A corrective lens is a lens normally used in sight to improve vision. The most common use is to treat bias errors: myopia, hypermethropia, astigmatism, and presbyopia. Glasses or "glasses" worn on the face at close range in front of the eyes. Direct contact lenses are worn on the surface of the eye. The surgical intraocular lens is most often implanted after cataract removal, but can be used for purely refractive purposes.
Video Corrective lens
Resep lensa korektif
Corrective lenses are usually prescribed by an ophthalmologist or an ophthalmologist. The recipe consists of all the specifications needed to make the lens. Recipes usually include the power specifications of each lens (for each eye). Strengths are generally determined in quarter-diopter steps (0.25 D) because most people can not distinguish generally between smaller increases (eg, eighth-diopter/0.125 D) steps. The inappropriate use of corrective lenses may not help and may even aggravate binocular vision disorders. Eye care professionals (optometrists and optometrists) are trained to determine the special corrective lens that will provide the clearest, most comfortable and most efficient vision, avoid double vision and maximize binocularity.
During counter correction
Ready-made single-vision reading glasses are used by many names, including over-the-counter glasses, ready readers, cheats, magnifying glasses, non-prescription readers, or general readers. They are designed to reduce the burden of near work focus, such as reading. They are usually sold at retail locations such as pharmacies and grocery stores, but also available in bookstores and clothing retailers. They are available in general reading recipes with strengths ranging from 0.75 to 3.50 diopters. While this "magnifying" does make images of objects that are viewed larger, their main advantage comes from focusing images, not enlargement.
These glasses are not adapted to one's individual needs. The difference in the bias error between the eyes or the presence of astigmatism will not be accounted for. People with little or no need for correction in the distance may find glasses outside the workplace good enough to look better during near vision tasks. But if the person has a significant need for distance correction, it is unlikely that over the counter glasses will be very effective. Although such glasses are generally considered safe, individual recipes, as determined by ophthalmologists or ophthalmologists and made by qualified opticians, usually result in better visual correction and less headache and visual discomfort. Another criticism of over the counter glasses is that they can relieve symptoms, causing one to forget the other benefits of routine vision checks, such as early diagnosis of chronic disease.
Self refraction
Although lenses are usually prescribed by optometrists or ophthalmologists, there is evidence from developing countries that allow people to choose lenses for themselves yielding good results in most cases and less than a tenth of the cost of prescription lenses.
Maps Corrective lens
Lens type
Single vision
Single vision lens is true only for one distance. If they are correct for long distances, the person must accommodate to see clearly up close. If the person is unable to accommodate, they may require separate correction for short range, or use multifocal lenses (see below).
Reading glasses are single vision lenses designed to work closely, and include over the counter glasses. They come in two main styles: full frame, where the entire lens is made in reading recipes, and half-eyes, style goggles that sit lower under the nose. Full frame readers should be removed to see the distance clearly, while the distance can be seen clearly above the eyes of the half-life reader.
Bifocal
A bifocal is a lens with two parts, separated by a line (see picture on the right). Generally, the top of the lens is used for distance visibility, while the lower segment is used for near vision. The area of ​​the lens that serves near vision is called the added segment. There are many different shapes, sizes, and positions for additional segments selected for functional differences as well as patient visual demands. Bifocals allow people with presbyter to see clearly at a distance and near without having to remove glasses, which will be required with single vision correction.
Trifocal
Trifocal lenses are similar to bifocals, except that the two focus areas are separated by a third area (with middle focus correction) in the middle. This segment corrects the user's vision for medium range approximately by arm range, distance of computer for example. . This type of lens has two segment lines, dividing the three different correction segments.
Progressive
Progressive or progressive varifocal lenses provide a smooth transition from correction of proximity to near correction, eliminating segment lines and allowing clear visibility at all distances, including medium range (approximately arm). The lack of abrupt changes in power and the uniform appearance of the lens give rise to the name "no-line bifocal".
Multifocal
Multifocal contact lenses (eg bifocal or progressive) can be compared with glasses with bifocal or progressive lenses because they have multiple focal points. Multifocal contact lenses are usually designed for continuous viewing through the lens center, but some designs do combine lens position shifts to see through the reading power (similar to bifocal glasses).
