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Lens Index Determination:
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Lens index refers to the measure of how efficiently a lens material refracts light. Higher index lenses are thinner and lighter for the same prescription strength, making them ideal for stronger prescriptions.
The calculator determines the appropriate lens index based on your prescription strength:
Where:
Explanation: Higher prescriptions require higher index lenses to maintain thinness and reduce weight.
Details: Choosing the right lens index is crucial for comfort, appearance, and optical performance. Higher index lenses reduce edge thickness and weight, improving wearability for strong prescriptions.
Tips: Enter your prescription strength in diopters (with positive or negative sign). The calculator will recommend the appropriate lens index for optimal thinness and comfort.
Q1: What's the difference between 1.67 and 1.74 index lenses?
A: 1.74 index lenses are approximately 10-15% thinner than 1.67 index lenses, making them ideal for very strong prescriptions.
Q2: Are higher index lenses always better?
A: While higher index lenses are thinner, they may have slightly more chromatic aberration and are more expensive. They're recommended primarily for stronger prescriptions.
Q3: Can I choose a different index than recommended?
A: Yes, but for strong prescriptions, a lower index will result in thicker, heavier lenses that may not fit properly in your frames.
Q4: Do all lens materials come in all indexes?
A: No, different materials have different available indexes. Polycarbonate is typically 1.59 index, while high-index materials range from 1.60 to 1.74.
Q5: Does lens index affect UV protection?
A: Lens index itself doesn't determine UV protection. Most modern lenses include UV protection regardless of index, but you should verify this feature.