted people generally have more difficulty with close work. In young people distance vision is often good, but in older patients it can become gradually reduced.
Short sight – Myopia: The image of a distant object is focused in front of the retina, because the eye may be too long or the refractive mechanism is too strong. Short-sighted people will have blurred distance vision, but normally have good near vision, often holding text very close.
Squint: This is when one eye turns and does not work properly with the other. The movements of the eyes are controlled by muscles which work in pairs. If one muscle is weak a squint can occur. A squinting eye may not develop it’s visiual path properly leading to a ‘lazy’ eye. A child may have to wear a patch over the non-squinting eye to stimulate the vision in the poorer eye. Often an operation, sometimes followed by exercises, can remedy the squint. Early diagnosis is important.
Prism: A prism is worked into a lens when your eyes are unable to focus together on one object, creating double vision. This can be either horizontal or vertical, and may be needed for all working distances or just one. There are many ways that we can correct this, with aesthetically pleasing options now available. Sometimes you may notice a rainbow effect from the prism, so we generally recommend choosing a full rimmed frame that isn’t too big to limit the amount of light entering the lens.
PD: PD refers to your pupil distance. This is the distance from the centre of the bridge of your nose to the centre of your pupil. This measurement is different depending on what you need glasses for, so it is different for reading compared to driving. This is measured by dispensing staff, not the optometrist. This measurement changes a lot as we grow but stabilises once in our twenties. As this is not part of the test this is not included in the testing fee. If you wish to have this measurement then there is a charge of £30. As you would only need this measurement if purchasing your spectacles online we will also fit your glasses to you when you receive them included in this price.
Varifocals: Varifocals, or progressive lenses, are lenses designed to correct vision at all distances, from far distance to around 30cm. These are recommended for those with presbyopia, and are available in varying qualities and designs dependent on your visual demands. These often take a little time to adjust to, like wearing in a new pair of shoes. If you’ve tried varifocals before with no success then it’s worth trying them again; modern technology has seen a huge shift in manufacturing techniques, which I’m sure our lovely team of staff will be happy to bore you with.
Bifocal: Bifocal lenses offer vision at two different distance. Normally this is distance and near, but can be made in other combinations for intermediate correction. A bifocal normally has a visible line where the prescription changes, although an invisible version is now available from Shamir.
Transitions: Transitions are a branded form of light reactive lenses and are recognised as the highest quality available on the market. It takes around 4 minutes for a lens to completely lighten or darken, with a life of approximately 2 years. They however do not work fully through a car window. We would normally recommend a pair of sunglasses also as whilst transitions are useful every day they will never be a replacement for sunglasses.
Index: The index of a lens refers to the material that is used to make the lens. The higher the number the thinner and lighter the lens. Thinner however does not always mean better so it’s best to trust our dispensing staff to advise what is best for you, your prescription and your frame selected.
MAR/anti-reflective coating: An anti-reflective coating is designed to reduce reflected light from artificial lighting such as head lights, computer screens and the television. The quality of coatings can vary so we make sure we source the highest quality for our customers. This will always be recommended on transitions lenses as improves the lens performance. A new coating that has proven very popular is a blue anti-reflective coating. This is designed to eliminate the blue flicker that, although invisible, is dominant in a lot of modern tablet/computer screens and white head lights. Not only does this reduce glare but also alleviates fatigue as it allows your eye muscles to relax more. We would recommend this for anyone who spends a lot of time on computers, has cataracts and for those with reduced/low vision.
Polarising: Polarising tints/filters are used for sunglasses and are available in grey, brown and green. They are fantastic near water and reflective surfaces such as snow and wet roads. We can source polarsing lenses for most prescriptions and lens types, and always carry a wide range of non-prescription polarised sunnies in stock. Polarising quality can vary hugely, naturally we only supply those that offer the best protection and vision for our customers.