Let's figure it out: what is the radius of curvature (base curvature) and how to measure it? Lens radius of curvature - what is it? Standard Lens Radius

Competent selection of contact lenses (CL) is not only compliance with diopters, but also compliance with the curvature of the cornea. This is an individual parameter determined by an ophthalmologist and ensures normal lens fit on the eye.

Each contact lens has a certain internal dimension - the base curvature. It should correspond as much as possible to the curvature of the cornea of ​​the eye. Its radius varies from 7.8 to 9.5 mm (the smaller, the “cooler” the lens), but this is purely individual for each person. The most common is 8.6-8.8 mm. The base curvature of contact lenses in the central part of the back surface for most of them is spherical, characterized by its radius of base curvature (BC).

If the contact lens does not fit properly to the eye, this can cause discomfort and complications. You can avoid this if you undergo an examination by an ophthalmologist before purchasing them for the first time.

The base curvature of lenses is a fundamentally important parameter that must be taken into account when purchasing them. In the recipe it is designated by the letters BC.

How is this parameter determined?

An ophthalmologist can take measurements using an autorefractometer. Next comes the fitting of trial contact lenses with parameters suitable for the patient. The doctor, using a slit lamp, should evaluate the correctness of their fit and mobility on the eye. To do this, a special “Fluorescein” solution is instilled, which, when illuminated with ultraviolet light, allows you to most fully assess the distribution of the product under the contact lens and its fit.

Afterwards a prescription is written, which should indicate:

1. Diameter.
2. Radius BC.
3. Optical power.

These parameters will be needed to purchase the correct CLs.

Is the correct selection of this parameter so important?

A properly determined base curvature of a CL is significant for the person who decides to use them. This will provide:

1. Comfortable to wear. The lens will not be felt by the eye, its mobility when blinking will be within normal limits. This means that the risk of it falling out will be eliminated, and vision will be extremely clear.
2. Eye safety and health. The use of CLs with inappropriate curvature can cause discomfort, hypoxia and swelling of the cornea, and infectious eye diseases.

That is why it is very important to choose a CL with the right parameters. Some lens manufacturers only produce standard products. This somewhat limits the choice. After all, even if the product is suitable in all other respects - material, gas permeability, degree of moisture, etc., then an unsuitable BC radius will still force you to refuse the brand you like.

But most lens manufacturers take maximum care of their customers and produce lenses in several versions. For example:

1. Acuvue TruEye – there are models with a radius of 8.5-9.0 mm
2. Acuvue Advance and Acuvue 2 are products from Johnson & Johnson, the BC radius varies between 8.3-8.7 mm.
3. Optima FW – base curvature starts from 8.3 mm and ends at 9.0 mm (different rulers).

What to do if the product has already been purchased, but the parameter is not suitable?

If the difference is no more than 0.2 mm, nothing bad will happen - such CLs can be worn without harm to the eyes. But it happens that the products of one manufacturer with a BC radius of 8.4 mm correspond to the products of another with a radius of 8.5 mm. If the deviation between brands exceeds 0.2 mm, then such products cannot be worn!

Symptoms of discomfort when wearing optics with inappropriate curvature:

1. Difficulty in mobility of the CL if it is more convex. In such cases, the eye is constantly tense, its blood vessels are compressed, which inevitably leads to redness. Tear exchange may also be disrupted, since the tear will not be able to pass through the lens closely adjacent to the cornea, and the risk of inflammatory processes will increase. Vision may be unstable.
2. Increased mobility of the CL if it is less convex. If the BC radius of a contact lens is larger than necessary, it becomes too mobile. It may then fall out of the eye, cause watery eyes, or damage the cornea. This happens because the flat lens moves away from the cornea easily and imperceptibly. This is felt only when blinking, when it begins to touch the upper muscles of the eye. Then there will be a feeling that something has got into the eye, itching and redness.

To avoid all this, you need to buy CL according to a prescription, which will indicate all the parameters necessary for the correct choice. Then wearing them will only be a joy and refractive errors will not be an obstacle to a life full of bright colors and colors!

