Intravitreal injection of low-dose gentamicin for the treatment of recurrent or persistent uveitis in horses: Preliminary results

Abstract

Background: Despite appropriate medical therapy, many horses with equine recurrent uveitis continue to suffer from recurrent bouts of inflammation. Surgical intervention via the pars plana vitrectomy or suprachoroidal cyclosporine implant placement may control and/or prevent recurrences, however, these procedures may be contraindicated, unavailable, or declined by an owner. Thus, an effective adjunctive treatment option may help to improve the clinical outcomes in those situations. There are several anecdotal reports on the use of intravitreal gentamicin injections, but to date, no data evaluating the complication rate and/or treatment effect following this treatment have been published. Thus, the aim of this prospective study was to describe the intravitreal gentamicin injection technique, describe the associated peri-injection (within 24 h) and post-injection (30 to 780 days) complications, and to report the effects of the injection on the clinical signs of uveitis. Additionally, evaluation of the systemic and ocular Leptospira-status, and its effect on the treatment outcome was performed. A total of 86 horses of various ages, breeds, and gender presenting with recurrent or persistent uveitis were treated via intravitreal injection of 4 mg of undiluted gentamicin (0.04 ml, Genta 100, 100 mg/ml in 35 horses) or preservative-free gentamicin (0.05 ml, 80 mg/ml in 52 horses) under sedation and local anesthesia. All 86 horses were observed for immediate peri-injection and post-injection complications. Response to therapy was evaluated in 59 of the 86 horses (follow-up: 30 to 780 days).

Results: Peri-injection complications consisted of subconjunctival (26/86; 30.2%) or intracameral hemorrhage (4/86; 4.7%); both of which completely resolved within 5 days. Post-injection complications consisted of cataract formation/maturation (5/59 horses, 8.5%) and diffuse retinal degeneration (3/59 eyes 5.1%). The majority of horses 52/59 (88.1%) with a minimum follow-up period of 30 days were controlled (absence of recurrent or persistent inflammation) at their last recheck examination. Recurrent inflammation was documented in 5/59 (8.5%) horses and persistent inflammation was diagnosed in 2/59 (3.4%) horses.

Conclusions: Intravitreal injection of low-dose gentamicin shows promise at controlling different types and stages of uveitis. The ability of intravitreal injections of low-dose gentamicin (4 mg) to control persistent and recurrent inflammation warrants further investigation.

Keywords: Equine ophthalmology; Equine recurrent uveitis; Gentamicin; Intravitreal injection; Leptospira.

Fig. 1

Twelve-year old warmblood mare that presented for a chronic-acute persistent panuveitis of the left eye (OS). Negative c-value for Leptospira. a. Initial presentation: Diffuse corneal edema, keratic precipitates, + 2/4 flare, fibrin, vitreal degeneration and retinal folds were present. Medical treatment was started (prednisolone acetate q 4–6 h, atropine q 8 h and flunixine meglumine 1.1 mg/kg twice daily). b. Ten days post initial presentation: The clinical signs worsened in the face of aggressive medical treatment. Intravitreal gentamicin injection and aqueocentesis were performed OS. c. Four days post-IVGI OS: Improvement of clinical signs can be readily appreciated. d. Twenty days post-IVGI OS: No flare present. e. Forty-nine days post-IVGI OS: Uveitis remains controlled without medications. The mare was euthanized due to complications associated with cervical spinal fracture 2 months after IVGI

Fig. 2

Nine-year old warmblood gelding presented with chronic-acute, persistent panuveitis of the right eye (OD). Negative c-value for Leptospira. a. Initial presentation: Blepharospasm, epiphora, diffuse corneal edema, 360° corneal neovascularization, + 4/4 flare, fibrin in anterior chamber and miosis were present. The posterior aspect of the eye could not be visualized. Inflammation was controlled with medical therapy. b. One-hundred-fifteen days post-initial presentation: Two additional bouts of inflammation since initial presentation. Both intravitreal gentamicin injection (IVGI) and aqueocentesis were performed. Immature cataract and posterior synechia were present at the time of IVGI OD. c. Seven days post-IVGI OD: Immature cataract. d. Sixty days post-IVGI OD: Medical treatment was discontinued 39 days prior to this examination. No signs of active inflammation could be identified. e. One-hundred-thirteen days post IVGI OD: Mature cataract (cataract maturation). No signs of active inflammation. f. Three-hundred-twenty-seven days post-IVGI OD: Uveitis remains controlled without medical treatment. g. Six-hundred-two days post-IVGI OD: No recurrent bouts of inflammation since IVGI

Fig. 3

Eight-year old warmblood mare that presented for chronic-acute, recurrent anterior uveitis in the left eye (OS). Negative c-value for Leptospira. a. Initial presentation: Two days following the onset of an acute bout of inflammation. Topical and systemic therapy were initiated by the referring veterinarian, when ocular signs were first identified. Inflammation was controlled via medical therapy. b1. Seven months after initial presentation: Active uveitis OS; + 4/4 flare, fibrin and complete miosis were present. b2. Infrared picture of OS at the same examination as in B1. c. Uveitis was controlled within 5 days of initiating medical therapy. d. Recurrent acute inflammation: 14 months later. Intravitreal gentamicin injection (IVGI) and aqueocentesis were performed. e. Ninety-eight days post-IVGI OS: Uveitis has remained controlled following IVGI. A focal area of tapetal hyperreflectivity identified during indirect ophthalmoscopy of the fundus. f. Fundus image of the lesion described in e. Retinal degeneration developed between the 30- and 98- day recheck examination. Subjective vision status unchanged from pre-IVGI. g. Two-hundred-seventy days post-IVGI OS: Uveitis controlled. Retinal degeneration remains static. h. Three-hundred-eighty-five days post-IVGI OS: Uveitis remains controlled. Retinal degeneration remains static

Fig. 4

Distribution of clinical signs of uveitis