Refractive and Surgical Management of Keratoconus: Contact Lenses, CAIRS, DALK, and PKP

Corneal crosslinking for keratoconus halts the progression of keratoconus but does not correct the irregular astigmatism and reduced visual acuity that the condition causes. Once the disease is stable, whether after crosslinking or because it has reached a naturally stable state, the focus of management shifts to visual rehabilitation. This begins with contact lenses and, for patients who cannot achieve adequate vision or comfort with lenses, moves through a spectrum of surgical options including intrastromal ring segments, CAIRS, deep anterior lamellar keratoplasty (DALK), and penetrating keratoplasty (PKP). This guide covers each option in detail, with the evidence behind them and how to navigate the decision-making process.

Why contact lenses are the foundation of keratoconus management

In all but the mildest keratoconus, spectacles cannot adequately correct irregular astigmatism. Contact lenses work by creating a smooth, regular refracting surface over the irregular cornea, allowing most patients with moderate to advanced disease to achieve functional visual acuity without surgical intervention. A systematic trial of appropriate lens types, guided by a practitioner experienced in keratoconus contact lens fitting, is essential before concluding that contact lenses cannot provide adequate vision or comfort.

The corneal surface in keratoconus is not uniformly curved, and spectacle lenses only correct regular astigmatism, leaving the higher-order aberrations produced by the irregular cone uncorrected. For most patients with moderate to advanced keratoconus, contact lenses are the primary means of achieving functional visual acuity.

Contact lenses work in keratoconus by creating a smooth, regular refracting surface over the irregular cornea. Rigid lenses achieve this by vaulting the irregular corneal surface and filling the space between the lens and cornea with tear fluid, which has a similar refractive index to the cornea. The result is that light enters through a smooth optical surface rather than the irregular corneal surface, dramatically improving visual acuity.

The critical clinical message is that patients should not abandon contact lenses after failing with one lens type. Different contact lens designs behave very differently on the keratoconic cornea, and a patient who is intolerant of rigid gas permeable lenses may achieve excellent vision and comfort with scleral lenses. A systematic trial of appropriate lens types, guided by a practitioner experienced in keratoconus contact lens fitting, is essential before concluding that contact lenses cannot provide adequate vision or comfort.

Contact lens options for keratoconus

The main contact lens categories used in keratoconus management are soft toric lenses, rigid gas permeable (RGP) corneal lenses, hybrid lenses, piggyback systems, and scleral lenses. Each has a distinct profile of visual performance, fitting complexity, and patient tolerance that makes it appropriate for different stages and patterns of the disease.

Soft toric lenses provide adequate vision correction in mild keratoconus with relatively regular astigmatism. They do not vault the cone and cannot fully correct irregular astigmatism in moderate or advanced disease. Their advantage is comfort and ease of handling, making them appropriate as a first lens option in early keratoconus or as part of a piggyback system.

Rigid gas permeable (RGP) corneal lenses are the traditional gold standard for keratoconus and remain widely used. They vault the corneal surface and fill the tear lens behind the lens with fluid, providing excellent optical correction. Fitting is complex and time-consuming, particularly in more advanced or irregular cones, and requires an experienced practitioner. RGP lenses can cause discomfort from edge lift and apical bearing in moderate to advanced keratoconus. Specialised designs such as the Rose K2 are designed specifically for the keratoconic cornea and have shown good visual outcomes in moderate keratoconus. A study comparing RGP lenses with hybrid lenses found no significant difference in corrected visual acuity between the two designs, though contrast sensitivity was higher with RGP lenses while patients reported greater comfort with hybrid lenses.

Hybrid lenses combine a rigid gas permeable central optical zone with a soft silicone hydrogel skirt. The RGP centre provides the optical correction of a rigid lens, while the soft skirt provides comfort and stability. Hybrid lenses have become an increasingly important option for patients who cannot tolerate RGP lenses due to discomfort. A 2023 study of 68 keratoconus patients fitted with hybrid lenses reported good visual outcomes and patient satisfaction, with hybrid lenses providing a viable alternative for RGP-intolerant patients [8]. Visual acuity outcomes with hybrid and mini-scleral lenses have been shown to be comparable in advanced keratoconus, with mean BCVA improving from logMAR 0.65 to 0.14 with hybrid lenses and logMAR 0.58 to 0.15 with mini-scleral lenses [7].

