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Pressure! So Much Pressure!
IN SMALL ANIMAL M E D I C IN E AN D SURG E RY
www.advancesinsmallanimal.com
Volume 28, Issue 1 • January 2015
Pressure! So Much Pressure! Caryn E. Plummer, DVM, DACVO Associate Professor, Comparative Ophthalmology Departments of Small and Large Animal Clinical Sciences College of Veterinary Medicine University of Florida Gainesville, FL 32610 Glaucoma is not a single disease entity, but a group of ocular diseases which are characterized by progressive death of retinal ganglion cells (the axons of which coalesce to become the optic nerve) and have the common, constant risk factor of elevated intraocular pressure (IOP). It is, unfortunately, an all too common condition in dogs with a prevalence similar to that occurring in human beings (close to 2% of both the human and canine populations). Because there are so many different forms of glaucoma, even beyond the simplistic categories of primary, secondary, congenital, open-angle, and narrow angle, treatment necessarily must target the risk factor that is common to all types. Therefore, the elevation in IOP, which is incompatible with the health of the eye and the maintenance of vision, becomes the factor we rely upon for diagnosis, treatment, and monitoring of glaucoma. Glaucoma Diagnosis Despite its being a common condition in dogs, the diagnosis of glaucoma can be challenging and is often delayed. The diagnosis should begin with an index of suspicion on the clinician’s part and should be considered when any patient presents with episcleral injection, corneal edema, mydriasis or any manifestation of ocular pain (blepharospasm, epiphora, reluctance to contact/petting on the head, inappetence, and lethargy). The index should rise further if the patient is a purebred dog, especially if it is a breed with a heritable predisposition to glaucoma (spaniels of every type, bassett
hounds, chow chows, shar peis, Boston terriers, poodles of every size, shih tzus, Pekingeses, Bichon frises, terriers of most varieties, Norwegian elkhounds, samoyeds, Siberian huskies, Australian cattle dogs, Akitas, Lhasa apsos, beagles, and Dalmatians, among others). The diagnosis is confirmed with tonometry when the IOP is above the reference range of normal, usually greater than 25 mmHg. It should be noted, however, that most dolicocephalic and mesocephalic dogs will run much lower than 25 mmHg normally, often in the low teens. So, an IOP in the mid-20s may be a significant elevation from normal for these dogs. There should be concern, also, if there is a greater than 5 to 6 mmHg difference between the two eyes.
“It is imperative that antiglaucoma therapy begin in the normotensive eye at the time the diagnosis is made in the hypertensive eye. ” There are two types of portable tonometers available to practicing veterinarians today. Applanation tonometers, such as the TonoPen®, TonoPen Vet®, TonoPen Avia Vet®, or the AccuPen®, estimate IOP by determining the external pressure necessary to indent a set amount of corneal surface area. These instruments can be finicky, and inaccurate readings can result if inexperienced users press too hard into the cornea. The alternative method, rebound tonometry, estimates IOP by determining the velocity with which a magnetized pin extruded from the instrument returns to the handpiece after striking the cornea. The TonoVet® rebound tonometer can also be difficult with its reproducibility, but it has the advantage of removing the onus of applying the
probe tip directly to the eye from the user. Several recent studies have examined the differences in the readings between these two types of instruments in both normal and diseased eyes, and the general consensus is that while both instruments give similar estimates, the rebound tonometer consistently gives slightly but statistically significantly higher readings in diseased eyes.1,2 This difference may not be clinically significant, but it is enough to recommend that the same device be used for the monitoring of IOP in individual patients. Glaucoma Management When glaucoma occurs in the absence of another preliminary or concurrent ocular condition, such as uveitis, lens luxation, or intraocular neoplasia, it is referred to as primary glaucoma. Several years ago, a
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multicenter trial was performed in dogs with primary glaucoma in which the normotensive fellow eye was either left untreated or treated with either a topical beta-blocker (betaxolol) or a topical parasympathomimetic (demecarium bromide) in combination with a topical steroid preparation (gentamicin/betamethasone).3 Untreated control dogs developed glaucoma significantly sooner (median, 8 months) than dogs treated with either betaxolol (median, 30.7 months) or demecarium and betamethasone (median, 31 months). This study changed the standard of medical care for glaucoma in dogs. It is now recommended that all fellow eyes of dogs affected with primary glaucoma begin consistent therapy with topical antihypertensive medications to delay the onset of vision decline and other clinical signs. A recent retrospective study identified 88 canine patients presenting with unilateral acute congestive primary angle-closure glaucoma.4 At the time of diagnosis, each patient had normal IOP in the fellow eye, and medical therapy for glaucoma was initiated in this normotensive contralateral eye. The study looked at the topical medications used and evaluated the time to medical failure (which was defined as IOP of 20 mmHg or more, the need for additional medications beyond the initial agents used or surgical intervention to maintain IOP at or below 20 mmHg, or the development of clinical signs consistent with glaucoma) for each anti-glaucoma medication. It also looked
