Corneal Crosslinking for Keratoconus: Procedure, Evidence, and Recovery

Corneal crosslinking (CXL) is the only treatment that has been shown to halt the progression of keratoconus. It works by creating new chemical bonds within the corneal stroma using ultraviolet A light and riboflavin (vitamin B2), stiffening the corneal tissue and preventing further ectatic change. When performed at the right time, crosslinking can preserve the cornea in its current state indefinitely, avoiding the need for corneal surgery or transplantation. It does not reverse existing cone shape or scarring, but it stops the condition from getting worse. This post covers the evidence base for crosslinking, the accelerated epithelium-off protocol used in current practice, how it compares to the original Dresden protocol, what the procedure involves, and what patients experience during recovery.

Why timing matters in keratoconus management

Crosslinking is most effective when performed while adequate corneal tissue remains and before scarring develops. The key decision trigger is documented progression on serial topography or tomography. Early intervention prevents thinning below safe treatment thresholds and preserves the cornea's capacity to respond to treatment.

Treating a stable keratoconus unnecessarily exposes the patient to the risks of the procedure without benefit. Waiting too long risks irreversible progression, thinning below the minimum corneal thickness threshold for safe crosslinking (typically 400 microns at the thinnest point), and the development of corneal scarring that limits best-corrected visual acuity regardless of treatment.

The decision to crosslink is made after reviewing serial topographic measurements over a minimum of three to six months. In younger patients and children, where progression is typically faster and more aggressive, a lower threshold for intervention is appropriate. In patients with newly diagnosed keratoconus who are still young, early crosslinking is often recommended even in the absence of documented progression, because the risk of future progression is high.

The Dresden protocol: the original standard

The Dresden protocol is the original and most extensively validated corneal crosslinking technique, with published follow-up data spanning up to 13 years. It delivers a total corneal energy dose of 5.4 J/cm2 using a 3 mW/cm2 UV-A source over 30 minutes, following epithelial removal and riboflavin saturation of the stroma. All subsequent crosslinking protocols are evaluated against it.

The Dresden protocol, developed by Wollenslaeger and Seiler in Germany in the early 2000s, uses a riboflavin concentration of 0.1 percent and an ultraviolet A irradiance of 3 mW/cm2 applied continuously for 30 minutes, delivering a total energy dose of 5.4 J/cm2. Before the riboflavin is applied, the corneal epithelium is removed over a 9 mm diameter zone to allow adequate riboflavin penetration into the stroma.

The Dresden protocol has the most extensive long-term follow-up data of any crosslinking technique. A 2024 review published in Current Opinion in Ophthalmology summarising data from 2018 to 2023 reported that the Dresden protocol halts keratoconus progression in the large majority of treated eyes, with improvements in multiple visual and topographic indices including uncorrected distance visual acuity, best-corrected visual acuity, maximum keratometry (Kmax), K1, and K2 sustained up to 13 years postoperatively (Curr Opin Ophthalmol. 2024;35(4):315-321).

A comprehensive systematic review published in PMC in 2025, covering randomised controlled trials, prospective and retrospective cohort studies, and meta-analyses from 2013 to 2025, found that conventional epithelium-off CXL using the Dresden protocol demonstrated the most consistent long-term keratometric stabilisation, with mean Kmax flattening of approximately 1.0 to 2.3 D at 12 to 36 months, and best-corrected visual acuity improvements of approximately 0.10 to 0.23 logMAR (PMC12867310).

The main limitation of the Dresden protocol is the 30-minute ultraviolet exposure time, which increases total procedure duration and patient discomfort.

Accelerated epithelium-off CXL: the current approach

Accelerated crosslinking delivers the same 5.4 J/cm2 energy dose as the Dresden protocol using a higher irradiance (typically 9 mW/cm2) for a shorter treatment time (10 minutes), reducing chair time without reducing the photochemical dose. Epithelial removal is still performed. This is now the most widely used approach in contemporary practice.

Accelerated crosslinking uses a higher irradiance for a proportionally shorter duration to deliver the same total energy dose of 5.4 J/cm2 more quickly. The most commonly used accelerated protocol in current practice delivers 9 mW/cm2 for 10 minutes, replacing the 30-minute Dresden exposure. Like the Dresden protocol, it uses epithelium-off (epi-off) technique, meaning the corneal epithelium is removed before the riboflavin is applied.