Scleral lenses vault the entire cornea and rest on the sclera, completely eliminating the contact between the lens and the irregular corneal surface. They are filled with saline before insertion, creating a fluid-filled chamber between the lens and cornea that provides both optical correction and protection of the corneal surface. Scleral lenses have transformed the management of advanced keratoconus and have become the preferred option for patients with moderate to advanced disease, contact lens-related corneal scarring, or poor tolerance of smaller-diameter lenses. Their advantages over corneal RGP lenses include superior comfort, greater stability, and the ability to fit eyes that were previously unfittable with corneal lenses. Scleral lenses accounted for 22 percent of all RGP lens fits globally in 2023, up from 6 percent in 2013, reflecting their growing clinical importance.

Piggyback systems involve wearing a soft lens beneath an RGP lens, with the soft lens providing a cushion that improves RGP comfort while the RGP provides optical correction. They are useful in patients who can achieve good vision with RGP but cannot tolerate the direct corneal contact.

The importance of trialling multiple lens types before abandoning contact lenses

A common and clinically significant error in keratoconus management is concluding that contact lenses cannot provide adequate vision or comfort after trialling only one lens type. The appropriate sequence is to trial at least two to three lens types before concluding that contact lens management has been exhausted, progressing from soft toric lenses through RGP and hybrid lenses to scleral lenses as disease severity increases.

The fitting of contact lenses in keratoconus is complex and highly dependent on cone location, cone morphology, corneal thickness, and patient factors [6]. A lens that fails in one patient may succeed in another with similar disease severity, and a lens that fails in one fitting session may succeed with a different design or base curve.

The appropriate sequence is to trial at least two to three lens types before concluding that contact lens management has been exhausted. For most patients, this means progressing from soft toric lenses in mild disease, through corneal RGP lenses and hybrid lenses in moderate disease, to scleral lenses in advanced or RGP-intolerant patients. A patient who reports that they have tried contact lenses and could not wear them should be asked specifically which type they tried, for how long, and whether they were fitted by a practitioner experienced in keratoconus. A negative experience with soft contact lenses is not a reason to conclude that scleral lenses will not work.

The combination of corneal crosslinking to halt progression and optimised contact lens fitting for visual rehabilitation allows the majority of keratoconus patients to achieve functional vision without surgical intervention, provided they are managed proactively and the full range of lens options is explored.

Intrastromal corneal ring segments (ICRS)

Intrastromal corneal ring segments are small arc-shaped polymethylmethacrylate (PMMA) implants inserted into the mid-peripheral corneal stroma to flatten and regularise the cone. They reduce irregular astigmatism and improve contact lens fit and uncorrected visual acuity, without halting progression, so they are typically combined with crosslinking in patients with documented progressive disease.

ICRS are implanted through tunnels created using a femtosecond laser or mechanical dissection. The most widely used designs include Intacs (AJL Ophthalmic), KeraRing, and Ferrara rings. A comprehensive literature review covering 108 studies published between 2000 and 2024 found consistent evidence of significant improvements in uncorrected and best-corrected visual acuity, reduction in keratometric values, and reduction in irregular astigmatism across all ICRS types in keratoconus patients.

ICRS are reversible in that the segments can be removed or exchanged, which is an advantage over more definitive surgical options. However, complications including segment migration, extrusion, and infection, while uncommon, do occur and must be discussed with patients before implantation.