Setable focus
The adjustable strength or focal length or variable can be changed to meet the needs of the wearer. Typical applications of such lenses are refocused correction that allows clear vision at any distance. Unlike bifocals, close vision correction is achieved across the field of view, in all directions. Switching between distance and near vision is achieved by adjusting the lens back, not by tilting and/or turning the head. The need for constant adjustment when one's attention shifts to objects at different distances is the design challenge of the lens. Manual adjustments are more complicated than bifocals or similar lenses. Automatic systems require electronic systems, power supplies, and sensors that increase the cost, size, and weight of corrections.
Plano
Corrective lens with zero strength is called a plano lens. This lens is used when one or both eyes do not require corrections of bias errors. Some people with good natural vision want to wear glasses as style accessories, or want to change the appearance of their eyes using new contact lenses.
Optical lens profiles
Although corrective lenses can be produced in many different profiles, the most common are ophthalmic or convex-concave. In the eyepiece, the front and rear surfaces have a positive radius, producing a positive/convergent front surface and a negative/diverging back surface. The difference in curvature between the front and rear surfaces leads to the corrective strength of the lens. In hyperopia a convergent lens is required, therefore a converging front surface beats a different back surface. For myopia, the opposite is true: the different back surfaces are larger than the converging front surface. To improve presbyopia, lens, or part of the lens, it should be more convergent or less different from the distance lens of the person.
The base curve (usually determined from the front surface profile of the eyepiece) can be altered to produce the best optical and cosmetic characteristics across the lens surface. Opticians may choose to specify a particular base curve when prescribing corrective lenses for any of these reasons. A large number of mathematical formulas and professional clinical experience have enabled ophthalmologists and lens designers to determine the ideal basic curve that is ideal for most people. As a result, the more standard front surface curves and characteristics that produce a person's unique recipe usually originate from the back surface geometry of the lens.
Bifocals and trifocals
Bifocals and trifocals produce more complex lens profiles, combining multiple surfaces. The main lens consists of a typical ophthalmic lens. Thus the base curve defines the front surface of the main part of the lens while the rear surface geometry is altered to achieve the desired distance strength. The "bifocal" is a third sphere segment, called add segment , found on the front surface of the lens. Steeper and more convergent from the base curve, the add segment combines with the back surface to provide a person near correction. Early manufacturing techniques fused separate lenses to the front surface, but modern processes cut all geometry into one piece of lens material. There are many locations, profiles, and sizes of segment additions, commonly referred to as segment types. Some examples of "seg type" include Flat top, Kryptok, Orthogon, Tillyer Executive, and Ultex A. Trifocals contain two additional segments to achieve the lens that corrects the person's vision for three different distances.
Optical centers of additional segments may be placed on the lens surface or may hang onto empty space near the lens surface. Although the surface profile of the bifocal segment is round, it is often trimmed to have a straight edge so that it is contained within a small area of ​​the lens surface as a whole.
Progressive lens
Progressive additional lenses (PAL, also commonly called a no-line or varifocal lens) eliminate lines in bi/tri-focals and are very complex in their profiles. PAL is a continuously varying parametric surface that begins to use a base curve of the sphere and ends on another, with radius of curvature that changes continuously when the transition is made from one surface to another. The shift in this curve produces different forces that are sent from different locations on the lens.
Vertex Distance
Distance vertex is the space between the front of the eye and the back surface of the lens. In glasses with a power exceeding Ã, Â ± 4.00D, point spacing can affect the effective strength of the glasses. Shorter point spacing may expand the field of view, but if the vertex distance is too small, the eyelashes will come into contact with the back of the lens, smear the lens and cause disruption to the wearer. A skilled frame designer will help the wearer choose a good balance of fashionable frame sizes with good vertex spacing to achieve the ideal aesthetics and field of view. Average angular distance in a pair of glasses is 12-14mm. The contact lens is placed directly on the eye and thus has a zero point distance.
