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Ouch!!! My Eye!!!
IN SMALL ANIMAL MEDICINE AND SURGERY
WWW.ADVANCESINSMALLANIMAL.COM
VOLUME 25, ISSUE 9 • SEPTEMBER 2012
Ouch!!! My Eye!!! CARYN E. PLUMMER, DVM, DIPLOMATE ACVO ASSISTANT PROFESSOR, COMPARATIVE OPHTHALMOLOGY DEPARTMENTS OF SMALL AND LARGE ANIMAL CLINICAL SCIENCES COLLEGE OF VETERINARY MEDICINE UNIVERSITY OF FLORIDA GAINESVILLE, FL 32610 Ocular pain can be miserable. Despite recognition of this and that one of the greatest concerns owners have for their pets is whether or not they are experiencing pain, signs of ocular pain in our veterinary patients are often overlooked or minimized by both pet owners and veterinary practitioners. Yes, the pet may be squinting and have some epiphora, but he is not in pain, right? The eye may be injected and cloudy, but she is still eating and going for walks as usual, so she could possibly be uncomfortable, right? This disconnect between recognition of signs and their association with discomfort can lead to missed opportunities for alleviation of pain. Consideration of pain control is an important facet of the treatment of ocular disease in all species.
Figure 1. Signs of ocular pain can include blepharospasm and epiphora.
CONTROL OF OCULAR PAIN FROM CORNEAL ULCERS The cornea is richly innervated with sensory nerves. When these nerves are structurally damaged, pain will result. Signs of corneal pain typically include blepharospasm, epiphora, conjunctival hyperemia, reflex uveitis, rubbing, and other incidents of self-trauma (Fig 1). Although limited options for the treatment of corneal pain have been available in the past, there are some viable and effective options today. A recent study by Clark et al. evaluated the use of topical nalbuphine, a synthetic mixed opiate, and oral tramadol, a synthetic codeine analog, to mitigate signs of pain associated with experimentally induced corneal ulcers in dogs.1 Animals enrolled in the study received either topical nalbuphine with an oral placebo, oral tramadol, and a topical saline or topical saline and an oral placebo (control). Pain scores were determined during the course of healing, and those individuals with scores exceeding a minimal threshold of acceptable pain were rescued with intramuscular morphine. Although the differences between the groups were not statistically significant, many fewer dogs in the tramadol group required rescue than those in the nalbuphine or control groups, suggesting that tramadol may be a better analgesic for dogs with corneal ulcers. Topical morphine has been used to control pain associated with corneal ulceration, but like nalbuphine, it must be prepared by a compounding pharmacy and is trickier to prescribe and dispense. Systemic nonsteroidal anti-inflammatory (NSAID) medications may alleviate the confounding inflammatory component of ocular pain, but controlled studies on their pain relieving abilities are lacking. They can also have systemic adverse effects, such as gastrointestinal ulcerations and renal toxi-
city. Additionally, topical NSAIDs can have toxic effects on corneal epithelial cells. Topical anesthetics should not be used for pain control, since they too have epitheliotoxic effects and can delay corneal wound healing. CONTROL OF OCULAR PAIN FROM GLAUCOMA Glaucoma, a condition associated with an elevated intraocular pressure (IOP), can be associated with significant pain. Both open-angle and closed-angle glaucoma are
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A D VA N C E S
recognized in humans and dogs. Acute angle closure glaucoma, wherein IOP abruptly rises to exceed 40 mmHg, is the most common form recognized in our canine patients. In people, it is cause for migraine-like head pain that is often reported to be excruciating. When dogs present acutely, they often will exhibit blepharospasm, epiphora, lethargy, and reluctance to be petted or touched on the head. As the condition becomes chronic, these signs of acute pain often abate, leading owners and veterinarians to surmise that their pain has also dissipated. We do not know if this is the case; however, veterinary ophthalmologists have recognized anecdotally for years that once a chronically hypertensive globe has been either removed or rendered normo- or hypotensive, the animal’s demeanor improves dramatically almost immediately, leading us to believe that the pet was indeed uncomfortable. Glaucoma pain, unfortunately, cannot be relieved without decreasing the IOP. Opiate analgesics, such as tramadol, may have sedative or neuroprotective effects, but they will not alleviate the pressure pain. Medical or surgical intervention to normalize IOP is necessary. Once medical and surgical options for ophthalmic disease treatment and pain control have been exhausted, it is sometimes necessary to consider removal of an eye. As much as I hate to think about, talk about, and perform enucleations (in my
Figure 2. In certain cases, enucleation can afford relief from otherwise intractable ocular pain.