CAIRS: corneal allogenic intrastromal ring segments

CAIRS uses ring segments prepared from donor corneal stromal tissue rather than synthetic PMMA, implanted into the corneal stroma in the same manner as conventional ICRS. The biological material is biocompatible, avoids the extrusion and hazing complications associated with synthetic implants, and allows greater customisation. The evidence base is growing rapidly, with a 2024 meta-analysis reporting a mean keratometry reduction of 4.31 D across 378 eyes.

The biological segments are trephined from donor cornea and implanted into femtosecond laser-created tunnels in the same manner as synthetic ICRS. A 2024 meta-analysis published in the American Journal of Ophthalmology reviewing studies up to November 2024 found that K1, K2, and mean keratometry were reduced by a mean of 4.31 D following CAIRS implantation across 10 studies comprising 378 eyes [4]. A literature review published in the Journal of Clinical Medicine covering 389 eyes from studies between 2018 and 2024 found clinical improvement in visual acuity and keratometry comparable to synthetic ICRS, with CAIRS demonstrating additional advantages in biocompatibility and customisation [5].

A study published in the Journal of Refractive Surgery (2023) evaluating 52 eyes treated with CAIRS without concomitant crosslinking found significant improvements in manifest refraction spherical equivalent (from -6.71 D to -3.78 D) and cylinder (from -4.02 D to -2.35 D), with maximum anterior keratometry decreasing from 58.09 D to 52.48 D at three months. No major complications were observed [3].

CAIRS offers the theoretical advantage of true biological integration with the host cornea, infinite customisation of segment dimensions, and the potential to achieve greater regularisation of asymmetric or decentred cones. However, it requires access to donor corneal tissue and a tissue bank supply chain, and the technique is performed at a smaller number of specialist centres. Long-term follow-up data beyond two years is still limited compared with synthetic ICRS.

I do not currently perform CAIRS but refer selected patients to centres with expertise in this technique when it is appropriate. The decision to consider CAIRS is made in the context of the full management discussion, including the patient's contact lens tolerance, keratometry values, and whether synthetic ICRS or corneal transplantation are more appropriate alternatives.

Deep anterior lamellar keratoplasty (DALK)

DALK replaces the anterior layers of the cornea while preserving the patient's own Descemet's membrane and endothelium, eliminating the risk of endothelial rejection. It is the preferred transplant technique for advanced keratoconus with healthy endothelium, and meta-analytic evidence shows comparable visual outcomes to PKP with significantly better safety and rejection profiles [1].

DALK is indicated in keratoconus patients who have failed contact lens rehabilitation and have no coexisting endothelial disease. It is the preferred surgical option for advanced keratoconus that has not responded adequately to crosslinking, ICRS, or CAIRS, provided the endothelium is healthy.

A meta-analysis examining 773 eyes (349 PKP, 424 DALK) found that graft rejection, high intraocular pressure, and cataract formation were all significantly more common in the PKP group. The DALK groups demonstrated significantly better outcomes in endothelial cell count preservation and spherical equivalent, while best-corrected visual acuity was comparable between groups [1].

A 2024 retrospective study comparing PKP and DALK found that DALK patients had significantly better uncorrected visual acuity and best-corrected visual acuity than PKP patients at 12 months (p-value 0.04 and 0.03 respectively), with a complication rate of 26.9 percent in the DALK group compared with 54.3 percent in the PKP group [2].

The technical challenge of DALK is achieving a clean dissection to Descemet's membrane, which requires significant surgical experience. Conversion to PKP intraoperatively is required in approximately 5 to 20 percent of DALK cases where Descemet's membrane is perforated during the dissection. This is not a complication in the usual sense but a surgical decision point, and patients are counselled about the possibility before the procedure.

Penetrating keratoplasty (PKP)

PKP replaces the full thickness of the cornea with donor tissue and has been the gold standard surgical treatment for advanced keratoconus for decades. It consistently achieves excellent visual outcomes, with the large majority of patients reaching best-corrected visual acuity of 6/12 or better, but carries a lifetime risk of endothelial rejection that is substantially higher than DALK [9].

PKP is indicated when DALK is not feasible, when there is coexisting endothelial disease, or when previous Descemet's membrane perforation has occurred.

