The last in our cycle of vision correction is hard contact lenses for night use. They are second in safety after the glasses. Conditionally the safest method of correction is unambiguously glasses (with strong polycarbonate lenses), then – ReLEx SMILE and stiff night lenses, then – femtoLASIK and PRK, then soft one-day lenses, then "barbaric methods" – soft long-wearing lenses and LASIK. Phakic intraocular lenses and artificial lenses stand separately – they should be done only on direct medical indications (a sufficiently invasive method for refractive indications).
The main advantage of night lenses is clinically proven that they stop the progressing myopia. Therefore, very often they are prescribed to children when the eye is actively developing. After 20 years, this effect decreases by an order of magnitude, but there remain a couple of other advantages.
How do hard lenses work for night wear
In the evening, you take a container with lenses and special manipulators. You put two hard lenses right before going to bed. The first few times it will be painful, but if you wore the usual soft, get used to get quick. If not – it is better to try one-day first for a couple of weeks, because to lose a hard lens from the inability to put on or wear (from the bathroom to the bed) is just a pity. After soft lenses, it is very, very easy to use hard nightlights because they keep the shape well.
These lenses begin to press on the cornea, "lowering" its center and the tissue under it in a position normal for normal vision. A correctly designed lens does not "rape" the eye, but returns the focal length of the eye to a natural physiological one. To make it clearer, I recall that short-sightedness is actually a stretching deformation of the eye.
The cornea has a fairly stiff collagen matrix, so it begins to "remember" the new shape installed by the lens. Conditionally for 3-5 nights of wearing, a normal stable vision is achieved within 95%, and then the result is fully reported in a couple of weeks. The first days will have to be worn or weak points (for example, for -5 on the first day it will be -3.5, then -2, then -0.5), or tolerate.
Then it will be necessary to comply with the regime. To preserve the shape, hard lenses will have to be worn every night and sleep for at least 7 hours (and try not to exceed 10-11 to remove them in time). Less – slightly worse vision in the afternoon. More – not very scary, the main thing is not to abuse so consecutively dozens of days.
If you miss the night, your vision will fall a little – the cornea will begin to take on the shape characteristic of your short-sightedness. On the first day, you will receive an underestimation of -1 or -1.5, further – on increasing, stabilization at the same time. If you miss the night and start to wear from the next night – the next morning everything will be all right again.
The only point: for those who have vision up to -2.0, you can wear a lens through night if desired.
What is the maximum correction?
From -0.5 to -6 diopters on the sphere, depending on the shape of the cornea and up to -1.75 on astigmatism. For some people with a flat cornea, this method of correction has a narrower corridor of limitations. There are Russian lenses with a large correction corridor, but less oxygen-permeable material.
Are there lenses for correction of farsightedness?
Yes, there have been experiments with lenses that have an inverse shape and press on the edges of the cornea. But they are more expensive and less often, they were done in one clinic by hand. As a result, this method was abandoned.
How to choose a hard night lens
These lenses can not just be bought and bought in a pharmacy (in theory, of course, you can, but you should not do so) – you first need to get the exact parameters for your eye. The procedure goes like this: after a standard diagnosis in the clinic choose lenses from the suitcase with approximately 160 lens options. Somewhere from half an hour to an hour you try them on, until you feel that this is exactly the one that sits perfectly (that's why I recommend that you first learn how to wear one-day, otherwise the diagnosis will be quite unpleasant – for example, children often cry when their eyes Touch). As soon as you grope for your ideal lens, the optometrist will apply a fluorescent solution to it, which will glow in the IR illumination of the microscope. In a circle on the epithelium of the cornea it will be possible to understand how correctly your "ideal" was sitting in fact. After a double check, you get either ready-made lenses (if the clinic specializes in their calculation), or they will be ordered for you in the US and will arrive in a couple of weeks. In our practice, taking into account not a very large number of options for busting (most often you need 10-20 most characteristic models), go home with new lenses at once.