at the efficacy of the combination therapy (topical anti-hypertensive agents with or without anti-inflammatory agents). None of the 4 anti-glaucoma medications (demecarium bromide 0.125%, demecarium bromide 0.25%, latanoprost 0.005%, or dorzolamide hydrochloride 2.0%) statistically delayed time to medical failure when compared with one another. Although not statistically significant, there was a difference in the median time to medical failure in patients receiving topical anti-glaucoma and anti-inflammatory medication (324 days) versus in patients receiving antiglaucoma medication alone (195 days). These data support the recommendations of the previous study that topical anti hypertensive medications be used in normotensive contralateral eyes and suggest that adjunctive use of topical anti-inflammatory medications (dexamethasone, prednisolone acetate, diclofenac) may be beneficial to the prophylactic medical therapy of primary glaucoma in dogs. Treatment Goals The broad goals of glaucoma therapy are to maintain vision as long as possible and to maintain or restore comfort to patients with ocular hypertension. Specific to those goals, it is ideal to confine the IOP to a range in which the damage to retinal ganglion cells from glaucoma is reduced to normal age-related levels of cell loss. Unfortunately, this range or threshold, is specific to the individual and will vary between patients. In gen-
eral, however, the greater the damage the eye has already sustained from glaucoma (vision loss, optic nerve atrophy, retinal degeneration), the lower the target should be. IOPs stable in the low teens are usually reasonable, and regular spot monitoring should be encouraged every few weeks to months. If an upward trend in IOP or a downward trend in vision is noted (or if the client is highly motivated or highly sensitive), early referral to a veterinary ophthalmologist for a discussion of sur gical options is recommended. Conclusions 1. The diagnosis of glaucoma can be a challenging one. Make sure to correlate clinical signs with your index of suspicion and use tonometry to confirm (rather than to make) your diagnosis and monitor response to therapy. 2. The values obtained with the portable tonometers available in veterinary medicine are generally reliable but subject to the skill and experience of the user and the degree of corneal pathology present. Since there will be slight differences in the values obtained between rebound and applanation tonometers, it is important to maintain consistency and use same instrument under same conditions to monitor IOP. Take measurements from the axial cornea unless the corneal architecture is altered there (scar, edema, stromal defect). 3. Glaucoma is a progressive condition, and primary glaucoma is a bilateral
A D V AN C E S
condition. It is imperative that antiglaucoma therapy begin in the “normal,” (i.e., normotensive) eye at the time the diagnosis is made in the “affected” (i.e., hypertensive) eye. Diligent and consistent medical therapy may delay the onset of hypertension in the second eye. It may be beneficial to add topical anti-inflammatory medications to the treatment protocol, as long as the cornea is healthy. 4. Medical therapy alone may not be enough to maintain IOP within the target range and permit vision retention. If an owner is motivated to pursue surgery, early referral for consultation with an ophthalmologist to discuss the surgical options and the advantages and disadvantages of each should be offered. References 1. von Spiessen L, Karck J, Rohn K, et al. Clinical comparison of the TonoVet® rebound tonometer and the Tono-Pen Vet® applanation tonometer in dogs and cats with ocular disease: glaucoma or corneal pathology. Vet Ophthalmol 2013:1-8. doi: 10.1111/ vop.12101. 2. Slack JM, Stiles J, Moore GE. Comparison of a rebound tonometer with an applanation tonometer in dogs with glaucoma. Vet Rec. 2012 Oct 13;171(15):373. doi: 10.1136/ vr.100967. Epub 2012 Aug 22. 3. Miller PE, Schmidt GM, Vainisi SJ, et al. The efficacy of topical prophylactic antiglaucoma therapy in primary closed angle glaucoma in dogs: a multicenter clinical trial. J Am Anim Hosp Assoc 2000;36:431-438. 4. Dees DD, Fritz KJ, MacLaren NE, et al. Efficacy of prophylactic antiglaucoma and anti-inflammatory medications in canine primary angle-closure glaucoma: a multicenter retrospective study (2004-2012). Vet Ophthalmol 2014;17:195-200.
