Selection of contact lenses

Electronic devices are an integral part of modern life. However, the daily use of smartphones, tablets and laptops leads to an increase in eye strain. As a result, visual acuity decreases.

About twenty years ago, for most people who could not boast of one hundred percent vision, the ability to see well without glasses seemed like a miracle. Today, vision correction with contact lenses has become widespread due to the convenience, aesthetics and ease of use of this modern way to improve the visual perception of the world.

Nevertheless, everyone who decides to switch from glasses to contact correction should remember that it will not work to choose the means for it on their own. This can only be done by an ophthalmologist with the help of special equipment. Independent experiments with lenses are fraught with serious complications: inflammation, dry eye syndrome, hypoxic changes in the cornea, as well as a further decrease in visual acuity.

What examination is carried out before the selection of lenses

As noted above, the selection of contact vision correction means is a procedure that includes several stages. The first of these is a visit to the ophthalmologist. Before starting the examination, the doctor must find out many details about the patient’s lifestyle. So, the specialist needs to be informed about concomitant diseases, bad habits, features of work and daily routine. After that, the doctor begins a comprehensive ophthalmological examination.

It includes several procedures. This is autorefractometry, which allows to establish the presence of myopia or hyperopia, as well as to identify astigmatism, keratometry (determination of the degree of curvature of the anterior surface of the cornea), biomicroscopy (detailed study of the structure of the eye). A fundus examination is also often performed to exclude the presence of organic pathology, which can reduce visual acuity.

Factors influencing the selection of lenses are also the incision and density of the eyelids, the structure of the vascular bed, the amount and composition of the secretion of the lacrimal gland. All these criteria help to determine the texture of the contact correction tool, the material from which it is made, the optimal wearing period and optical power.

After the specialist selects the model and strength of the contact lens, he must evaluate the features of its fit on the cornea, as well as check the visual acuity and residual refraction of the patient when wearing the correction. Trying on contact correction products is necessary because the specialist should make sure that the patient does not experience discomfort, and the lens does not “slip” during blinking or eye movement.

Finally, it is mandatory for the doctor to teach the patient how to remove and put on contact correction means, and also tell them what kind of care they need. However, this selection cannot be considered completely completed. A month after the start of the contact correction, the patient should visit the ophthalmologist again to conduct dynamic vision control and check the condition of the eyes. In the future, it will be necessary to visit a specialist every six months.

It should be remembered about the contraindications for the use of contact correction. Refuse to use this method of improving vision should be people prone to allergies, those who have been diagnosed with glaucoma, subluxation of the lens or impaired tear production, suffering from strabismus and frequent inflammatory processes of the organs of vision.

Characteristics of contact lenses

As noted above, when selecting a means of contact correction, many characteristics are taken into account. This is the texture of the product, the material from which it is made, the period of wearing, as well as the optical power. All these criteria are extremely important because they allow you to ensure that the product is right for you and will provide a comfortable and safe correction.

In addition, you should carefully study the packaging. The designations that are present on it are also a source of important information about the characteristics of the lenses.

So, D is an indicator of optical power expressed in diopters. BC is the base curvature. It usually varies from 8,4 to 8,6 mm. It is this parameter that is responsible for ensuring that wearing the product does not cause physical discomfort. DIA is the diameter, it ranges from 14 to 14,2 mm. Finally, Dk/t is the degree of oxygen permeability. It is believed that the higher it is, the better.

Also on the package may be depicted the sun. This is an indication that this model protects the eyes from the negative effects of ultraviolet rays. Pay attention also to the hourglass icon and the numbers next to it. This is the expiration date. In this case, you should take into account the fact that the time is counted from the moment when the integrity of the package was violated, and not from the day you put on the lenses for the first time.

How to choose lenses by texture

One of the main characteristics of contact lenses is their texture. Means of contact correction are hard and soft. Each product type has its own advantages and disadvantages.

Soft contact lenses

It is soft means of contact vision correction that are most popular. Even people who have never used contact correction before can adapt to their use quite quickly. Soft lenses cover the entire cornea, they are completely invisible, perfectly adhere to the surface of the eye and are practically not felt.

If we talk about the features of these products, then these are, first of all, the following characteristics:

1. Simplicity and comfort in use. Due to the soft texture of the product, patients do not feel a foreign body in the eye.
2. Fragility. These lenses need to be handled with extreme care because they are very easy to damage, making them unusable. In addition, fingerprints may remain on the surface.
3. Good visibility from any angle, as the specialist selects a product that will completely cover the patient’s cornea.
4. Wide range of wear times. Such products are one-day, monthly, quarterly and annual.
5. The ability to accumulate protein deposits. Therefore, they should often be washed with a special solution.

