Infracyanine Green-Based Photodynamic Therapy for Immune-Mediated Keratitis in Horses

To describe infracyanine green-based photodynamic therapy (InfraCG-PDT) and evaluate outcomes in horses with immune-mediated keratitis (IMMK).

Medical records from 2014 to 2020 from the Equine Clinic Munich-Riem, Germany, and Auburn University Equine Ophthalmology Service identified horses diagnosed with IMMK following ophthalmic examination that had undergone InfraCG-PDT.

Multiple intrastromal injections of EmunDo (InfraCG, A.R.C. Laser, Nuernberg, Germany) within an affected quadrant or the entire cornea were treated with diffuse diode laser energy (FOX A.R.C., Laser, Nuernberg, Germany, 500 mW at 30s cycles) irradiation between 75 J (J, quadrant) and 300 J (entire cornea).

Fifty-one eyes (22 OS, 19 OD, 10 OU) from 47 horses were included (22 geldings, 20 mares, and 5 stallions) from 15 breeds aged between 4 and 29 years (median 14 years). Individual quadrants (28/51 eyes, 54.9%) or the entire cornea (23/51 eyes, 45.1%) were treated. Complications were defined as immediate: intrastromal fracture (4/51 eyes, 7.8%), intracameral InfraCG (7/51 eyes, 13.7%), and an epithelial blister (1/51 eyes, 1.9%) or short term: prolonged dye retention (51/51 eyes, 100%, with gradual reduction over a 12-week period) and superficial corneal ulceration (15/51 eyes, 29.4%). Globe threatening ulcers (3/51 eyes, 5.9%) resolved without significant complications. IMMK remained inactive (controlled or managed with improvement in ocular lesions) in 31/40 horses (77.5%) during follow-up (mean 223.0 ± 269.3 days; range 14-1095 days), 4/40 horses (10.0%) required additional treatment, and 5/40 horses (12.5%) were lost to follow-up.

InfraCG-PDT may be an effective treatment for horses with IMMK. Further studies are needed to optimize this treatment modality.