Professional knowledge Q&A on optometry and glasses fitting

Question 1: What is the difference between resin lenses and glass lenses? What are the advantages of resin lenses?

Answer: Comparison between resin lenses and glass lenses

CR39 resin lens glass lens

1. Transmittance: 92% 91%

2. Specific gravity: 1.32g/cm3 2.54g/cm3

3. Impact resistance test (16g steel ball)

1.27m free fall] does not shatter

4. Crushing condition: Large blocks, no sharp edges, fine fragments, sharp edges

5. UV blocking: 390nm 290-300nm

6. Refractive index 1.502 1.523

7. Thickness: thicker, thinner

8. Wear resistance: Glass is better than resin

9. Atomization trend: Resin is better than glass, reducing 60-75%

10. Dyeing: Easy to dye, not easy to dye

Question 2: What kind of glasses are good for children with amblyopia?

Answer: Children with monocular or binocular amblyopia often have weaker defense responses to sudden risk factors than normal children due to visual impairments. According to Professor Richard London, an optometrist at the School of Optometry at the University of California, Berkeley, amblyopia patients, especially children, are 17 times more likely to suffer from eye injuries than normal individuals. Experts emphasize that resin lenses must be used when preparing corrective glasses for amblyopia patients. Because the impact resistance of resin lenses is more than 8 times that of glass lenses. By utilizing the high impact resistance of resin lenses, it can be said that they provide a protective barrier for the eyes.

If such children are given glass lenses, it undoubtedly increases the risk of eye trauma for visually impaired children. This applies not only to children with amblyopia, but also to all patients with poor vision.

Given the high impact resistance of resin lenses, developed countries including Japan, Australia, the United Kingdom, France, and other Western European countries have legislated to require the use of resin lenses for minors under the age of 16 from the perspective of protecting their visual health. The US Food and Drug Administration (FDA) stipulates that all formulated frame glasses must use resin lenses, unless specifically prescribed by a doctor.

Question 3: What is the significance of hardening eyeglass lenses?

When we go to an eyewear store to get glasses, especially resin lenses, we often hear the fitting personnel ask: Do we need to add hard lenses or not? Consumers often hesitate about this.

Answer: Lens hardening is achieved by organic silicification of the inner and outer surfaces of the lens, forming thermochemical and mechanical protective layers on the inner and outer surfaces of the lens to increase the corrosion resistance and friction resistance of the resin material.

The anti friction performance of resin materials is not as good as that of glass materials, but after organic silicification and hardening treatment, the surface anti friction performance of resin lenses is very close to that of glass lenses.

Some consumers now believe that resin eyeglass lenses are not resistant to friction, often because they use uncured resin lenses, coupled with improper care methods. In just a few months, the effect of correcting vision is affected by scratches on the surface of the lenses, which affects consumers' visual health and increases their economic burden.

Currently, in developed countries, resin lenses without hardening are no longer used except in special circumstances. In recent years, domestic experts have also proposed to stop using uncured resin lenses in order to protect the interests of consumers. For example, the Shanghai Glasses Industry Association has made regulations to prohibit the sale of uncured resin lenses within the city limits in order to protect the legitimate rights and interests of consumers.

Question: 4. How to use and maintain glasses correctly?

Fully qualified glasses also require proper use and careful maintenance. Improper use or maintenance can cause deformation of the mirror frame and abrasion of the lenses, which can affect the wearing effect and even cause damage to the eyes.

1. When not wearing glasses, it is best to keep them in the glasses case. The surface of the lens should not come into contact with hard objects, especially be careful not to place the legs of the lens facing upwards and the mirror surface facing downwards. Especially for children with farsightedness or amblyopia, convex lenses are prone to wear and tear in the optical center. If the lens is not used properly, it may become frosted into a ground glass shape, which can even cause form deprivation amblyopia and make treatment difficult.

2. It is best to clean the lenses with water, using 1-2 drops of dishwashing detergent. After washing, rinse thoroughly with clean water, air dry or use a soft tissue to absorb dry.

3. Resin lens specific fiber wiping cloth can be used for wiping, and the cloth should be washed with clean water. Be especially careful not to wipe with clothing corners or hard cloth.

