Which Lens Index is Best for You?
With all the lens technology advancements, there are more options than ever when it comes to buying eyeglasses. Standard, polycarbonate, and high index—what do all the different lens offerings mean to you? Strip away all the fancy terminology and you’re left with a decision that impacts your lens thickness.
What is a Lens Index Number
The lens index number indicates the thickness of lenses. The higher the index number, the thinner the lenses will be. Comparing two lenses with the same prescription, a lens with an index number of 1.59 is 22% thinner than a lens with an index number of 1.49.
Other Factors Affecting Lens Thickness
- Prescription Strength: The power of the prescription affects how thick the lens will be. Those with a strong prescription should choose lenses with a higher index number.
- Other Prescription Elements: Astigmatism and pupillary distance (PD) both have slight effects on lens thickness. Whereas an astigmatism will cause the lens to be thicker, a wider PD (larger number) yields a thinner lens.
- Frame Size: Larger frames will cause the lenses to be slightly thicker. Incidentally, stronger prescriptions (which generally results in thicker lenses) also work better in larger frames.
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Which Lenses to Choose Based on Your Prescription
Prescription type, prescription strength, and lifestyle are all important factors in determining the best lens for your needs.
- Strong Prescriptions: We recommend the high index lens for prescriptions higher than +/-4.00. Lenses thicker than the high index would stick out significantly from the eyeglass frame and feel heavy on your face.
- Weak Prescriptions: People with prescriptions lower than +/-4.00 have the luxury of being able to select any lens they want based on their needs. If they’re active and want impact-resistant lenses, polycarbonate is the way to go. If their goal is to have the thinnest and most lightweight pair of glasses, we recommend the high index lens. If they simply want the lowest priced option, CR-39 plastic lenses are also available.
- Kids' Prescriptions: For all kids’ eyeglasses, we recommend polycarbonate lenses for their impact resistant quality. It’s the safest and most durable option for all kids.
Frequently Asked Questions
Q: What is considered a “strong” prescription?
A: The ‘sphere’ (or SPH) column on your glasses prescription lists the main strength that represents how nearsighted or farsighted you are. The closer that number is to zero, the better your vision. A number greater than +/- 5.00 indicates severe nearsightedness or farsightedness. Minus lenses with high powers of -4.00 and up will be thick on the sides of the lens. Plus lenses with high powers of +4.00 or more will be thick in the center of the lens.
Q: When are high index lenses recommended?
A: High index lenses are strongly recommended for those with prescriptions higher than +/-4.00. Other lens options that are thicker than the high index would result in a heavy pair of glasses and lenses that would protrude from the frame itself.
Q: What type of lens should I get?
A: Your lens type depends on various factors such as your prescription and lifestyle. Standard CR-39 plastic lenses are inexpensive, but thick around the edges. Polycarbonate lenses are thinner and lighter than plastic and impact resistant for active use. High index lenses are the thinnest and lightest option for strong prescriptions, but they’re usually an upgraded option compared to CR-39.
Q: What are the best eyeglass frames for thick lenses?
A: Thick lenses will need a larger frame to ensure the lenses will hold in place. Rimless or semi-rimless frames should be avoided. Look for small round or oval frames that will even out the thickness across the lens with less peripheral blur.