A meta-analysis of 22 studies comprising 1,158 eyes (Dresden protocol: 577 eyes; accelerated: 581 eyes) found that the Dresden protocol was superior in reducing minimum keratometry and producing a deeper demarcation line, a surrogate marker of stromal penetration depth. However, accelerated CXL achieved comparable short-term outcomes in terms of Kmax flattening at 6 to 12 months (approximately 0.8 to 1.5 D), with greater variability in durability at longer follow-up compared with the Dresden protocol.

A 2024 comparative study in paediatric patients found that the accelerated protocol was as efficient as the Dresden protocol in stabilising keratoconus progression, with no significant difference in corrected distance visual acuity between the groups at 12 months, though the Dresden protocol was superior in reducing Kmax (PubMed: 39607156).

In summary, accelerated epi-off CXL is well-supported as an effective treatment for progressive keratoconus. It reduces procedure time significantly and achieves good stabilisation outcomes in the majority of patients. The Dresden protocol has a stronger long-term evidence base, but accelerated protocols have become the standard in most contemporary practice given the equivalent short-term outcomes and patient tolerance advantages.

Transepithelial (epi-on) crosslinking: why it is not the preferred approach

Transepithelial crosslinking attempts to deliver riboflavin through the intact epithelium, avoiding the discomfort of epithelial removal. In practice, the epithelium is a significant barrier to riboflavin penetration, and epi-on protocols consistently produce inferior stromal penetration, shallower demarcation lines, and lower stabilisation rates than epi-off techniques.

The 2025 systematic review referenced above found that transepithelial protocols showed the weakest and most variable outcomes across all protocols studied, with limited long-term durability data. For this reason, epi-off crosslinking, whether Dresden or accelerated, remains the standard of care for progressive keratoconus in most experienced centres.

Who is suitable for corneal crosslinking?

Standard candidacy for crosslinking requires documented progression on serial topography or tomography, a minimum corneal thickness of 400 microns at the thinnest point, and absence of significant central corneal scarring. The procedure can be performed in patients from early adolescence onward, and in paediatric patients with aggressive disease, earlier intervention is often appropriate.

The standard criteria for crosslinking candidacy are: documented progression of keratoconus on serial topography or tomography, minimum corneal thickness of 400 microns at the thinnest point (to allow safe stromal treatment while maintaining an adequate stromal bed above Bowman's layer), absence of significant corneal scarring that would contraindicate the procedure or limit the expected benefit, and age typically 14 years and over (though crosslinking can be performed in younger children in centres with appropriate experience).

Patients who are not suitable candidates include those with a corneal thickness below 400 microns at the thinnest point (though hypotonic riboflavin can be used to temporarily swell the cornea in borderline cases), those with significant central corneal scarring, those with active ocular surface disease or severe dry eye, and those with stable keratoconus who are not showing documented progression.

Contact lens wearers should cease rigid lens wear for at least two weeks before topographic assessment to allow the corneal shape to return to its natural state, as rigid lenses temporarily mask the degree of cone distortion.

What does the accelerated epi-off crosslinking procedure involve?

The procedure is performed under topical anaesthesia with anaesthetic eye drops applied to the eye. No injection or general anaesthetic is required, and most patients are comfortable throughout. The total procedure time is approximately 45 to 60 minutes per eye.

The corneal epithelium is removed from the central 9 mm zone of the cornea using a blunt spatula or the application of a dilute alcohol solution, followed by gentle debridement. This is the part of the procedure that patients most commonly describe as uncomfortable in the postoperative period, because the corneal epithelium is the eye's protective surface layer and its removal causes a raw area that takes several days to heal.

Riboflavin 0.1 percent solution is then applied to the cornea every two to three minutes for a soaking period, typically 10 minutes, to saturate the corneal stroma. The riboflavin solution appears yellow and causes the eye to appear yellow during this phase.

Ultraviolet A light is then applied to the cornea at 9 mW/cm2 for 10 minutes, with riboflavin continued during the exposure phase. The UV light activates the riboflavin, which generates reactive oxygen species that create new covalent bonds between collagen fibrils in the stroma, stiffening the tissue.

At the completion of the UV exposure, a bandage contact lens is placed on the eye. This remains in place for three to five days while the epithelium heals. Antibiotic and anti-inflammatory eye drops are commenced on the day of the procedure and continued for four to six weeks.

What does the procedure feel like?

The procedure itself is painless under topical anaesthesia. Patients typically lie under the UV lamp for 10 minutes and are asked to look at a fixation light. Some patients experience mild discomfort from the eye speculum used to keep the eyelids open.

