10’ O clock limbal incision for retrieval of Setaria digitata eyeworm in horses

Introduction

Equine ocular filariasis is a clinical condition caused by the ectopic migration of parasites belonging to the genus Setaria spp. (Gangwar et al. 2008) [4] . Although the peritoneal cavity is the usual site for adult Setaria worms, they may also be found in the uterus, urinary bladder, heart, lungs, rumen, reticulum, abomasum (Mandal and Ray, 1994) [8] and occasionally in the eye or central nervous system (Yadav et al. 2006) [16] . The disease is transmitted via mosquito bites and is most frequently observed during the summer and autumn seasons. The lashing movements of the worm cause severe trauma and irritation to the cornea, leading to opacity that can progress to blindness if left untreated (Basak et al. 2007; Jaiswal et al. 2006) [1,6] . Common clinical signs include excessive lacrimation, photophobia, and conjunctivitis (Basak et al. 2007; Gangwar et al. 2008) [1,4] . The condition typically affects only one eye, however bilateral ocular parasitism has also been reported (Shin and Wee, 2002; Buchoo et al. 2005) [13,2] . Treatment aims to remove the worm, either surgically-which offers the best results (Tuntivanich et al. 2011) [15] or through medical management (Muhammad and Saquib, 2007) [10] . Medicinal treatment may lead to the death of the worm in situ, causing it to adhere to the corneal endothelium and release toxins into the anterior chamber, resulting in corneal edema (Basak et al. 2007) [1] . Potential complications include cataracts, iris adhesions, and retinal detachment (Paglia et al. 2004) [11] . This article details the 10' o clock limbal incision technique for eyeworm retrieval in cases presented to the Department of Veterinary Surgery and Radiology, College of Veterinary Science and Animal Husbandry, Kamdhenu University, Sardarkrushinagar, Gujarat, India.

Materials and Methods

Case history Case 1:

A 22 months old, female Marwari mare was presented with a chief complaint of progressive corneal opacity, excessive lacrimation and impaired vision in the OS (left eye; oculus sinister) since 4 weeks. The mare was raised for marriage procession and did not have a history of deworming. Case 2: A 13 months old, Male, Marwari stallion was presented with mild corneal opacity, excessive lacrimation and reduced vision in OS since 2 weeks and anamnesis revealed no deworming was done.

Ophthalmic examination

Ophthalmic examination revealed blepharospasms, mild conjunctivitis and a whitish, hazy cornea with moderate opacity (Fig. 1). Close observation revealed a white, threadlike worm continuously swirling in the anterior chamber of the eye (Fig. 2). The affected eye showed positive menace reflexes but pupillary light reflexes (PLR) that were not clearly evident as pupil was not visible. A Schirmer Tear Test (STT) (Fig. 3) was performed to assess tear production, and a fluorescein dye test (Fig. 4) was conducted to evaluate corneal epithelial integrity. In the mare with severe corneal opacity, ocular ultrasonography confirmed the worm's presence in the anterior chamber.

Pre-operative preparation

Preoperatively, the horses were fasted for 24 hours and water was withheld for 12 hours prior to general anesthesia. Preoperatively both horses were administered 5 ml of tetanus toxoid intramuscularly. Dexamethasone and gentamicin eye drop were instilled topically in the affected eye before surgical intervention for better visualization of eye worm during surgery.

Operative procedure

The horses were sedated with xylazine hydrochloride at @ 1.1 mg/kg body weight (BW) intravenously. Side-line restraint was applied, followed by induction using ketamine hydrochloride at @ 2.2 mg/kg BW intravenously. General anaesthesia was maintained with top up dose of xylazine and ketamine mixture (1:1) by administrating half of induction dose as per need.

Local anaesthesia was achieved via auriculopalpebral and peterson nerve blocks using 2% lignocaine hydrochloride to minimize ocular movement during surgery. Horses were positioned in lateral recumbency on a padded surface with the affected eye facing towards surgeon. The eye was flushed thoroughly with betadine solution diluted with 0.9% sterile normal saline, and a surgical drape was applied.

