A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories
International Research Journal of Natural and Applied Sciences (IRJNAS)
Website: www.aarf.asia. Email: editoraarf@gmail.com , editor@aarf.asia Page 192
CANINE GLAUCOMA AND MANAGEMENTAL MODALITIES
Rai Somil1 & Chandrapuria V.P.2 1
PhD Scholar
2
Professor & Director Clinics
Department of Surgery and Radiology, College of Veterinary Science and A.H.,
Nanaji Deshmukh Veterinary Science University, Jabalpur (M.P.)
INTRODUCTION
Glaucoma is a syndrome in which progressive elevation in intraocular pressure (IOP)
of the eye results in damage to the optic disc and retina and characteristic changes of
glaucoma include disrupted axoplasmic flow in the optic nerve head, death of retinal ganglion
cells and their axons, cupping of the optic disc, and visual impairment or blindness. Normal
canine IOP is reported as approximately 10 to 20 mmHg. Glaucoma starts occurring at IOP
above 25 mmHg in dogs. The elevated IOP is due to a disharmony between production and
outflow of the aqueous humor. More specifically, a reduction in the outflow rate of the
aqueous humor is responsible for the elevated IOP, not the overproduction of the aqueous
humor (Magrane, 1977). The most commonly affected breeds are Labrador retriever, Toy
poodle, Chow chow, American cocker spaniel, Basset hound, Samoyed, Beagle, Siberian
husky (Maggs et al., 2013). Glaucoma is result of impaired aqueous humor outflow. The
mechanism of this impairment may be etiologically classified as Primary glaucoma have no
association with another ocular or systemic disorder, are typically bilateral, have a strong
breed predisposition, and hence are believed to have a genetic basis. Primary glaucoma is
subdivided into two main forms.
Primary open angle glaucoma (POAG), in which the drainage angle appears
gonioscopically normal. POAG is a bilateral disorder in which IOP tends to increase in a
slow, insidious fashion simultaneously in both eyes in young to middle aged dogs. Initially
the gonioscopically visible angle is open. Over time the angle closes, the globe becomes
buphthalmic, and the lens may subluxate (Curtis and Barnett, 1980). The precise mechanism
of POAG in dogs is unclear, but it most likely results from biochemical alterations in the
trabecular meshwork that ultimately leads to greater resistance to aqueous outflow and
A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories
International Research Journal of Natural and Applied Sciences (IRJNAS)
Website: www.aarf.asia. Email: editoraarf@gmail.com , editor@aarf.asia Page 193 Primary angle closure glaucoma (PACG), in which the drainage angle appears
gonioscopically narrowed or closed. PACG is also a bilateral disorder but it tends to manifest
as an initially unilateral, rapid, marked increase in IOP in middle aged to older dogs. Again,
the precise mechanism by which PACG occurs is uncertain, but there is a clear association
with congenital pectinate ligament dysplasia. It is also associated with a female sex
predisposition, periods of stress or excitement, and dim light. In the dog, PACG is at least
eight times more common than POAG. Acute PACG also is two times more common in
female dogs than in male dogs (Ekesten et al., 1997)
Secondary glaucoma is at least twice as common as primary glaucoma in dogs and is
associated with other ocular or systemic disorders that alter aqueous humor dynamics
(Kennard, 2009). Secondary glaucoma may be unilateral or bilateral and may or may not be
inherited and the cause such as iridocyclitis, intraocular neoplasm, inflammation, lens
displacement, uveitis, intraocular hemorrhage and advance cataracts in the eye can be
identified (Crispin, 1988).
Glaucoma is one of the most commonly misdiagnosed eye conditions. The signs
present in a particular animal depend on the duration, intensity, and causes of the pressure
elevation and commonly includes Descemet’s streaks, Aphakic crescent, Luxated lens,
Corneal edema, Iris atrophy, Enlarged episcleral vessels, Fixed dilated pupil, Shallow
anterior chamber, Cupping of optic disc, Bupthalmos, Increase intraocular pressure, Partial or
complete loss of vision and Ocular pain (Allgoewer, 2006).