Refractive index
In the United Kingdom and the United States, the refractive index is generally determined in relation to the yellow Fraunhofer He-d line, commonly abbreviated as n d . Lense materials are classified according to their refractive index, as follows:
- Normal index: 1.48 <= n d & lt; 1.54
- Mid-index: 1.54 <= n d & lt; 1.60
- High index: 1.60 <= n d & lt; 1.74
- The index is very high: 1.76 <= n d
This is a general classification. Index n d values ​​that> = 1.60 can, often for marketing purposes, are referred to as high indexes. Likewise, Trivex and other normal/mid-index material materials, can be referred to as the middle index.
Advantages of higher index
- Thin, sometimes lighter lens (See below).
- Enhanced UV protection through CR-39 and glass lenses.
Lack of index increases
- The lower Abbe score, which means, among other things, increases colored deviations.
- The worse light transmission and increased reflections of the rear and inner surface (see Fresnel's reflection equation), increase the importance of the anti-reflective coating.
- Manufacturing defects have a greater impact on optical quality.
- Theoretically, the optical degradation of off-axis (oblique astigmatic error). In practice, this degradation should not be visible - the current frame style is much smaller than it should be for this irregularity to be visible to the patient, a distortion occurring some distance from the optical center of the lens (off-axis).
Optical quality
Abbe Number
Of all the properties of a particular lens material, most closely related to optical performance is the dispersion, which is specified by the Abbe number. Lower Abbe numbers result in chromatic aberrations (ie, color borders on/down or to the left/right of high contrast objects), especially in larger lens sizes and stronger recipes (above Ã, Â ± 4.00D ). Generally, the lower Abbe number is the middle and higher index lens properties that can not be avoided, regardless of the material used. The Abbe number for materials on a particular refractive index formulation is usually defined as its Abbe value.
In practice, a change from 30 to 32 Abbe will have no visible benefits, but a change from 30 to 47 can be beneficial to users with powerful recipes that move their eyes and look "off-axis" the optical center of the lens.. Note that some users do not feel the fringing color directly but will only describe "blurriness off-axis". The abbe value is even as high as that (V d <= 45) produces chromatic aberrations that can be felt by the user in lenses larger than 40 mm and especially in strengths in excess of  ± 4D. In Ã,  ± 8D even glass (V d <= 58) produces a chromatic aberration that the user may notice. Chromatic aberration does not depend on a spherical, aspheric, or atoric lens.
The Abbe number of the eye does not depend on the importance of corrective lens, Abbe, because the human eye:
- Move to keep the visual axis close to its acromatic axis, which is completely free of dispersion (that is, to see the dispersion that must be centered on points on the periphery of vision, where visual clarity is very bad)
- Very insensitive, especially for color, in the periphery (ie, at the point of the retina far from the acromatic axis and thus does not fall on the fovea, where the cone cells responsible for color vision are concentrated. See : Retinal Anatomy and Physiology. )
Instead, the eye moves to see various parts of the corrective lens when the lens shifts its view, some of which can reach several centimeters from the optical center. Thus, despite the dispersive nature of the eye, corrective lens dispersion can not be dismissed. People who are sensitive to the effects of chromatic aberrations, or who have more powerful prescriptions, or who often see the optical center of the lens, or who prefer larger corrective lens sizes may be exposed to chromatic aberrations. To minimize chromatic aberrations:
- Try to use the smallest comfortable size vertical lenses. In general, colored aberrations are more noticeable when the pupil moves vertically below the optical center of the lens (for example, reading or viewing the ground while standing or walking). Keep in mind that smaller vertical lens sizes will produce more vertical head movements, especially when engaging in activities involving short- and medium-range observations, which can lead to increased neck tension, especially in jobs involving large vertical fields. from the view.
- Limit the selection of lens materials to the highest Abbe value at acceptable thickness. The most commonly used most common lens materials also have the best optical characteristics at the expense of corrective lens thickness (ie, cosmetics). Newer materials have focused on improving cosmetics and enhancing impact security, at the expense of optical quality. Lenses sold in the US must pass the influence of the ball-effect Administration of Food and Drug Administration, and depending on the required index it seems that it currently has the "best in class" Abbe vs Index (N d ) : Glass (2x plastic weight) or CR-39 (thickness 2 mm vs. 1.5 mm on new material) 58 @ 1.5, Sola Spectralite (47@1.53), Sola Finalite (43@1.6), and Hoya Eyry (36 @ 1.7). For impact resistance glass is offered on various indexes on high Abbe numbers, but still 2x plastic weight. Polycarbonate (V d = 30-32) is highly dispersive, but has excellent crushing power. Trivex (V d = 43 @ 1.53), is also highly marketed as a polycarbonate-resistant alternative, for individuals who do not require polycarbonate index. Trivex is also one of the lightest materials available.
