Spectacle Lens Material Decision Tree

Transcription

1 Spectacle Lens Material Decision Tree We will investigate Lens material considerations gravity value Impact strength Lens material technical data comparisons and selling ophthalmic lenses Disclaimer Refraction I Valerie Manso am President of Manso Management Resources, Inc. A consulting company specializing in business and people development in the ophthalmic industry. I currently have ongoing relationships with Eye Solutions Technologies; and OD Excellence A numerical expression comparing the speed of light in a transparent medium, (the lens), with the speed of light in air. The higher the index of, the thinner the lens will be. 2 Learning Outcomes Calculating the Refraction At the conclusion of this session the participants should be able to: 1. Describe and compare the inherent characteristics of today s most popular lens materials: Value; ; gravity 2. Understand the importance of lesser known values such as material Clarity Index 3. Dissect and understand the importance of - Impact resistance and Light transmittance 4. Translate the key lens material characteristics into customer/patient features and benefit Speed of light in air = Speed of light through the lens Polycarbonate 186,000 miles per second (air) = Index 117,276 miles per second

2 Refraction Crown glass (1.52 index) and CR-39 plastic (1.498) are the basis for comparing lens indexes. This is the measurement of physical density, or weight of a material... expressed in grams per cubic centimeter. Lens materials with an index higher than CR-39 or crown glass are considered High Index. Refraction The higher the index of, the greater the bending (or ) of light. The lower the specific gravity of a lens material, the lighter the weight of the lens will be. This results in a thinner lens because less curvature is needed for a given power. Refraction To grasp the concept of the bending of light...think about placing a portion of a stick into a glass of water. The stick appears to bend where it meets the top of the water. This optical illusion occurs because the index of of the water and air is different. value The number or value that indicates the amount of chromatic aberration present in a lens material. The higher the value, the lower the amount of chromatic aberration.

3 Incident White Light What is chromatic aberration? Dispersed into monochromatic parts Transverse Chromatic Aberration Chromatic aberration occurs when light is bent through any lens. The greater the distance between the component wavelengths and colors, the higher the dispersion...resulting in color fringing, or blurred images through the periphery of the lens. Impact strength The impact strength of a lens material is established and measured by the FDA standard drop ball test. The greater impact resistance of a material, allows the lab to grind lenses thinner than 2.0 mm center thickness...like Trivex What is chromatic aberration? Chromatic aberration occurs when light is bent through any lens. Thicker lenses (higher powers), combined with lower values, produce greater awareness of the color dispersion. High plus and high minus wearers may notice the effects. Impact strength Some high index materials may be ground to a 1.5 mm center thickness. Others are available in stock form at 1.0 mm...still maintaining the required impact strength. value A German study suggests that patients are more likely to perceive color blur with values of less than 40. Safe Lenses for USA Drop ball test Introduced in 1972 Lenses must meet specified FDA safety standards

4 Light Transmittance All lenses reflect light in varying directions Reflections reduce transmittance Manufacturers balance all of these factors when creating a lens material... gravity value Impact strength Transmittance Transmittance Loss CR-39 (Front surface) Technical Data Comparisons Lens Type CR Value Crown Glass High Index (Resin) Polycarbonate Reflection measured through a Spectrophotometer Material 1.50 Hard Resin Reflection Per Surface Total Reflected Transmitted 4.0% 7.8% 92.2% Polycarbonate 5.1% 9.9% 90.1% 1.60 High-Index 5.3% 10.3% 89.7% 1.66 High-Index 6.0% 11.6% 88.4% Resin Comparisons Lens type value Cr Sola Japanese X-Cel Hoya Optima Zeiss

5 High Index Resin Comparisons value A D or D lens of the same diameter and center thickness would be approximately 8% heavier in the higher index material...and the lower value of the higher index material may cause the wearer visual acuity problems in the periphery of the lens. Additionally, all high index and glass materials provide more U.V. protection than CR-39 The benefit of added protection for your customers. Safety Resin Comparisons Lens type Polycarbonate Trivex (Younger) Trivex (Hoya) value However, some high index resin materials are soft and require backside surface scratch resistant coating. This may add to the processing time and may be a consideration when one hour turnaround is required. Glass Comparisons Lens type Crown Glass Flint (Tital) Flint (Lantal) Flint (Lantal) Borosilicate (Photochromic) Borosilicate (Photochromic) Barium Flint (segments) 1.68 n/a 44 value Most high index materials allow less light transmittance than CR-39 and Crown glass Some patients may complain they just don t see as clearly

6 Lens Materials and Light Transmittance Lens Material Index Transmittance % CR % Crown Glass % Polycarbonate % Mid-Index % - 92% High Index % - 89% Super high index % Recommending Balance the features of each material and select the benefits required by your customer Thinner...good cosmetics Lighter...improved comfort Optical performance...good vision Reasonable cost...value Lens Materials and Clarity Value ANSI Test Performed by COLTS Laboratory in conformance with the Code of Federal Regulation Recommending Balance the features of each material and select the benefits required by your customer Test Results: Plano lenses: 6.00 Base, 2.00 mm CT (Glass = 40) high index 28 CR-39 surfaced 24 Polycarbonate surfaced Considerations Multi-layer A.R. Coating improves CR-39 transmittance by 8%. High index wearers gain 11% to 13%. (When matched to substrate) Recommend A.R. coating on higher index lenses Recommending Establish realistic expectations for your customer Talk about a change in how they see due to a different lens material and different base curve being used Explain that this is normal and will disappear in a few days

7 Recommending Establish realistic expectations for your customer Select the features and benefits required by you Talk about the slight color dispersion they may notice at the edges of the lenses Explain that this is normal and will disappear in a few days No backside coating...quick turnaround time Reasonable cost...value for you and your customers Recommending Use good dispensing skills Select appropriately sized frames Whenever possible center the eye within the frame...too much decentration will defeat the benefits of a thinner lens material Select the features and benefits required by you Good optical performance...high value Good availability...increased sales opportunities Select the features and benefits required by you Ease of processing...fits in your standard flow Ease of tinting...nothing new to learn or execute You must balance all of these factors when selecting a lens material The higher the index the more effectively light is bent...the thinner the resultant lens...keeping in mind the need to meet FDA impact standards

8 You must balance all of these factors when selecting a lens material... gravity... The lower the specific gravity, the lighter the lens will be...regardless of index You must balance all of these factors when selecting a lens material... Answer the customer s needs with the benefits they require... use good dispensing skills and... You must balance all of these factors when selecting a lens material... value... The lower the value, the more chromatic aberration...the greater the likelihood your customer will experience visual acuity problems in the periphery of the lens.... You will navigate the spectacle lens decision tree! You must balance all of these factors when selecting a lens material... Light Transmittance... More mature patients will value increased light transmittance