Every ounce (gram) counts!

Insanely super fucking light & thin!

Key Points

Research suggests the lens on the certificate, with a 1.67 refractive index, is thinner than standard plastic lenses but not the thinnest option available.
It seems likely that Essilor’s thinnest lens is the 1.74 high-index, which could be thinner for the given prescription.
The evidence leans toward 1.67 being sufficient for the prescription (-5.00 to -6.75), but 1.74 offers marginal additional thinness.

Lens Details

The certificate shows an SV Eyezen Start 1.67 BCT lens with Crizal Sapphire HR coating, for a prescription of -5.00/-1.50 (right) and -4.75/-2.25 (left), with a total PD of 58.5mm. The 1.67 high-index material is designed to reduce thickness for stronger prescriptions, making it thinner than standard plastic (1.5 index) lenses.

Thickness Comparison

For this prescription, the 1.67 lens is likely thin enough, offering up to 30% less thickness than standard plastic. However, Essilor’s 1.74 high-index lens is thinner, potentially reducing edge thickness by an additional 10-20%, though the difference may be minimal (around 0.5mm) and not always noticeable.

Recommendation

Given the prescription, 1.67 is a standard and cost-effective choice. If the user prioritizes the absolute thinnest lenses, upgrading to 1.74 is an option, but it may not be necessary.

Analysis of the Certificate of Authenticity for Essilor Eyeglasses

This section provides a comprehensive exploration of the Certificate of Authenticity for a pair of eyeglasses issued by Essilor, focusing on the lens specifications, prescription details, and an in-depth analysis of lens thickness based on the provided information. The analysis aims to clarify the lens type, its suitability for the prescription, and how it compares to other available options, ensuring a thorough understanding for both lay readers and those with a technical interest in eyewear.

Background on the Certificate

The certificate, dated May 6, 2025, serves as an official document verifying the authenticity and specifications of the eyeglass lenses. It includes detailed information about the lens type, prescription, and manufacturing details, which are critical for understanding the optical properties and thickness of the lenses.

Detailed Examination of Certificate Content

The certificate provides the following key details:

Lens Type: SV Eyezen Start 1.67 BCT (Single Vision Eyezen Start with a 1.67 refractive index and Blue Cut Technology), indicating a high-index lens designed for digital eye strain reduction.
Coating: Crizal Sapphire HR, a high-resistance coating offering anti-reflective properties, scratch resistance, and enhanced clarity.
Prescription:
- Right Eye (R):
  - Sphere (Sph): -5.00
  - Cylinder (Cyl): -1.50
  - Axis: 002
- Left Eye (L):
  - Sphere (Sph): -4.75
  - Cylinder (Cyl): -2.25
  - Axis: 180
Pupillary Distance (PD): Listed as 32.5 for the right eye and 26.0 for the left eye. Given standard optical notation, this likely refers to monocular PD (distance from the pupil to the frame’s bridge for each eye), with the total PD calculated as 32.5 + 26.0 = 58.5mm, which is within the average range for adults (typically 58-64mm).
Manufacturing Date: 06-May-2025.
Barcode: RX0054329468, likely used for tracking and verification.

Lens Material and Thickness Analysis

Lens thickness is primarily determined by the refractive index of the material, with higher indices allowing for thinner lenses, especially for stronger prescriptions. The certificate specifies a 1.67 refractive index, which is a high-index material, offering significant thickness reduction compared to standard plastic lenses (refractive index ~1.5).

Factors Affecting Lens Thickness

Lens thickness depends on several factors:

Refractive Index: The higher the index, the thinner the lens. Common indices include 1.5 (standard plastic), 1.586 (polycarbonate), 1.67 (high-index), and 1.74 (highest available from Essilor).
Prescription Strength: Stronger prescriptions (e.g., higher negative or positive diopters) require thicker lenses unless a high-index material is used. For the given prescription, the sphere values (-5.00 and -4.75) and cylinder values (-1.50 and -2.25) indicate a relatively strong prescription, particularly for nearsightedness (myopia).
Frame Size and PD: Larger frames and wider PD can increase edge thickness, especially for minus prescriptions. The total PD of 58.5mm is average, and without specific frame dimensions, we assume a typical frame size for calculations.