Perhaps in the near future the choice of CL will not depend on the radius of the BC! Video:

How do you buy CL? Do you pay attention to the radius of curvature when purchasing them? We are waiting for your answers in the comments!

12.07.2014 | Viewed by: 6,121 people.

Great Contact Lens Reviews:

Contact lenses help those suffering from visual impairments to see the world in a new way and not experience the inconvenience of constantly wearing glasses. Today, inventors and doctors strive to make people's lives easier with innovations in all areas, including ophthalmology.

Not so long ago, ophthalmologists’ patients did not know how to replace vision correction with glasses. Yes, and glasses used to be very bulky and far from safe to use, and besides, they were not suitable for everyone.

Initially, contact lenses were made from hard materials, and they were used as a means of vision correction for long-term wear.

Preparations—solutions, drops—that could clean lenses did not yet exist, so protein deposits accumulated on the products. This greatly aggravated the situation, as it often led to inflammation and other eye diseases.

Now contact lenses have improved, and there is a huge range of them on the market. Lenses vary in color and shade, period of wear, and type of use (therapeutic, cosmetic, decorative).

Thus, contact lenses can not only improve vision qualitatively, but also change the tone of the iris, make the look more expressive, and also hide defects in the structure of the eyes.

Colored soft lenses have become extremely popular in recent years. Their selection is simply huge, and any self-respecting manufacturer has a variety of palettes.

You can easily transform yourself by purchasing decorative lenses, create a new style and improve your own mood. Colored lenses are also available without diopters, so they are suitable even for those who do not suffer from visual impairments.

The range of shades of colored lenses is amazing. You can simply and quickly choose one that suits your hair color, skin tone, design and style of clothing, as well as based on personal preferences or the theme of a particular party. In any case, the owner of colored lenses will never go unnoticed!

Colored contact lenses can also correct vision defects if needed. The range of diopters of products is very large, so they are suitable for every person.

The use of care products depends on the period of wearing lenses, and therefore the doctor will recommend the necessary solutions, tablets or drops. These medications will help preserve not only the lenses themselves, but also the health of your eyes.

How to choose contact lenses?

Before purchasing lenses at an optical salon, you should definitely visit an ophthalmologist or contact correction specialist. Typically, the choice of colored lenses is based on available data on product parameters and personal color preferences.

You can read reviews from those who have already tried certain lenses: this information will certainly be useful. The price of contact lenses depends on the length of time they are worn, the material and the manufacturer, and is often very affordable.

Which lenses are right for you?

Any patient needs an individual choice of not only glasses, but also lenses. Only a specialist will accurately take the necessary measurements, recommend and help you put on test lenses, and will probably tell you the brand and model of lenses that will ideally suit a person.

To select soft contact lenses, the refractokeratometry procedure is used. More precisely, this procedure is necessary to measure the parameters of the cornea of ​​the eye.

What is the radius of curvature of the cornea?

Curvature of the cornea - the most important parameter, without which even a specialist will not be able to choose the right lenses. When choosing soft lenses, the name of this indicator is the radius of base curvature, or simply the radius of curvature.

It is measured as the curvature of the center of the back surface of the lens and is indicated on the lens box as BC or BCR.

The radius of curvature will help identify the type of lens fit on the ocular surface. If you choose the wrong lenses based on this indicator, then the person will not feel comfortable while wearing them.

The indicator is indicated in millimeters, with its average size being 8-9 mm. The most common radius of curvature is 8.6 mm. If it is larger, the lens fits flatter.

Cornea diameter. To obtain the value of this indicator, you need to measure the cornea. The diameter of the cornea is equal to the distance between the edges of the lens when passing through its central part in millimeters. Its average size is 13-15 mm, indicated on the lens box as D, mm.

Optical power. This is the size of the patient’s visual acuity, expressed in diopters - plus or minus. On lenses this indicator is indicated as Sph, Pwr. Often these indicators are not the same for the eyes if the patient's vision in the right and left eyes is different.

Base lens curvature is the most important indicator that you need to know when selecting contact lenses for any person. Let's take a closer look at what type of parameter this is.

If a patient visits a specialist and a decrease in visual acuity is detected, in addition to the usual examination of the eye structures and determining the degree of deviation, the need for contact correction should be clarified.

