- Prescription lenses aren’t all the same
- Types of optical lenses for glasses
- The optics of prescription lenses
- Optical lens index
- Abbe value
- Lens finishes and coatings
- Prescription lenses are complex!
Prescription lenses aren’t all the same
Types of optical lenses for glasses
Two main categories of optical lenses exist. Lenses can be either single-vision or multifocal in design. Most prescription optical lenses are now manufactured from plastic resin. Although we can still access glass prescription lenses, a high-quality plastic resin is generally more suitable, much lighter weight, and doesn’t smash when dropped.
Single vision lenses
Single-vision or single-focus lenses are common lens types. Designed to correct one type of vision only, single-vision lenses provide a single focal distance. In other words, they will allow you to see at one distance only. For example, up close (reading glasses) or over long distance (driving glasses). Consequently, these lenses are restrictive where multiple vision distances are required. So you can’t drive in reading glasses and driving glasses won’t be great for reading a book.
These lenses are simple to produce and come in a wide range of powers to suit almost any prescription type. The best type of single-vision lens is made specifically for the wearer. It will precisely account for your exact prescription, eye movements, and position and also the unique differences in your frame of choice.
Multifocal lenses allow multiple focusing distances. Bifocal lenses and progressive addition lenses are the two most common types of multifocal lenses. The complexities of multi-tasking mean these lenses generally cost more to produce. When you need prescription lenses for both long vision and near vision, a multifocal lens is the most convenient solution. As a result, you may not need to have quite so many pairs of glasses as one pair of glasses will achieve more.
The latest and most sophisticated progressive lens designs deliver more seamless and natural vision. As a result, we prefer to prescribe these designs. Progressive lenses are made with two or three target focal points that gradually and smoothly change throughout the lens. This allows you to achieve natural vision up close, at arm’s length, and at long distances.
Extended near lenses
Also known as vocational lenses or office lenses, extended near-vision lenses are designed to help you read both up close and at arm’s length, such as on the computer screen. This eliminates the need to constantly remove, or swap glasses to focus on objects at different distances. They are ideal in an indoor or office situation and can be tailored to match your specific environment, visual tasks, and ergonomics.
Bifocal lenses are similar to progressive lenses except there is no gradual transition, there is a line on the lens. So, two separate focal powers are produced by splitting the lens into two distinct and fixed parts. Today progressive lenses have largely replaced bifocal lenses. The use of technology means almost everyone now works with multiple and varying focus distances.
The optics of prescription lenses
Different manufacturers use different techniques to generate a prescription lens. When it comes to optical precision, you get what you pay for. A precision lens optimizes the prescription over a greater area, rather than just the center of the lens. This makes a difference to your peripheral vision and the level of visual comfort provided by the lens.
Optical lens index
The index of a lens determines the thickness and weight of the lens. Generally speaking, the higher the index, the thinner and therefore the lighter the lens. In contrast, a hi-index glass lens may be super thin, but it will be comparatively heavier (and more breakable). So, it’s not as straightforward as choosing the highest index.
Furthermore, different resin types can have the same index number, but have different:
- clarity factor (Abbe number)
- crack resistance
- bending resistance
- chipping resistance
- UV light resistance
- chemical resistance (e.g. metho and acetone)
- heat resistance
We’ll prescribe a lens index that matches your prescription, frame choice, and lifestyle needs. We won’t compromise on lens qualities that will place your eyes or glasses at risk.
Abbe value defines lens clarity. This is the lens feature that determines the optical quality of the lens. It’s also a feature that chain stores and discount lens makers don’t talk about. The Abbe number refers to the degree of chromatic aberration (light scatter) caused by a lens material. The higher the number, the better the quality of the lens material. In our view, a large number of lenses available to consumers have an unacceptable Abbe number. We prescribe lenses with high Abbe numbers because this translates to better vision.
Lens finishes and coatings
Lens options including photochromatic (change colour), anti-reflective, tinting, and polarising technology will enhance your visual performance and the look of your lenses. Good quality lenses will have lens treatments automatically built into them. Cheaper lenses won’t and you’ll have to pay extra to have them added on.
Tinting a prescription optical lens has come a long way. You can choose from a wide range of colours and include a polarising filter for added glare reduction.
Commonly referred to as “Transitions”, these lenses react to light and/or UV by changing from clear to dark and back to clear again. This allows for a smooth transition from indoors to outdoors without the need to change from spectacles into sunglasses.
Multicoated lenses have undergone a number of finishing treatments. It depends on the manufacturer, but a multicoated lens will include at least an anti-reflective coating and a hard coating. Better multi-coats are thicker, have more layers, and include additional features like UV protection, dust repellence, and hydrophobic and oleophobic layers. A good multi-coat will also last longer.
Anti-reflective treatments improve the visual performance, comfort, and look of your lenses by reducing unwanted glare and reflection.
Scratch resistant coatings
Automatically applied to all our lenses at no extra cost, this improves durability. So lenses are less likely to become scratched. There are vast differences in the level of scratch protection provided by different coatings. No lens is completely scratch-proof. To prevent scratches, a little care is still required.
UV coatings are automatically built into all of our lenses at no extra cost. So you will get 100% UV protection.
Easy clean coatings
A bit like a Teflon pan, they help to repel dirt, water, and oil. So your lenses require less frequent cleaning and are easier to clean.
Prescription lenses are complex!
The lenses are arguably the most important part of your glasses, and they are the most complex part. Invest in a precision optical lens and your eyes will be happy.
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