- Use contact lenses instead of glasses. Contact lenses are located directly on the surface of the cornea and move in tune with all eye movement. As a result, contact lenses are always straight in the center with pupils and there is never an off-axis imbalance between the pupil and the optical center of the lens.
Power error
The power failure is the optical power change of the lens when the eye sees through various points on the lens area. Generally, it is at least in the optical center and gets worse as one looks toward the edge of the lens. The actual number of power errors is highly dependent on the strength of the recipe as well as whether the best spherical shape or optimal optical asferic shape is used in the manufacture of the lens. Generally, the best spherical lens attempts to keep the ocular curve between four and seven diopters.
Lens induced oblique astigmatism
As the eye shifts its view from viewing through the optical center of the corrective lens, the value of lens-induced astigmatism increases. In round lenses, especially one with strong correction whose base curves are not in the shape of the best balls, the increase can significantly impact the clarity of the vision at the edges.
Minimizing power errors and lens induces astigmatism
As the corrective force increases, the optimally designed lens will have distortions that the user may notice. This primarily affects individuals who use their off-axis lens area for visual demanding tasks. For individuals who are sensitive to lens errors, the best way to remove irregularities caused by the lens is to use contact lenses. Contact eliminates all these irregularities because the lens then moves with the eye.
Except for contacts, good lens designers do not have many tradable parameters to improve vision. Index has little effect on error. Note that, although chromatic aberrations are often regarded as "blurred vision" on the periphery of the lens and give the impression of a power fault, this is actually due to a shift in color. Chromatic aberration can be improved by using materials with enhanced ABBE. The best way to combat lens errors caused by the lens is to limit the selection of corrective lenses with the best spherical lens. A lens designer determines the best ball shaped curve using the Oswalt curve on the Tscherning ellipse. This design provides the best attainable optical quality and the smallest sensitivity for lens mounting. The flat base curve is sometimes chosen for cosmetic reasons. Aspheric or atoric design can reduce errors caused by the less optimal use of flat base curves. They can not exceed the optical quality of the best spherical lens, but can reduce the induced error by using a flatter base curve than optimal. The increase due to the clearest alignment for the powerful nearsighted lens. High Myopes (-6D) can see a slight benefit of cosmetics with larger lenses. A lightweight recipe will have no obvious benefits (-2D). Even on high recipes, some high-myopia recipes with small lenses may not notice any difference, as some aspheric lenses have a spherically designed center area to improve vision and suitability.
In practice, the laboratory tends to produce finished and finished lenses in a narrow power range group to reduce inventory. The strength of the lens that falls into the range of recipes each group shares a constant base curve. For example, the correction from -4.00D to -4.50D can be grouped and forced to share the same basic curve characteristics, but the ball shape is only best for the -4.25D recipe. In this case his faults will be invisible to the human eye. However, some manufacturers may further reduce inventory costs and categorize larger ranges which will result in a clear error for some users within the range that also use their off-axis lens area. In addition some manufacturers may approach a slightly more flat curve. Although if only a small bias against the plano is introduced, it can be neglected cosmetically and optically. This optical degradation is due to the base-curve grouping also applicable to aspherics because the shape is deliberately flattened and then aspirated to minimize errors for the average base curve in grouping.
Cosmetics and weight loss
Reduce lens thickness
Note that the largest cosmetic increase in lens thickness (and weight) is obtained from selecting frames that store small lenses physically. The smallest adult lens size available in retail outlets is about 50 mm (2.0 inches). There are several adult sizes of 40 mm (1.6 inches), and although they are quite rare, can reduce the weight of the lens to about half of the 50 mm version. Curves in the front and back of the lens are ideally formed with a certain radius sphere. These fingers are arranged by lens designers based on prescription and cosmetic considerations. Choosing a smaller lens means less than the surface of the ball is represented by the lens surface, which means the lens will have a thinner edge (myopia) or center (hyperopia). The thinner edges reduce the incoming light to the edges, reducing additional sources of internal reflections.