Selecting lenses is not as easy as it seems. The ophthalmologist must absolutely accurately calculate all the parameters of the lenses, which are purely individual.

After all, the quality of correction and comfort directly depend on whether the product is suitable for the patient.

Why is the correct selection of lenses so important?

The base curvature of lenses refers to the curvature that touches the surface of the eyeball. In this way, the lens can perfectly fit the eye, tightly joining with the cornea. The unit of measurement for the indicator is millimeter.

As a rule, the curvature varies between 7.8-9.5 mm. If the curvature is chosen incorrectly, then, like shoes or clothes that do not fit, the lenses will cause severe discomfort and irritate the wearer.

Among the consequences that result from the wrong choice of lenses, which often happens when purchasing on your own without an ophthalmological consultation, there are also burning and excessive dryness of the eyes, and loss of products.

If the difference between the base curvature of the lens and the eyeball is significant, then a feeling of the presence of a foreign body appears, even if the quality of the lenses themselves is not satisfactory. In patients prone to allergies, rubbing the eye can lead to a severe pathological reaction.

Often patients begin to use special medications - solutions, drops, but this is unlikely to help correct the situation if the curvature of the lenses is calculated incorrectly. But if the error in the selection turns out to be small, then the person may not feel it.

Subtleties of calculating curvature

Many lens manufacturers still continue to produce products with a standard curvature that is the same for all lenses. In this case, the doctor’s work will become very difficult.

But such well-known brands as CIBA Vision, Bausch + Lomb, Johnson & Johnson have not been doing this for a long time, but are trying to produce lenses with a small interval of base curvature. These lenses, even with a slight error, will fit perfectly on the surface of the eye. Common types of lenses that differ in curvature are 8.7-8.9, 8.5-9.

In Western countries, it is customary to prepare lenses to order, which has been popular there for a long period. Unfortunately, our service has not yet found its consumer.

Detecting the curvature of a contact lens can be done at every certified optical center, as well as at an appointment with any ophthalmologist. It takes a minimum of time and does not cause any discomfort.

After the diagnostic procedure, the specialist writes out a referral for contact correction, which indicates the optical power of the lens (D), lens diameter (mm), and radius of curvature (mm).

An experienced and responsible doctor will also give advice on the quality of lenses of different brands, rules for caring for lenses, features of their use and storage.

What is the reason for the popularity of eye lenses?

In the modern world, environmental living conditions leave much to be desired. Therefore, keeping your eyes healthy and your vision excellent is very difficult. Often, the peculiarities of work activity further aggravate the condition of the visual organs.

Low visual acuity brings its own adjustments to life, often limiting a person’s capabilities. In addition to discomfort, people experience uncertainty and their mood drops.

But not everyone is ready to wear glasses, especially since they do not fit well on every face. Sometimes glasses don't suit your style at all, and they can be uncomfortable to wear.

If you don’t like seeing poorly, but have no desire to wear glasses, then contact vision correction may be the solution. Eye contact lenses are a safe and comfortable alternative to glasses and an ideal way to see better.

Eye lenses are sold everywhere, in any vision store. But you should not purchase lenses on your own without first consulting a doctor, as there are a number of important parameters that they must meet.

Why is visiting an ophthalmologist before purchasing lenses so important?

Only a specialist will be able to choose lenses that will fit exactly on the surface of the eye, as they will suit you individually. In addition, matching the lens to the eyeball will give a feeling of comfort while wearing it, or rather, create the feeling of the complete absence of any foreign object in the eyes.

If the doctor recommends hard lenses, then you need to adapt to them, and this will take some time (no more than 2 days). Next, a person will definitely feel all the advantages of lenses over glasses.

A consultation with an ophthalmologist will allow you to choose the most acceptable lifespan for contact lenses.

If you do not want to use special solutions, store lenses and monitor their condition, then one-day products will be an excellent solution. But if you need to save money, then it is better to buy lenses for routine replacement.

There are also lenses to correct certain conditions, such as astigmatism. The choice of such products is a matter for a specialist.

