The Equine Eye Clinic

This is my approach to enucleation in the standing horse - information about different approaches and blocks and a great article by Brian Gilger & Michael Davidson which is a must read before embarking on standing surgery in the horse can be found in the notes at the bottom of this page - these notes where produced for a series of equine ophthalmoogy surgucal wet labs which we have run many times both at the clinic and more recently as part of the Advanced Equine Ophthalmology course for BEVA - come and join us for two great days of practical and theoretical equine ophthalmology and ophthalmic surgery or contact us to see if we can run something similar for you in your area.

http://www.beva.org.uk/news-and-events/beva-courses/view/413

Standing enucleation in the horse.

BLOCKS

Notes

• Local – use Mepivicaine (intra-epicaine) as lignocaine too short acting for blocks, proxymetacaine for local (corneal) application.

• Treat all blocks as sterile procedures - clip, clean, glove.

• Use smallest needle available - 23gage ideally, 1/2 " for all blocks apart from line blocks where 1" needles make it much easier and the retrobulbar block (3" 21 gage is my preference)

Good local blocks are essential for success, perform blocks carefully and in the order described. 

1)      AP block – palpate dorsal to zygomatic arch

2)      Frontal block – palpate infra-orbital foramen medial to dorsal orbital rim

3)      Perform retrobulbar block: (NB this takes 20mins to work)

·         Position head in a neutral position.

·         Sterile gloves,  clip and prep  retrobulbar space with dilute iodine (1 in 50).

·         Draw virtual line from middle of pupil to brain

·         Draw virtual line at 90 degrees to this line as it passes caudal to the doral orbital rim  to determine your point of entry.

·         Inject 1-2ml local at caudal edge of  dorsal orbital rim at point of entry for block.

·         Pass 3” spinal needle through skin, walk needle off back of dorsal orbital rim

·         Now look from the side , assess position of the caudal pole of the globe  and adjust angle of needle so that when advance you are aiming sufficiently caudally that you do not hit the back of the globe.

·          Start wriggling the needle up and down as you  advance slowly whilst looking at the globe.

·         As the needle point touches the dorsal rectus muscle you will see a definite dorsal globe rotation.

·         At this point you will need to advance the needle a further ½” through the dorsal rectus in to the muscle cone – this will feel similar to passing a needle through a joint capsule. The optic nerve is positioned very ventrally in the horse so the risk of injecting local in to the meninges  surrounding the optic nerve is very low.

·         Inject 10mls local slowly after drawing back – there should be little resistance. It is possible to inject in to the globe - while not dangerous it will not work.  

If successful you should see 

• mild exophthalmos with no third eye lid protrusion

• no ballooning of the conjunctiva.

• Progressive mydriasis after 5-10 minutes

• Loss of corneal sensation after 15-20 mins

4)      Infratrochlear block – palpate the infratrochlear notch on the medial aspect of the orbit, leave finger on  notch whilst pass needle from skin of medial upper eye lid until point of needle palpable.  Inject 1ml local over this notch.

5)      Perform line block along ventral orbital rim starting medially.

6)      Extend line block along lateral orbital wall.

7)      Perform line block 1” from lid margin starting with upper lid before repeat in lower lid.

8)      Topical local anaethetic application to cornea – use procymetacaine in pref but tetracaine or amethocaine are also effective – give 6 applications 10 secs apart blinking for the patient to spread the local evenly across the cornea.

PREP:

Clean washed, sterilised, rope head collar

Dilute iodine – povidine iodine – make sure no spirit or detergent in. Ensure flush conjunctival sack thoroughly – use a large syringe and lots of power – flush dorsally, ventrally in front of and behind third eye lid.

DON’T CLIP VIBRISSAE – these have a valuable sensory function in the horse – thinkl of them likle cats whiskers.
Drape  - clip drape to head collar.

Glove

SURGICAL TECHNIQUE:

I prefer a transpalpebral technique and salvage the  upper lid margin and eye lashes by splitting the upper lid – this requires magnification, practice and small instruments and is not essential (*leaving the vibrissae IS though) so I would suggest keeping it simpler and removing both upper and lid margins.

15 blade – incise lid skin 10mm from lid margin upper and lower lids.

Using a gloved finger inside the eye lids to palpate scissors as dissect aim to dissect caudally from skin incision to conjunctival surface then follow plane of dissection until you reach the limbus.

You should appreciate the medial and canthal ligament as you dissect down to the conjunctiva medially and laterally.

Once at the limbus continue discection staying as close to the sclera as possible.

Identify the dorsal medial and lateral rectus  and dorsal oblique muscles and section them at their insertions (anterior to the globe equator) – if you are struggling to find you are probably not dissecting close enough to the sclera.

Once sectioned the globe should be very mobile.

Use curved artery forceps – spread “blades” pass behind globe ensuring tips very ventral and passed either side of axis – then gently push back apprx 10mm and clamp.

Pass curved scissors between globe and clamp to section the optic nerve

Should be able to rotate globe out of orbit and continue dissection of ventral muscle and third eye lid from the behind the globe before removing the globe, the third eye lid and conjunctival sack in one unit.

Pack orbit with swab for 5 mins.

Spray 10mls intra-epicaine in to base of the orbit.

CLOSURE:

If not using an implant.

Identify connective tissue attached to orbital rim (the orbital ligament)

Flush orbit with sterile fluid prior to close

Weave a mesh of nylon across orbital opening making sure use the orbital ligament to secure the mesh.

Close connective tissue in 2 more layer over the nylon before close skin. This is a minimum of 3 layers of tissue closure before close skin.

Close skin – ensure get first intention healing at skin margin by placing skin sutures carefully – skin edge to skin edge (I use 6-0 vicryl)

Place temp stent over orbit – remove 6 hours + later

If using an implant:

Identify connective tissue attached to orbital rim (the orbital ligament)

Flush orbit with sterile fluid prior to close

Flush orbital implant with sterile fluid.

Place orbital implant in to orbit (round face INTO orbit, flat face outwards).

Secure implant to orbital implant to orbital ligament usine simple interrupted nylon sutures to dosal, medial, lateral and ventral orbital ligament.

Weave a mesh of PDS (1) across orbital implant making sure use the orbital ligament to secure the mesh.

Close connective tissue in 2 more layer over the nylon before close skin. This is a minimum of 3 layers of tissue closure before close skin.

Close skin – ensure get first intention healing at skin margin by placing skin sutures carefully – skin edge to skin edge (I use 6-0 vicryl)

Place temp stent over orbit – remove 6 hours + later

POST OP MEDS:

If place implant:

10 days post op TMPS and NSAID

If no implant placed

5 days post op TMPS and NSAID