4. We should develop the habit of wearing glasses with both hands. Long term single handed wearing of glasses can cause the frame to gradually twist and deform, resulting in a skewed mirror surface or even different inclinations of the lenses on both sides, causing the center of the lens to shift and resulting in the prism effect - affecting vision and visual fatigue. Due to long-term effects, the lack of awareness exacerbates the decline in vision.

Loose frame can also cause misalignment between the optical center and the pupil, resulting in prism effect and causing visual fatigue.

Over time, if you get used to crooked glasses, you may not be able to accept completely qualified glasses when replacing them. Especially for adolescent students who wear progressive multifocal lenses for the prevention and treatment of myopia, as well as elderly people who need to wear close range lenses, attention should be paid, as the effectiveness of progressive multifocal glasses is closely related to the specifications of the frame.

5. Regularly inspect and if the frame is found to be twisted or damaged, promptly seek professional repair and correction from an eyewear store.

6. I feel that the effect of correcting vision is not as good as before. I should investigate the cause and promptly re evaluate and adjust my glasses.

Question 5: Why do eyeglass lenses need to be coated, and what are the advantages of coated lenses?

The coating of eyeglass lenses refers to the physical and chemical methods used to coat the surface of eyeglass lenses with a certain thickness of single-layer or multi-layer optical films, so that the lenses can obtain some new and excellent properties that were not originally possessed.

At present, there are mainly: 1. Anti reflection film. 2. Top membrane

1. Anti reflective film (anti reflective film) is a multi-layer film.

Both resin and glass lenses cannot achieve 100% transmittance, and some light will be reflected back by the two surfaces of the lens. The higher the refractive index of the lens, the higher the reflectivity. Resin 4%, glass 4.3%.

The reflection of lenses can reduce the transmittance of light and form interference images in the retina, affecting the quality of imaging and the appearance of the wearer. If the appearance of the lens has obvious vortices, the camera reflects light, and the wearer's eyes cannot be seen. wait.

Anti reflection film is the most commonly used type in optical coating, which interferes and eliminates the reflected light of the mirror surface and the reflected light of the coating based on the principle of light interference. By selectively eliminating the reflection of light in the corresponding wavelength band through different film layers, interference light is removed, and visible light transmittance is increased to improve image quality. Make the imaging clearer and reduce visual fatigue.

It is also possible to selectively reduce the transmission of harmful rays such as ultraviolet rays, X-rays, etc., in order to minimize their damage to the eyes and protect them from harm.

At present, the anti reflection film of resin lenses has reached up to nine layers, reducing the reflectivity to around 0.2% and making the transmittance of resin lenses reach over 99%. Greatly improving the quality of imaging and achieving the best correction effect.

2. Top membrane (waterproof membrane, anti fog membrane)

Due to the technical requirements of the anti reflection film, there are large gaps between the molecules of the film, which makes it easy for dirt and grime to accumulate on the surface of the lens.

The top film material has small molecular particles and small gaps between molecules, making the surface of the lens smoother and adding functions such as waterproof, anti fog, dustproof, and pollution prevention.

Question 6: What kind of glasses are suitable?

Whether glasses are suitable should be measured from two aspects: the quality of assembly and production of glasses, and the wearing effect.

1、 The quality of glasses assembly is judged by whether the optical quality of the glasses meets the national standards for assembling glasses. The main indicators include:

1. Allowable deviation of lens vertex power (allowable error between lens power and refractive power)

2. Optical center horizontal deviation (deviation of 9-2mm between the optical center distance of the glasses and the prescription pupillary distance of the wearer)

3. Vertical difference between optical centers (the difference in height between the optical centers of two lenses is 3-0.5mm)

4. Allowable error in the axis position of the prism. 6--20

Whether the assembly of glasses complies with GB is a very professional issue, which is controlled by technical supervision departments at all levels using specific instruments and equipment to regularly supervise and inspect eyewear stores. Consumers cannot confirm whether the above indicators are qualified with their naked eyes.

2、 The main criteria for determining whether the wearing effect is good or not include:

1. Safe. Whether the glasses are safe is very important.

2. Comfortable. Are the completed glasses suitable for the wearer themselves.

3. Ideal for correcting vision. Whether the optimal optical effect for correcting refractive errors has been achieved.

Question 7: How can I get a suitable pair of glasses?