At the same time, soft products have one, but an extremely significant drawback. They can only be used to correct minor visual impairment.

Rigid contact lenses

In the minds of people who are not too aware of the features of contact correction, the concept of “hard lenses” still evokes associations with the very first such products. Once they were made from PMMA – the so-called organic glass. Such “primitive” devices could not be called convenient: they did not let oxygen through (they were gas-tight), and boiling and special cleaners were used to disinfect them. In addition, there was no need to talk about ease of use – even the most persistent daredevils could not get used to a foreign body in the eye. In addition, the gas-tight devices did not completely cover the cornea, resulting in varying visibility depending on the angle. It was possible to wear such products only for a short time, since without oxygen access to the cornea, its edema could develop.

However, to date, technology has long stepped forward and these “torture devices” of the past can be forgotten once and for all. Modern rigid lenses are made from polymer and silicone. These products are gas-permeable – in other words, they pass oxygen to the cornea.

It should be noted that the oxygen transmission coefficient (Dk/t) is generally one of the main characteristics of modern means of contact vision correction. The thing is that the cornea receives oxygen from the outside. In the event that the lens covering the cornea “does not breathe”, serious complications develop. This may be chronic hypoxia, corneal edema, and vascular ingrowth. As a result, the transparency of the cornea decreases, which entails an irreversible decrease in visual acuity. Silicone – the material from which modern contact lenses are made today – has an incredibly high gas permeability, and therefore does not have a negative impact on the physiology of the cornea of ​​​​the organs of vision.

However, high gas permeability is not the only positive characteristic of rigid lenses. Other advantages should also be mentioned.

1. Since the products are made of dense material, they retain their shape much better and are more securely fixed. Also, when blinking, they do not wrinkle, which contributes to the stability of the image.
2. Rigid means of correction are less fragile than soft ones. That is why they do not need the same reverent attitude as soft ones that are torn from any external influence.
3. Such lenses are more resistant to protein deposits that form on the lens due to exposure to tear fluid. It should be noted that the absence of such deposits prolongs the period of comfortable and safe use of the product.
4. In terms of their diameter, hard lenses are usually slightly smaller than soft lenses and, accordingly, inferior in size to the cornea. As a result, the extreme peripheral part of the cornea is available for the flow of tears and additional oxygen access. The tear fluid effectively washes away tiny foreign particles and dead cells, providing greater image clarity.
5. Since, unlike soft lenses, hard lenses do not contain water, they do not dry out in the wind or in conditions of low humidity. As a result, there is no need to use moisturizing drops.
6. As long as you take proper care of the product, its lifespan is limited solely to changes in vision – in other words, it will only be necessary to change lenses if you need a correction tool of greater optical power. Thus, rigid lenses can be considered more economically advantageous.

In addition, for some diseases, it is the correction with the help of rigid lenses that is more effective and can guarantee high visual acuity. So, hard lenses are recommended for the following problems:

1. With severe astigmatism, when the use of soft toric lenses does not provide a sufficient effect.
2. With keratoconus – in other words, with a cone-shaped deformation and thinning of the cornea.
3. With presbyopia (age-related farsightedness).
4. For orthokeratological vision correction to change the shape of the cornea.

However, one should take into account the fact that hard contact lenses also have their drawbacks, and quite significant ones. First of all, they are pretty inferior to their soft “competitors” in terms of comfort of use. It takes a lot more time to get used to them. Most patients adapt to this remedy in a week, but if you take a break from using such lenses for a few days, you will have to get used to it again.

Also in ophthalmic practice, there are cases when, after using hard lenses, patients were no longer physically able to use glasses. They complained that the image was blurry and indistinct. There is a physiological reason for this phenomenon – the whole point is that rigid lenses slightly change the shape of the cornea, putting pressure on it. Gradually, the original form returns, so that over time, the clarity of the picture in the glasses will be restored, but this will not happen immediately.

In addition, gas permeable rigid lenses are more difficult to fit than soft lenses. They should ideally match the surface of the cornea of ​​​​the eye, and therefore it will take much more time to select.

Finally, ophthalmologists recommend wearing rigid products for a limited time – no more than eighteen hours in a row. After that, they must be placed in a special solution.