discipline, retention of the globe is the ideal goal), they are sometimes absolutely necessary for a patient’s comfort, quality of life, or survival (Fig. 2). Post-operative pain can be considerable with a major procedure such as enucleation, but it can be mitigated with the use of appropriate pre-operative regional anesthesia. A recent study by Myrna et al. looked at the use of bupivicaine injected into the retrobulbar space for adjunctive retrobulbar analgesia.2 Its use prior to enucleation in dogs improved post-operative comfort and reduced the need for additional postoperative analgesics. An older study by Accola et al. investigated different techniques for retrobulbar anesthesia in the dog and found that the
inferior-temporal palpebral approach provided an easy, effective block with the fewest complications.3 Retrobulbar blocks are underused in veterinary medicine, despite being an effective tool for analgesia with minimal risk if performed with proper technique. For the surgical procedure of enucleation itself, there are potential complications, including infection, hemorrhage, cellulitis, and orbital emphysema. Chronic complications may develop as well, but these can be minimized with careful technique. A recent report of enucleation complications from Ward et al. described cases that had chronic swelling and discharge even several years after the original enucleation.4 All 3 cases in that series had residual adnexal tissue within the orbit that resulted in either nictitans inclusion cyst, orbital pneumatosis, or conjunctival mucocele. This underscores the importance of closely examining the orbit following removal of the globe for any tissue that may potentially be secretory in order to minimize the risk of complications in the long-term follow-up period. PEARLS Remember that corneal ulceration can be accompanied by considerable discomfort and consider the use of analgesic medications, such as tramadol, for control of pain.
A D VA N C E S
1. Retrobulbar blocks are standard of care prior to enucleation. Remember to remove all secretory tissue from the orbit during enucleation procedures. 2. It is often inappropriate to anthropomorphize, but when it comes to ophthalmic disease, when we do not do so, we risk discounting a painful condition that we may be able to mitigate. REFERENCES 1. Clark JS, Bentley E, Smith LJ. Evaluation of topical nalbuphine or oral tramadol as analgesics for corneal pain in dogs: a pilot study. Vet Ophthalmol 2011;14:358-364. 2. Myrna KE, Bentley E, Smith LJ. Effectiveness of injection of local anesthetic into the retobulbar space for post-operative analgesia following eye enucleation in dogs. J Am Vet Med Assoc 2010;237:174-177. 3. Accola PJ, Bentley E, Smith EJ, et al. Development of a retrobulbar injection technique for ocular surgery and analgesia in dogs. J Am Vet Med Assoc 2006;229;220-225. 4. Ward AA, Neaderland MH. Complications for residual adnexal structures following enucleation in three dogs. J Am Vet Med Assoc 2011;239:1580-1583.
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WWW.ADVANCESINSMALLANIMAL.COM
VOLUME 25, ISSUE 9 • SEPTEMBER 2012
Ouch!!! My Eye!!! CARYN E. PLUMMER, DVM, DIPLOMATE ACVO ASSISTANT PROFESSOR, COMPARATIVE OPHTHALMOLOGY DEPARTMENTS OF SMALL AND LARGE ANIMAL CLINICAL SCIENCES COLLEGE OF VETERINARY MEDICINE UNIVERSITY OF FLORIDA GAINESVILLE, FL 32610 Ocular pain can be miserable. Despite recognition of this and that one of the greatest concerns owners have for their pets is whether or not they are experiencing pain, signs of ocular pain in our veterinary patients are often overlooked or minimized by both pet owners and veterinary practitioners. Yes, the pet may be squinting and have some epiphora, but he is not in pain, right? The eye may be injected and cloudy, but she is still eating and going for walks as usual, so she could possibly be uncomfortable, right? This disconnect between recognition of signs and their association with discomfort can lead to missed opportunities for alleviation of pain. Consideration of pain control is an important facet of the treatment of ocular disease in all species.
Figure 1. Signs of ocular pain can include blepharospasm and epiphora.
