Photodynamic therapy with infracyanine green induces keratocyte depopulation in the normal equine cornea.
Abstract: Use of photodynamic therapy (PDT) for the treatment of immune-mediated keratitis (IMMK) in horses is becoming common. The safety and morphologic impact on the normal equine cornea have not been investigated, and the mechanism of its efficacy is unknown. Objective: To investigate the morphologic effects and safety of in vivo PDT on healthy equine corneas. Methods: In vivo experiment. Methods: Six university-owned horses underwent unilateral corneal PDT with intrastromal infracyanine green (EmunDo®) and photoactivation with an 810 nm diode laser (500 mW for 2.5 min = 75 Joules). Complete ophthalmic examinations, clinical scoring, digital and infrared photography, ocular thermography, in vivo confocal microscopy (IVCM), and ultrasound biomicroscopy were performed pre-treatment and post-treatment on study days 1, 5, 15, 33, and 103. Results: Post-treatment, corneal ulceration occurred in all treated eyes. In all horses, IVCM identified destroyed keratocytes immediately post-treatment followed by keratocyte depopulation on days 5 and 15. Slow keratocyte repopulation was evident on days 33 and 103. Stromal keratitis was seen on day 5 and persisted through day 103. EmunDo® remained visible in the cornea on study day 103 in 5/6 horses. No horses developed blinding complications. Conclusions: Limited sample size included horses of various ages. Conclusions: Corneal ulceration, keratocyte depopulation, prolonged stromal keratitis, and prolonged corneal dye retention occurs with PDT in normal equine corneas. Corneal stromal cellular depopulation is proposed as the mechanism by which PDT is effective in the treatment of equine IMMK.
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Publication Date: 2026-03-08 PubMed ID: 41795906DOI: 10.1002/evj.70159Google Scholar: Lookup
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Summary
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Photodynamic therapy using infracyanine green causes a temporary loss of keratocytes (corneal cells) and prolonged stromal inflammation in healthy horse corneas, which helps explain its use in treating immune-mediated keratitis. This study assessed the safety and cellular effects of this treatment in normal equine eyes.
Study Overview and Objective
- Photodynamic therapy (PDT) with infracyanine green (EmunDo®) is increasingly used to treat immune-mediated keratitis (IMMK) in horses.
- The safety and cellular changes in normal horse corneas following PDT had not been previously studied.
- The study aimed to evaluate the morphologic effects and safety of in vivo PDT on healthy equine corneas to better understand its mechanism of action.
Methods
- Six healthy horses owned by the university participated in the study.
- Each horse received PDT in one eye involving:
- Intrastromal injection of infracyanine green dye (EmunDo®).
- Photoactivation with an 810 nm diode laser delivering 75 Joules over 2.5 minutes (500 mW power).
- Comprehensive ophthalmic exams and imaging studies were performed before treatment and on days 1, 5, 15, 33, and 103 after treatment including:
- Clinical scoring and photography (digital and infrared).
- Ocular thermography to assess temperature changes.
- In vivo confocal microscopy (IVCM) to examine corneal cell morphology.
- Ultrasound biomicroscopy to image the corneal layers.
Key Findings
- All treated eyes developed corneal ulcers following PDT.
- In vivo confocal microscopy revealed:
- Immediate destruction of keratocytes (stromal corneal cells) right after treatment.
- Continued keratocyte depopulation on days 5 and 15.
- Slow repopulation of keratocytes starting at day 33 and continuing by day 103.
- Stromal keratitis (inflammation of the corneal stroma) was present by day 5 and persisted through day 103.
- Infracyanine green dye (EmunDo®) remained visible in the cornea at day 103 in 5 out of 6 horses, indicating prolonged dye retention.
- No horses experienced severe adverse effects like vision loss.
Conclusions and Implications
- The study indicates that PDT causes:
- Corneal ulceration.
- Keratocyte depopulation lasting several weeks.
- Prolonged inflammation in the corneal stroma.
- Retention of the dye within corneal tissue for months.
- The transient removal of keratocytes likely reduces immune cell activity in the stroma, which may explain how PDT helps treat immune-mediated keratitis.
- Despite the side effects seen, no blinding complications occurred, supporting relative safety in healthy eyes.
- Limitations include small sample size and inclusion of horses of different ages, which could affect healing rates.
- Overall, the findings provide insight into the cellular mechanisms of PDT and inform its use and safety considerations in equine ophthalmology.
Cite This Article
APA
Rogers CM, Ledbetter EC, Reid AM, Scott EM, Knickelbein KE.
(2026).
Photodynamic therapy with infracyanine green induces keratocyte depopulation in the normal equine cornea.
Equine Vet J.
https://doi.org/10.1002/evj.70159 Publication
Researcher Affiliations
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA.
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA.
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA.
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA.
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA.
Grant Funding
- VAF2024-5 / ACVO (American College of Veterinary Ophthalmologists) Vision for Animals Foundation
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