A Surgical Technique for Removal of Setaria digitata From the Anterior Chamber Under Standing Sedation: Outcomes in 12 Horses.

Overview

• This study presents a minimally invasive surgical technique to remove the parasitic worm Setaria digitata from the front part of the eye (anterior chamber) in horses under standing sedation, and reports the outcomes in 12 horses treated with this method.

Introduction and Purpose

• The research addresses the problem of intraocular infection by the parasite Setaria digitata in horses, which requires removal to restore or preserve vision.
• Traditional surgical removal often requires general anesthesia, which has more risks and logistical challenges.
• The aim was to develop and describe a rapid, minimally invasive technique for worm removal under standing sedation, suitable for use in field conditions, and to evaluate the clinical outcomes of this approach.

Methods

• Subjects: 12 client-owned horses presenting between 2021 and 2026, each with a visible, motile worm inside the anterior chamber of one eye.
• Sedation and anesthesia:
  • Standing sedation was utilized, with intravenous administration of xylazine (1.1 mg/kg) and butorphanol (0.1 mg/kg).
  • Regional nerve blocks were applied using 2% lidocaine to provide local anesthesia.
  • Topical anesthesia was achieved with proparacaine drops to numb the eye surface.
• Surgical technique:
  • A 2.8 mm uniplanar oblique corneal incision was made ventrolaterally about 2 mm from the limbus (the border of the cornea and sclera) using a keratome blade.
  • The anterior chamber was filled with a dispersive viscoelastic agent, hydroxypropyl methylcellulose (HPMC), to maintain chamber depth and protect intraocular structures.
  • Controlled egress of the viscoelastic fluid facilitated gentle extrusion of the worm through the incision.
  • The small corneal incision was left unsutured, relying on its self-sealing nature.

Results

• Success rate:
  • In 11 out of 12 eyes (91.7%), the worm was successfully removed using this technique.
  • In one case, the worm was suspected to be adherent to the iris, preventing removal.
• Speed:
  • The median time from incision to worm extraction was 2 minutes, ranging from 1 to 3 minutes, indicating a rapid procedure.
• Visual outcomes:
  • Nine eyes (75%) either retained vision or regained it within 7 days after surgery.
  • Three eyes remained non-visual, but these had pre-existing severe ocular damage such as end-stage glaucoma or suspected retinal detachment, which likely limited the visual prognosis regardless of worm removal.
• Complications:
  • One horse developed transient peripheral corneal edema, which resolved with medical treatment.
  • In one eye where viscoelastic was not used, anterior chamber fibrin formation occurred postoperatively, highlighting the protective role of viscoelastic in reducing intraocular inflammation and trauma.

Conclusions

• The study demonstrates that viscoelastic-assisted removal of S. digitata through a small, self-sealing corneal incision is a safe and efficient method when done by trained ophthalmic surgeons.
• This technique can be performed under standing sedation in field conditions, offering a valuable alternative to more invasive surgery under general anesthesia.
• While not completely replacing general anesthesia methods, this approach minimizes surgical time, invasiveness, and recovery complications, enabling quicker return of function and care outside refined surgical suites.
• Proper use of viscoelastic materials is important to minimize postoperative inflammation.

Implications for Veterinary Practice

• This technique may improve animal welfare by reducing anesthesia-related risks and allowing prompt treatment of intraocular parasites.
• Field applicability means more horses can be treated in various locations without access to advanced surgical facilities.
• The method requires specialized ophthalmic skills and equipment to ensure successful outcomes, emphasizing the need for trained veterinary ophthalmologists.