In both cases, the worm's movement was most prominent in the upper right quadrant of the eye; therefore, a small corneal stab incision was made at the 10 o'clock limbal position using a No. 11 BP blade (Fig. 5).

In Case 1, the aqueous humour flowed out naturally through the incision, carrying the worm along with it (Figs. 6,7). In Case 2, where the worm did not emerge spontaneously, a mosquito forceps was inserted through the extended incision to retrieve it (Fig. 8). As the aqueous humour volume decreased, the worm's free movement became restricted.

The anterior chamber was flushed with sterile normal saline using a blunt, manually curved needle attached to a syringe to avoid trauma to ocular tissues. Following irrigation, the worm was easily removed (Fig. 9). Corneal incisions were left unsutured to heal naturally. Auto-blood therapy was performed by collecting 2 ml of the horse's own blood and injecting it sub-conjunctively into both dorsal and ventral palpebral conjunctiva to promote healing of the limbal incision and reduce the corneal opacity (Fig. 10). A temporary tarsorrhaphy was placed using non-absorbable suture material to protect the eye from external contaminants.

Post-operative care

Post-operative management included Inj. Streptopenicillin 5 gram intramuscularly and Inj. Flunixin meglumine at @ 1.1 mg/kg BW intravenously were administered for three days. The temporary tarsorrhaphy sutures were removed after 24 hours. Post operative topical therapy included gentamicin eye drops, dexamethasone eye drops, and Placentrex® gel thrice a day for one week. Bolus fenbendazole (3000 mg) and ivermectin (100 mg) was prescribed for deworming. Both cases recovered uneventfully. Corneal opacity gradually diminished over a 14-day period, with complete restoration of vision (Fig. 13).

Morphological analysis

The worm collected in a physiological normal saline solution and sent for parasitological examination. Gross examination showed the worm to be long, milky white, and thread-like, with tapering ends particularly at the posterior end (Fig. 11). Microscopic examination of the anterior and posterior ends revealed characteristic prominences at the anterior end (Fig. 12), confirming the species as Setaria digitata (Kaur et al. 2015) [7] .

Results and Discussion

In present study Marwari mare was presented with history of progressive corneal opacity, ocular discharge and conjunctivitis since 4 weeks whereas Marwari stallion presented with mild corneal opacity and ocular discharge since 2 weeks. Similarly, (Dabas et al. 2021) [3] stated that ocular discharge and conjunctivitis is main clinical sign in early presentation followed by the cloudiness of cornea and ultimately corneal opacity in later presentation. Patil et al., (2012) [12] concluded that B-mode ultrasonography using 12 to 18 MHz linear transducer is valuable examination tool for horses with severe corneal opacity. Similarly in present study ultrasonography was used for better visualization of worm in anterior chamber of eye in Marwari mare with severe corneal cloudiness.

In both cases of present study, we remove eye worm through taking clear corneal stab incision at 10 o'clock limbal position using a No. 11 BP blade. This incision was helpful in prevention of excessive leakage of aqueous humour post operatively and for easy retraction of worm if worm's movement was most prominent in the upper right quadrant of the eye in both cases. Various incision sites such as the 2 to 9 o'clock (Gosai et al. 2025) [5] and even the 12 o'clock position (Buchoo et al. 2005) [2] have been used for removal of eye worm. According to (Patil et al. 2012) [12] the site of clear corneal stab incision was decided on the basis of corneal edema, corneal opacity and movement of the worm. In Case 1, the aqueous humour flowed out naturally through the incision, carrying the worm along with it however, in Case 2, where the worm did not emerge spontaneously due to reduction of aqueous humour volume, anterior chamber was flushed with sterile normal saline solution to facilitate worm retrieval. Patil et al., (2012) [12] suggested that whenever the worm could not be retrieved by a single stab, viscoelastic substance was injected into the anterior chamber to decelerate the vigorous movement of the worm. Later the worm was grasped with capsular forceps and taken out.

