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LENS
In sport eyewear the lens is the product.
The frame holds it, but the lens is what protects and what is looked through. Its material, curve and coating are the specification.
- Material
- Impact resistance against optical clarity, and the two trade
- Base curve
- How much the lens already bends, which limits the prescription
- Coating
- Hard coat, anti-reflection, hydrophobic · layered, and each layer can fail
- Tint
- A category rather than a colour, and it changes the light reaching the eye
- Impact standard
- Which test the lens has to pass, and for which use
- Centration
- Where the optical centre sits, which depends on how the frame wraps
Illustrative lens record
| Property | Set by | What changes it |
|---|---|---|
| Impact | The standard for the intended use | Material and thickness together |
| Clarity | The material's dispersion | A higher index disperses more colour |
| Prescription limit | The base curve already in the lens | A stronger wrap limits the power |
| Coating life | How it is cleaned and stored | Grit in a case, or a dry cloth |
Why a sport lens is centred differently.
Because the frame wraps. The optical centre has to sit in front of the pupil in the position the eye actually occupies when the frame is on, which for a wrapped frame is not where a flat frame would put it.
The question worth asking instead.
Which standard the lens is dispensed to, and whether the prescription can be cut into the base curve chosen. A supplier who can answer that has checked the frame against the prescription rather than the frame alone.