The very thick lenses for myopia can be tilted to reduce the flaring out from the very thick edges. Thick nearsighted lenses are usually not mounted on a wire frame, because thin wire contrasts with thicker lenses, to make the thickness much clearer to others.
The index can increase lens thinness, but at one point, no more improvements will be realized. For example, if the index and lens size are chosen with a difference in thickness between 1 to 1 mm then the index change can only increase the thickness by a fraction of this. This is also true with aspheric design lenses.
The minimum thickness of the lens can also vary. FDA ball drop test (5/8 "0.56 ounces steel ball dropped from 50 inches) effectively regulates minimum material thickness Glass or CR-39 requires 2.0 mm, but some newer materials only require 1.5 mm or even 1.0 mm minimum thickness.
Weight
Material density usually increases as lens thickness decreases with increasing index. There is also the minimum lens thickness required to support lens shapes. These factors produce thinner lenses that are not lighter than the original. There is a lens material with a lower density on the higher index that can produce a lens that is actually lighter. These materials can be found in the material properties table. Reducing the size of the lens frame will provide the most noticeable weight increase for the given material. How to reduce the weight and thickness of the corrective lens, in order of importance are:
- Choose a frame of glasses with a small lens; that is, so that the longest measurements across the lens at each angle are as short as possible. This provides the greatest benefit of all.
- Choose a frame that allows the pupil to occupy the center of the lens.
- Select the lens as close as you can. It's less common than other forms.
- Select a high refractive index for lens materials as licensing fees.
It is not always possible to follow the above points, because of the scarcity of such frames, and the need for a more pleasing appearance. However, this is a major factor to consider if it is necessary and possible to do so.
Glasses for far-sighted or far-sighted people cause visible distortions on their faces as seen by others, in clear eye size and facial features visible through eyeglasses.
- For farsightedness the eyes look small and concave to the face, and the side of the skull can be seen through the lens. This gives the wearer the appearance of having a very large or fat head contrasting with their eyes.
- For the farsighted eyes look very large on the face, making the head of the wearer look too small.
Both situations can lead to social stigma due to some face distortion. This can lead to low self-esteem wearers and cause difficulties in making friends and developing relationships.
People with very high-strength corrective lenses can obtain social benefits from contact lenses because these distortions are minimized and the appearance of their faces to others is normal. The design of asperic/atoric glasses can also reduce enlargement and enlargement of the eyes for observers in some angles.
Lens materials
The optical crown glass (B270)
Schott B270 is an optical glass used in precision optics. This is not a glass eye. Schott glass type is S-1 and S-3. The problem here is the wrong number for UVA and UVB transmissions, as well as other related product type issues.
Glass lenses are becoming less common because of the danger of breakage and relatively high weight compared to CR-39 plastic lenses. They are still used for special circumstances, for example in very high prescriptions (currently, glass lenses can be made up to a refractive index of 1.9) and in certain jobs where hard glass surfaces offer more protection than splashes or fragments of material.. If the highest Abbe value is desired, the only options for common optical lens materials are optical glass and CR-39.
High quality optical glass materials exist (eg Borosilicate crown glasses such as BK7 (n d = 64,17/D = 2.51 g/cmÃ,³), commonly used in telescopes and binoculars, and fluorite crown goggles such as Schott N-FK51A (n d = 1.48656/V d = 84.47/D = 3.675 g/cmÃ,³), which is 16.2 times the price of a comparable number of BK7, and is usually used in high-end camera lenses). However, one would find it very difficult to find a laboratory that would be willing to acquire or form a special eyeglass lens, since the sequence most likely consists of only two different lenses, from these materials. Generally, the value of V d above 60 is a dubious value, except in combination of extreme recipes, large lens size, high user sensitivity to dispersion, and work involving work with high contrast elements (eg reading dark print on very bright white paper, construction that involves contrasting building elements against a cloudy white sky, a workplace with hidden tins or other concentrated small area lighting etc.).