DIAGNOSTIC MODALITIES
Normal canine IOP is reported as approximately 10 to 20mmHg. However, significant
variation is noted among individuals as well as among techniques and the time of day at
which IOP is measured. Therefore, comparison of IOP between right and left eyes of the
same animal is critical to interpretation of results. A good rule of thumb is that IOP should
not vary between right and left eyes of the same patient by more than 20%. Diagnostic
procedures are invaluable for the diagnosis and treatment of the glaucoma that are
particularly useful include:
Tonometry
Tonometry measure intraocular pressure (IOP) and is perhaps one of the most important
diagnostic tests in veterinary practice. Before use, a drop of topical anesthetic is applied to
A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories
International Research Journal of Natural and Applied Sciences (IRJNAS)
Website: www.aarf.asia. Email: editoraarf@gmail.com , editor@aarf.asia Page 194 IOP via direct pressure on the jugular veins, and the operator carefully retracts the eyelids
using the nondominant hand. Care must be taken not to place pressure on the globe. Its three
types: (Maggs et al., 2013). Indentation Tonometry in which the Schiotz tonometer relies
upon indentation tonometry. In this method, a standard force is applied with a metal rod over
the anesthetized cornea. The distance of the rod indents the cornea is measured and is
inversely related to the IOP (i.e., the greater the tonometer scale reading, the lower the patient’s IOP). This requires that the head be elevated so that the corneal surface is
horizontal. The tonometer is placed on the eye and scale reading is recorded. The calibration
table supplied with the instrument is then used to convert the scale reading to the IOP via the
appropriate column.
Applanation tonometry using the Tono-Pen is suitable for large animals, is unaffected
by variations in ocular rigidity, requires no conversion tables, and needs no sterilization. The
principle of applanation tonometry is that the force required to flatten a given area of a
sphere is equal to the pressure within the sphere (the Imbert-Fick law). Therefore, if the area
is known and the force is measured, the pressure can be calculated (Barnett, 2006).
Rebound tonometer eject a small probe (such as a metal pin with a rounded end) at a
fixed distance from the cornea and assess the motion of the probe as it strikes the cornea and
is returned to the instrument. Eyes with higher IOP cause a more rapid deceleration of the
probe and shorter return time to the instrument. This technique is affected by ocular surface
tension and so should be performed before application of any topical medications.
Ophthalmoscopy
Direct or indirect ophthalmoscope may be used to examine the optic nerve head for
evaluate the ocular fundus and cupping of the optic disc, which is the hallmark of glaucoma.
The red-free filter (green light) of these instruments facilitates examination of the optic nerve
and retinal nerve fiber layer. The ocular fundi of both eyes of the canine glaucomatous
patients must be evaluated and compared. In the event IOP is elevated above normalcy,
critical evaluation of the ocular fundus must be delayed until IOP is decreased. Corneal
transparency may be reduced by IOP, which tends to obscure interpretation of the optic disc.
Frequently, elevated IOP also cause reversible compression of the retinal vessels, Cupping of
the optic disc, loss of myelin in the lateral aspects of the optic disc as well as enlargement of
the optic disc. Its two types (Gelatt, 1981) direct and indirect opthalmoscopy. The Direct
A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories
International Research Journal of Natural and Applied Sciences (IRJNAS)
Website: www.aarf.asia. Email: editoraarf@gmail.com , editor@aarf.asia Page 195 pupil. The 14 to 15 X upright magnification of the ocular fundus by direct ophthalmoscope
may be valuable in the evaluation of details of the optic disc. The indirect ophthalmoscopy
can also be performed through a small pupil provided. The special monocular or binocular
small pupil indirect ophthalmoscope is use. The 2 to 4 X upside down and backward
magnification of the ocular fundus with the indirect method is useful in the presence of
corneal and lens opacities.