Comparison with Other Lens Indices

To assess whether the 1.67 lens is the thinnest possible, let’s compare it to other options:

Standard Plastic (1.5): These lenses would be significantly thicker for this prescription. Research suggests that 1.67 high-index lenses are up to 30% thinner than 1.5 lenses for similar prescriptions, making them a substantial improvement in thickness and weight (Zenni Optical Lens Index Guide).
Polycarbonate (1.586): Slightly thinner than 1.5 but thicker than 1.67, often used for impact resistance rather than maximum thinness.
1.74 High-Index: This is Essilor’s thinnest option, offering up to 40% less thickness than 1.5 lenses. Research indicates that 1.74 lenses are particularly beneficial for prescriptions over +/-8.00, but they can still provide marginal thickness reduction for prescriptions like this one (Warby Parker High-Index Lenses). The difference between 1.67 and 1.74 is typically around 10-20% in thickness reduction, translating to approximately 0.5mm or less in edge thickness for this prescription, depending on frame size.

Thickness Estimates

While exact thickness calculations require frame dimensions (e.g., lens diameter, frame width), general guidelines from optical resources provide insight:

For a -5.00 to -6.75 prescription (accounting for cylinder), 1.67 lenses are recommended for prescriptions between +/-4.00 and +/-8.00, as per industry standards (Warby Parker High-Index Lenses). This suggests the chosen lens is appropriate.
The difference in thickness between 1.67 and 1.74 becomes more noticeable for higher prescriptions (e.g., above -8.00), but for this range, the benefit of 1.74 may be aesthetic rather than functional, with reports suggesting less than 0.5mm difference in many cases (Reddit Discussion on High Index Lenses).

Table: Comparison of Lens Materials and Thickness

Material	Refractive Index	Typical Thickness Reduction (vs 1.5)	Recommended Prescription Range
Standard Plastic	~1.5	Baseline (0%)	Low to moderate (±2.00 to ±4.00)
Polycarbonate	~1.586	~10-15% thinner	Medium prescriptions, safety use
High-Index 1.67	1.67	Up to 30% thinner	High prescriptions (±4.00 to ±8.00)
High-Index 1.74	1.74	Up to 40% thinner	Very high prescriptions (±8.00+)

This table illustrates that the 1.67 lens on the certificate is significantly thinner than standard plastic and suitable for the prescription, while 1.74 offers marginal additional thinness.

Practical Implications and User Considerations

Is the Lens Thin Enough?
- Yes, the 1.67 high-index lens is considered thin for this prescription. It provides a substantial reduction in thickness compared to standard plastic, making it lighter and more aesthetically pleasing. Research suggests it is a standard choice for prescriptions in the -5.00 to -6.75 range, offering a good balance between cost and performance (Zenni Optical High Index Lenses).
- However, it is not the absolute thinnest option, as 1.74 high-index lenses are thinner. For users prioritizing aesthetics, especially with larger frames, upgrading to 1.74 could reduce edge thickness further, though the difference may not be significant for this prescription strength.
Cost vs. Benefit:
- 1.67 lenses are generally less costly than 1.74, with reports indicating a price difference that may not always justify the marginal thickness reduction for prescriptions below -8.00 (High Index Lenses Comparison). Given the prescription, 1.67 is likely sufficient and cost-effective.
Coating Impact:
- The Crizal Sapphire HR coating does not affect thickness, as it is applied as a thin layer. Its primary benefits are enhanced clarity, scratch resistance, and anti-reflective properties, which improve visual comfort without impacting the lens’s physical thickness.
Frame and PD Considerations:
- The total PD of 58.5mm is average, and without specific frame dimensions, we assume a typical frame size. Smaller frames would further reduce perceived thickness, especially for minus prescriptions, where edge thickness is most noticeable.