Plastic
For CR-39:
- Refractive index (n d ): 1,498 (standard)
- The value of Abbe (V d ): 59.3
- Density: 1.31 g/cmÃ, ³
- cutoff UV: 355
Current plastic lenses are the most commonly prescribed lenses, due to their relative safety, low cost, ease of production, and high optical quality. The main disadvantage of many types of plastic lenses is the ease with which the lens can be scratched, and the limitations and costs of producing higher index lenses. The CR-39 lens is an exception because it has an inherent scratch resistance.
Trivex
- The refractive index (n d ): 1.532
- Abbe value (V d ): 43-45 (depending on manufacturer license)
- Density: 1.1 g/cmÃ,³ (lightweight corrective lens material commonly used)
- UV cutoff: 394Ã, nm
Trivex was developed in 2001 by PPG Industries for the military as a transparent armor. With Hoya Corporation and Younger Optics PPG announced the availability of Trivex for the optical industry in 2001. Trivex is a pre-polymer based urethane. PPG named Trivex material because of its three main performance properties, superior optics, ultra light weight, and extreme strength.
Trivex is a newcomer who has UV-blocking properties and destructive resistance of polycarbonate while at the same time offering far superior optical quality (ie, higher Abbe values) and slightly lower density. Its lower bias index of 1,532 vs 1,586 polycarbonates can produce a slightly thicker lens depending on the prescription. Along with polycarbonate and various high index plastics, Trivex is a favorite laboratory for use in frameless frames, due to its drillability and its resistance to cracking around the borehole. One other advantage Trivex has over polycarbonate is that it can be colored.
Polycarbonate
- The refractive index (n d ): 1.586
- Abbe value (V d ): 30
- Density: 1.2 g/cmÃ,³
- UV cutoff: 385 nm
Polycarbonate is lighter than ordinary plastic. It blocks UV rays, crush resistance and is used in sports cups and glasses for children and adolescents. Because polycarbonate is soft and easily scratched, a scratch-resistant coating is usually used after forming and polishing the lens. Standard Polycarbonate with Abbe value 30 is one of the worst materials optically, if chromatic false intolerance becomes a concern. Along with Trivex and high index plastic, polycarbonate is an excellent choice for borderless glasses. Similar to high index plastics, polycarbonate has a very low Abbe value, which can disrupt individuals sensitive to chromatic aberrations.
High-index_plastics_.28thiourethanes.29 "> High index plastic (thiourethanes)
- Refractive index (n d ): 1.600-1.740
- Abbe value (V d ): 42-32 (higher index generally yield lower abbe value)
- Density: 1.3-1.5 (g/cmÃ,³)
- UV cutoff: 380-400Ã, nm
High index plastic allows for thinner lenses. The lens may not be lighter, however, due to increased density vs. mid and normal index materials. The disadvantage is that high index plastic lenses suffer from much higher levels of chromatic aberrations, which can be seen from their lower Abbe values. In addition to thinness of the lens, another advantage of high index plastic is its strength and resilience to crush it, although it can not stand to break apart like polycarbonate. This makes them very suitable for borderless glasses.
Plastics with high refractive index are typically thiourethan, with sulfur atoms in the polymer responsible for high refractive index. The sulfur content can reach 60 weight percent for the material n = 1.74.
Property table of endalmic materials
The reflected light is calculated using the Fresnel reflection equation for the normal wave to air at the two interfaces. This is a reflection without AR coating.
Refractive index for various materials can be found in the refractive index list.
Lens coating
Anti-reflective
An anti-reflective coating helps make the eye behind the lens more visible. They also help reduce the reflection of the white back of the eyes as well as the bright objects behind the wearer's glasses (eg windows, lamps). Such a reduction of rear reflection increases the apparent contrast of the surrounding environment. At night, the anti-reflective coating helps to reduce the light from the oncoming car, the street lights, and the very bright lights or fluorescent lights.
One problem with anti-reflective layers is that historically they are very easily scratched. Newer layers, such as Crizal AlizÃÆ' Â © UV with 5.0 and Hoya's Super HiVision ratings of 10.9 on the Bayer Abrasion Test COLTS (12-14 glass average), try to overcome this problem by combining scratch resistance with an anti-reflective coating.. They also offer a measure of dirt and stain spots, due to its hydrophobic nature (contact angle of droplet 110 Â ° for Super HiVision and 116 Â ° for Crizal AlizÃÆ' Â © UV).
