Why is the image stretched?
The ideal cornea is close in shape to part of a sphere: its curvature is the same in all directions. With astigmatism, it is more like the side surface of a rugby ball or the convex side of a spoon - in one meridian the bend is stronger, in the perpendicular one it is weaker. Rays passing through different meridians are refracted with different strengths and collected at different depths. In principle, there is no single point of focus, so blur cannot be removed either by squinting, or by approaching the subject, or by ordinary spherical glasses. Hence the characteristic complaint: “I see as if with a shadow”, “letters are double with one eye”, “lanterns stretch into stripes”.
The second important difference between myopia and farsightedness is the direction of blur. With myopia, the picture loses clarity evenly in all directions, and squinting can help prevent this. With astigmatism, the blur is directional: horizontal lines can be sharp and vertical lines blurry, or vice versa. Therefore, a person often says that he sees some letters normally, but some not, and this is not an exaggeration, but an accurate description of how the optics of his eye behave. For the same reason, astigmatism is often combined with myopia or farsightedness and is almost never found in its pure form.
- Corneal astigmatism is the most common variant and is associated with the shape of the cornea
- Lenticular - related to the shape and inclination of the lens, usually smaller in size
- Correct astigmatism - the main meridians are perpendicular to each other, this can be easily corrected with glasses
- Incorrect - the surface is distorted chaotically, more often after keratoconus, scars, injuries and operations; glasses don't help much
- Based on the combination with myopia and farsightedness, simple, complex and mixed astigmatism is distinguished.
- Direct astigmatism is the most common variant, in which the vertical meridian refracts more strongly; reverse and oblique axes are more difficult to carry and require more precise correction
How does it manifest itself?
Astigmatism rarely causes a sharp drop in vision. Much more often, a person lives for years with the feeling that the picture is a little unclean, and explains this by fatigue or the monitor. The child does not complain at all: he does not know that it can be different, and simply considers his vision to be normal.
- Blurriness and “shadow” around objects at any distance
- Stretching point light sources into stripes, especially when driving at night
- Double vision when looking with one eye
- Headache and heaviness in the eyebrows after reading and working at the computer
- Eye fatigue, lacrimation, desire to squint
- The habit of tilting or turning your head to get a better angle
- Difficulty distinguishing between similar letters and numbers: “O” and “S”, “3” and “8”, “N” and “I”
Separately, it is worth dispelling the expectation that astigmatism must manifest itself as a severe decrease in vision. Most people have a small cylinder within 0.5 diopters and do not interfere with life in any way - it does not require any correction or observation. Astigmatism of approximately 0.75-1.0 diopters is considered significant, and it is from this border that complaints of fatigue and blurriness appear. Therefore, “astigmatism” found on the form is not a diagnosis in itself and is not a reason to immediately order glasses: it is not the number that decides, but visual acuity and well-being.
A special situation is driving in the dark. At night, the pupil dilates, and the peripheral areas of the cornea, where the distortions are most pronounced, are included in the work. The headlights of oncoming cars blur into long beams, road signs lose their clarity, and your eyes get tired faster. Many drivers first learn about their astigmatism after complaining about driving at night, although they considered their vision to be quite sufficient during the day.
Astigmatism in children and the risk of amblyopia
Slight astigmatism in infants is common and often decreases on its own in the first year or two of life. But if it remains significant, the main problem of childhood begins. The visual cortex of the brain is formed in the first years of life and learns from the image it actually receives. If the picture is always blurry, the cortex simply does not develop the ability to see clearly - and then even perfect glasses at 12 years old will no longer improve visual acuity. This condition is called refractive amblyopia.
The insidiousness of the situation is that with astigmatism, amblyopia often develops in both eyes at once, and outwardly the child looks completely normal: he does not squint, does not complain, calmly plays and draws. Therefore, parents find out about the problem by chance - during a medical examination before school, when precious years have already been spent. The earlier glasses are put on, the more fully visual acuity is restored: for a three-year-old child the chances are almost one hundred percent, for a seven-year-old it is already noticeably lower, and after nine to ten years it is usually not possible to achieve a significant improvement.
