If you’ve ever shopped for prescription glasses—especially with a high prescription—you may have heard the term “Index.” But what exactly does it mean, and how does it affect your lenses? Today, we’re breaking it down in the simplest way possible.
What Is an Index?
The Index (or Refractive Index) refers to how efficiently a lens material bends light.
The higher the refractive index, the thinner the lens can be — even with the same prescription strength.
In short:
➡️ Higher Index = Thinner, lighter lenses
➡️ Lower Index = Thicker lenses
Common Lens Index Options
Prescription lenses typically come in these refractive index levels:
- 1.50 – Standard plastic lenses (non-thin, thickest option)
- 1.60 – Thin lens option
- 1.67 – Extra-thin lenses
- 1.70 / 1.74 – Ultra-thin lenses for very high prescriptions
Standard plastic lenses usually begin at Index 1.50, while “thin lenses” start from 1.60 and up.
Who Should Choose High-Index Lenses?
High-index lenses are recommended for people with:
- High myopia (nearsightedness)
- High hyperopia (farsightedness)
Typically from -3.50 diopters or +3.50 diopters and above.
Thinner lenses help the glasses look better, reduce lens bulging, and improve overall comfort and appearance.
Tips for Choosing Frames for Strong Prescriptions
If you have a high prescription, consider these guidelines:
✔ Choose thicker or sturdy frame rims
They help support the lens edge and hide lens thickness.
✔ Avoid oversized frames
Larger frames require more lens surface area—making lenses look thicker.
✔ Select thin or high-index lenses
This ensures your glasses look sleek and well-balanced.
Choosing the right combination of frame + lens index will keep your glasses looking stylish and comfortable without compromising vision quality.