Sometimes patients are sent to us from lens manufacturers for diagnostics to get the results of shimpflug- Camera (Pentakama), because you need a combination of the convenience of finding the lens on the eye and their accuracy of selection. We need both sets of equipment – expensive diagnostics and a suitcase with a bunch of accessories.
These lenses are expensive, they cost about 28 thousand rubles for a couple, plus it is necessary to do 4 inspections in the first month, then – every 3 months. In general, and with regular contact lenses, you need to regularly look around, but very few people do so.
Every year you need to throw out old ones and buy new ones without paying too much. They also need a usual storage solution (first portion), containers and manipulators – in general, everything you need. This is also usually included in the price, as well as diagnosis.
If night lenses are selected for children with progressive myopia (to stabilize the process due to peripheral defocus), there is another feature. Until the age of 18, according to the law, the parent is fully responsible for his child, therefore the procedure for choosing and teaching the use is strictly done together with the mother or father at 15 and 6 years. Yes, they can be used starting somewhere from the age of 6, it does not make sense earlier – the child is likely to lose them.
Access of oxygen: why are they so steep and safe
There are a lot of good Russian models cheaper, but we use American ones – they are thinner by about half. This immediately excludes all other lenses from the choices. Yes, there are options cheaper, but we put on hard contact lenses, when the patient needs a comfortable vision without glasses, and without surgery, or when you need to stop the progressive nearsightedness in the child. It would be cheaper – stop by the glasses, this is more reasonable on safety.
So, despite the rigidity of the material, fluorine-silicone-acrylate has a structure that does not prevent the flow of oxygen to the eye (almost mythic 100% oxygen permeability), that is Night lenses are much safer than soft ones in this regard. Given the almost guaranteed limited time of wearing (I know very few people who can regularly sleep for 12 hours), the security requirements will be respected almost automatically. Hence the direct consequence: patients with complications for such lenses we do not. But, really, I must say that we are somewhat cunning when talking about long-term wearing: usually by the end of the year the patient is so used to the fact that one can freely run, jump and swim, that he really wants to get such a sight, but the lenses are already wearing laziness, And the timetable to observe also.
Therefore, the patient usually comes to laser correction, rejoicing in life and calculating the costs for the coming years. As a result of long, long-term cases of wearing hard night-time contact lenses in Russia, there are hundreds of them – as a rule, those who use them because of the impossibility of another correction and unwillingness to wear glasses at the same time. Usually – women-models and sportsmen, basically, boxers and hockey players.
Who uses hard night lenses?
- Those who can not correct, but want to walk without glasses
- Those who engage in active sports (it's hard to imagine a surfer with a dropped lens or a tennis player with glasses). And at night he blasphemered – took it out for the day.
- Those who are waiting for vision correction and want to understand how it will be after (note: hard lenses should be stopped a month before preoperative diagnosis).
- Those who live and work in regions where there are frequent changes from heat to cold (glasses mist over and interfere comfortably, for example).
- Children and adolescents with progressive myopia, when physical restriction of the mechanics of the cornea is needed.
- Those who are not sure that vision is stabilizing after laser correction.
Another moment. All that is written in the post regarding the safety of hard contact lenses, concerns only and exclusively special lenses for nighttime use during sleep. There are still hard contact lenses that are used for normal corrections, and those that are used after operations to create an additional exogenous eye skeleton. Almost none of the above does not apply to them, they are most often worn out of forced necessity.
And one more important point: yes, there are rigid lenses that are turned individually under the curve like a sinus cornea (usually after transplantation or serious operations) and Give an ideal vision. In such corneoscrial lenses, the mechanism of creating a fluid medium (tears) between the corneal tissues and the lens – they sit not on the cornea, but on the conjunctiva. They are made only by one clinic in Russia, as a solution to the "last chance", the testimony is extremely specific. If interested, I'll give a tip in PM.