Lens thickness in glasses: what it depends on and how to reduce it
Prescription, refractive index, frame size and shape, centring: the factors that affect the thickness of glasses lenses and how to choose them for thinner lenses, with four suitable frames.
A thin lens is chosen together with the frame.
The thickness of a prescription lens depends on the prescription, but not only on that. The material, the size of the frame, its shape and the way the lens is centred in front of the eye can change the result a great deal for the same dioptres. Here are the factors one by one, and how to combine them for thinner, lighter lenses.
where a lens for myopia is thick; a lens for hyperopia, instead, is thick at the centre
the higher the refractive index of the material, the thinner the lens
a smaller, well-centred lens is a thinner lens
What affects lens thickness
1. The prescription. It is the starting point. A lens for myopia (minus) is thin at the centre and thick at the edges; one for hyperopia (plus) is thick at the centre and thin at the edges. Astigmatism adds thickness in one direction.
2. The refractive index. It is the material's ability to bend light. For the same prescription, a higher-index material (1.6, 1.67, 1.74) achieves the same correction with less thickness than the standard one (1.5). With mild prescriptions the difference is small; with strong prescriptions it is obvious.
3. The frame size. In lenses for myopia the thickness grows the further you move from the centre. A large frame leaves more lens far from the centre, and therefore thicker edges. A smaller frame cuts the lens where it is thinnest.
4. Centring. The optical centre of the lens has to sit in front of the pupil. If the frame is much wider than the distance between the pupils, the lens has to be shifted and one edge becomes thicker than the other. A frame proportioned to the face, with lens width and bridge close to the pupillary distance, gives thinner, more even lenses.
5. The lens design. Aspheric lenses have flatter curves: for the same prescription they are thinner and stick out less from the frame.
How to choose a frame for thin lenses
- Round and oval shapes: they have no corners far from the centre, where a lens for myopia would be thicker.
- Moderate lens width: proportioned to the face, without going far beyond the width of the eyes.
- Thick acetate: with medium and strong myopic prescriptions it hides the edge of the lens inside the rim.
- Be careful with rimless and nylon-thread frames: the edge of the lens stays on show; with strong prescriptions the thickness is visible.
Four suitable frames
Lesca Lunetier Burt Miel
Round and small, lens width 41: the lens stays close to the optical centre. It is the shape that gives the thinnest edge to people with myopia.
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KameManNen KMN 775P Gold/Matte Black
Sabae titanium, lens width 42: a small, light lens, for mild and medium prescriptions that should not show.
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Kuboraum P26 Transparent Brown
The full acetate front by Kuboraum, lens width 50: the thick rim takes in the edge of the lens and hides it.
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AHLEM Houdon Petrol Light
8-millimetre acetate in petrol blue: the thickness of the front covers that of the lens, even with significant myopia.
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Bifocal lenses · Progressive lenses · Photochromic lenses · How to read glasses measurements · Titanium or acetate · Rimless glasses
What does the thickness of glasses lenses depend on?
On the prescription, the refractive index of the material, the size and shape of the frame, the centring of the lens in front of the pupil and the lens design (spherical or aspheric).
How can I get thinner lenses?
Choose a high-index material, an aspheric lens and a frame proportioned to the face, with a moderate lens width and a round or oval shape. With myopia, a thick acetate front hides the edge of the lens.
Why are lenses for myopia thick at the edges?
The minus lens that corrects myopia is thin at the centre and gets thicker towards the edge. The larger the frame, the more lens stays far from the centre and the thicker the edge.
Are high-index lenses always needed?
No. With mild prescriptions the difference in thickness is minimal. They become useful with medium and strong prescriptions, especially on large or rimless frames.
Can I wear rimless glasses with a strong prescription?
You can, but the edge of the lens stays on show and the thickness is noticeable. With strong prescriptions a full acetate frame is better or, if you want rimless, a high-index lens and a small lens width.
The right lens for the frame you love
In our boutique in Crema we look at your prescription and the frame together and tell you which index and which design you need for thin lenses. Online, send us your prescription on WhatsApp with the model you are interested in.