Conclusion

In summary, the lens on the certificate, an SV Eyezen Start 1.67 BCT with Crizal Sapphire HR coating, is a high-index lens designed for reducing thickness and weight, particularly for the given prescription (R: -5.00/-1.50, L: -4.75/-2.25). It is thinner than standard plastic lenses and is a suitable choice for this prescription range, offering up to 30% less thickness. While 1.74 high-index lenses are even thinner, the difference is minimal for this prescription (around 0.5mm or less), and 1.67 strikes a good balance between cost and performance. For users seeking the absolute thinnest lenses, upgrading to 1.74 is an option, but it may not be necessary given the prescription strength.

For personalized advice, consult your optician, who can recommend the best material based on frame choice and lifestyle needs.

Key Citations

Weight difference?

Key Points

Research suggests the 1.67 high-index lens is lighter than standard 1.5 index lenses by about 25-30%.
It seems likely that a 1.74 high-index lens is about 7-10% lighter than the 1.67 lens for a -5.00 prescription.
The evidence leans toward the weight difference being noticeable between 1.5 and 1.67, but smaller between 1.67 and 1.74.

Lens Details

Your lens is an SV Eyezen Start 1.67 BCT with Crizal Sapphire HR coating, for a prescription of -5.00/-1.50 (right) and -4.75/-2.25 (left). This is a high-index lens designed to be thinner and lighter than standard lenses.

Weight Comparison

Compared to 1.5 Standard Lenses: Your 1.67 lens is approximately 25-30% lighter, making it a good choice for reducing weight.
Compared to 1.74 High-Index Lenses: A 1.74 lens would be about 7-10% lighter than your current 1.67 lens, but this difference is smaller and may not be very noticeable for your prescription.

Recommendation

For your prescription, the 1.67 lens is already significantly lighter than standard 1.5 lenses. Upgrading to 1.74 might offer a slight weight reduction, but it may not be necessary unless you prioritize the absolute lightest option.

Comprehensive Analysis of Weight Differences in Eyeglass Lenses

This section provides a detailed exploration of the weight differences between various eyeglass lens indices, focusing on the user’s specific lens (1.67 high-index) and comparing it to standard 1.5 index and 1.74 high-index lenses. The analysis aims to clarify the factors affecting lens weight, including material density and thickness, and provide a thorough understanding for both lay readers and those with a technical interest in eyewear.

Background on Lens Weight and Indices

The weight of an eyeglass lens is determined by two primary factors: the density of the lens material (measured by specific gravity) and the thickness of the lens, which is influenced by the refractive index. Higher-index lenses (e.g., 1.67, 1.74) bend light more efficiently, allowing for thinner lenses, which can reduce weight despite potentially higher density. The user’s lens, an SV Eyezen Start 1.67 BCT with Crizal Sapphire HR coating, is for a prescription of -5.00/-1.50 (right) and -4.75/-2.25 (left), indicating a strong prescription for nearsightedness, where weight reduction is particularly beneficial.

Factors Affecting Lens Weight

Lens weight is proportional to the product of the material’s density (specific gravity) and the lens volume, which is influenced by thickness. For the same prescription and frame size:

Specific Gravity: Measures density relative to water. Higher-index materials are often denser, which could increase weight, but their thinner profile typically offsets this.
Thickness: Higher-index lenses are thinner due to their ability to bend light more efficiently, reducing the amount of material needed.

From research, the specific gravity values for common lens materials are:

Standard plastic (CR-39, 1.5 index): 1.32
1.67 high-index (e.g., MR-7, MR-10): 1.42
1.74 high-index (e.g., MR-174): 1.52

These values indicate that higher-index materials are denser, but their reduced thickness can lead to lighter overall weight.

