Cylindrical lenses: main characteristics and applications

What is the radius of curvature in contact lenses

Radius of curvature, or base curvature, is a parameter that shows the curvature of the inner surface of the lens. A simple inverse relationship principle applies here: the smaller it is, the more convex the product will be. Conversely, with a large value of this indicator, the inner surface of the lens will have an almost flat shape.

How well the lens will stay on the eye largely depends on the inner surface and the degree of its curvature. Therefore, the optics you need are selected taking into account the radius of curvature of the cornea.

How to determine the radius of curvature yourself? Look at the packaging and find the BC parameter there. This is what you need. Less often it is indicated after the letter R. Typically this parameter varies in the range from 8.4 to 9.0 mm. If you want to determine this indicator in order to order lenses for the first time, consult a doctor - you will not be able to measure the parameter yourself.

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Cylinder transposition

There are often cases when patients are faced with a phenomenon that is incomprehensible to them. When ordering glasses from a workshop, the customer can change the lens parameters. For example, an optician wrote the following prescription: OD sph - cyl +0.5 ax 180 OS sph - cyl +0.5 ax 0 DP=52mm In the workshop, the following entry may appear on the order form: OD sph +0.5 cyl −0.5 ax 90 OS sph +0.5 cyl −0.5 ax 90 DP=52mm

Don't worry - this is a normal phenomenon, a purely technical issue without any deception. An astigmatic lens always corresponds to two equivalent entries: one with a plus cylinder, and the other with a minus cylinder. The transition from one record to another is called cylinder transposition. Its principle is as follows: 1. Add the force of the sphere and the cylinder, taking into account the sign, to obtain a new value of the sphere force: In this case, 0 + 0.5 gives a value of sph +0.5 2. Change the sign of the cylinder force to obtain a new value of the cylinder force : +0.5 we replace + with - and we get cyl −0.5 3. Change the position of the axis by 90 degrees: 180 degrees turns into 90, the same as 0 into 90.

This is how two outwardly different entries can appear, but essentially meaning the same parameters of lenses for glasses.

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experienced participants and may differ significantly from

Glasses prescription

- a form containing the data necessary for the correct manufacture or purchase of finished glasses.

Why is it important to choose the right base curvature?

So, the radius of curvature affects the fit of the lens. What happens if you ignore this indicator and try to wear the first optics you come across, even those that match the diameter?

Let's say you bought a lens with a lower curvature on the inner surface than you need. Too little curvature results in a steep lens fit, which can lead to blurred vision by creating space between the cornea and the inner surface of the lens. Blurred vision can be temporarily relieved by “blinking,” that is, intense blinking movements.

Consider another situation: you bought lenses whose radius of curvature is larger than what you need. Too much base curvature will result in a flat fit. At the same time, the lenses slide over the eyes and do not keep up with their movements. When blinking, due to the movement of the eyelids, wrinkles may appear on the lenses. Often a person begins to rub his eyes to restore clarity of vision and get rid of unpleasant sensations. This may cause the lens to fall out.

The radius of curvature determines how the lens will stay on the eye.

Thus, wearing lenses with an incorrectly chosen base curvature can cause discomfort, as well as the fact that you will not perceive the world around you clearly enough.

What is astigmatism

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In Latin, the concept of “astigmatism” stands for lack of focus. Pathology can be acquired or congenital. Refractive error is characterized by the fact that the rays that enter the eye are located at several points. Because of this, images cannot focus on the retina, but only behind or in front of it. There is a distortion of the visible, blurriness, and double vision.

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Astigmatism is a visual pathology that is very difficult to recognize at an early stage. This is its difference from myopia and farsightedness. The patient experiences uneven refraction of light rays in different parts of the lens and cornea. Therefore, correcting vision with such a diagnosis is much more difficult.

Best Lens Solutions for 2021

When compiling the review, the following characteristics were taken into account: price, ease of use, quality of packaging, presence of containers in the packaging.

Best Cleaning Products

These products are necessary for long-term wear lenses (from a week or more). Contains hydrogen peroxide and enzymes to remove protein and lipid deposits on the surface. Should be used if the following symptoms occur:

• feeling of a veil before the eyes;
• sensation of a foreign object in the eye (if the surface of the lens is not deformed and has no defects);
• discomfort, redness of the eyes;
• feeling of decreased visual acuity.

All of the above signs, in the absence of eye diseases, indicate insufficient cleaning of contact lenses.

AOsept Plus

A true optical cleaning and care system from Alcon. The kit includes a solution for storage and rinsing and a product based on hydrogen peroxide. Convenient to use, provides cleaning from bacteria and lipid deposits

Unlike tablets, it is non-aggressive towards the optical material; after 6 hours it becomes neutral, so it is impossible to burn or damage the mucous membrane of the eyes and cornea. Important: not suitable for frequent use. The recommended frequency of treatment is once every 14 days. Suitable for sensitive eyes

Can be used with silicone hydrogel lenses.