It should be borne in mind that it is impossible to give an unambiguous answer to the question of whether hard or soft lenses are better. In each case, it is necessary to focus on medical indications and on individual preferences. Most often, in cases where vision is severely impaired, hard texture models are used, since they have more optical power. Soft products, in turn, are usually chosen by those whose visual acuity is not too much reduced, as well as beginners who want to get used to contact correction.

How to choose lenses by material

To date, two main materials are used to create contact lenses: hydrogel and hydrogel with silicone.

Hydrogel lenses

Products made from hydrogel are characterized by a high content of internal moisture. They have a very comfortable fit, but they do not pass oxygen well. This is explained by a technical contradiction: for a hydrogel lens to be comfortable, it must contain a lot of water, which inevitably makes it denser. However, in order for oxygen to enter the cornea, the thickness of the product must be minimal.

One of the characteristics of hydrogel lenses is the coefficient Dk / t – the ratio of gas permeability (Dk) and the thickness of the lens in the center of the product (t). As practice shows, it is very difficult to achieve a high value of this coefficient. The lens, which is thin enough, inevitably dries out by the end of the day. Therefore, most of these products are designed exclusively for daytime wear, you can not sleep in them. Typically, the Dk/t for most hydrogel lenses is between 20 and 40 units.

Silicone hydrogel lenses

The invention of silicone hydrogel lenses was a real breakthrough in solving the problem of limited gas permeability. Silicone boasts a very high oxygen permeability. As a result, the coefficient Dk/t can reach 175 units.

As a result, the risk of corneal hypoxia is significantly reduced.

Other advantages of silicone hydrogel correction products should also be mentioned. So, they contain less water than simple hydrogels. Therefore, the evaporation of the liquid does not affect them so noticeably, as a result of which you can wear lenses for a longer time, and there will be no discomfort and a feeling of drying out. It is the lenses of this material that are allowed not to be removed at night. At the same time, since the moisture content in such products is less than in conventional hydrogel ones, special moisturizing agents are added to the material and the surface of the lens is treated with a plasma method.

In addition, protein and lipid deposits accumulate more slowly on silicone hydrogel products, as a result of which the period of their comfortable use increases.

Ophthalmologists recommend silicone hydrogel lenses for extended use up to thirty days.

It should be taken into account the fact that, since the silicone in the composition makes such lenses quite rigid, their selection must be carried out as carefully as possible, paying special attention to the choice of the radius of the base curvature. In the event that the patient has previously used conventional hydrogel lenses, it must be taken into account that a silicone hydrogel product of the same base curvature may have a different fit. Therefore, it is imperative to carry out a fitting.

How to choose lenses by optical power

Any person who is faced with the problem of visual impairment knows that one of the main characteristics of vision correction means is their optical power – in other words, the very “diopters” that are necessary to improve visual acuity.

Often, people who decide to switch from glasses to contact correction assure the doctor that there is no need to check their vision during the selection of lenses – they supposedly already know the optical power of their glasses. However, such an approach is fundamentally wrong. The thing is that there is a distance between the eye and the glass of the glasses, while the lens is attached directly to the cornea. Therefore, it is impossible to rely on data on the optical power of glasses for the selection of lenses, the parameters will be completely different. Therefore, in order to correctly select contact lenses according to optical power, visual acuity testing is necessary.

How to choose lenses by wearing period

The wearing period is one of the most important characteristics of contact correction means. The older generation still remembers those very first lenses, which could only be worn for a few hours – after that, the eyes began to hurt and dry out, itching and inflammation appeared. Modern technologies have since stepped far forward: modern lenses have appeared that can be worn for thirty days, without even taking off for sleep. Of course, for people who lead an active lifestyle, travel a lot or work in shifts, this mode is very convenient. However, most ophthalmologists recommend the use of daily wear lenses as the most gentle on the eyes. However, the final choice always remains with the patient.

Advantages of day lenses

Daily lenses are suitable for people who use this method of correction only from time to time: for example, during sports or at special occasions. They will also be a real salvation for people who do not like to mess with care solutions and cannot boast of enough free time. One-day correction products are hydrogel, so your eyes will definitely not dry out. They do not need any care and storage conditions, therefore, they are ideal for travel and business trips.

Benefits of bi-weekly lenses

The so-called “frequently scheduled replacement lenses” are very popular. Their period of wearing is from a week to two weeks. As a rule, they are chosen by those who do not want to remove the corrective means during sleep, but for some reason do not yet dare to choose extended-use lenses for themselves. Due to the fact that their service life is relatively short, such correction tools are more comfortable.