PKP consistently achieves excellent visual outcomes in keratoconus, with the large majority of patients achieving best-corrected visual acuity of 6/12 or better and many achieving 6/6. However, it carries a lifetime risk of endothelial rejection that is substantially higher than DALK. Rejection-free survival rates for PKP have been reported at 96.2 percent at one year, 80.1 percent at two years, and 67.1 percent at five years, compared with 96.6 percent at all three time points for DALK in a comparative study [9].

The long-term management of PKP patients includes ongoing monitoring for rejection episodes (red eye, pain, photophobia, reduced vision), careful steroid management to suppress the immune response, and management of post-PKP astigmatism which is frequently significant and often requires contact lens fitting for optimal visual correction.

For keratoconus patients who are young with healthy endothelium, DALK is the preferred transplant option given the superior endothelial preservation and lower rejection risk. PKP remains an important option for patients where DALK is not technically feasible or where endothelial disease is present. Full detail on both procedures is available on the corneal surgery and transplantation page.

How the management spectrum fits together

For most keratoconus patients the journey begins with spectacles in early disease, progresses to contact lenses as the disease advances, involves crosslinking when progression is documented, and requires surgical escalation only for patients who cannot achieve adequate vision or comfort with contact lenses after a thorough trial of all appropriate lens types. The decision to proceed to surgery should never be made without first ensuring that the full contact lens repertoire has been explored.

The management of keratoconus follows a logical progression based on disease severity, rate of progression, contact lens tolerance, and visual needs. Scleral lenses in particular have transformed what is achievable with contact lenses in advanced keratoconus, and many patients who might previously have proceeded to transplantation are now achieving excellent functional vision with optimised scleral lens fitting.

For patients who do require surgical intervention, DALK is preferred over PKP in the setting of healthy endothelium, given the superior long-term endothelial preservation and rejection profile. PKP remains an important option for appropriate patients.

When should optometrists refer for surgical management assessment?

Refer for surgical management assessment when a patient has stable keratoconus but cannot achieve adequate vision with optimised contact lens management, when scleral lenses have been trialled and found inadequate, when progressive corneal scarring is limiting best-corrected visual acuity, or when the cornea has reached a stage where crosslinking is no longer safely possible.

Useful information to include in a referral: current best-corrected visual acuity with and without contact lenses, contact lens types that have been trialled and the outcome, current topographic and tomographic data, and any history of previous keratoconus surgery.

For referral information see referral information for optometrists.

References

1. 1.Shams T, et al. Penetrating Keratoplasty versus Deep Anterior Lamellar Keratoplasty for Keratoconus: A Systematic Review and Meta-analysis. PMC8850853.
2. 2.Aldebasi T, et al. Comparison of Long-Term Outcomes of the Lamellar and Penetrating Keratoplasty Approaches in Patients with Keratoconus. BMC Ophthalmology 2024;24:501.
3. 3.Bteich Y, et al. Corneal Allogenic Intrastromal Ring Segments (CAIRS) for Corneal Ectasia: A Comprehensive Segmental Tomography Evaluation. J Refract Surg. 2023;39(11):767-776.
4. 4.Visual and Topographic Outcomes After Corneal Allogeneic Intrastromal Ring Segments for Keratoconus: A Systematic Review and Meta-Analysis. American Journal of Ophthalmology 2025.
5. 5.Corneal Allogenic Intrastromal Ring Segments: A Literature Review. J Clin Med 2025.
6. 6.Decoding Cone Morphology in Keratoconus: A Retrospective Study on Contact Lens Selection. PMC13075918.
7. 7.Comparison of Clinical and Topographic Outcomes of Hybrid and Scleral Lenses in Advanced Keratoconus. PMC8874257.
8. 8.Clinical Performance and Patient Satisfaction of Hybrid Contact Lenses in Patients with Keratoconus. PMC10442754.
9. 9.Endothelial Protection Better With DALK Than PKP. Ophthalmology Advisor, May 2024.