Post operative Placentrex® gel, gentamicin eye drops along with dexamethasone eye drops prescribed for one week. Placentrex facilitate post-surgical healing at the insertion site in equine ocular setariasis (Mritunjay et al. 2011) [9] . Polydeoxy ribonucleotide present in placental extract possess anti-inflammatory, immunomodulatory properties and promote neovascularization, epithelization, fibrogenesis, collagenases and enhance wound healing (Shukla et al. 2004) [14] . Oral deworming with bolus fenbendazole and ivermectin was done in present study for further prevention of Setaria digitata migration. Muhammad and Saquib (2007) [10] appreciated ivermectin as medicinal treatment in case where surgical management is difficult and stated that death of the parasite in the eye took place in 15 days with a single subcutaneous injection of 0.3 mg/kg body weight ivermectin.

References

1. Basak SK, Hazra TK, Bhattacharya D. Persistent corneal edema secondary to presumed dead adult filarial worm in the anterior chamber. Indian J Ophthalmol. 2007 Jan-Feb;55(1):67-69.
2. Buchoo BA, Pandit BA, Shahardar RA, Parrah JD, Darzi MM. Surgical management and prevalence of ocular filariasis in equines. Indian Vet J. 2005 Jan;82:81-82.
3. Dabas VS, Tyagi SK, Jhala SK, Suthar DN, Bhatt RH. Management of ocular Setaria in horses: A review of 16 cases. Indian J Anim Res. 2021 Feb;11(1):143-146.
4. Gangwar AK, Sangeetha D, Singh HN, Singh A. Ocular filariasis in equines. Indian Vet J. 2008 May;85:547548.
5. Gosai RK, Patel A, Patel JB, Patel AM. Ocular worm extraction surgery in equines. Int J Vet Sci Anim Husb. 2025;10(6):334-336.
6. Jaiswal S, Singh SU, Singh B, Singh HN. Ocular setariosis in a horse. Intas Polivet. 2006;7(1):67-68.
7. Kaur D, Ganai A, Parveen S, Borkataki S, Yadav A, Katoch R, et al. Occurrence of Setaria digitata in a cow. J Parasit Dis. 2015 Jul-Sep;39(3):477-478.
8. Mandal SC, Ray S. Note on uncommon occurrence of Setaria labiatopapillosa. Indian Vet J. 1994;71:726726.
9. Mritunjay K, Monsang SW, Pawde AM, Singh SK, Madhu DN, Zama MMS. Post-surgical healing effect of placentrex in equine (Equus caballus) ocular setariasis: A review of 22 cases. Indian J Field Vet. 2011 Jan;6(4):71-73.
10. Muhammad G, Saqib M. Successful treatment of ocular equine microfilariasis (Setaria species) with ivermectin. Vet Rec. 2007 Jan;160(1):25-26.
11. Paglia DT, Miller PE, Dubielzig RR. James Wardrop and equine recurrent uveitis. Arch Ophthalmol. 2004 Aug;122(8):1218-1223.
12. Patil DB, Parikh PV, Nisha J, Jhala SK, Din DMU, Tiwari DK. Equine eye worm: A review of 50 cases. Indian J Vet Surg. 2012 Jun;33(1):61-62.
13. Shin S, Cho K, Wee SH. Ocular infection of cattle with Setaria digitata. J Vet Med Sci. 2002 Jan;64(1):7-10.
14. Shukla VK, Rasheed MA, Kumar M, Gupta SK, Pandy SS. A trial to determine the role of placental extract in the treatment of chronic non-healing wounds. Wound Care. 2004 May;13(5):177-179.
15. Tuntivanich N, Tiawsirisup S, Tuntivanich P. Success of anterior chamber paracentesis as a treatment for ocular setariasis in equine eye: A case report. J Equine Vet Sci. 2011 Jan;31(1):8-12.
16. Yadav A, Kumar A, Bhadwal MS, Khajuria JK, Gupta A. Ocular setariosis in horses: A case study. J Vet Parasitol. 2006 Jan;20(2):1-10.