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www.advancesinsmallanimal.com
Volume 28, Issue 1 • January 2015
Pressure! So Much Pressure! Caryn E. Plummer, DVM, DACVO Associate Professor, Comparative Ophthalmology Departments of Small and Large Animal Clinical Sciences College of Veterinary Medicine University of Florida Gainesville, FL 32610 Glaucoma is not a single disease entity, but a group of ocular diseases which are characterized by progressive death of retinal ganglion cells (the axons of which coalesce to become the optic nerve) and have the common, constant risk factor of elevated intraocular pressure (IOP). It is, unfortunately, an all too common condition in dogs with a prevalence similar to that occurring in human beings (close to 2% of both the human and canine populations). Because there are so many different forms of glaucoma, even beyond the simplistic categories of primary, secondary, congenital, open-angle, and narrow angle, treatment necessarily must target the risk factor that is common to all types. Therefore, the elevation in IOP, which is incompatible with the health of the eye and the maintenance of vision, becomes the factor we rely upon for diagnosis, treatment, and monitoring of glaucoma. Glaucoma Diagnosis Despite its being a common condition in dogs, the diagnosis of glaucoma can be challenging and is often delayed. The diagnosis should begin with an index of suspicion on the clinician’s part and should be considered when any patient presents with episcleral injection, corneal edema, mydriasis or any manifestation of ocular pain (blepharospasm, epiphora, reluctance to contact/petting on the head, inappetence, and lethargy). The index should rise further if the patient is a purebred dog, especially if it is a breed with a heritable predisposition to glaucoma (spaniels of every type, bassett
hounds, chow chows, shar peis, Boston terriers, poodles of every size, shih tzus, Pekingeses, Bichon frises, terriers of most varieties, Norwegian elkhounds, samoyeds, Siberian huskies, Australian cattle dogs, Akitas, Lhasa apsos, beagles, and Dalmatians, among others). The diagnosis is confirmed with tonometry when the IOP is above the reference range of normal, usually greater than 25 mmHg. It should be noted, however, that most dolicocephalic and mesocephalic dogs will run much lower than 25 mmHg normally, often in the low teens. So, an IOP in the mid-20s may be a significant elevation from normal for these dogs. There should be concern, also, if there is a greater than 5 to 6 mmHg difference between the two eyes.
“It is imperative that antiglaucoma therapy begin in the normotensive eye at the time the diagnosis is made in the hypertensive eye. ” There are two types of portable tonometers available to practicing veterinarians today. Applanation tonometers, such as the TonoPen®, TonoPen Vet®, TonoPen Avia Vet®, or the AccuPen®, estimate IOP by determining the external pressure necessary to indent a set amount of corneal surface area. These instruments can be finicky, and inaccurate readings can result if inexperienced users press too hard into the cornea. The alternative method, rebound tonometry, estimates IOP by determining the velocity with which a magnetized pin extruded from the instrument returns to the handpiece after striking the cornea. The TonoVet® rebound tonometer can also be difficult with its reproducibility, but it has the advantage of removing the onus of applying the
probe tip directly to the eye from the user. Several recent studies have examined the differences in the readings between these two types of instruments in both normal and diseased eyes, and the general consensus is that while both instruments give similar estimates, the rebound tonometer consistently gives slightly but statistically significantly higher readings in diseased eyes.1,2 This difference may not be clinically significant, but it is enough to recommend that the same device be used for the monitoring of IOP in individual patients. Glaucoma Management When glaucoma occurs in the absence of another preliminary or concurrent ocular condition, such as uveitis, lens luxation, or intraocular neoplasia, it is referred to as primary glaucoma. Several years ago, a
Page 2
A D V AN C E S
multicenter trial was performed in dogs with primary glaucoma in which the normotensive fellow eye was either left untreated or treated with either a topical beta-blocker (betaxolol) or a topical parasympathomimetic (demecarium bromide) in combination with a topical steroid preparation (gentamicin/betamethasone).3 Untreated control dogs developed glaucoma significantly sooner (median, 8 months) than dogs treated with either betaxolol (median, 30.7 months) or demecarium and betamethasone (median, 31 months). This study changed the standard of medical care for glaucoma in dogs. It is now recommended that all fellow eyes of dogs affected with primary glaucoma begin consistent therapy with topical antihypertensive medications to delay the onset of vision decline and other clinical signs. A recent retrospective study identified 88 canine patients presenting with unilateral acute congestive primary angle-closure glaucoma.4 At the time of diagnosis, each patient had normal IOP in the fellow eye, and medical therapy for glaucoma was initiated in this normotensive contralateral eye. The study looked at the topical medications used and evaluated the time to medical failure (which was defined as IOP of 20 mmHg or more, the need for additional medications beyond the initial agents used or surgical intervention to maintain IOP at or below 20 mmHg, or the development of clinical signs consistent with glaucoma) for each anti-glaucoma medication. It also looked