An experienced doctor will recommend care products and tell you how exactly the lenses should be stored and processed. If you take into account all these tips, you can not only gain clear vision, but also protect your eyes from various pathologies.

If you try to choose contact lenses on your own, you can not only experience a lot of inconvenience, but also achieve sad consequences. Vision may well deteriorate further as a result of such experiments.

An ophthalmologist will also help you figure out the lens color that best suits your look. Nowadays, many prescription lenses are colored. They are very popular because, in parallel with vision correction, they create an unimaginable decorative effect of transformation and brightening of the eyes.

Prices for such lenses can be similar to simple optical ones, but sometimes they are slightly higher, which, however, depends on the manufacturer.

Contact lenses are a modern alternative to glasses for those who need vision correction. A similar correction is used for plus and minus defects, astigmatism and more complex ophthalmological disorders. When selected correctly, lenses have a number of undeniable advantages, but require more painstaking and careful selection. One of the important parameters when selecting is the radius of curvature, which affects the perfect wearing and comfort.

What is the curvature of contact lenses for the eyes and how is it indicated?

Many, when faced with a statement from an ophthalmologist for the first time, wonder how to choose the radius of curvature, what it is and what it affects.

DIA - characterizes the diameter; in some people it may differ in the right and left eyes depending on physiology and concomitant diseases.

BC or BS is the basic curvature parameter. The arc of the eye must coincide with the curvature of the selected eyepiece, then, regardless of the rigidity of the product, the cornea will feel comfortable throughout the day.

The convex part follows the shape of the eyeball, the inner concave part fits tightly to the cornea. If the fit is too tight, mini injuries form on the cornea. If it is free, then vision correction will not occur.

The base curvature is always written on the packaging, next to the diopters and is measured in millimeters. Some manufacturers put a stamp on the product itself; it is visible when holding the product up to the light.

The value is inversely proportional to the convexity: a smaller number means a larger arc and vice versa, with high values ​​the lens will be almost flat.

Curvature options

BS varies from 7.4 to 9.5 mm and depends on the following factors:

• possible injuries;
• past ophthalmological diseases;
• structural features of the eyeball;
• myopia or farsightedness.

For example, with myopia, the cornea stretches and becomes conical, with farsightedness it flattens. In ophthalmology there is such a thing as base curvature.

Basic (standard) curvature

In most cases, its standard ranges are located in the range of 8.3 – 9.00 mm. These are the most common and typical indicators. The permissible error in determining the curvature of the lens is 0.2 mm, with these indicators 75% of people do not experience discomfort.

For example, Acuvue TruEye range from 8.5 to 9.0. Optima FW is suitable for patients with indicators of 8.3, 8.4, 8.7 and 9.00. Acuvue Advance and Acuvue 2 lenses have a narrower spread: 8.3-8.7 mm.

Pure Vision offers 8.3 and 8.6 mm. Softlens Natural Colors color solutions are suitable only for people with a corneal curve of 8.4 and 8.8 mm.

Each manufacturer tries to create a unique lens shape, patenting the degree of curvature and diopter spread.

Read about long-wear lenses in.

Radius 8.8

Radius 8.8 cannot be called basic. Only a few companies work with this value. Some of the popular ones that have proven themselves on the market for several years include:

• Maxima 55 UV;
• Biomedics 55 Evolution;
• Acuvue Oasis.

All of the above brands have a two-week continuous wearing period.

Radius 9

Contact lenses with a radius of 9.00 mm - . They are softer, more flexible and thinner. Most popular models:

• 1-Day ;
• Acuvue 1-Day Moist;
• Acuvue Oasys 1-Day.

These lenses are considered disposable and are replaced daily. They do not require additional cleaning, are comfortable to the eye, but are also more expensive.

Definition of curvature

Determining the curvature of the eyeball is a basic procedure when selecting a corrective product from an ophthalmologist. The lens fits tightly to the cornea, thereby eliminating the ingress of dust and small particles. They should fit snugly, but not too tightly, so determining the curvature plays a crucial role in creating a comfortable and safe fit.

Why define curvature and what does it characterize?

If the curvature is incorrectly determined, there are two unfavorable developments:

• the corrective product puts pressure on the apple;
• the eyepiece has a low degree of adhesion.