Frequently scheduled replacement lenses can be of two types: those that can be left in during sleep and those that need to be removed at night. In the latter case, before going to bed, they must be placed in a container with a special solution that disinfects and moisturizes the product.

The undeniable advantage of the lenses of frequent scheduled replacement is the fact that they are highly hygienic and help save money, since there is no need to use a new product every day.

Benefits of extended wear lenses

Prolonged – up to a month – wear lenses are chosen by adherents of an active lifestyle and busy people who do not always have the opportunity to remove contact correction products at night. Silicone hydrogel products are allowed for continuous wear for up to thirty days in a row, providing sufficient hydration of the cornea and oxygen access.

However, one should take into account the fact that at least once a week the product will still have to be removed – for cleaning procedures and disinfection, so that pathogenic microorganisms do not begin to develop on their surface and deposits do not appear.

How to choose toric lenses

Toric lenses have appeared on the market relatively recently. They have become a real salvation for people who have been diagnosed with astigmatism. Lenses of this type help to solve this problem, while the quality of the image obtained with their help is much higher than when corrected with glasses with special lenses.

Toric lenses are both hydrogel and silicone hydrogel. According to the duration of use, they are divided into one-day and requiring monthly replacement.

Before the advent of toric products, rigid gas-permeable products were used to correct astigmatism. However, they did not provide sufficiently high image quality, and besides, they were not well tolerated by some patients.

For the production of toric lenses, the same materials are used as for conventional spherical lenses: hydrogel and silicone hydrogel. However, devices for astigmatists are distinguished by a special design. Toric lenses are spherical in shape, that is, they have two optical powers at once. One of them helps to correct astigmatism, and the second corrects nearsightedness or farsightedness.

The peculiarity of a toric lens is that it must be very tightly fixed on the eye in a strictly defined position. Therefore, these correction tools have a special fixation mechanism that securely fixes them, preventing them from moving when the eyelids move.

It should be taken into account the fact that the selection of toric contact lenses is more time-consuming and time-consuming than the procedure for selecting conventional means of correction. The thing is that it is necessary not only to carry out all standard studies, but also to select both components of the correction as accurately as possible, as well as to calculate the position of the toric lens.

How to choose lenses with a UV filter

Contact lenses with a filter that protects the eyes from the harmful effects of ultraviolet light are another of the recent innovations.

Such means of correction reliably protect the retina from ultraviolet radiation.

It is noteworthy that ophthalmologists recommend using products with a UV filter not only in the summer season, while staying on the beach or walking, but also when working at a computer for a long time. Studies have shown that the UV layer in this case contributes to the fact that the eyes are less tired.

The presence of a UV filter does not mean that such contact products should be classified in a separate category. Their selection is carried out in the same way as the selection of conventional products for contact correction.

How to choose colored lenses

Colored lenses are primarily designed not to correct vision, but to change the color of the iris. However, they are also divided into “zero” and having a certain optical power and allowing you to adjust visual acuity.

Depending on the purpose, colored lenses are so-called “masquerade” and “cosmetic”. The former are intended for use during parties and carnivals, they are distinguished by a bright unnatural color and may have an unusual pattern. Wearing such lenses is indicated only for a limited time. In addition, ophthalmologists do not recommend using them in low light and while driving.

Cosmetic lenses are a lifesaver for people diagnosed with iris defects. Such deficiencies may appear as a result of operations or injuries, or may be a congenital feature. As a result, the eye may look unnatural, provoking complexes and self-doubt. A cosmetic lens, which is made to order and outwardly completely corresponds to a healthy eye, will help to solve this problem.

To choose the right color products, several factors should be considered. First of all, the design of such a device provides for the presence of an uncolored center opposite the pupil, as a result of which there is no distortion of color perception. However, at dusk, when the pupil dilates, the quality of vision may decrease.

Instead of conclusions

Given all of the above, ophthalmologists recommend having several different types of contact correction products. This will allow you to adapt to all the features of the daily routine and lifestyle. So, one-day contact lenses can be used when visiting the pool and playing sports, while traveling or during a business trip.

For those who spend a lot of time at the computer, it is recommended to use lenses of frequent scheduled replacement. During periods of emotional and physical stress, when a person experiences stress, it is better to use continuous wear contact lenses, and in exceptional cases, colored or tinted lenses are suitable.