at the efficacy of the combination therapy (topical anti-hypertensive agents with or without anti-inflammatory agents). None of the 4 anti-glaucoma medications (demecarium bromide 0.125%, demecarium bromide 0.25%, latanoprost 0.005%, or dorzolamide hydrochloride 2.0%) statistically delayed time to medical failure when compared with one another. Although not statistically significant, there was a difference in the median time to medical failure in patients receiving topical anti-glaucoma and anti-inflammatory medication (324 days) versus in patients receiving antiglaucoma medication alone (195 days). These data support the recommendations of the previous study that topical anti hypertensive medications be used in normotensive contralateral eyes and suggest that adjunctive use of topical anti-inflammatory medications (dexamethasone, prednisolone acetate, diclofenac) may be beneficial to the prophylactic medical therapy of primary glaucoma in dogs. Treatment Goals The broad goals of glaucoma therapy are to maintain vision as long as possible and to maintain or restore comfort to patients with ocular hypertension. Specific to those goals, it is ideal to confine the IOP to a range in which the damage to retinal ganglion cells from glaucoma is reduced to normal age-related levels of cell loss. Unfortunately, this range or threshold, is specific to the individual and will vary between patients. In gen-
eral, however, the greater the damage the eye has already sustained from glaucoma (vision loss, optic nerve atrophy, retinal degeneration), the lower the target should be. IOPs stable in the low teens are usually reasonable, and regular spot monitoring should be encouraged every few weeks to months. If an upward trend in IOP or a downward trend in vision is noted (or if the client is highly motivated or highly sensitive), early referral to a veterinary ophthalmologist for a discussion of sur gical options is recommended. Conclusions 1. The diagnosis of glaucoma can be a challenging one. Make sure to correlate clinical signs with your index of suspicion and use tonometry to confirm (rather than to make) your diagnosis and monitor response to therapy. 2. The values obtained with the portable tonometers available in veterinary medicine are generally reliable but subject to the skill and experience of the user and the degree of corneal pathology present. Since there will be slight differences in the values obtained between rebound and applanation tonometers, it is important to maintain consistency and use same instrument under same conditions to monitor IOP. Take measurements from the axial cornea unless the corneal architecture is altered there (scar, edema, stromal defect). 3. Glaucoma is a progressive condition, and primary glaucoma is a bilateral
A D V AN C E S
condition. It is imperative that antiglaucoma therapy begin in the “normal,” (i.e., normotensive) eye at the time the diagnosis is made in the “affected” (i.e., hypertensive) eye. Diligent and consistent medical therapy may delay the onset of hypertension in the second eye. It may be beneficial to add topical anti-inflammatory medications to the treatment protocol, as long as the cornea is healthy. 4. Medical therapy alone may not be enough to maintain IOP within the target range and permit vision retention. If an owner is motivated to pursue surgery, early referral for consultation with an ophthalmologist to discuss the surgical options and the advantages and disadvantages of each should be offered. References 1. von Spiessen L, Karck J, Rohn K, et al. Clinical comparison of the TonoVet® rebound tonometer and the Tono-Pen Vet® applanation tonometer in dogs and cats with ocular disease: glaucoma or corneal pathology. Vet Ophthalmol 2013:1-8. doi: 10.1111/ vop.12101. 2. Slack JM, Stiles J, Moore GE. Comparison of a rebound tonometer with an applanation tonometer in dogs with glaucoma. Vet Rec. 2012 Oct 13;171(15):373. doi: 10.1136/ vr.100967. Epub 2012 Aug 22. 3. Miller PE, Schmidt GM, Vainisi SJ, et al. The efficacy of topical prophylactic antiglaucoma therapy in primary closed angle glaucoma in dogs: a multicenter clinical trial. J Am Anim Hosp Assoc 2000;36:431-438. 4. Dees DD, Fritz KJ, MacLaren NE, et al. Efficacy of prophylactic antiglaucoma and anti-inflammatory medications in canine primary angle-closure glaucoma: a multicenter retrospective study (2004-2012). Vet Ophthalmol 2014;17:195-200.
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