How to choose the radius

The refractokeratometry process is carried out only by a doctor in a specialized office. The refractometer displays the degree of corneal convexity on the monitor screen, without causing discomfort or unpleasant sensations during the procedure. The procedure takes 5-7 minutes.

After receiving the parameters, the doctor selects the desired lens and gives it to the patient to try on. This is how the adhesion density is determined. The slit lamp helps the ophthalmologist see the degree of fit of the product. For an additional test, fluorescein is dropped into the eye, which glows and flickers under ultraviolet light.

The intensity of the glow shows how ideally the corrective eyepiece is selected. Only after this is a prescription issued with an exact indication of the diagnosis, diopters, radius of curvature and diameter.

Consequences of the wrong choice

The consequences of incorrectly selected contact devices can be very unpleasant and in some cases lead to serious health problems. In addition to selecting the technical parameters of the lens from a doctor, you should also listen to your feelings regarding hardness, degree of hydration and individual intolerance to individual components or solution.

If the curvature is less than necessary, as noted above, free movement within the eye will occur, causing the lens to fall out. Irritation, watery eyes and itching under the eyelids may occur.

With a tight fit, more serious negative consequences arise:

• decreased air exchange, capillary degeneration;
• lack of natural irrigation in the form of tears;
• double image and pain in the eyes.

Split image

Prolonged hypoxia becomes a catalyst that includes inflammatory processes. In advanced cases, they require surgical intervention.

Read also about hypermetropia.

How to determine if the lenses are chosen correctly

Sensitive people, experiencing any discomfort, begin to fear the correct selection of lens curvature. First of all, it is worth understanding that the ideal contact of the corrective product and the cornea is influenced by:

• internal state of the body, possible cold symptoms;
• ambient air humidity level;
• windiness;
• adaptation period (if the pair is dressed for the first time).

According to research, the adaptation process occurs over two or more weeks, depending on the body’s susceptibility. You should also monitor the cleanliness of the product and the replacement period.

If these parameters are met, but the discomfort when wearing does not go away (itching, headaches and eye pain appear), then you should consult a doctor for advice.

With a correctly selected pair, the lenses are not felt on the cornea of ​​the eye, do not slip or stick. For comfortable wear, natural irrigation is sufficient.

Is it possible to determine it yourself at home?

It is believed that the degree of curvature can be determined experimentally at home. But this is far from true. As noted, the degree of convexity is recorded by the device, and then the final fitting occurs.

It is important to take into account the fact that discomfort may not arise immediately, but after 1-3 months and have a sluggish inflammation of the eye that does not cause a strong external reaction.

In addition to BS, he will also select the material of the corrective product, the diameter, taking into account possible negative allergic reactions to individual components.

Can the radii be different?

In addition to the classic spherical shape, there are toric ones for adjustment. With this disease, changing the refractive ray in one plane is not enough, since there is a different deformation of the lens, both horizontally and vertically. Therefore, the sphere of an astigmatic lens has two different convex angles and is marked with two curvature indicators.

Scientists do not yet understand why there are different deformations. Climate, standard of living and location influence.

Formula for a thin lens using the radius of curvature: how to calculate

There is a formula for a thin lens, derived through the radius of curvature of the product, which helps to understand how to mathematically calculate the convexity.

The focal length of the eyepiece in a vacuum state is calculated by the radius of the convexity of the surface of the corrective product and the absolute refractive index of the substance from which the lens is made.

When calculating the focal length of a complex concave-convex lens, a different formula is used.

In this case, optical power is a value inversely proportional to the focal length of the contact lens:

D – diopter equal to 1/m. In other words, one unit of diopter = optical capability of the eyepiece at a focal length of 1 m.

Video

conclusions

1. The radius of curvature of the lens is important for comfortable wearing of the product.
2. It cannot be determined at home and requires qualified assistance from an ophthalmologist.
3. If selected incorrectly and after wearing pairs that are too tight or too loose for a long time, negative consequences are possible.
4. It is impossible to understand during the first days whether the lenses suit you or not. You can find out the degree of comfort and correct selection after 2-3 weeks of wear.

