Keratoconus and what “progression” means
In keratoconus the cornea gradually thins and becomes conical toward the front. This change does not occur at the same speed or to the same degree in every person. In some patients no marked difference is seen for years, while in others the shape of the cornea changes at short intervals. Physicians call this change “progression”.
Progression cannot be understood from a single examination. Corneal mapping (topography), thickness measurement and level of vision are repeated at intervals and compared with one another. A glasses prescription that changes often within a short time is also among the findings the physician takes into account.
Symptoms can include blurred or distorted vision, a frequently changing glasses prescription, light sensitivity and halos around lights. Because these symptoms can also occur in other eye problems, a definite distinction can be made only by examination.
What is cross-linking?
Corneal cross-linking (CXL) is a procedure that aims to create new bonds in the corneal collagen by applying ultraviolet A light at a controlled dose after riboflavin (vitamin B2) has been dropped onto the cornea. The aim is to increase the structural strength of the cornea and thereby slow or halt progression.
The procedure is performed under numbing drops. Depending on the method the physician chooses, the outermost layer of the cornea (the epithelium) may be removed or preserved during the procedure; riboflavin is then dropped on and the light is applied. The light dose and the duration of the procedure vary with the protocol chosen.
The goal of cross-linking is not to correct vision but to slow the progression of the cornea.
For this reason no increase in visual acuity is expected from the procedure; in some patients changes may be seen in the measurements, but this is unpredictable and varies from person to person. The need for glasses or lenses most often continues.
In whom is it considered?
The physician brings up cross-linking in keratoconus patients who show signs of progression, that is, in whom a change over time has been identified in the examination measurements or in the glasses prescription. Age alone is not decisive; it can also be considered in children and young people if there is progression. In eyes that are thought not to have progressed yet, or that appear stable under close follow-up, the physician may prefer to observe first.
The decision is made by evaluating corneal thickness, topographic findings, the condition of one or both eyes and the person's circumstances together. What matters is that the decision is based not on a single examination finding but on the change over time; so if no procedure is recommended at the first examination, it does not mean the disease has been overlooked.
Is cross-linking the whole of the treatment?
No. Cross-linking is not the only treatment for keratoconus and most often does not solve the vision problem by itself. Glasses or special contact lenses continue to support vision; options such as intracorneal rings or topography-guided surface procedures may be added to cross-linking according to the physician's assessment, and in advanced stages a corneal transplant may be considered.
In other words, cross-linking is not a “vision correction” method but one of the steps in managing the course of the disease. The details of the options are given on the Keratoconus page.
In whom may it be unsuitable?
If the corneal thickness is not sufficient, if there is an active infection or a marked scar in the cornea, if the person is pregnant or breastfeeding, or if the aftercare recommendations cannot be followed, the physician may suggest a different course. In these situations another method may be applied, or observation alone may be carried out.
What to expect after the procedure
During the procedure the eye is numbed with drops. In the first days burning, stinging, watering and light sensitivity may occur; the severity varies from person to person. The physician gives the necessary drops and care recommendations. Not rubbing the eye, following the recommendations and attending follow-up examinations are part of healing. Those who wear lenses learn from the physician when they can return to them.
Healing of the cornea and the settling of the measurements into their new pattern take time; follow-up examinations and, if needed, repeat measurements are therefore planned. Time may need to be allowed for the glasses or lens prescriptions to settle. The physician determines when and with which measurements follow-up is carried out.
Results may vary from person to person in any surgical or interventional procedure.
This article is for information only and does not replace diagnosis or treatment. For your own situation, consult your physician by having an examination.
Sources
The framework of this article is at textbook level. Some of the author's own studies on the subject:
- Different accelerated corneal collagen cross-linking treatment modalities in progressive keratoconus. Eye and Vision, 2019.
- Accelerated Corneal Collagen Cross-Linking in Thin Keratoconic Corneas. Journal of Refractive Surgery, 2015.
- Complications of accelerated corneal collagen cross-linking: review of 2025 eyes. International Ophthalmology, 2020.
- Accelerated corneal crosslinking in children with keratoconus: 5-year results and comparison of 2 protocols. Journal of Cataract & Refractive Surgery, 2020.