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An Urban Experience
After surgery has been completed but before anesthesia is terminated local anesthetic can be in ltrated into the area using a small gauge needle and syringe. The needle should be inserted into the skin and subcutaneous tissues adjacent to the wound to in ltrate local anesthetic. It may be useful to insert the needle to the hub and inject local anesthetic as the needle is slowly withdrawn. Typically, 2 – 3 different injection sites will be necessary to adequately in ltrate an upper or lower eyelid in its entirety.
Topical anesthesia Indications
Topical local anesthesia is routinely used in the ophthalmic examination to facilitate applanation tonometry, corneal and conjunctival scraping or biopsy, and foreign body removal. Topical anesthesia can
also be used to supplement analgesia during corneal- conjunctival surgery.
Proparacaine / Proxymetacaine
In clinically normal dogs a single drop of 0.5% proparacaine produced corneal anesthesia for approximately 45 minutes with the maximal effects for 15 minutes. A second drop applied 1 minute after initial treatment resulted in an increase of anesthetic effects
to 55 minutes with maximum effects for 25 minutes (Herring et al. 2005). Recovery from topical anesthesia is dose dependent, with lower doses having the shortest duration of action (Polse et al. 1978). An increase in duration of anesthesia may be seen in dogs and cats with decreased corneal sensitivity. Decreased corneal sensitivity has been associated with diabetes mellitus (Good et al. 2003), mesaticephalic and brachycephalic skull conformation in dogs and brachycephalic conformation in cats (Blocker & Van Der Woerdt
2001). Duration of anesthetic effects on the domestic shorthair feline cornea induced by a single topical application of 0.5% proparacaine ophthalmic solution
is considerably shorter than the reported duration of corneal anesthesia in dogs (Binder & Herring 2006). One drop of 0.5% proparacaine produced maximal anesthesia for 5 minutes and lasted for approximately 25 minutes (Binder & Herring 2006).
Tetracaine is not commonly used in veterinary medicine as it often causes marked conjunctivalhyperemia, chemosis, and pain on application. Proparacaine is generally recommended as an alternative (Bart eld et al. 1994).
Other topical anesthetic agents
Limited options have been available for treatment of ocular pain. Topical use of morphine has been shown to control pain associated with corneal wounds in
dogs without systemic side effects or delayed corneal wound healing, but is a controlled drug (Stiles et al. 2003). Nalbuphine, a potent synthetic mixed opiate with some analgesic effects is a non-scheduled drug and might represent a useful alternative to topical morphine. A pilot study evaluating topical nalbuphine compared to oral tramadol in the treatment of corneal pain in dogs suggests that topical nalbuphine is not effective for treating corneal pain (Clark et al. 2011). 5%
Clinical Tips
Using too large a syringe will increase the pressure required to inject local anesthetic into the subcutis
and may result in inadequate levels of anesthetic distribution. Similarly, using too large needle gauge
will result in a needle tract that leaks local anesthetic instead of enabling drug diffusion into the eyelids. Expect the eyelids to swell slightly with local anesthetic administration which will distort lid conformation. For
this reason, I recommend in ltration of the tissues after any reconstructive surgery is planned (e.g. entropion/ ectropion repair). By contrast, if local anesthetic with epinephrine is used, injection of the eyelid margin prior to their removal in an enucleation procedure will lessen the amount of bleeding encountered.
Advantages and Disadvantages
Advantages include improved analgesia in the post- operative period, smoother recovery, decreased need for opioid analgesia, decreased sedation, and faster recovery time. A surgical advantage of in ltrative anesthesia in eyelid surgery is its ‘space-occupying’ effect. This is particularly relevant in patients with a strong spastic component to their entropion which
may be exacerbated from surgical manipulation of the eyelids and result in sutures rubbing on the cornea
and possible ulceration during recovery from general anesthesia. In ltration of local anesthetic to slightly evert the eyelids may negate the need to place additional tacking sutures (Giuliano 2008). Disadvantages of in ltration anesthesia include delayed wound healing and wound break down. In the author’s opinion, this is rarely encountered when used as an adjunct for ophthalmic surgery, as the volume of drug injected is small. As
with all loco-regional anesthesia, care must be taken
to ensure that toxic systemic doses are avoided. When operating on small dogs or cats, if a greater volume of drug is needed (e.g. when performing an enucleation surgery and a RBB, 4 – point peritomy block, and regional eyelid in ltration are all planned), dilution of the appropriate local anesthetic dose is recommended using sterile saline.

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