How to find out and choose the correct size of contact lenses that are suitable for your eyes? What is the diameter and radius of base curvature of a contact lens? Should the size of contact lenses match the size of the cornea?

In this article we will look at an important and frequently asked question regarding the correct selection of contact lens size and determining the correct parameters.

Determining your contact lens size

If the lens diameter is not selected correctly

If the diameter of the lens is not selected correctly, the lens will either fit loosely; if the diameter is too large, then the lens will be excessively mobile, which will lead to discomfort. The fit will be tight if the diameter is small - in this case, the edges of the lens will be in the limbus area, which will lead to disruption of the blood supply to the cornea.

The size of the contact lens and the size of the cornea do not have to match

When developing the design and size of a contact lens, the size of the “universal” cornea of ​​the eyes on which this contact lens will fit ideally is calculated. When calculating the parameters of a “universal” cornea, the size of a huge number of corneas is taken into account, from which the arithmetic average is calculated.

This is why a contact lens with a universal size will fit most people. And this is the only reason why manufacturers do not produce contact lenses individually for each size of the cornea of ​​the eye.

Some manufacturers, in addition to the standard lens size, specially produce lenses for non-standard cornea sizes. But such corneas are the exception rather than the rule.

Determining lens size using Acuvue lenses as an example

You might be interested:

Inna 02/17/20

Hello! When checking, they said that a flat cornea and lenses are needed for 10.3, but such are not available. Is it possible to somehow correct the situation? Do the exercises? Drops? Previously, I could easily wear lenses, but now only for a radius of 9 and then no more than 2 hours, otherwise my eyes hurt a lot

Natalia Gusakova 08.11.19

Anastasia, hello! The choice of the size of the base curvature of the lens is possible only by assessing the fit of the lens on the cornea; lenses of different materials and different designs can fit completely differently even if they have similar sizes. Therefore, the choice of lens size is possible only in the contact correction office.

Anastasia 07/30/19

Hello. Please tell me. I wear daily lenses with a diameter of 14.3 and a radius of 8.5. I want to switch to two-week ones, what diameter do I need?

Natalia Gusakova 22.07.19

Hello, Alexander. The main criterion for selecting lenses is. Lenses with the same parameters but from different manufacturers will fit differently. The correct fit can only be determined by an ophthalmologist or optometrist in an optical salon.

Natalia Gusakova 22.07.19

Hello Igor. Standard lenses with a radius of curvature of 7.5 are not available. The only option is Concor lenses made to order; we do not cooperate with this company.

Igor 04/30/19

Hello. Tell me the possibility of purchasing contact lenses: +11 diopters, curvature 7.5

Alexander 03/30/19

Hello, I am currently using 1day acuvue trueye 8.5, 14.2 lenses. Will soflens daily disposable 8.6, 14.2 be suitable?

Natalia Gusakova 16.03.19

Karina, hello. To properly select toric lenses, it is necessary to evaluate the fit of the lens on the cornea. The main criterion for correct selection is a good fit of the lens on the cornea of ​​the eye.

Karina 03/02/19

Hello. I have astigmatism and it is difficult to choose lenses. According to the data, the radius of curvature is 8.6, the diameter is 14.5 large. But it’s impossible to choose. All presented toric (astigmatic) lenses with a diameter of 14.5 What to do?

Natalia Gusakova 26.11.18

Olga, hello! The selection of colored lenses is carried out according to the same parameters as regular lenses.

Olya 11/24/18

Hello. Is all this necessary for colored lenses?

Natalia Gusakova 23.04.18

Alexey, hello! The main indicator of correctly selected contact lenses is their fit on the cornea. The size of the lenses you have previously used is not the standard when choosing lenses of a different design and material.

Alexey 04/23/18

Good afternoon. I have been wearing since I bought my first pair of Ophthalmix 55uv lenses, radius 8.6, diameter 14.2 and -4.25 diopters. These lenses have now been discontinued. As can be seen from the above text, it is impossible to change the diameter of the lenses to a smaller or larger direction. Will you have to select from those available or can you vary it slightly by 0.1-0.2 mm?