The most significant discomfort occurs in the first 24 to 72 hours after the procedure, when the corneal epithelium is absent. Patients describe this as a gritty, burning, foreign body sensation similar to a corneal abrasion. This is managed with the bandage contact lens, regular lubricating drops, oral analgesia if needed, and avoidance of bright light. Most patients find the first two days the most uncomfortable, with significant improvement by day three to four when the epithelium begins to close.

Recovery and what to expect after crosslinking

Vision is typically reduced and variable for four to eight weeks after crosslinking as the corneal stroma remodels. This is normal and expected. The bandage contact lens is removed at approximately day five once the epithelium has healed, and most discomfort resolves by this point. Full visual stabilisation takes three to six months.

The visual fluctuation after crosslinking is caused by corneal oedema (swelling) as the tissue responds to the treatment, and by changes in corneal shape as the stroma remodels following the procedure. This is a normal and expected part of the healing process and is not a sign that the treatment has failed.

Vision typically returns to close to the pre-treatment level by six to eight weeks and may continue to improve over the following months. A small proportion of patients experience a meaningful improvement in their best-corrected visual acuity after crosslinking, most likely because the procedure causes some mild regularisation of the corneal surface. However, crosslinking is not primarily a visual rehabilitation procedure and patients should not expect improved vision. The goal is stabilisation.

Serial topographic monitoring continues at three, six, and twelve months after crosslinking, and then annually. Stabilisation is confirmed by the absence of progression on serial topography over a minimum two-year follow-up period.

Can crosslinking be combined with other procedures?

In selected patients with progressive keratoconus and significant irregular astigmatism, crosslinking can be staged with topography-guided PRK to both halt progression and regularise the corneal surface. Crosslinking can also be performed in conjunction with intrastromal corneal ring segment implantation. The sequence and timing of combined procedures depends on the individual clinical situation.

In patients with keratoconus who have both progressive disease and significant irregular astigmatism limiting their visual acuity, crosslinking can be combined with topography-guided photorefractive keratectomy (PRK) in a staged approach. The PRK regularises the corneal surface to reduce irregular astigmatism and improve contact lens fit and uncorrected visual acuity, while the crosslinking halts progression. This combined approach is an example of CXL Plus (CXL+), a term describing any refractive procedure performed in combination with crosslinking. CXL+ options include topography-guided PRK combined with crosslinking in the same sitting, and ICRS or CAIRS implantation combined with crosslinking. The goal in each case is to combine the progression-halting effect of crosslinking with a refractive or regularisation procedure to improve vision in the same treatment episode.

When is crosslinking not enough?

Crosslinking halts progression but does not correct the irregular astigmatism or visual impairment already present at the time of treatment. Patients who achieve stable disease after crosslinking but continue to have poor best-corrected visual acuity, contact lens intolerance, or corneal scarring require additional management beyond crosslinking alone.

The management options for patients with stable post-crosslinking keratoconus who still have visually significant disease include rigid contact lens fitting (the most common first step), intrastromal corneal ring segment (ICRS or CAIRS) implantation to regularise the cone, and corneal transplantation (DALK or PKP) for advanced disease where other approaches have failed or are not feasible. These options are covered in detail in the refractive and surgical management of keratoconus guide.

When should optometrists refer for crosslinking assessment?

Optometrists should refer for crosslinking assessment when serial topography shows measurable progression over three to six months, when the patient is young with newly diagnosed keratoconus even without documented progression, or when a strong family history and early topographic changes are present together. The best outcomes from crosslinking are achieved before significant corneal thinning or scarring has occurred.

Do not wait for vision to deteriorate significantly before referring. Once the minimum corneal thickness drops below 400 microns, the window for safe crosslinking may close. Earlier referral preserves options.

For referral guidance including what to include in a crosslinking referral and how to manage post-crosslinking patients in co-management, see the referral information for optometrists and GPs.

References

1. 1.Hersh PS, et al. Long-term outcomes of corneal crosslinking. Curr Opin Ophthalmol. 2024;35(4):315-321.
2. 2.Comparative efficacy and safety of conventional Dresden, transepithelial, and accelerated corneal collagen cross-linking protocols for progressive keratoconus: a systematic review. PMC12867310. 2025.
3. 3.Vieira JM, et al. Corneal crosslinking via the Dresden protocol versus the accelerated approach in pediatric patients. Arq Bras Oftalmol. 2024;88(3).
4. 4.Mazzotta C, et al. Corneal collagen cross-linking in patients with keratoconus: from the Dresden protocol to customised solutions. PMC11074195.