Gonioscopy
Gonioscopy describes examination of the iridocorneal or “drainage” angle (the
junction between the iris and cornea). In the normal eye of most species light rays that are
reflected from the drainage angle strike the posterior cornea and undergo total internal
reflection as in a prism. This occurs because of the difference in refractive index between the
cornea and the surrounding air, and the high angle of incidence of the light rays from the
drainage angle. By replacing the air surrounding the cornea with a goniolens that has an index
of refraction close to that of the cornea, total internal reflection is avoided and light rays from
the drainage angle can be viewed directly through the goniolens. Gonioscopy is used
primarily to determine whether the angle is open, narrow, closed, or obstructed by
mesodermal remnants, and to check for the presence of foreign bodies, tumors, and
inflammatory exudates (Bedford, 1985).
MANAGEMENT
In most canine glaucomatous patients, the condition is presented in an advanced stage
often requiring intensive medical treatment as well as combination with a surgical
antiglaucoma procedure. Medical treatment of glaucoma often becomes a long term
administration of single or a combination of drugs to maintain IOP within normal limits, and
to prolong vision for as long as possible (Reinstein et al.,2009). Medications, often in the
form of eye drops, work to decrease intraocular fluid production, increase fluid drainage, or
both. These medications are associated with side effects, including burning sensations in the
eye, headaches, cardiac fluctuations and blurred vision. The administration of medications for
the treatment of animals is difficult and ineffective (Abrams, 2001).
Iridencleisis
A fixation suture is placed through the conjunctiva and tenon’s capsule close to the
A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories
International Research Journal of Natural and Applied Sciences (IRJNAS)
Website: www.aarf.asia. Email: editoraarf@gmail.com , editor@aarf.asia Page 196 sclera (Gupta et al., 1966). The conjunctival flap has been freed to the limbus and a deep,
grooved incision is made on the sclera side of the limbus with a 64 beaver blade. Pin point
coagulation of episcleral vessels is necessary for hemostasis. The anterior chamber is entered at the 12 o’clock position with a 65 beaver blade. Entrance into the anterior chamber is
shallow to avoid damage to the iris, and the blade is positioned parallel to the surface of the
iris. Corneoscleral scissors are used to extend the incision for the entire length of the groove.
The incision is opened after cauterizing the corneal and sclera lips with electrocautery. An
iris hook is used to withdraw the iris through the incision. The superior papillary border of
the iris is grasped with two iris forceps and a radial iridotomy is performed with an
electroscalpel. Each iris pillar is sutured to the sclera with a simple interrupted 6/0 gut suture. The conjunctiva and tenon’s capsule have been closed with a simple continuous suture
pattern using 6/0 gut. Closure of the lateral canthotomy has been completed (Lew and Lew,
2009).
Sclerectomy and Iridocyclectomy
A 20 mm long incision parallel to and 8 mm from the limbus has been made through
the conjunctiva utilizing a stevens tenotomy scissors. The conjunctiva and tenon’s capsule are
bluntly dissected and reflected at the limbus. A no. 15 blade is used to create a sclera window
and thermal cautery is used to control haemorrhage. The sclera window as outlined is
removed exposing the suprachoroidal space. A cyclodialysis spatula is passed into the
anterior chamber from the suprachoroidal space to separate the ciliary body from the sclera
for approximately 120 degree superiorly. The arrow indicates the direction of motion of the
cyclodialysis spatula. The iris hook has grasped the iris root and withdrawn the iris and
ciliary body through the sclera window. An electroscalpel is used to create an iridocyclectomy. Closure of the conjunctiva and tenon’s capsule is done with a simple
continuous 6/0 suture(Gelatt, 1981).
Anterior chamber implants
A conjunctival-Tenon’s capsule incision makes parallel to and approximately 5mm
posterior to the limbus. The dissection continues down to the sclera and extended both
anteriorly toward the limbus and posteriorly between the extraocular muscle to form a
subconjuctival-Tenon’s capsule pocket After preparing pocket the Ahmed’s gonioimplant
valve (AGV) verify to be patent by flashing it with 0.9% normal saline and blunt tipped 27
A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories
International Research Journal of Natural and Applied Sciences (IRJNAS)
Website: www.aarf.asia. Email: editoraarf@gmail.com , editor@aarf.asia Page 197 anchored to the sclera with 8-0 monofilament Polyamide using simple interrupted suture
technique 8 mm posterior to limbus. After using 23-gauge needle to enter the anterior
chamber and make a tunnel. The Ahmed's gonioimplant tube was inserted through the 23
gauge needle track. The tube ideally protrudes into the anterior chamber 2 mm so that not to
touch the cornea, and not to extended into the papillary aperture. To secure the tube, Tenone’s capsule and conjunctiva close with a simple continuous suture using 7-0 polyglactin
910 (Fattahian et al., 2008).