Natalia Gusakova 18.03.18

Elena, hello! The diopters in contact lenses and the diopters corresponding to your visual acuity in spectacle correction differ due to the presence of the vertex distance (see the article "Vertex distance"). Therefore, diopters of -12.0 in contact lenses correspond to diopters of -14.0 with spectacle correction.

Elenka 03/18/18

Hello, I have glasses -15.0 and lenses -12.0 Acuvue Oasys. Should I increase the diopter of the lenses? If so, by how much to feel comfortable? Thank you.

Natalia Gusakova 12.03.18

Love, hello! It is not correct to recommend contact lenses based solely on refractometer data. The main indicator of correctly selected contact lenses is their correctness.

Love 03/10/18

Hello! Please tell me which lenses might be suitable? Weak small-scale nystagmus (almost imperceptible) Autorefractometer data: R 8.02/8.03, D 42.5/43.0

Alla 01/27/18

Good afternoon. My husband has -15.0; radius of curvature according to autorefractometer OD 7.29/7.25 OS 7.3/7.25. We can't find contact lenses for him. We tried lenses from different manufacturers, because... Lenses with standard parameters are not comfortable for him. Maybe this is due to its small radius? According to the autorefractometer data, tell me what radius you would recommend for him: 8.0; 8.2 or 8.4? Thank you in advance.

Natalia Gusakova 10.01.18

Victoria, hello! In addition to diameter, there are many other parameters that affect the fit of contact lenses, such as lens material, base curvature, and edge design. Different lenses have completely different parameters, but this does not mean at all that they will not suit you. Likewise, it does not mean that other lenses having the same parameters as your previous lenses will necessarily suit you. Therefore, the main criterion for correctly selected soft contact lenses is.

Victoria 01/08/18

Hello! Please tell me! I used to take lenses clarity 8.8 minus 3.25 and a diameter of 14.1, but now I can’t find one, they offer me a diameter of 14.2 or 14.5, tell me the diameter plays a role in the lenses? Thanks in advance!!!

Natalia Gusakova 15.12.17

Venus, hello! The principle of selecting colored contact lenses is the same as for regular lenses. If you take regular -5.25 lenses, then you need to take colored ones with the same diopters. But colored lenses with such diopter values ​​are only available from Alcon. By the way, these are safe silicone hydrogel lenses, unlike other colored lenses, which are hydrogel.

As for the size of the lenses, the only criterion for the correct choice of the size of any lenses is their correct fit on the cornea of ​​the eye and in no case is the criterion the size of the previous lenses, since lenses from different manufacturers or even different lenses from the same manufacturer will have different designs and consist of different materials, so if some lenses have a base curvature size of 8.4 and fit you well, then other lenses with other parameters will also fit well on the cornea with a size of 8.6 and a diameter of 14.2.

Therefore, the selection of lenses or the transition to lenses of a different design must be carried out in the doctor’s office, who will be able to assess the correct fit of the lens on the cornea; this will be the criterion for the correctly selected lens size. The only thing to consider when purchasing colored lenses is the possibility of a feeling of “fog” in the lenses due to narrowing of peripheral vision due to the pattern of colored lenses.

Venus 12/15/17

Good afternoon My daughter wears lenses with a radius of curvature of 8.4 in diameter 14.0 minus 5.25. But she really wants colored lenses, but with a radius there are only infinity lenses (Korea), we don’t want them, because... there the lens is completely colored, and therefore distorts color perception. Could you tell me: 1) are colored lenses different than colorless ones (different radius and diameter)?; 2) if -5.25, then you need - 5.50 with colored lenses. Thank you!

Natalia Gusakova 23.11.17

Daria, hello!

Acuvue 1 day TruEye and Acuvue Oasys lenses are different in design. The standard size for TruEye is 8.5, and the standard size for Oasys is 8.4. Therefore, the selection of TruEye lenses always begins with a base curvature size of 8.5 and only if they fit tightly on the cornea, size 9.0 is selected.

With Acuvue Oasys, you always start with size 8.4, no matter what base curvature your previous lenses had. The fit of the size 8.4 lens on the cornea is assessed and only if the Oasys size 8.4 fits snugly, size 8.8 or a different lens design (i.e., another brand) is selected.

