Hi Index Spectral Lens Understanding
Most of the glasses wearing a relatively strong glasses correction are likely to have the Hi index lenses heard at a time. In the optical industry today, Hi index refers to any lens material that is thinner than conventional plastic, commonly known as CR39. Over the past 10 to 15 years, several new Hi index materials have been developed, making the average consumer more confusing to know what their best is.
The term "Hi index" refers to the refractive index of a particular lens material. The refractive index is the degree to which the lens material bends or distorts the light. When referring to the Hi index lenses, Eye Doctor or Optician may refer to the lens index. For example, Hi index 1.60 or Hi index 1.67 lenses. Generally, the higher the lens index, the thinner it will be for a particular glasses recipe. As a reference point, a plastic CR39 lens index is 1.49.
As a professional glasses dispenser, the Hi index lens recommendation is primarily determined by the strength of the eyepiece correction. For specimens of less than +/- 2.00, the advantages of the hi index lenses are negligible in terms of weight and thickness reduction. Often, the added cost associated with Hi Index Lenses can not be justified for lower corrections. If the recipe for glasses exceeds +/- 3.00, I usually recommend 1.60 Hi Index lenses. This lens material is 25-30% thinner than the CR39 plastic and produces a lens that is noticeably thinner and more attractive to the wearer. For recipes over +/- 5.00, the 1.67 Hi Index lens will be the selected lens. The 1.67 Hi Index lens is 40% thinner than Cr39 and works very well in this recipe range.
The Hi Index Lens is the latest generation of 1.71 and 1.74 index lenses. I will often refer to these ultra- or hyperindexs simply to differentiate them from other Hi index materials. These lenses are usually offered to people who have a correction greater than +/- 8.00. The 1.74 Hi index lenses are close to half the thickness of CR39 lenses. If you are one of the few people who have eyeglasses in this range, I can tell you that the cosmetic benefits of the 1.74 lens are surprising.
In addition to the Hi index lens, besides the thinner, natural UV blockers are also beneficial. Therefore, no UV protection or coating is required for these lenses. Angular lenses are standard with scratch-resistant coating. Some Hi index lenses also include anti reflective coatings, which is very beneficial because the Hi index lens results in greater light exposure due to the higher density of the material.
In summary, these recommendations are guidelines and there are exceptions. For example, in the case of children's glasses, the lens material is polycarbonate or trivex. These materials have a much higher impact resistance and are much safer. Use trivex or 1.67 inch index lenses for full frame frames. The material of other lenses is not a good choice for drilling and it is very easy to break through the entire frame. To achieve the best lens profile, with the high index lens you should choose the smallest frame that is still cosmetically attractive. Choose a frame with which the center of your eye is the best. The oversize frame may give the lens a thickness, especially for larger corrections.
- Published On : 4 years ago on June 6, 2018
- Author By : 346@dmin
- Last Updated : June 6, 2018 @ 11:15 pm
- In The Categories Of : Uncategorized