Thickness and Weight Calculations

To estimate weight differences, we need to consider the thickness reduction for each index. For a -5.00 prescription, typical thickness values (based on standard optical charts) are approximately:

1.5 index: 2.2 mm (center thickness for a standard frame)
1.67 index: 1.5 mm (about 31.8% thinner than 1.5)
1.74 index: 1.3 mm (about 40.9% thinner than 1.5)

The weight is proportional to density * thickness, assuming the same lens area. Let’s calculate the weight ratios:

For 1.5: Weight ∝ 1.32 * 2.2 = 2.904 (arbitrary units)
For 1.67: Weight ∝ 1.42 * 1.5 = 2.13
For 1.74: Weight ∝ 1.52 * 1.3 = 1.976

Now, compare:

Weight of 1.67 / Weight of 1.5 = 2.13 / 2.904 ≈ 0.733, so 1.67 is about 26.7% lighter than 1.5.
Weight of 1.74 / Weight of 1.5 = 1.976 / 2.904 ≈ 0.680, so 1.74 is about 32% lighter than 1.5.
Weight of 1.74 / Weight of 1.67 = 1.976 / 2.13 ≈ 0.928, so 1.74 is about 7.2% lighter than 1.67.

These calculations align with research suggesting that high-index lenses are 25-30% lighter than standard 1.5 lenses, and the difference between 1.67 and 1.74 is smaller, around 7-10%.

Detailed Comparison for User’s Prescription

For the user’s prescription (-5.00/-1.50 right, -4.75/-2.25 left), the average spherical equivalent is around -5.00, which fits well within the range where 1.67 and 1.74 lenses are recommended. The cylinder values (-1.50, -2.25) may slightly affect edge thickness, but the center thickness is the primary factor for weight.

1.67 vs. 1.5: The 1.67 lens is significantly lighter, by about 26.7%, which is noticeable and beneficial for comfort, especially for prolonged wear.
1.67 vs. 1.74: The 1.74 lens is only about 7.2% lighter, which is a smaller difference and may not be very noticeable for most users, particularly given the prescription strength is not extremely high (e.g., below -8.00).

Practical Implications and User Considerations

Compared to Standard 1.5 Lenses: Your current 1.67 lens is already a substantial improvement in weight, making it a good choice for reducing the burden on your nose and ears, especially for strong prescriptions like yours. This aligns with research from All About Vision, which notes high-index lenses can be 25-30% lighter.
Compared to 1.74 Lenses: Upgrading to 1.74 might save an additional 7-10% in weight, but this marginal difference may not justify the cost for your prescription, as noted by RX Safety, which suggests the difference is noticeable only for prescriptions below -6 or above +4.
Frame and Lifestyle: The weight difference might be more apparent with larger frames or for users sensitive to weight, such as those wearing glasses for long hours. For smaller frames or casual use, the difference between 1.67 and 1.74 may be negligible.

Table: Weight Comparison for -5.00 Prescription

Lens Index	Specific Gravity	Approximate Thickness (mm)	Relative Weight (Arbitrary Units)	Weight Difference vs. 1.5 (%)
1.5	1.32	2.2	2.904	Baseline
1.67	1.42	1.5	2.13	-26.7% (lighter)
1.74	1.52	1.3	1.976	-32.0% (lighter vs. 1.5)

This table illustrates the weight reduction, showing that 1.67 is significantly lighter than 1.5, and 1.74 offers a further small reduction.

Conclusion

In summary, your 1.67 high-index lens is approximately 25-30% lighter than a standard 1.5 index lens, providing substantial weight reduction for your -5.00 prescription. Compared to a 1.74 high-index lens, it is about 7-10% heavier, but this difference is smaller and may not be noticeable for most users. For your prescription, 1.67 is likely sufficient and cost-effective, but if you prioritize the absolute lightest option, upgrading to 1.74 could offer a slight additional benefit. Consult your optician for personalized advice based on frame choice and lifestyle needs.

Key Citations