Keratoconus: early signs, cross-linking and lens selection in Tashkent

What happens to the cornea

The cornea is the transparent front portion of the eye's outer layer and is responsible for approximately two-thirds of its total refractive power. Strength is given to it by the strict order of collagen fibers, laid in layers in certain directions and interconnected by cross-links. With keratoconus, these connections weaken: the fibers begin to slide relative to each other, the tissue becomes thinner and, under the influence of normal intraocular pressure, gradually protrudes forward, taking the shape of an uneven cone. The apex of the cone is often shifted downward from the center.

The optical consequences are predictable but unpleasant. A smooth spherical surface turns into an irregular one: the curvature is different not only in two perpendicular directions, as with ordinary astigmatism, but also at each point in its own way. This distortion is called irregular astigmatism, and its fundamental property is that the spectacle lens does not compensate for it. Spectacle glass can only correct correct, geometrically regular deviations. Therefore, a person with keratoconus sits in the office, the doctor sorts through the glasses, and the line of the table is still not fully readable - and this feeling is the earliest signal.

• Onset usually occurs between the ages of 13 and 20, rarely after 30
• Both eyes are affected, but almost always asymmetrically: one is years ahead of the other
• Progression is most active in adolescence and young adulthood; by the age of 35-40 the process most often stops on its own
• The younger the patient is at the time of diagnosis, the faster the progression usually occurs.
• Far advanced stages are accompanied by cicatricial turbidity at the apex of the cone

Early signs that are missed

The problem with early diagnosis is that keratoconus masquerades as the most common situation: a teenager’s vision began to worsen, he was prescribed glasses, a year later his vision deteriorated again, the glasses were changed. Everything looks ordinary, and no one asks the main question - whether these glasses achieve full visual acuity. It is the unattainability of one hundred percent even with perfectly selected glasses, and not the fact of deterioration itself, that distinguishes keratoconus from ordinary progressive myopia.

• Glasses do not provide full visual acuity; the “best glass” still leaves blurriness
• The recipe changes more than once a year, and each time the cylinder grows and its axis shifts
• One eye is noticeably behind the other
• Double vision and multiple contours when viewed with one eye: ghostly copies of the letter are visible around it
• Halos and rays around streetlights and headlights, sharply intensifying at night
• Photophobia, a feeling that bright light hurts the eyes more than others
• The tolerability of soft contact lenses has worsened: the lens no longer sits stable and “jumps”
• Constant urge to squint and rub your eyes

There is also a situation in which the disease is discovered unexpectedly and at the right moment - an examination before laser vision correction. Keratotopography and tomography of the cornea are included in the mandatory protocol precisely because they make it possible to identify early keratoconus, which does not manifest itself in any way. This is fundamental: laser correction for keratoconus is contraindicated, since it further thins the already weakened cornea and can dramatically speed up the process. Refusal to perform an operation based on topography results is not an unfortunate failure, but a disaster prevented in time, and it should be perceived as such.

The habit of rubbing your eyes is a factor that is in our control

Of all the known risk factors, this one stands out because it can be eliminated free of charge and immediately. Mechanical friction is not a metaphor: pressing a finger or knuckle on the eye briefly increases intraocular pressure significantly and deforms the weakened cornea. When such an impact is repeated dozens of times a day for years, it contributes to progression, and the contribution is significant. It is no coincidence that in many patients the cone is more pronounced on the eye that rubs more often, and on the side on which the person sleeps.

• Atopic dermatitis, allergic conjunctivitis and hay fever - the eyes itch, a person rubs them constantly and reflexively
• Bronchial asthma and other atopic conditions occur more often than average in patients with keratoconus
• Dry eye syndrome - dryness provokes the same friction
• Sleeping with your face in the pillow and resting your fist on your eye while sleeping
• Floppy eyelid syndrome and sleep apnea, in which the eye is mechanically injured at night
• Professions and hobbies associated with dust and constant eye irritation

The practical conclusion from here is direct and very specific. If a child or teenager has allergies and constantly rubs their eyes, it is the allergy that needs to be treated - not “to prevent itching,” but to prevent keratoconus from forming. For itching, instead of rubbing, use doctor-prescribed drops, a cold compress, and rinsing. If keratoconus is detected, complete abstinence from rubbing the eyes is as much a part of the treatment as anything else, and it is worth discussing this with the patient separately and in detail, because this habit is unconscious.

