We conducted a single-center, single-patient case study to evaluate the efficacy of a combined same-session approach using PACK-CXL with sequential RF/UV-A and RB/green light in treating AK.

A 44-year-old patient was referred to our clinic with active AK in the left cornea after extended contact lens wear. Before referral, the AK diagnosis was confirmed using culture from both the cornea and the contact lens case, Giemsa staining, confocal microscopy, and polymerase chain reaction. The patient was then treated unsuccessfully for a total of 10 months according to the American Academy of Ophthalmology guidelines [18] without resolution or clinical improvement in corneal findings before referral. Specifically, the initial therapy consisted of hexamidine diisethionate 0.1% eyedrops (Desomedin DD, Bausch + Lomb, Zug, Switzerland) four times daily, chlorhexidine 0.002% every 2 h (q2h), propamidine isethionate 0.1% q2h and polyhexamethylenebiguanide (PHMB) 0.02% (all prepared by the referring hospital’s compound pharmacy).

Furthermore, the patient received oral valaciclovir (Valtrex 500 mg, GlaxoSmithKline, Münchenbuchsee, Switzerland) twice daily, nightly topical acyclovir ointment (Acivision Augensalbe 30 mg/g, OmniVision AG, Neuhausen am Rheinfall, Switzerland), and topical 1% voriconazole drops (Pfizer AG, Zurich, Switzerland) five times daily. For full details, please refer to Appendix A, Supplemental Table 1. Written informed consent was obtained regarding the publication of the case.

Upon presentation, the patient exhibited intense ocular pain, excessive epiphora, photophobia, and blepharospasm in the left eye. Corrected distance visual acuity (CDVA) was 20/200. Slit-lamp examination revealed diffuse hyperemia of the conjunctiva, and the cornea presented with diffuse full-thickness infiltrates in the absence of a ring infiltrate. The remainder of the slit-lamp examination was normal (Fig. 1a). Acanthamoeba cysts were identified in the fluid from the contact lens container via polymerase chain reaction. Confocal microscopy showed Acanthamoeba cysts in the superficial and deep corneal stroma.

Same-session photoactivated chromophore for keratitis-corneal cross-linking (PACK-CXL) treatment using two chromophores. a Irradiation with UV-A using a commercially available CXL device; b Irradiation with green light using a custom-built irradiation device

Following national legal guidelines for compassionate use and a detailed informed consent signed by the patient, we performed the initial combined PACK-CXL treatment on June 14, 2021. In brief, following a 9-mm epithelial layer abrasion, 0.1% RF solution (Ribo-Ker, EMAGine, Zug, Switzerland) every 2 min for 20 min, followed by instillation of 0.1% RB solution (Grosse Apotheke Bichsel, Interlaken, Switzerland) every 2 min for 20 min. The chromophores were instilled onto the surface of the cornea, ensuring the site of infection became saturated. After rinsing off the excess chromophore from the corneal surface with balanced salt solution, the cornea was irradiated with 365 nm UV-A light at 18 mW/cm2 for 9 min and 15 s (C-eye device, EMAGine, Zug, Switzerland), corresponding to a total fluence of 10 J/cm2. UV-A irradiation was immediately followed by irradiation with 522 nm green light at 15 mW/cm2 for 6 min, corresponding to a total fluence of 5.4 J/cm2 (Fig. 2).

Photograph of the cornea before and after the same-session dual chromophore photoactivated chromophore for keratitis-corneal cross-linking (PACK-CXL) treatment. a Prior to initiation of the PACK-CXL treatment, the cornea presented with all signs of acute Acanthamoeba keratitis; b Six months after the third same-session PACK-CXL treatment, the cornea displays a quiescent deep stromal scar

We reperformed the combined procedure twice, at 4 weeks (July 15) and 16 weeks (October 4, 2021) after the initial procedure. Each PACK-CXL treatment comprised of same-session sequential RF/UV-A (365 nm) irradiation with 10 J/cm2 (C-eye and Ribo-Ker, EMAGine, Switzerland) and RB/green light (522 nm) irradiation (custom-built device, 0.1% RB) with 5.4 J/cm2 in a single setting.

Despite a reduction in AK activity and an improvement in the patient’s symptoms in the 4 weeks following the first combined PACK-CXL procedure, signs of active infection persisted. The initial therapy was therefore modified to hexamidine diisethionate eyedrops three times daily and dexamethasone sodium phosphate eyedrops (DexaFree, Théa Pharma, Switzerland) twice daily.

A second combined same-session RF/UV-A & RB/green light treatment with similar irradiation settings to the primary procedure was performed on July 15, 2021. Clinical signs of active infection improved further, however, corneal edema and infiltrates remained visible in the deep stroma, and medication remained unchanged.

A third combined procedure was performed on October 4, 2021, again using the same technical irradiation settings. Following the third combined same-session procedure, the cornea showed resolution of edema (Fig. 3) and a steady decrease in infiltrate size over the next 6 months and presented as a quiescent scar in April 2022. Medication was tapered out between November 2021 and April 2022. The patient’s previous symptoms of ocular pain, photophobia, epiphora, and blepharospasm had resolved (Fig. 1b). The patient’s CDVA improved to 20/100, and confocal microscopy was unable to detect Acanthamoeba cysts.

Anterior segment-optical coherence tomography. a Before initiation of the photoactivated chromophore for keratitis-corneal cross-linking (PACK-CXL) therapy, the cornea showed marked edema; b Six months after the third same-session PACK-CXL treatment, the central cornea shows a full-thickness scar and epithelial remodeling

Slit-lamp biomicroscopic and corneal topography assessments demonstrated a progressive reduction in corneal infiltration, epithelial defects, and stromal haze throughout the follow-up period. By the end of the 18-month follow-up, the cornea appeared clear and stable, with no signs of residual AK or complications.

Confocal microscopy examination in April 2022 did not reveal any detectable Acanthamoeba cysts in the corneal stroma. The patient is currently awaiting a penetrating keratoplasty to restore visual function further. These findings suggest that the combined approach of sequential RF/UV-A and RB/green light PACK-CXL was effective in treating this case of confirmed AK, which had been resistant to conventional medical treatment for 10 months prior to our intervention.