AOsept Plus Advantages:

• does not contain preservatives;
• does not destroy or affect optical properties;
• easy to use;
• no need to time it.

Flaws:

Sauflon One Step

From a subsidiary of CooperVision. Thanks to its special composition, it cleans the entire surface of the lens, and not just the top part, as with mechanical treatment. The kit includes a cleaning system with a platinum catalyst that enhances the effect of the solution.

Suitable for daily use, provides comfort and hydration to the eyes while wearing contact lenses.

Sauflon One Step Advantages:

• safety;
• convenient use;
• Platinum-plated container included;
• use of innovative developments;
• suitable for daily use;
• does not require rinsing.

Flaws:

There are no significant ones, possible allergic reactions are associated with individual intolerance to the components.

The best enzyme products

AVIZOR Enzyme

Available in tablet form. Directions for use: place the tablet in the solution, wait until it is completely dissolved and lower the lenses to disinfect for at least 2 hours. Thanks to the components included in the composition, the tablets provide deep cleaning and are suitable for weekly use.

Important: after treatment, the lens must be rinsed thoroughly - residual cleaning components can lead to irritation and redness of the eyes. The manufacturer promises complete removal of contaminants, restoration of transparency, absence of toxic components and safety for the eyes.

The manufacturer promises complete removal of contaminants, restoration of transparency, absence of toxic components and safety for the eyes.

AVIZOR Enzyme Advantages:

• cleans well;
• lasts a long time;
• safe for the eyes;
• convenient packaging;
• acceptable price.

Flaws:

• take a long time to dissolve;
• The processing time recommended by the manufacturer must be observed.

Optimized

Available in the form of a solution, it contains a purified enzyme that helps safely clean the surface of protein deposits. The solution is convenient and easy to use. All you need to do is drop the solution into each cell of the container, previously filled with fresh solution, lower the lenses and leave for 4 hours. Afterwards, rinse and replace the solution in the container.

Optimed solution Advantages:

• convenient to use;
• Shelf life – 60 days after opening the package;
• Suitable for all types of optics, indispensable for long-term wearing (with planned replacement from 1 month).

Flaws:

• not suitable for sensitive eyes;
• Thorough rinsing is required after use.

Likontin F

From the Russian company Medstar. Enzyme solution for enzyme cleaning completely replaces tablets. Cleans and does not harm the optics material. Can be used with any lenses, including colored ones. Convenient to use, you can leave the lenses in the solution overnight - there will be no harm. Directions for use: add a few drops of the drug to the container with the solution, lower the lenses, and shake. Before use, rinse the optics with fresh solution.

Likontin F Advantages:

• patented technology;
• You can leave the optics in the container with the drug overnight;
• cleans well, easy to use;
• Suitable for colored lenses.

Flaws:

• It is not recommended to use together with solutions of other brands;
• may cause irritation of the mucous membrane.

The Best Multi-Tools

Designed for storing, disinfecting and cleaning contact lenses. In this case, one product successfully replaces tablets and special drops for deep cleaning. Plus, the special formula does not harm the optics material. Many drugs can replace moisturizing drops for dry eye syndrome.

Maxima

A universal product, the use of which does not require mechanical action - no need to wipe, just shake the container with the solution several times.

The neutral PH level is suitable even for sensitive eyes and does not cause a feeling of dryness or allergic reactions.

The minimum exposure time for complete cleansing and disinfection is 4 hours.

Maxima solution Advantages:

• ease of use;
• low consumption;
• proven brand;
• Suitable for hydrogel lenses.

Flaws:

no significant ones.

Opti-Free

From Alcon. Suitable for storing and disinfecting all types of lenses. The formula contains substances that destroy pathogenic bacteria, but are harmless to the eyes. The citrate in the composition breaks down and destroys protein deposits, and moisturizing components provide comfort and hydration of the eyes while wearing contact lenses. Convenient, tamper-evident packaging is made of white plastic, instructions for use are glued to the inside of the box, the container is included.

Opti-Free solution Advantages:

• cleans well;
• suitable for long-term storage;
• can replace moisturizing drops;
• convenient packaging;
• The container closes tightly.

Flaws:

high consumption.

Renu MultiPlus

From Bausch & Lomb. Provides cleansing and hydration. Minimum exposure time is 4 hours. Well tolerated, does not cause allergies or dry eyes. Contains poloxamine to remove surface contaminants while maintaining clear vision. EDTA provides deep cleaning of protein deposits. Special ingredients destroy pathogenic bacteria and fungi, eliminating the occurrence of inflammation. Suitable for sensitive eyes. The packaging is convenient and tamper evident. Container and instructions for use included.

Renu MultiPlus solution Advantages:

• meets the stated characteristics;
• suitable for sensitive eyes;
• does not cause allergies;
• suitable for storage;
• convenient container.

Flaws:

No.

When purchasing contact lens solution for the first time, it is better to consult an ophthalmologist. Subsequently, you can periodically change the products to choose the most suitable composition and comfortable to use.