Cataracts are one of the most common treatable causes of blindness in dogs.1 Consequently, cataract surgery is also common, with phacoemulsification as the preferred technique.2 Intraoperative and postoperative pain can be caused by intraocular manipulations that irritate the iris, ciliary body, and zonular tissue and by pressure changes in the anterior chamber of the eye.3 Eyes are quite sensitive to surgical pain because they are densely innervated with AD and C fiber nociceptors, which are necessary for perception of acute pain and are particularly sensitive to mechanical stimulation.3,4 Alleviation of surgical pain in animals that have undergone ocular surgery is important for humane reasons and for preventing postoperative complications, delayed wound healing, and self-mutilation at the surgical site.3
For pain management in dogs undergoing intraocular surgery, systemic opioid administration and systemic and topical NSAID administration are usually performed before and after surgery. These medications, however, have several limitations in dogs and other animals. Preoperative systemic opioid administration can cause miosis, which can impede intraocular surgery.5 However, the pupillary constriction cannot be reversed by application of mydriatics before or after opioid injection.5 Systemic administration of NSAIDs can cause gastrointestinal distress, hemorrhage due to platelet activity impairment, renal failure, and hepatotoxic effects.6–8 Therefore, their use may not be appropriate in dogs with preexisting gastrointestinal, hematologic, renal, or hepatic diseases. Several topically administered NSAIDs reportedly delay corneal wound healing and cause corneal perforation and melting in humans.8,9 In dogs, an association of topical NSAID treatment with delayed corneal epithelial healing has also been suggested.10 Preoperative topical treatment with NSAIDs can cause ocular irritation, increase the risk of intraocular hemorrhage during surgery, and lead to postoperative ocular hypertension.11,12
Lidocaine, a local anesthetic that blocks conduction of nerve impulses by binding at voltage-gated sodium channels, interrupts neural transmission in sensory nerves and tracts.13 In dogs undergoing intraocular surgery, systemic lidocaine infusion has a preemptive analgesic effect but no effect on pupil size and no important adverse effects on cardiorespiratory or visceral organ systems.3 The analgesic effects of systemic lidocaine administration are believed to be attributable to the fact that lidocaine blocks sodium channel subtypes that are upregulated from injured peripheral nerves.3,14 Systemic use of lidocaine is still limited in animals with liver and heart problems.15
Intracameral lidocaine injection is reportedly a safe means of providing additional analgesic effects in humans undergoing cataract surgery.16–20 Clinical trials in humans have revealed that intracameral lidocaine injection increases patient cooperation, compared with the effects of topical anesthetic administration alone.16,18–20 Intracamerally administered lidocaine is believed to diffuse into the iris and ciliary body and to be directly absorbed by the unmyelinated small nerve fibers located therein.21
A potential analgesic effect of intracameral lidocaine administration in dogs has been suggested.22 The safety of intracamerally injected, preservative-free 1% or 2% lidocaine hydrochloride solution was established in another study.22 It is likely that lidocaine administered via this route has a remarkable analgesic effect in dogs undergoing intraocular surgery, but to the authors' knowledge, clinical studies on intracameral anesthesia in companion animals have not been reported. The purpose of the study reported here was to evaluate the intraoperative and postoperative analgesic effects of intracameral lidocaine injection in dogs undergoing phacoemulsification.
Balanced salt solution
SL-202, Shin-Nippon, Tokyo, Japan.
Keeler Vantage, Keeler, Windsor, Berkshire, England.
Tonopen, Mentor, Norwell, Mass.
Vet-Dop Doppler, Vmed Technology Inc, Mill Creek, Wash.
Daehan Lidocaine HCl 2%, Dai Han Pharm Co Ltd, Seoul, Republic of Korea.
Balanced salt solution plastic bag type, Baxter Co, Alliston, ON, Canada.
Sedaject, Samwoo Medical, Yesan, Republic of Korea.
Chong Kun Dang Pharm, Seoul, Republic of Korea.
Ocutropic, Sammil Pharm Co, Seoul, Republic of Korea.
Provive 1%, Claris Lifesciences, Vasana, India.
Forane solution, Choongwae Pharm Co, Seoul, Republic of Korea.
Datex-Ohmeda S/5, GE Healthcare, Madison, Wis.
Ventilator Ace-3000, Acoma Co Ltd, Tokyo, Japan.
Peripheral nerve locator-stimulator, Life-Tech Inc, Stafford, Tex.
Leica M-651, Leica Microsystems, Heerbrugg, Switzerland.
Acrium, Myung Moon Pharm, Seoul, Republic of Korea.
Acri Bio Visc, Acri-Tec Inc, Salt Lake City, Utah.
Heparin Sodium, Choongwae Pharm Co, Seoul, Republic of Korea.
Epinephrine inj, Dai Han Pharm Co Ltd, Seoul, Republic of Korea.
Toranzin, Samsung Pharm Ind, Seoul, Republic of Korea.
SPSS, version 12.0, SPSS Inc, Chicago, Ill.
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Subjective pain scoring system (modified from Smith et al3) used to assess the analgesic effects of intracameral lidocaine injection in dogs undergoing phacoemulsification.
|Comfort||0||Asleep or calm|
|1||Awake and interested in surroundings|
|2||Mild agitation or depressed and uninterested in surroundings|
|3||Moderate agitation, restless, and uncomfortable|
|4||Extremely agitated or thrashing|
|1||1 to 2 position changes/min|
|2||3 to 6 position changes/min|
|3||Continuous position changes|
|Appearance of treated eye||0||Normal|
|1||Mild changes (affected eye partially closed)|
|2||Moderate changes (blinking or third-eyelid protrusion of affected eye)|
|3||Severe changes (affected eye continuously closed or pawing at eye)|
|Behavior (unprovoked)||0||Too sedate to evaluate|
|3||Moderately abnormal (less mobile or alert than normal, unaware of surroundings, or restless)|
|4||Markedly abnormal (very restless, vocalizing, self-mutilating, grunting, or facing back of cage)|
|Interactive behaviors||0||Too sedate to evaluate|
|2||Pulls away or blepharospasm when surgical site touched; mobile|
|3||Vocalizes when wound touched and reluctant to move but will when coaxed|
|4||Violent reaction to touching of surgical site, snapping, growling when approached, or failing to move when coaxed|
|1||Crying but responds to quiet voice and stroking|
|2||Intermittent crying, with no response to quiet voice and stroking|
|3||Constant crying (unusual for this particular dog), with no response to stroking or voice|