We know what qualified glasses are and how to choose suitable glasses? This requires close cooperation between hospitals, eyewear stores, and individual consumers.

For eyewear stores, accurate optometry, accurate assembly of glasses, and accurate calibration of eyeglass frames are all indispensable.

For consumers, choosing the right lenses, choosing the right frame, and carefully cooperating with optometry and calibration are all essential.

The selection of lenses mainly considers products that are safe, lightweight, have high light transmittance, can absorb harmful rays to the eyes, wear-resistant, have good chemical stability, and are practical.

The most important consideration when choosing a frame is the conformity between the pupillary distance (PD) and the frame, followed by aesthetics.

Attention should be paid to: 1. Horizontal position: The horizontal position of the pupil inside the eyeglass frame should be located near the geometric center of the frame.

2. Vertical position: The edge of the lower eyelid should be located at the vertical center of the frame.

The drawbacks of choosing a too large frame: a. Increased weight, causing discomfort b. Excessive displacement of the center of the frame, affecting quality

c、 Forming a reflection image, causing visual interference and edge distortion, affecting the appearance

It is best for children to choose plastic frames, as the metal frame has a larger nose support and the weight is concentrated in the nasal bone area, which affects the development of the nasal bone. Children's eyeglass frames should pay special attention to the consistency between PD (pupillary distance) and FPD (geometric center distance of the frame), and replace the frame in a timely manner according to growth and development.

The main cooperation in optometry is to promptly inform the optometrist of any discomfort during the optometry or fitting process, so that adjustments can be made in a timely manner to find a more suitable degree.

When fitting the mirror frame, it is necessary to cooperate with the fitting inspector and promptly point out any uncomfortable areas to wear.

The calibration of mirror frames generally includes three aspects:

1. The plane of the eyeglass lens is perpendicular to the frame leg and tilts inward by about 10-15 degrees

2. The distance between the back of the lens and the vertex of the cornea is about 12 mm.

3. The center of the pupils in both eyes is located slightly above 1/2 of the height of the lens when viewed from the front.

The calibration quality of the frame is related to the optimal optical fit between the glasses and the eyes, and is an essential factor in obtaining a suitable pair of glasses.

Question8: What kind of lenses should school aged children choose?

Answer: School aged children are lively and active, but their awareness and ability to protect themselves are relatively poor. It is not uncommon for them to break their lenses or even injure their eyes. When choosing lenses for children, safety should be the top priority, and it is advisable to choose resin lenses for children's glasses.

1. The impact resistance of resin lenses is 8 times or even higher than that of glass lenses, and the lenses generally do not break. Given this safety feature of resin lenses, there are legal regulations in developed countries that designate them as designated products for lenses for children under 16 years old. The FDA in the United States stipulates that, unless specifically requested by ophthalmologists, all individuals must use resin lenses for eyeglass fitting.

2. Resin lenses are lightweight and can reduce concerns about poor nasal bone development in children caused by eyeglass compression. Good comfort can reduce children's rebellious psychology towards glasses.

3. Resin lenses can absorb ultraviolet radiation and block harmful rays with wavelengths below 400nm, which can protect the eyes.

4. The transmittance of resin lenses treated with coating has exceeded 99%. The quality of imaging is better.

5. Resin lenses can serve as a protective barrier for the eyes. According to a report by Beijing Evening News, there are over 100000 cases of eye injuries among primary and secondary school students in the United States due to participating in sports activities each year. The American Academy of Ophthalmology and the Academy of Pediatrics have jointly called for the mandatory use of resin based eye protection glasses for children and adolescents to participate in sports activities. Experts point out that 90% of the above-mentioned accidents can be avoided if goggles are worn.

Question: 9. What is progressive multifocal lens and what are its advantages?

Progressive multifocal lens is a type of lens with different degrees of magnification, with the upper part used for looking far and the lower part used for looking close. The fixed distance power above the lens to the fixed near power below the lens does not change suddenly, but gradually transitions between the two through a gradual change in refractive power. Compared with ordinary dual or triple lenses, it has the following advantages.

1. The appearance of the lens is like a single lens, and there is no visible boundary between the degree changes. Not only does it have a beautiful appearance, but more importantly, it protects the age privacy of the wearer, so there is no need to worry about leaking age secrets due to wearing glasses.