Daria 11/23/17

Hello! Previously, I took 1-Day Acuvue Trueye -3.75 lenses with a curvature of 8.5. Now, to save money, I want to switch to 2-week lenses and chose Acuvue Oasys. But there the curvature is only 8.4 and 8.7. Which ones to choose?

Natalia Gusakova 30.08.17

Vitaly, hello! Comfort in lenses depends on many factors, including. Assessing the correct fit of the lens is an important point in choosing the lens size; without assessing the fit, it is not possible to say what size of the base curvature and lens diameter will be optimal for you. At the same time, lenses made of different materials having the same dimensions will fit completely differently on the cornea. Unpleasant sensations in the lenses can be not only due to improper fit, but also due to an inappropriate solution, with conjunctivitis, meibomitis, with.

Vitaly 08/28/17

Hello, I am being fitted for contact lenses and have been wearing them for 6 days. The left eye is almost used to it, but the right one feels like the wind is blowing into the eye. Lens parameters: radius of curvature 8.6 diameter 14.00 mm. I tried contact lenses with the same radius, but with a diameter of 14.1 mm, very unpleasant sensations in the eyes, a constant feeling of interference in the eye. Tell me, please, can a diameter of 13.8 mm be suitable for my right eye? Or what do you recommend? Best regards, Vitaly

The larger the radius of curvature, the more similar the curve is to a straight line.

The radius of curvature is determined for a specific point on a specific curve; it is equal to the radius of the osculating circle.

Calculation

Let the curve be specified parametrically, r(τ) Then the radius of curvature can be found using the formula:

Derivation of the formula in the 2-dimensional case

s = R * α

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See what “Radius of curvature” is in other dictionaries:

radius of curvature- The radius of the circular arc that most closely matches the rounding shape of the element in question. [GOST R 41.61 2001] Topics: motor transport equipment...

Radius of curvature R n- Radius of the working surface of the transducer Source...

radius of curvature- 2.8 radius of curvature: The radius of the arc of a circle that most closely matches the curvature shape of the element in question. Source … Dictionary-reference book of terms of normative and technical documentation

radius of curvature- kreivumo spindulys statusas T sritis Standartizacija ir metrologija apibrėžtis Kreivės arba kreivo paviršiaus spindulys. atitikmenys: engl. radius of curvature vok. Krümmungsradius, m rus. radius of curvature, m pranc. rayon de courbure, m... Penkiakalbis aiškinamasis metrologijos terminų žodynas

radius of curvature- kreivumo spindulys statusas T sritis fizika atitikmenys: engl. radius of curvature vok. Krümmungsradius, m rus. radius of curvature, m pranc. rayon de courbure, m … Fizikos terminų žodynas

The radius of the circle of curvature (See Curvature) at a given point on the curve... Great Soviet Encyclopedia

See art. Differential calculus and art. Curvature... Encyclopedic Dictionary F.A. Brockhaus and I.A. Ephron

Radius of curvature of the displacement trough- the reciprocal value of the curvature of the displacement trough. Source … Dictionary-reference book of terms of normative and technical documentation

radius of curvature of the tread running track- radius of curvature of the tread The radius of the outer surface of the tread in the radial plane of the wheel. Rpr radius of curvature of the treadmill; With a solution of sides; Wb is the tire bead width. [GOST 22374 77] Topics: pneumatic tires... ... Technical Translator's Guide

radius of curvature of the line of blunting of the longitudinal edge of the tooth- (Pk) radius of curvature of the blunt line [GOST 16530 83] Topics of gear transmission General terms concepts related to the gear wheel tooth profile Synonyms radius of curvature of the blunt line ... Technical Translator's Guide

Books

• Analytical theory of two-wave proton physics, Lyutko Mikhail Grigorievich. The first part of the book presents theoretical and applied work on the physics of extended elementary particles oscillating in time, closed by the wave interval of the self-interaction of the field g(e). Particle…
• Geometry of algebraic equations solvable in radicals, G. P. Kutishchev. This book examines in great detail, at a theoretical level somewhat higher than school level, algebraic equations that can be solved in elementary operations, or solved in...