Ultraviolet protection
The UV layer is used to reduce the transmission of light in the ultraviolet spectrum. UV-B radiation increases the likelihood of cataracts, while long-term exposure to UV-A radiation can damage the retina. DNA damage from UV rays is cumulative and irreversible. Some materials such as Trivex and Polycarbonate, naturally block most UV rays; they have a UV-cutoff wavelength just outside the visible range, and do not benefit from the application of UV coating. Many modern anti-reflective coatings also block UV.
Scratch resist
Rejects lens surface damage from light scratches.
Confusing the corrective lens industry terminology
Spheric vs. asferic, atoric, etc.
Lens manufacturers claim that aspheric lenses enhance vision through traditional spherical lenses. This statement can be misleading to individuals who do not know that the lens is implicitly compared to "a spheric leveled off the best shape for cosmetic reasons". This qualification is necessary because the best form of the ball is always better than aspheric for eyepiece applications. Aspherics are only used for corrective lenses when, to achieve a flat lens for cosmetic reasons, lens design deviates from the best shape; this results in degradation of visual correction, degradation which can, in some parts, be compensated by aspheric design. The same is true for atoric and bi-asferic.
While it is true that aspheric lenses are used in cameras and binoculars, it would be wrong to assume that this means aspherics/atorics produces better optics for eyeglasses. Cameras and telescopes use many lens elements and have different design criteria. Glasses are made of only one eyepiece, and the best shape spherical lenses have been shown to provide the best vision. In cases where the best shape is not used, such as uneven cosmetics, thinning or wrap-around sunglasses, aspheric design can reduce the amount of optical distortion caused.
It should be noted that the aspheric lens is a broad category. The lens is made of two curved surfaces, and an aspheric lens is a lens where one or both surfaces are not round. Further research and development is underway to determine whether the mathematical and theoretical benefits of aspheric lenses can be implemented in practice in a way that results in better vision correction.
Optical lens eyepiece vs. corrective lens
The term optics is used to describe errors in the lens of the eye and the corrective lens. This can cause confusion because "astigmatism" or "ABBE" has a very different impact on vision depending on the lens that has errors.
Disambiguation syndrome
Astigmatism of the eye: People prescribe ball and cylinder prescriptions have eye astigmatism and can be given toric lenses to correct them.
Corrective lens astigmatism: This phenomenon is called lens-induced astigmatism error (OAE) or power errors and is induced when the eye sees through the lens of the eye at an angled point to the optical center (OC). It may become very clear outside -6D.
Example: A patient with astigmatism (or no astigmatism) eyes and a high prescription may pay attention to lens astigmatism (OAE) when looking through the corner of their glass.
Asperic and atoric deviation
In the terminology of the eye, "aspheric lens" specifically refers to the subclass of aspheric lenses. The design features a "flat" optical quality trading curve for cosmetic appearance. By using non-spherical lens shapes, aspheric lenses try to correct errors caused by flattening the lens. Typically, the design focuses on reducing errors (OAE) across the horizontal and vertical lens axis sides. This is especially useful for people who are far-sighted, whose lenses have a thick center.
Atorik lens design refers to a lens with a more complex aspheric lens design. Atorik lens design can overcome errors in more lens angles, not just horizontal and vertical axes.
Toric lenses are designed to compensate for the astigmatism of the patient's eyes. Although these lenses are technically "aspheric", the terms "aspheric" and "atoric" are provided for lenses that correct errors caused by evenly distributed cosmetic lenses.
US. legal requirements for recipes
In the US, federal and state laws at the federal and state levels govern the terms and dates of effective prescriptions for contact lenses and eyeglasses. The federal law requires that glasses and prescription contact lenses be given to every consumer, and that the prescription is at least one year old. (FTC Section 456.2 "Separation of checks and expenses" reviewed in 2004: FTC 2004 review of section 456.2)).
State laws vary. For example, California law also requires a prescription to be given to the client whether asked or not. Prescription glasses should be at least 2 years, and contact recipes should be at least 1 year.
See also
- Contact lens
- Dioptre
- Prescription eyewear
- Lorgnette
- Monocle
- Photochromic Lenses
- Pince-nez
- Visual acuity
References
Source of the article : Wikipedia
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