Cullen frontal sinus shunt
A long incision made over the zygomatic process of the frontal bone. The frontal sinus
end of the shunt is placed within the trephined hole of the sinus and can be held in place by
slight compression of the sealing device. A conjunctival incision is made from the limbus to
the fornix and extended through to the episclera. A small forceps is used to bluntly dissect a
tunnel from the conjunctival incision to the frontal sinus incision. When the tip of such
instrument can be visualized it can be used to grasp the free end (anterior chamber end) of the
shunt. The anterior chamber end of shunt enter in the anterior chamber at 10-25° anterior to
the limbal plane to ensure that the shunt is positioned equal distance between the iris and the
cornea to avoid contact. The shunt is anchored to the sclera with nonabsorbable suture in a
simple interrupted pattern. The Tenon's capsule and conjunctiva are closed with absorbable
7-0 suture in a simple interrupted suture pattern. The frontal sinus end of the shunt is withdrawn
from the frontal sinus and monitored for flow of aqueous humor through the shunt. When
fluid flow through the shunt is confirmed, such flow is adjusted by valve device.
Subcutaneous tissues and skin are closed with routinely manner (Cullen et al., 1998).
Cyclocryothermy
Cyclocryothermy is the application of intense cold directly through the bulbar
conjunctiva and sclera to the ciliary body to reduce the rate of aqueous humor formation. The
advantage of this procedure is that it may be applied repeatedly because the bulbar
conjunctiva and sclera are not adversely affected. The cryoprobe is applied 5 mm from the
limbus directly on the dorsal bulbar conjunctiva and 3 to 5 sites are frozen to - 60ºc for 60
seconds each (Benson and Nalson,1990).
LASER SURGERY
Lasers are routinely used in veterinary ophthalmology for the treatment of a number of
A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories
International Research Journal of Natural and Applied Sciences (IRJNAS)
Website: www.aarf.asia. Email: editoraarf@gmail.com , editor@aarf.asia Page 198 as ruby, Neodymium:Yttrium-Aluminium-Garnet (Nd:YAG, argon, krypton, diode but the
aim is to damage the cells, which secrete aqueous in the eye:
Trans Scleral CycloPhotocoagulation (TSCP)
The delivery of laser energy through the sclera may be performed by either the
non-contact or non-contact method. In the non-non-contact approach, a slit lamp is employed to apply laser
energy through the conjunctival/ scleral surface. A contact lens may be used to keep the
eyelids open. The focus of 4-8 Joule energy for 10-20 second delivers 1–1.5 mm behind the
limbus so that maximal therapeutic effect is at the level of the ciliary body. The total number
of laser applications is usually about 32 (eight per quadrant), for 360˚ circumference but avoiding the 3 and 9 o’clock positions in order to preserve the long posterior ciliary arteries
(Martin and Broadway, 2001). While in contact cyclophotocoagulation,
Neodymium:Yttrium-Aluminium-Garnet (Nd:YAG) laser was more effective in penetrating
the sclera and optimizing energy absorption by the ciliary epithelium. In the Nd:YAG laser, a
hand held sapphire tipped quartz probe is placed on the conjunctiva and sclera, centered 1–2
mm behind the limbus, for the transmission of 4-9 watts energy for 0.5-0.7 sec. The total
number of laser applications is usually about 32, for 360˚ circumference but also avoiding the 3 and 9 o’clock positions. Energy levels are titrated to avoid an audible “pop” sound which
indicates overtreatment of the ciliary body tissue (Nasisse et al.,1990).
