# Refractive index: why prescription power alone is not enough

Index describes an optical property of a material. Choosing a lens also requires considering the frame, design, fitting and wearer priorities.

## Comparing options

Compare materials with the same prescription and frame. Changing shape, diameter or minimum thickness at the same time prevents attributing differences solely to index.

## Example question

For a −9.00 D prescription, also gather cylinder, axis, monocular PD, fitting height and frame shape and size. Sphere power alone does not select the best option.

## Limit

There is no universal recommendation of 1.60, 1.67 or 1.74 based only on power. Final selection depends on available options and professional assessment.

## References

- [ZEISS — High index lenses](https://www.zeiss.com/vision-care/us/eye-health-and-care/lifestyle-fashion/fashionably-sleek-high-index-lenses.html)

## Related topics

- [Lens materials: compare more than index](https://lensas.com.br/en/knowledge/lens-materials/)
- [Lens thickness: inputs needed for an estimate](https://lensas.com.br/en/knowledge/lens-thickness/)

Educational content · Fictional examples · Automated technical review, no claimed clinical validation.

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Version: 2026-09-15.1