Ray-Ban RX8421 Optical Frames

This measurement can be requested from your optician.

Your pupillary distance (PD) is the distance in millimetres between the centres of your pupils. It tells us exactly which part of the lens you look through, ensuring your glasses are correctly centred for your eyes.

The most accurate way is to have it measured by your optician – worth asking at your next eye exam if it isn't already on your prescription. To measure it yourself at home, you'll need a mirror and a millimetre ruler. Stand about 20cm from the mirror, hold the ruler flat against your browline, and align the zero with the centre of one pupil. Without moving the ruler, read the measurement at the centre of the other. Repeat a couple of times to confirm.

On average, the distance is 62mm for men and 60mm for women.

No – this is a common concern but there's no evidence to support it. Wearing glasses corrects your vision to where it should be; it doesn't change the underlying structure of your eye or accelerate any deterioration.

If your prescription changes over time, that's the natural progression of your vision – not a consequence of wearing glasses. In fact, wearing the correct prescription reduces eye strain, which is only a good thing for long-term comfort.

Eyeglass prescriptions can look unfamiliar at first, but the key values are straightforward once you know what they refer to.

SPH (Sphere) is the main correction for short or long sight. A minus value means you're short-sighted; a plus value means long-sighted. CYL (Cylinder) and Axis relate to astigmatism – an irregularity in the curvature of the eye that affects sharpness at certain angles. ADD appears on prescriptions for varifocal or reading lenses and indicates the additional power needed for close vision.

You'll also see OD (right eye) and OS (left eye) labelling the two columns. If you're unsure about any aspect of your prescription, your optician will always be happy to explain it.

The safest method is warm water, a small drop of washing-up liquid, and a clean microfibre cloth. Rinse the lenses under lukewarm water first to remove any dust or grit – wiping a dry lens can cause fine scratches. Apply a tiny amount of washing-up liquid, gently work it across both sides of the lens, rinse thoroughly, and dry with the microfibre cloth using light circular motions.

Avoid paper towels, clothing, or tissues – these are rougher than they seem and can dull the lens surface over time. Keep your glasses in their case when not wearing them, and never leave them lens-down on a surface.

Computer lenses – also known as occupational lenses – are designed specifically for near to intermediate distances, making them ideal for screen-based work, reading, or any environment where you're focused within arm's reach rather than at distance.

Unlike everyday varifocals, which divide the lens across near, intermediate, and far zones, computer lenses dedicate more of the lens to the distances you actually use at a desk. The result is a wider, more comfortable field of vision for extended periods of close work – and less strain at the end of the day. They're not suited for driving or general outdoor use, so most wearers use them alongside a separate pair for everyday wear.

The Varilux XR Series is Essilor's most advanced progressive lens, designed for those who want the best available performance. It uses behavioural AI – built from over a million real-world data points – to predict how your eyes naturally move and optimises the lens design accordingly.

The practical result is instant sharpness at every distance, even when you're in motion, with a significantly larger volume of clear vision compared to previous generations. For anyone spending long days switching between screens, paperwork, and conversation, it's the lens that keeps up.

The Varilux Comfort Max is an Essilor progressive designed with natural posture in mind. Most varifocals require you to hold your head in specific positions to find the right zone – the Comfort Max, powered by Flex Optim™ technology, adapts to how you naturally move and look, rather than the other way around.

The result is a wider useful vision zone, reduced peripheral distortion, and a lens that feels comfortable from the first day of wear. A particularly good option for those who have previously struggled to adapt to progressive lenses.

Progressive lenses – also known as varifocals – correct vision at near, intermediate, and distance in a single lens, with no visible line between zones. The Visio is an entry-level progressive produced using digital freeform technology, which optimises the lens for a wider, clearer field of view compared to traditional varifocal designs.

It's a strong starting point for those new to progressive lenses, and comes with blue light filtering and UV protection included as standard.

Transitions® GEN S lenses combine single vision prescription correction with photochromic technology. They're fully clear indoors and darken automatically when exposed to UV light outdoors – reaching full darkness in around 25 seconds and returning to clear in under two minutes.

GEN S is the most responsive generation of Transitions® lenses to date, making them a practical choice for anyone who moves regularly between indoor and outdoor environments and prefers a single pair for both.

Single vision lenses carry one prescription across the entire lens, correcting vision at a single distance – whether near, intermediate, or far. They're the most straightforward lens type and suit most people who need correction for one specific task, such as reading or driving.

Clear lenses are the everyday standard. Tinted lenses work in the same way but with a fixed colour or shade applied – useful for light sensitivity or simply as a style choice.