Lens index and thinning: how to choose?
Choosing the index of your lenses can seem technical if you are not an optician. However, this choice has a direct impact on the thickness, weight, and aesthetics of your glasses. Even with a very elegant frame, thick lenses can quickly become uncomfortable and unflattering.
This guide explains what the index is for, how to choose it based on your prescription, and why other parameters – such as the frame size – are just as important for obtaining thin lenses.
1What is the lens index and what is it for?
The refractive index of a lens corresponds to the material used. The higher the index, the more the lens "bends" light for the same power. The result: it is possible to make a thinner and lighter lens for the same prescription.
For identical correction, a high index lens will therefore be thinner than a standard lens. This is particularly interesting for:
- strong myopia (lenses thickened at the edge),
- strong hyperopia (lenses curved and thick at the center),
- wearers wishing a discreet and aesthetic result on a thin frame.
Each index is associated with a specific material with its own properties (weight, resistance, light transmission, etc.). To better understand these materials and their advantages, you can consult our page dedicated to organic lenses.
In summary: the higher the index, the thinner the lens can be for the same correction... but the choice of frame and other parameters also plays a key role (see below).
2How to choose your lens index?
The first criterion to look at is the strength of your prescription, expressed in diopters ("Sphere" and "Cylinder" values on your prescription). As an indication:
- Small corrections (approximately -2 to +2 diopters): a standard index is sufficient in the vast majority of cases.
- Medium corrections (from ±2 to ±4 diopters): an intermediate thinning is often recommended to limit thickness at the edge or center.
- Strong corrections (from ±4 to ±6): very thin lenses provide real aesthetic comfort and a more pleasant weight for daily wear.
- Very strong corrections (beyond ±6 diopters): it is generally preferable to opt for a maximum index adapted to your prescription.
The type of frame (full-rim, semi-rimless, rimless), the material (acetate, thin metal), and your priorities (aesthetics, budget, weight) also guide the final choice.
Hesitating between two indexes? Do not hesitate to contact us with your prescription: we can advise you on the best index + frame combination to obtain lenses as thin as possible.
3The index is not the only criterion: what influences lens thickness
Many wearers think that choosing a high index is enough to guarantee a very thin lens. In reality, the index is only part of the equation. Other parameters have an equally important impact on the final result.
1 — The size of the frame lenses
This is one of the most determining factors. The larger the lens size (effective diameter), the more the lens must be cut from a large diameter blank. For identical correction and the same index, a lens mounted on a large frame will therefore be thicker than a lens mounted on a smaller frame.
- For myopia, thickness is mainly visible at the edges: a very wide frame accentuates this effect.
- For hyperopia, thickness is concentrated at the center: the larger the lens, the more visible the curvature.
This is why, for strong prescriptions, it is often recommended to favor rather compact frames (lenses not too wide, slightly rounded or oval shapes) to minimize thickness as much as possible, even with an already thinning index.
2 — Frame shape and centering
The shape (round, square, rectangular, cat-eye...) and how your pupils are positioned in the lenses also influence thickness. If your pupils are very off-center relative to the geometric center of the lens, part of the lens must be more worked, which can increase thickness on one side.
3 — Type of mounting
A full-rim frame better conceals the edges of a thick lens. With semi-rimless (nylor) or rimless frames, the edges of the lens are visible: the optician will often prefer a higher index and an adapted diameter.
4 — Material and treatment
Certain high-end materials and treatments (anti-reflective, hardening, specific filters) may not exist in all indexes. It may therefore be more relevant to choose a slightly lower index but compatible with the desired treatment, rather than aiming solely for ultra-thinning.
In practice, the best result is often obtained by a compromise: choosing a frame well suited to your prescription, then selecting the index that offers the best balance between thickness, comfort, and budget.
4The different lens indexes offered
At Visionet, we offer several indexes to best adapt lens thickness to your prescription and frame. For an overview of our complete range of lenses, their characteristics, and prices, you can consult our prescription lenses.
1Index 1.50: standard lenses
Ideal for small corrections, generally up to approximately ±2 diopters. The lenses are comfortable, robust, and economical. On a reasonably sized frame, the thickness remains quite aesthetic.
2Index 1.60: thinned lenses
Recommended for corrections of approximately ±2 to ±4 diopters. The lenses are thinner and lighter than the standard index, which improves both aesthetics and comfort, especially on thin or metal frames.
3Index 1.67: very thinned lenses
Recommended for strong corrections (approximately ±4 to ±6 diopters) or when a truly discreet result is desired. The thickness at the edge (myopia) or center (hyperopia) is significantly reduced compared to lower indexes.
4Index 1.74: super thinned lenses
Intended for very strong corrections, beyond ±6 diopters. This is the preferred choice when wishing to minimize visible thickness as much as possible, especially for thin or small frames.
Important: we provide prescription lenses up to ±10 diopters and/or ±4 for cylinder. Depending on your prescription and the chosen frame, we will guide you towards the most suitable index.
5FAQ – Frequently Asked Questions about lens index and thickness
Can I choose a high index if my prescription is low?
Yes, it's possible, but it's not always necessary. For a small correction, lens thickness often remains very reasonable with a standard index, especially on a well-chosen frame. A higher index can be interesting if you absolutely want a very thin result or if the frame is particularly thin or wide.
Will my lenses necessarily be thick if I choose a large frame?
The larger the frame, the more the lens must be cut from a large diameter, which naturally increases thickness. By combining a reasonably sized frame and an adapted index, however, a very harmonious result can be obtained. For strong corrections, it is strongly advised to avoid overly wide shapes.
Up to what prescription can you manufacture lenses?
We produce prescription lenses up to ±10 diopters and ±4 diopters for cylinder. Depending on your prescription, we can recommend the most suitable index and frame type to reconcile comfort, aesthetics, and budget.
How can I be sure to make the right choice from home?
The simplest way is to keep your current frame as a reference: look at its size and the thickness of your lenses, then compare with the information on Visionet product sheets. You can then adjust the size of the frame and the chosen index according to your desired thinning. If you have any doubts, contact us with your prescription: we will guide you to the best combination.
