What is keratoconus? Definition, causes and progression

Keratoconus is a progressive deformation of the cornea, which gradually thins and bulges into a cone shape. Vision becomes blurred and distorted, often despite repeated changes of glasses. Detected early, it can be monitored and stabilised effectively. Here is how to recognise it, what encourages it to develop, and the examination that confirms the diagnosis.

Direct answer: how do you know if you have keratoconus?

Key point. Keratoconus presents as blurred, distorted vision that worsens, an astigmatism that changes frequently, and glasses prescriptions that can no longer keep up. It most often begins in adolescence or in young adulthood, and eye rubbing is a major aggravating factor. The diagnosis rests on corneal topography, a quick and painless examination that maps the shape of the cornea.

What is keratoconus, in practical terms?

The cornea is the transparent window at the front of the eye. Normally smooth and evenly curved, it provides much of the eye’s focusing power. In keratoconus, this cornea gradually thins and loses its regularity: under the effect of the internal pressure of the eye, it deforms and bulges forwards, taking on a cone shape.

This deformation alters the way light enters the eye. It creates an irregular astigmatism, that is, a distortion of images that cannot be fully corrected with ordinary glasses. Keratoconus usually affects both eyes, but often asymmetrically, with one eye more advanced than the other.

What are the symptoms of keratoconus?

The signs generally appear gradually and may go unnoticed at first. The most common are:

  • blurred or distorted vision that worsens over time;
  • a progressive astigmatism, with frequent and unsatisfactory changes of prescription;
  • discomfort in bright light (photophobia), haloes and glare, especially at night;
  • sometimes double vision in a single eye (monocular diplopia) or “ghost” images;
  • visual fatigue and a need to squint in order to see clearly.

One warning sign: glasses prescriptions that change frequently, without ever giving fully satisfactory vision. This is often what prompts a consultation and leads to the discovery of early keratoconus.

To spot these signs as early as possible, particularly in young adults, see our dedicated guide: the early signs of keratoconus.

What are the causes and risk factors?

Keratoconus results from a combination of factors, with no single cause. Several are well identified:

  • Eye rubbing: this is the most important and most avoidable aggravating factor. Rubbing the eyes repeatedly and vigorously weakens the cornea and encourages it to deform.
  • A genetic predisposition: a family history of keratoconus increases the risk, even though the condition is not systematically inherited.
  • Allergies and an atopic background (eczema, asthma, rhinitis): they maintain itching and therefore rubbing.
  • Age: keratoconus most often begins in adolescence or in young adulthood, a period when it may progress more quickly.

Stopping eye rubbing is the most useful preventive measure. It is often the first piece of advice given after diagnosis, as it helps to limit progression.

How is the diagnosis made?

The diagnosis rests above all on corneal topography (or tomography). This examination maps the shape and contour of the cornea and measures its thickness. It detects the deformations characteristic of keratoconus, sometimes well before vision is markedly affected. It is quick, involves no painful contact, and is the reference for making and following the diagnosis.

The examination is completed by measuring corneal thickness (pachymetry) and analysing the regularity of the surface. Repeated over time, these examinations show whether the keratoconus is stable or progressing, which guides management.

Topography also plays an essential role before any refractive surgery: it makes it possible to detect early or “forme fruste” keratoconus, which is a contraindication to LASIK. This is one of the reasons the pre-operative assessment is so thorough.

Key facts

Keratoconus: a deformation of the lower cornea

In keratoconus, the cornea thins and bulges into a cone, most often in its lower part. In advanced forms, this cone can mark the lower eyelid in a V shape on downgaze: this is Munson’s sign.

What happens after the diagnosis?

Receiving a diagnosis of keratoconus does not mean losing your sight. The great majority of keratoconus cases remain moderate and are managed very well. Management depends on the stage and the rate of progression: regular monitoring, glasses or lenses suited to more advanced stages, and treatment to slow progression when it is documented. The key is to act early and to eliminate eye rubbing.

Your care pathway at the practice

The screening and monitoring of keratoconus (corneal topography, pachymetry, vision measurement) take place at the Cachan practice. If you notice vision that is becoming distorted or prescriptions that change frequently, especially in a teenager or a young adult, an assessment makes it possible to confirm the diagnosis and set up appropriate monitoring. The earlier keratoconus is spotted, the more scope there is to stabilise it.

FAQ

Frequently asked questions about keratoconus

Does keratoconus cause blindness?

No. Keratoconus can impair vision, sometimes markedly, but it does not lead to blindness. Most forms remain moderate and are corrected with glasses or contact lenses. In advanced cases, solutions exist to rehabilitate vision. The main concern is to slow progression in time.

At what age does keratoconus appear?

Keratoconus most often begins in adolescence or in young adulthood. It is also during this period that it may progress the fastest, which is why early diagnosis matters. It generally stabilises with age, but monitoring remains useful for as long as vision may change.

Can eye rubbing cause keratoconus?

Repeated and vigorous eye rubbing is the main known aggravating factor. It does not create the condition on its own, but it encourages and accelerates the deformation of the cornea in a predisposed individual. Stopping eye rubbing is the most effective preventive measure, particularly where there is allergy.

Which examination diagnoses keratoconus?

Corneal topography is the reference examination. It maps the shape and thickness of the cornea and detects the deformations of keratoconus, sometimes before symptoms appear. Quick and painless, it also serves to detect early keratoconus before refractive surgery.

Can you have LASIK when you have keratoconus?

No, LASIK is contraindicated in keratoconus, because it would further weaken an already fragile cornea. It is precisely to rule out this risk that the pre-operative assessment includes a topography. Other correction options exist and are discussed case by case with the ophthalmologist.

Sources

  1. Centre de Référence National Kératocône (Pr P. Fournié, Pr D. Touboul), filière SENSGENE — Protocole National de Diagnostic et de Soins (PNDS): Kératocône. Haute Autorité de Santé, novembre 2021. has-sante.fr/jcms/p_3301044/fr/keratocone
  2. American Academy of Ophthalmology (AAO) — Corneal Ectasia Preferred Practice Pattern®, 2023. aao.org/education/preferred-practice-pattern/corneal-ectasia-ppp-2023

Further reading

Keratoconus screening and monitoring at the Cachan practice · Tel. +33 1 45 47 08 11

In summary

Keratoconus is a progressive deformation of the cornea that makes vision blurred and distorted, with an astigmatism that keeps changing and glasses that can no longer keep up. It often begins in adolescence, and eye rubbing makes it worse. The diagnosis rests on corneal topography, a simple and early examination. Detected early, keratoconus can be monitored and stabilised in the great majority of cases: seeking advice at the first signs makes all the difference.

This article is intended to inform and educate. It does not replace a medical consultation. Only an examination by an ophthalmologist can confirm a diagnosis and propose management suited to your situation.

Written and reviewed by Dr Moïse Tourabaly, ophthalmic refractive surgeon — former chef de clinique (Quinze-Vingts National Eye Hospital).

Last updated: September 11, 2026

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