- Первый осмотр офтальмолога — в роддоме и далее по графику диспансеризации; обязательная проверка рефракции с каплями обычно проводится в возрасте около года и перед школой.
- При выявлении значимого астигматизма очки назначают в любом возрасте, включая малышей: современные детские оправы рассчитаны даже на грудничков.
- Критический период развития зрения — примерно до 7-8 лет; чем раньше начата коррекция, тем выше шанс полностью восстановить остроту зрения.
- При уже сформированной амблиопии к очкам добавляют окклюзию — заклейку лучше видящего глаза по схеме врача, чтобы заставить работать слабый глаз.
- Контроль каждые 6-12 месяцев: у растущего ребёнка величина и ось цилиндра могут меняться.
Survey
- Визометрия с подбором сферической и цилиндрической коррекции.
- Авторефрактокератометрия — прибор оценивает и рефракцию, и кривизну роговицы в разных меридианах.
- Рефрактометрия в условиях циклоплегии у детей, подростков и молодых взрослых.
- Кератотопография — карта поверхности роговицы. Это ключевое исследование, если астигматизм высокий, неправильный или быстро растёт: именно оно позволяет заподозрить кератоконус на ранней стадии.
- Пахиметрия — измерение толщины роговицы, обязательна при планировании лазерной коррекции.
- Осмотр глазного дна и измерение внутриглазного давления.
- Проба с пробной оправой: пациент ходит в подобранной коррекции 15-20 минут, чтобы оценить переносимость.
How to correct
- Glasses with spherocylindrical lenses are the main method for correct astigmatism. Lenses must be made according to an individual recipe indicating the axis.
- Toric soft contact lenses - have stabilization that holds the lens in the desired position on the eye; give a more natural image without distortion of dimensions.
- Rigid gas-permeable and scleral lenses are used for irregular astigmatism and keratoconus, when conventional optics can no longer cope: the rigid lens forms a new, smooth refractive surface.
- Laser correction - corrects correct astigmatism, usually up to approximately 4.0-6.0 diopters of the cylinder, with stable refraction and a healthy cornea.
- Toric artificial lenses are installed during cataract surgery, which allows you to remove astigmatism at the same time as a clouded lens.
- Corneal collagen crosslinking is not a vision correction, but a method of stopping the progression of keratoconus.
The choice of method depends not only on the dioptres, but also on the cause of astigmatism. If it is correct and stable, almost any method is suitable. If incorrect, caused by keratoconus, scar or previous surgery, laser correction may be contraindicated, and rigid or scleral lenses come to the fore, which form a smooth refractive surface over the deformed cornea. Another nuance concerns those who are about to undergo cataract surgery: if a person has significant corneal astigmatism, it is logical to take it into account when choosing an artificial lens, and not then decide separately with glasses. This conversation should begin before surgery, not after it.
Getting used to the first glasses
The first days with astigmatic glasses are almost always unusual, and it is important to know this in advance, otherwise the person decides that the glasses are “wrong” and puts them away in a drawer. A cylindrical lens changes the geometry of the image: straight lines may bend slightly, the floor appears inclined or raised, and slight dizziness occurs when walking. The brain is usually rebuilt in a few days, less often in one or two weeks.
- Носите очки постоянно с первого дня, а не «по чуть-чуть»: прерывистое ношение растягивает адаптацию.
- В первые дни избегайте вождения в темноте и работы на высоте.
- Лёгкое искажение пространства и утомление — ожидаемая реакция, а не признак ошибки.
- Если через две недели сохраняются головная боль, тошнота или явное двоение — нужна повторная проверка рецепта и оси.
- При высоком цилиндре врач иногда сознательно назначает неполную коррекцию с постепенным увеличением.