CONTROL OF OCULAR PAIN FROM CORNEAL ULCERS The cornea is richly innervated with sensory nerves. When these nerves are structurally damaged, pain will result. Signs of corneal pain typically include blepharospasm, epiphora, conjunctival hyperemia, reflex uveitis, rubbing, and other incidents of self-trauma (Fig 1). Although limited options for the treatment of corneal pain have been available in the past, there are some viable and effective options today. A recent study by Clark et al. evaluated the use of topical nalbuphine, a synthetic mixed opiate, and oral tramadol, a synthetic codeine analog, to mitigate signs of pain associated with experimentally induced corneal ulcers in dogs.1 Animals enrolled in the study received either topical nalbuphine with an oral placebo, oral tramadol, and a topical saline or topical saline and an oral placebo (control). Pain scores were determined during the course of healing, and those individuals with scores exceeding a minimal threshold of acceptable pain were rescued with intramuscular morphine. Although the differences between the groups were not statistically significant, many fewer dogs in the tramadol group required rescue than those in the nalbuphine or control groups, suggesting that tramadol may be a better analgesic for dogs with corneal ulcers. Topical morphine has been used to control pain associated with corneal ulceration, but like nalbuphine, it must be prepared by a compounding pharmacy and is trickier to prescribe and dispense. Systemic nonsteroidal anti-inflammatory (NSAID) medications may alleviate the confounding inflammatory component of ocular pain, but controlled studies on their pain relieving abilities are lacking. They can also have systemic adverse effects, such as gastrointestinal ulcerations and renal toxi-
city. Additionally, topical NSAIDs can have toxic effects on corneal epithelial cells. Topical anesthetics should not be used for pain control, since they too have epitheliotoxic effects and can delay corneal wound healing. CONTROL OF OCULAR PAIN FROM GLAUCOMA Glaucoma, a condition associated with an elevated intraocular pressure (IOP), can be associated with significant pain. Both open-angle and closed-angle glaucoma are
PAG E 2
A D VA N C E S
recognized in humans and dogs. Acute angle closure glaucoma, wherein IOP abruptly rises to exceed 40 mmHg, is the most common form recognized in our canine patients. In people, it is cause for migraine-like head pain that is often reported to be excruciating. When dogs present acutely, they often will exhibit blepharospasm, epiphora, lethargy, and reluctance to be petted or touched on the head. As the condition becomes chronic, these signs of acute pain often abate, leading owners and veterinarians to surmise that their pain has also dissipated. We do not know if this is the case; however, veterinary ophthalmologists have recognized anecdotally for years that once a chronically hypertensive globe has been either removed or rendered normo- or hypotensive, the animal’s demeanor improves dramatically almost immediately, leading us to believe that the pet was indeed uncomfortable. Glaucoma pain, unfortunately, cannot be relieved without decreasing the IOP. Opiate analgesics, such as tramadol, may have sedative or neuroprotective effects, but they will not alleviate the pressure pain. Medical or surgical intervention to normalize IOP is necessary. Once medical and surgical options for ophthalmic disease treatment and pain control have been exhausted, it is sometimes necessary to consider removal of an eye. As much as I hate to think about, talk about, and perform enucleations (in my
Figure 2. In certain cases, enucleation can afford relief from otherwise intractable ocular pain.
discipline, retention of the globe is the ideal goal), they are sometimes absolutely necessary for a patient’s comfort, quality of life, or survival (Fig. 2). Post-operative pain can be considerable with a major procedure such as enucleation, but it can be mitigated with the use of appropriate pre-operative regional anesthesia. A recent study by Myrna et al. looked at the use of bupivicaine injected into the retrobulbar space for adjunctive retrobulbar analgesia.2 Its use prior to enucleation in dogs improved post-operative comfort and reduced the need for additional postoperative analgesics. An older study by Accola et al. investigated different techniques for retrobulbar anesthesia in the dog and found that the
inferior-temporal palpebral approach provided an easy, effective block with the fewest complications.3 Retrobulbar blocks are underused in veterinary medicine, despite being an effective tool for analgesia with minimal risk if performed with proper technique. For the surgical procedure of enucleation itself, there are potential complications, including infection, hemorrhage, cellulitis, and orbital emphysema. Chronic complications may develop as well, but these can be minimized with careful technique. A recent report of enucleation complications from Ward et al. described cases that had chronic swelling and discharge even several years after the original enucleation.4 All 3 cases in that series had residual adnexal tissue within the orbit that resulted in either nictitans inclusion cyst, orbital pneumatosis, or conjunctival mucocele. This underscores the importance of closely examining the orbit following removal of the globe for any tissue that may potentially be secretory in order to minimize the risk of complications in the long-term follow-up period. PEARLS Remember that corneal ulceration can be accompanied by considerable discomfort and consider the use of analgesic medications, such as tramadol, for control of pain.
A D VA N C E S
1. Retrobulbar blocks are standard of care prior to enucleation. Remember to remove all secretory tissue from the orbit during enucleation procedures. 2. It is often inappropriate to anthropomorphize, but when it comes to ophthalmic disease, when we do not do so, we risk discounting a painful condition that we may be able to mitigate. REFERENCES 1. Clark JS, Bentley E, Smith LJ. Evaluation of topical nalbuphine or oral tramadol as analgesics for corneal pain in dogs: a pilot study. Vet Ophthalmol 2011;14:358-364. 2. Myrna KE, Bentley E, Smith LJ. Effectiveness of injection of local anesthetic into the retobulbar space for post-operative analgesia following eye enucleation in dogs. J Am Vet Med Assoc 2010;237:174-177. 3. Accola PJ, Bentley E, Smith EJ, et al. Development of a retrobulbar injection technique for ocular surgery and analgesia in dogs. J Am Vet Med Assoc 2006;229;220-225. 4. Ward AA, Neaderland MH. Complications for residual adnexal structures following enucleation in three dogs. J Am Vet Med Assoc 2011;239:1580-1583.
PAG E 3