Corneal medicine

Keratoconus

Keratoconus is a disease of the cornea that progressively alters its shape and its strength. It most often begins in adolescence or in young adults, and first shows itself through vision that blurs and that glasses correct less and less well. Detected early, there are ways of acting on how it progresses — which is what makes early diagnosis decisive.

What keratoconus actually is

The cornea is the transparent window at the front of the eye. Beyond its protective role, its curvature provides most of the eye’s optical power: it is the cornea that focuses light even before it reaches the crystalline lens. To fulfil this function, it must remain both perfectly transparent and perfectly regular.

In keratoconus, the cornea progressively loses its mechanical cohesion. It thins and distorts under the effect of the internal pressure of the eye, gradually taking on the shape of an irregular cone. Light is then no longer focused to a single point but scattered, which produces what is known as irregular astigmatism — a defect that ordinary spectacle lenses cannot compensate for.

This is the central point to understand: keratoconus is not a refractive error that worsens, it is a disease of the very structure of the cornea. Progressing myopia and progressing keratoconus may initially feel similar in everyday life, but they share neither the same mechanism nor the same care.

Cross-sectional diagram of a normal cornea and a cornea affected by keratoconus On the left, a normal cornea seen in cross-section: regular curvature and uniform thickness; the light rays passing through it converge to a single point. On the right, a cornea affected by keratoconus: the wall thins and distorts into a cone whose apex is displaced downwards, departing from the regular reference profile; the light rays no longer converge to a single point, which blurs vision. CORNEAL CROSS SECTION NORMAL CORNEA Regular curvature, uniform thickness. KERATOCONUS Thinning and cone shaped distortion. Anterior surface Posterior surface Apex displaced downwards Thinned cornea Regular reference profile OPTICAL CONSEQUENCE Light rays converge to a single point. Light rays no longer converge: vision blurs. Schematic. Proportions are deliberately exaggerated; this is not an actual scan.

Who is affected

Keratoconus generally appears between puberty and the age of thirty, more rarely beyond. It almost always affects both eyes, but asymmetrically: it is not unusual for one eye to be markedly more advanced than the other, to the point where the second goes unnoticed without a suitable examination.

Its true frequency remains debated. Estimates vary widely depending on the populations studied and, above all, on the diagnostic means used: early forms, invisible on simple clinical examination, are only detected by modern corneal imaging. Recent work reports a prevalence appreciably higher than the figures historically accepted.

A familial component exists in a minority of cases. When keratoconus is diagnosed, screening of first-degree relatives is warranted, particularly in adolescents.

The signs that should alert you

Keratoconus is silent for a long time, and its first manifestations are easily put down to a simple refractive error:

  • blurred or distorted vision, which glasses correct only partially;
  • frequent changes of prescription, in particular an astigmatism whose magnitude and, above all, whose axis shift from one check-up to the next;
  • double vision perceived with one eye alone, or “ghost” images that overlap;
  • halos around light sources, marked glare, considerable difficulty driving at night;
  • growing intolerance to soft contact lenses, which no longer stay in place or no longer correct sufficiently.

None of these signs is specific on its own. It is their combination, and above all their rapid progression in a young person, that should lead to an examination of the cornea.

The factor you can act on

Eye rubbing

Of all the elements associated with keratoconus, eye rubbing is the one most consistently found and the only one that can be acted upon immediately. Repeated rubbing exerts considerable mechanical stress on the cornea, and it is regularly observed that the more rubbed eye is also the more affected.

This rubbing is often involuntary, and sometimes nocturnal. It is frequently sustained by an identifiable cause: ocular allergy, dryness, blepharitis, poorly tolerated contact lens wear, sleeping face down against the pillow.

Stopping the rubbing, changing the sleeping position, treating the cause of the itching: this is therefore an integral part of care, in the same way as visual correction itself.

The message is simple and holds for everyone, with or without keratoconus: do not rub your eyes! This is the “No Rub No Cone” principle.

Frequently associated conditions

Several situations are found more often in patients with keratoconus: an atopic background (eczema, asthma, allergic rhinitis or conjunctivitis), sleep apnoea syndrome, Down syndrome, certain inherited connective tissue disorders, or floppy eyelid syndrome.

These associations do not mean that these conditions directly cause keratoconus. In several of them, eye rubbing — encouraged by itching or by the sleeping position — is in all likelihood a common denominator.

How it progresses

The progression of keratoconus varies greatly from one patient to another, and it is neither steady nor predictable. It is as a rule more active in young patients, and tends to slow down over the years — without this constituting an absolute rule on which to base a decision.

Two practical consequences follow. First, keratoconus diagnosed in adolescence warrants closer monitoring than keratoconus discovered at forty. Second, a mildly advanced form is not necessarily a stable form: only the comparison of examinations repeated over time makes the difference apparent.

Progression and monitoring →

Keratoconus and refractive surgery

Keratoconus contraindicates corneal refractive surgery, in particular LASIK and KLEx, which weaken an already fragile cornea. This is precisely why every preoperative assessment for refractive surgery includes a detailed analysis of corneal shape and thickness, in order to seek to rule out any subclinical and asymptomatic keratoconus.

If refractive surgery has been declined for you because your cornea was judged suspicious, it generally means that screening did its job. Other means of correction exist, including surgical ones, but they presuppose a stabilised disease and call for a specific assessment.

When laser surgery is not indicated →

When to seek advice

A consultation dedicated to the cornea is warranted in the following situations:

  • several of the signs described above, particularly in a young person;
  • an optical correction that changes rapidly from one check-up to the next;
  • a first-degree relative with keratoconus;
  • refractive surgery declined for a corneal reason;
  • keratoconus already known, without regular monitoring.

The examination relies on an analysis of the geometry and the thickness of the cornea, painless and without contact.

Screening and diagnosis →

Suspected keratoconus, or an opinion to compare?

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The other situations where the cornea calls for care

The cornea — overview →
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