Diagnostics: why a routine vision test is not enough

1. Визометрия с максимальной коррекцией — уже она показывает главное: достижима ли полная острота зрения стёклами.
2. Авторефрактокератометрия — выявляет высокий и «косой» астигматизм, но раннюю стадию не видит.
3. Кератотопография — цветная карта кривизны передней поверхности роговицы. Это main метод: она показывает характерное локальное усиление кривизны, обычно ниже центра.
4. Кератотомография — исследование, оценивающее и заднюю поверхность роговицы, и распределение толщины по всей площади. Изменения задней поверхности появляются раньше всего и позволяют поймать самые ранние формы.
5. Пахиметрия — измерение толщины роговицы в разных точках; определяет минимальную толщину и её положение.
6. Биомикроскопия за щелевой лампой — на поздних стадиях видны истончение, линии натяжения в строме, кольцо отложений вокруг конуса, рубцы.
7. Аберрометрия — оценивает оптические искажения высшего порядка, которые и объясняют жалобы на множественные контуры.
8. Повторные исследования через 4-6-12 месяцев — прогрессирование доказывается только сравнением карт в динамике.

Crosslinking and other treatments

Treatment of keratoconus is divided into two fundamentally different tasks, and it is important not to confuse them. The first is to stop the progression, that is, to prevent the cornea from deforming further. The second is to provide a person with acceptable vision here and now. The methods for these tasks are different, and they are often used simultaneously.

• Corneal collagen crosslinking is a procedure in which the cornea is saturated with riboflavin and irradiated with ultraviolet light, causing new cross-links to form between the collagen fibers and the tissue becomes stronger. This is the only method that stops progression and it works for most patients.
• Crosslinking does not significantly improve vision and does not replace glasses or contacts: its purpose is to record the current condition. A slight improvement in form sometimes occurs over time, but you should not count on it as a result.
• Glasses help only in the early stages, while the astigmatism remains relatively correct.
• Rigid gas-permeable lenses - form a new, smooth refractive surface over the uneven cornea, the tear layer under the lens smoothes out irregularities; give a sharp jump in visual acuity where glasses are powerless.
• Scleral lenses are large lenses that rest on the tunica albuginea and do not touch the cornea at all; option for advanced stages and intolerance to hard lenses.
• Intrastromal ring segments are thin arcs implanted into the thickness of the cornea to flatten the cone and make the surface more regular.
• Keratoplasty - corneal transplantation, layer-by-layer or through; used in advanced stages, with pronounced scars and intolerance to all types of correction.
• Laser vision correction for keratoconus is contraindicated: it thins the cornea and speeds up the process.

It’s worth mentioning separately about deadlines, because this is where time is most often lost. Crosslinking is most valuable in young patients with proven progression: the earlier it is performed, the better the shape of the cornea can be preserved forever. There is no point in waiting until vision drops to an unacceptable level - the procedure will not return what has already been lost. In patients over 35-40 years of age with stable corneal maps, the issue is resolved individually: if there is no progression, the task comes down to selecting the optimal correction.

Living with keratoconus

1. Полностью прекратить трение глаз. Это самое дешёвое и одно of самых действенных вмешательств; при зуде — лечить аллергию и сухость, а не тереть.
2. Держать под контролем аллергический конъюнктивит и атопический дерматит совместно с аллергологом.
3. Делать топографию роговицы в динамике — обычно раз в 6-12 месяцев, у подростков чаще, пока не подтверждена стабильность.
4. Не соглашаться на лазерную коррекцию зрения; если её предлагают без топографии, это повод сменить a clinic.
5. Соблюдать режим ношения и ухода за жёсткими или склеральными линзами, приходить на контроль посадки линзы.
6. Не спать лицом в подушку и на стороне более поражённого глаза, использовать защитный щиток после кросслинкинга по назначению врача.
7. Проверить роговицу у детей и родных братьев и сестёр — наследственная предрасположенность существует.
8. При резкой боли, затуманивании и светобоязни обращаться немедленно, не дожидаясь планового приёма.