Endolaser Cyclophotocoagulation (ECP)
In the limbal approach cyclophotocoagulation is done through a temporal and nasal
limbal site. After dilatation of the pupil, paracentesis is created and the anterior chamber is
filled with viscoelastic agent. A 2.2 mm keratome is then used to enter into the anterior
chamber at the temporal limbus. After orientation of the probe image outside of the eye, the
20 gauge probe is inserted through the incision and into the posterior sulcus (Ofri and
Narfstrom, 2007). At this time, the ciliary processes are viewed on the monitor and treatment
can begin. The laser is set at continuous wave and energy settings are 60–90 mW.
Approximately 180 degree span of ciliary processes is photocoagulated. Laser energy is
applied to each process until shrinkage and whitening occur. If excessive energy is used, the process explodes (or “pops”) with bubble formation, leading to excessive inflammation and
breakdown of the blood-aqueous barrier. After the temporal ciliary processes are treated, a
A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories
International Research Journal of Natural and Applied Sciences (IRJNAS)
Website: www.aarf.asia. Email: editoraarf@gmail.com , editor@aarf.asia Page 199 the wounds, viscoelastic is flushed out using balanced salt solution irrigation of the anterior
chamber (Lin, 2002).
Cyclodialysis
A lateral canthotomy is made to exposure of the globe. A fixation suture has been placed through the conjunctiva at the limbus, and the conjunctiva and tenon’s capsule are
incised to exposed the sclera. The sclera is grooved (between the 10 and 1 o’clock position)
with a 15 no. blade. The incision is made 6 mm from and parallel to the limbus. Alternating
incisions with cauterization helps to deepen the groove, retract the wound edges, and
maintain haemostasis. Once the sclera groove has been extended down to the suprachoroidal
space (appearance of heavily pigmented tissue), a cyclodialysis spatula is introduced into this
space. Careful sweeping motion of the spatula separates the ciliary body from the sclera and
permits entrance into the anterior chamber through the ciliary cleft. Sweeping of the spatula
to either side now breaks the iris root attachments at the limbus. Spatulate anterior chamber
irrigator now replaces the cyclodialysis spatula. The anterior chamber is reformed with
balanced salt solution. The conjunctiva and tenon’s capsule are closed with a simple
continuous 6/0 gut suture. Closure of the lateral canthotomy has begun(Bistner et al., 1977).
Iridectomy for Iris Bombe
The posterior chamber is distended and drainage angle occluded by the forword
displacement of the iris. A lateral canthotomy is performed. A limbal based conjunctival flap
has been made. The anterior chamber has been entered at the limbus and iris tissue bulges out
through the incision. An iris hook fixes the iris base and a basal iridectomy is made with and
electroscalpel. The corneoscleral incision has been closed with simple interrupted 7/0 gut
sutures buried beneath the conjunctiva. The conjunctiva has been closed with a simple
continuous 6/0 gut suture. Closure of the lateral canthotomy has begun(Magrane, 1977).
CONCLUSION
Glaucoma remains a leading cause of blindness in veterinary patients. Because of the
nature of the disease, many pets are presented at a time when it is not possible to restore
vision to the first eye affected. Glaucoma is very difficult to treat in pets. Unlike humans
where medication resolves over 80% of the cases of glaucoma, surgery is almost always
required in veterinary patients. The goal of the Veterinary Ophthalmologist in treating a pet
A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories
International Research Journal of Natural and Applied Sciences (IRJNAS)
Website: www.aarf.asia. Email: editoraarf@gmail.com , editor@aarf.asia Page 200 remain pain free. Additionally, for want to maintain vision in the second eye as long as
possible.
REFERENCES
Abrams, K.L., Medical and surgical management of the glaucoma patient, Clinical
Techniques in Small Animal Practice, 16, 2001, 71–76.
Allgoewer, I., Glaucoma, Animal Eye Research, 25 (1), 2006,7-12.
Barnett, K.C., Diagnostic Atlas of Veterinary Ophthalmology (2nd Edn., Mosby Elsevier,
London, 2006, pp 89–96).