2. Due to the gradual change in lens power, there will be no image jumping. Comfortable to wear and easy to adapt. Therefore, it is easily accepted.

3. Due to the gradual change in degree, the substitution of regulatory effects gradually increases with the shortening of visual proximity, without any fluctuations in regulation, which is less likely to cause visual fatigue.

4. Clear vision can be obtained at various distances within the visual range. A pair of glasses can meet the needs of long-distance use, close range use, and various distances in between. Especially for teachers, doctors, musicians, and computer operators, it brings good news because these people not only need to see distant and close objects clearly, but also need to be able to see objects in the middle distance such as blackboards, sheet music, computer screens, etc. most of the time. This is something that no lens other than progressive multifocal lenses can achieve.

5. At present, both domestic and international ophthalmic experts unanimously advocate the use of low refractive index lenses for teenagers to reduce near vision adjustment when reading and writing, thereby alleviating or preventing the occurrence and development of myopia (1). This has given new meaning and mission to progressive multifocal lenses.

Question: 10. Can crystal lenses really nourish the eyes?

As an optical material, the biggest advantage of crystal is its high hardness, making the lenses less prone to wear and tear. It was popular in the 1920s and 1930s. Due to its durable lenses and high price, it is often passed down to the next generation. There is a saying in folk culture that 'crystals nourish the eyes'.

The main component of crystal is SiO2, which is a natural transparent mineral.

The absorption rate of crystals for ultraviolet rays is only 14.5%, while that of glass is 52%. Currently, resin lenses with added UV materials have an absorption rate of over 90% for ultraviolet rays.

The damage of ultraviolet rays to the human eye is well known. Ultraviolet radiation is the main culprit of age-related cataracts, and its damage to the cornea and retina is also certain. According to reports, the damage caused by ultraviolet radiation to the eyes is cumulative, so preventing UV damage is important for everyone at every time.

In addition, natural crystals often contain impurities, uneven density, bubbles, and stripes, which can cause birefringence and affect vision.

It can be seen that crystals not only do not have nourishing effects, but their high transmittance to ultraviolet radiation is harmful to the eyes. In today's rapidly developing world of science and technology, eyeglass lenses made of new optical materials such as resin are far superior to crystals in terms of their optical performance, safety performance, and ability to prevent harmful radiation and protect the eyes.

Question: 11. What is ultra-thin lens?

Lighter, thinner, and more comfortable eyeglass lenses have been the direction and goal of eyeglass scientists since the advent of glasses.

Ultra thin lenses currently refer to lenses made of high refractive index materials. High refractive index materials can be used to obtain concave lenses with the same degree but thinner edges or convex lenses with thinner centers by reducing the curvature of the lenses.

Glass materials increase their refractive index by adding lead containing heavy metal oxides to increase their density, and the refractive index is positively correlated with their specific gravity. The increase in refractive index also significantly increases the weight of the lens

Resin materials increase their refractive index by altering their molecular structure. As the refractive index increases, the weight of the lens does not necessarily increase, and some may even decrease.

For example: refractive index specific gravity

Glass resin

1.523 2.54 1.32(1.502)

1.56 1.23

1.6 2.90 1.39

1.67 1.40

1.7 3.2 1.3 or 1.4

Question: 12. Under what circumstances do I need to wear ultra-thin lenses?

1. Individuals with high myopia>-6.0DS have thick edges, prism effect, aberration, limited field of view, and poor appearance

2. High hyperopia>+6.0DS or cataract surgery without lenses - heavy lenses

Due to the high price of ultra-thin lenses, there are also many people who can afford them economically. For the sake of aesthetics and comfort, ultra-thin lenses are currently used for refractive abnormalities around 4.0DS.

Patients below 3.0DS generally do not consider it necessary to use ultra-thin lenses.

Question: 13. What is the difference between progressive multifocal lenses for preventing myopia and bifocal glasses?

1. Unparalleled jumping, easy to adapt to, easy to accept

2. There is no boundary in appearance and no psychological burden.

3. The replacement of regulation is gradual and unadjusted, making it less prone to visual fatigue.

4. No sense of jumping, able to move freely indoors and outdoors.