Short answer
Keratoconus is a thinning cornea that bulges into a cone. It usually starts between 12 and 25 and announces itself through a fast-changing cylinder, ghost images and glare at night. A standard sight test does not see it early — only 3D corneal topography does. The gold-standard treatment is cross-linking, whose purpose is not to restore vision but to stop the disease. And active keratoconus rules out laser correction entirely.
Have you noticed your prescription changing unusually fast lately, particularly the astigmatism — the cylinder? Or that text and light sources come with distracting ghost shadows, stretched contours or streaky halos that even new lenses cannot sharpen?
If that sounds familiar, it may be keratoconus, a progressive condition of the cornea, the clear window at the front of the eye. Keratoconus is not an infection or inflammation. It is a gradual thinning and mechanical weakening of corneal tissue, which lets the normally round cornea bulge forward into a cone.
It is most often diagnosed in young people between 12 and 25. Because it can cause significant vision loss without timely intervention, finding it early is what decides the outcome.
Why the cornea changes shape
In a healthy eye the cornea has a smooth, symmetrical curvature that focuses light rays directly onto the retina. In keratoconus, the structural collagen fibrils within the corneal stroma lose their mechanical cross-links.
Weakened in that way, the cornea can no longer withstand normal intraocular pressure. The central or lower cornea thins progressively and bulges forward into an asymmetrical cone.
Because the surface is now uneven and conical, light rays no longer meet at a single retinal point but scatter. The result is irregular astigmatism and rapidly progressive myopia. That is precisely why new lenses stop helping: glasses correct a regular error, not an irregular surface.
Early warning signs
Keratoconus usually begins in one eye and eventually affects both, though the severity often differs noticeably between them.
- Rapidly changing prescriptionLens power — especially the cylinder dioptres and axis — shifts noticeably within months rather than years.
- Blurry vision glasses cannot fixStandard glasses and soft contact lenses no longer give sharp vision, because they do not compensate for an irregular corneal surface.
- Ghost images with one eyeLit objects and text develop multiple faint shadows, doubled contours or a trailing image. In medical terms, monocular polyopia.
- Severe photophobia and halosAt night, streetlights and headlights turn into long, streaky flares, which makes driving in the dark genuinely difficult.
- Eyestrain and the urge to rubThe constant effort to focus creates muscle strain and chronic discomfort.
Causes, and the one risk factor you can change
- Genetic predispositionAbout 10% of patients have keratoconus in the family. If a relative has it, a child's cornea is worth checking before symptoms appear.
- Atopic conditionsAsthma, eczema, hay fever and vernal conjunctivitis are strongly associated with keratoconus — partly through the condition itself, partly because itchy eyes get rubbed.
- Chronic eye rubbingClinical evidence identifies vigorous, repeated eye rubbing as a primary mechanical trigger for both the onset and the acceleration of keratoconus. Rubbing creates micro-trauma, raises local temperature and breaks the bonds between collagen fibres.
Genetics are not a choice. Rubbing is. And if the eyes itch because of allergy or dry eye, the right move is to treat that cause instead.
Diagnosis: why a standard sight test misses it
A standard sight test and an autorefractor cannot detect early, subclinical keratoconus. Finding it early requires 3D corneal topography and tomography, which maps the curvature of the front and back corneal surfaces and measures corneal thickness across thousands of points to the micron.
What KSA does
At KSA this work is done by the SCHWIND SIRIUS+, which combines a rotating 3D Scheimpflug camera with Placido topography and carries a dedicated keratoconus screening module. Every Audit eye examination includes this analysis for everyone, not only when there is a suspicion.
Active keratoconus is an absolute contraindication for any laser vision correction, Flow3 included. Lasering a keratoconic cornea would leave it thinner and less stable still. The screening is therefore not an optional step here but a safety protocol — and it is the reason KSA has had no case of corneal weakening, that is ectasia, in 21 years.
When keratoconus is found, KSA's role is to stage it and to watch whether it progresses: repeat topography shows whether the cornea is holding still or moving. That is the finding that sets the timing of treatment, and it cannot be established from one measurement.
The gold standard: corneal cross-linking
Decades ago the only definitive answer to keratoconus was to wait for it to worsen until a corneal transplant. Today the gold standard is corneal collagen cross-linking, or CXL.
- Riboflavin drops. The corneal tissue is saturated with a vitamin B2 solution.
- UV-A light. Controlled ultraviolet-A light is applied to the cornea.
- Photochemical reaction. Together they form new covalent cross-links between the collagen fibres of the stroma.
The goal of cross-linking is not to restore vision or to free you from glasses, but to halt progression. The procedure makes the cornea 150 to 300% stiffer, preventing further thinning and bulging. Visual acuity is then restored with lenses or glasses.
How vision is recovered afterwards
Once the disease has been stopped, the next question is how to see sharply with an irregular cornea. The answer depends on how far the cone has progressed.
Rigid gas-permeable lenses · RGP
A rigid lens forms a tear-fluid layer between itself and the cornea, which neutralises the irregular curvature.
Advantage. Delivers good acuity even on a clearly irregular cornea.
Limitation. Takes getting used to and can feel uncomfortable at first.
Scleral lenses · large diameter
Large-diameter lenses rest on the sclera and do not touch the sensitive cornea at all.
Advantage. Comfortable, and sharp when an RGP no longer fits.
Limitation. Need specialist fitting and careful maintenance.
Intrastromal ring segments · Intacs
Small plastic arcs are placed inside the cornea to pull the cone flatter.
Advantage. Improve corneal shape and make glasses workable again.
Limitation. A surgical procedure.
Corneal transplant · keratoplasty, DALK or PKP
The diseased corneal layer, or its full thickness, is replaced with donor tissue.
Advantage. The answer in end-stage disease and with heavy scarring.
Limitation. Surgical risk, long recovery and the possibility of rejection.
When to have the cornea checked
If the prescription has changed several times in a year, if the cylinder is growing, if vision stays soft even in new lenses, or if keratoconus runs in the family — then topography is the right next step, and sooner is better. In keratoconus, timing decides the outcome: what can be stopped is what has not happened yet.
We examine in Tallinn and Tartu.
Closely related: astigmatism, myopia and the equipment we measure with.