Bedford, P.G.C., A simple method of gonioscopy for the dog and cat. Journal of Small
Animal Practice, 26, 1985, 407–410.
Benson, M.T., and Nelson, M.E., Cyclocryotherapy: a review of cases over a 10-year period,
British Journal of Ophthalmology, 74, 1990, 103-105.
Bistner, S.I., Aguirre, G., and Batik, G., Atlas of veterinary ophthalmic surgery (WB
Saunders Co, Philadelphia, 1977, pp 223-243).
Crispin, S.M., Uveitis in the dog and cat. Journal of Small Animal Practice, 29, 1988, 429–
447.
Cullen, C.L., Allen, A.L., and Grahn, B.H., Anterior chamber to frontal sinus shunt for the
diversion of aqueous humor: A pilot study in four normal dogs. Veterinary
Ophthalmology, 1, 1998, 31-9.
Curtis, R. and Barnett, K.C., Primary lens luxation in the dog. Journal of Small Animal
Practice, 21, 1980, 657–668.
Ekesten, B., Bjerkas, E., Kongestengen, K. and Narfstrom, K., Primary glaucoma in the
Norwegian elkhound. Veterinary & Comparative Ophthalmology, 7, 1997, 14-18.
Fattahian, H., Molookpour, H., Mohyeddin, H., and Hoseinzadeh, A., Using Ahmed’s
Gonioimplant Valve to Surgical Treatment of Glaucoma in Two Dogs. Iranian Journal
of Veterinary Surgery, 3(2), 2008, 93-97.
Gelatt, K.N., Text book of Veterinary Ophthalmology (3rd Edn., Lea and Febiger Publishing,
Philadelphia, 1981, pp 390-432).
Gupta, S.P., Garg, K.C. and Bisaria, K.K., Different techniques of iridencleisis and their
value in glaucoma – a study of 60 cases. Indian Journal of Ophthalmology, 14, 1966,
A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories
International Research Journal of Natural and Applied Sciences (IRJNAS)
Website: www.aarf.asia. Email: editoraarf@gmail.com , editor@aarf.asia Page 201 Kennard, G., Glaucoma: 5 o’clock emergency (proceeding). CVC in kansas city proceedings.
2009, DVM360 magazine.
Lew, M., and Lew, S., Combined iridencleisis and posterior sclerectomy in surgical treatment
of glaucoma secondary to uveitis in a dog: a case report. Veterinarni Medicina, 54 (3),
2009, 142–148.
Lin, S., Endoscopic cyclophotocoagulation. British Journal of Ophthalmology, 86(12), 2002,
1434-1438.
Lovekin, L.G., Primary glaucoma in dogs. Journal of the American Veterinary Medical
Association, 145, 1964, 1081-1091.
Maggs, D.J., Miller, P.E., and Ofri, R., Slatter’s Fundamentals of Veterinary Ophthalmology,
(5th Edn., WB Saunders Co, Philadelphia, 2013, pp 247-271).
Magrane, W.G., Canine ophthalmology, (3rd Edn., Lea & Febiger publishing, Philadelphia,
1977, pp 197-228).
Martin, K.R., and Broadway, D.C., Cyclodiode laser therapy for painful, blind glaucomatous
eyes. British Journal of Ophthalmoogy, 85(4), 2001, 474-476.
Nasisse, M.P., Davidson, M.G. and English, R.V., Treatment of glaucoma by use of
transscleral neodymium:yttrium aluminium garnet laser cyclophotocoagulation in
dogs. Journal of the American Veterinary Medical Association, 197(3), 1990,
350-354.
Ofri, R. and Narfstrom, K., Light at the end of the tunnel? Advances in the understanding and
treatment of glaucoma and inherited retinal degeneration. Veterinary Journal, 174,
2007, 10–22.
Reinstein S.L., Rankin A.J., and Allbaugh, R., Canine glaucoma: medical and surgical
treatment options. Compendium counting education for veterinarians, 2009, 454-458.
Sapienza, J.S. and Van der woerdt, A., Combined transscleral diode laser
cyclophotocoagulation and ahmed gonioimplantation in dogs with primary glaucoma: