Full text of DOI:10.1111/j.1751-0813.2002.tb11292.x

Clinical
Primary glaucoma in Burmese cats
Australian
VETERINARY
ECGM HAMPSON, RIE SMITH and ME BERNAYS
JOURNAL
Animal Eye Services, Kessels Road Veterinary Hospital, Macgregor, Queensland 4072.
C L I N I C A L S E C T I O N
Objective
To document the clinical signs and management of primary glaucoma
in Burmese cats.
EDITOR
MAUREEN REVINGTON
Design
A retrospective study of six affected Burmese cats, from 1996 to 2001.
ADVISORY COMMITTEE
Procedure Six Burmese cats diagnosed with primary glaucoma were managed
over periods varying from 3 months to 4.5 years. Clinical details were obtained from
practice records. Gonioscopic examination of the drainage or iridocorneal angle in
eyes of these affected cats was made.
ANAESTHESIA
LEN CULLEN
AVIAN MEDICINE AND SURGERY
GARRY CROSS
EQUINE MEDICINE AND SURGERY
Results
Six desexed female Burmese cats (ages 7.0 to 10.5 years) presented
JOHN BOLTON
with complaints of either unilateral (n = 4) or bilateral (n = 2) red eye, dilated pupil or
enlarged eye. In one of the affected cats, one eye had been enucleated prior to the
commencement of the study, thus a total of 11 eyes were examined. Clinically, all
affected eyes (n = 8) had injected episcleral blood vessels and elevated intraocular
pressure. Gonioscopy revealed the presence of nine narrow and two closed irido-
corneal angles. Medical therapy included topical 2% dorzolamide (n = 8), 0.5%
timolol maleate (n = 1), 0.005% latanoprost (n = 1) and 0.5-1.0% prednisolone
acetate (n = 8). Surgery was performed in six eyes using either diode laser (n = 5)
and/or cryothermy (n = 2) and one eye was eviscerated, with implantation of a pros-
thesis. With therapy, five affected eyes maintained vision and normal intraocular
pressure, one eye remained blind with normal intraocular pressure, one eye
remained blind with elevated intraocular pressure and one eye was eviscerated.
LABORATORY ANIMAL MEDICINE
MALCOLM FRANCE
OPHTHALMOLOGY
JEFF SMITH
PATHOLOGY
CLIVE HUXTABLE
PHARMACOLOGY / THERAPEUTICS
STEPHEN PAGE
PRODUCTION ANIMAL MEDICINE
JAKOB MALMO
RADIOLOGY
ROBERT NICOLL
REPRODUCTION
PHILIP THOMAS
SMALL ANIMAL MEDICINE
BRIAN FARROW
Conclusions
The Burmese cat may be predisposed to primary narrow-angle
DAVID WATSON
glaucoma. Early diagnosis and continuous antiglaucoma therapy can help control
intraocular pressure and maintain vision.
SMALL ANIMAL SURGERY
GEOFF ROBINS
Aust Vet J 2002;80:672-680
GERALDINE HUNT
WILDLIFE / EXOTIC ANIMALS
LARRY VOGELNEST
ICA
IOP
PLR
FP
Iridocorneal angle
Intraocular pressure
Pupillary light reflex
Prostanoid selective FP-receptor
EDITORIAL ASSISTANT AND
DESKTOP PUBLISHING
ANNA GALLO
laucoma is currently defined as an optic neuropathy caused by a number of
different conditions that can affect the eye. This group of diseases is charac-
terised by an elevated IOP and results in a final common pathway leading to
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G
optic nerve head and retinal degeneration, and visual field loss.1 Because elevated IOP
can be measured when glaucoma becomes clinically apparent, recognition of the clin-
ical signs associated with elevated IOP is important in early diagnosis. The clinical
signs are obvious in the dog, but in the cat they are subtle and insidious.2
Consequently, feline glaucoma is commonly not recognised until affected eyes have
advanced changes such as buphthalmia and blindness.
Glaucoma in the cat usually occurs secondary to inflammation (uveitis) and
neoplasia (melanoma), but in the absence of any primary ocular lesion, the infrequent
diagnosis of primary glaucoma can be made.3, 4 To date, primary glaucoma has been
reported in the Siamese,5-7 Persian and European Short Hair cats6 and has been classi-
fied on the appearance of the ICA as an open-angle glaucoma3, 5, 6 or a narrow-angle
glaucoma.8 Because few clinical cases have been reported,4, 6, 9 the best medical and
surgical management options for feline primary glaucoma are still unclear.
It is the purpose of this study to document the clinical signs, gonioscopic findings
and management of six Burmese cats in which primary narrow-angle glaucoma was
diagnosed.
Editor, AVJ Clinical Section
AVA House, 272 Brunswick Road,
Brunswick, Vic. 3056,
Case Reports
Case 1
Phone: (03) 9387 2982
Fax: (03) 9388 0112
A 9-year-old desexed female Burmese cat was referred in October 1998. The cat had
been vaccinated recently, at which time the referring veterinarian had noted an
Email: desktop@ava.com.au
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Aust Vet J Vol 80, No 11, November 2002

Clinical
Table 1. Details of six Burmese cats with primary glaucoma at initial presentation.
enlarged left eye. Ophthalmic
examination included indirect
a
Case
(no.)
Age
History
Ocular findings
Diagnosis
ophthalmoscopy
(Heine,
(years)
Germany Omega 150/180
with a 20D lens) to assess the
eyelids, conjunctiva, sclera,
PLR and fundus, and slit-
lamp biomicroscopy (Kowa
SL14, Japan) to assess the
cornea, anterior chamber, iris
and lens. On initial presenta-
tion, abnormalities were noted
in both eyes (Table 1). The left
eye was buphthalmic and had
a dilated pupil, poor PLR and
injected episcleral blood
vessels (Figures 1 and 2). The
optic disc was cupped, but
there were no signs of retinal
degeneration. The left eye also
1
9.0
OS: Enlarged eye
OS: Buph, poor PLR, SFT +ve
OU: IEV, ODC
Primary glaucoma OU
Primary glaucoma OD
IOP: (OD 27, OS 49)
2
3
9.0
OD: Red eye
OD: IEV
b
IOP: (OD 22 , OS 13)
10.5
OD: Poor vision
: Dilated pupil
OD: Poor PLR, IEV
OD: TH
Primary glaucoma OD
Early RD OD
c
OS: Enucleated eye
IOP: (OD 45, OS n/a)
4
5
6
8.5
7.5
7.0
OD: Red eye
OD: IEV
Primary glaucoma OD
Primary glaucoma OU
IOP: (OD 31, OS 17)
OU: Red eyes
: Discharge
OU: IEV
IOP: (OD 27, OS 23)
OS: Discharge
: Dilated pupil
OS: Buph, poor PLR, IEV
OS: ODC, TH, BVA
Primary glaucoma OS
Early RD OS
: Blind, enlarged eye
IOP: (OD 13, OS 55)
a
All cats were desexed females
Subsequent IOP >25 mm Hg
IEV = Injected episcleral vessels
SFT +ve = Positive swinging flashlight test
ODC = Optic disc cupping
RD = Retinal degeneration
TH = Tapetal hyperreflectivity
PLR = Pupillary light reflex
OD = Right eye
OS = Left eye
b
c
demonstrated
a
positive
Treatment for iris melanosis
Buph = Buphthalmos
swinging flashlight test, which
is pathognomonic for unilat-
eral retinal disease or unilat-
eral prechiasmal optic nerve
disease, or both.10 The right
OU = Both eyes
BVA = Blood vessel attenuation
eye had injected episcleral blood vessels and slight optic disc
cupping without signs of retinal degeneration. Vision was
assessed by menace response, and the ability to visualise a
moving cotton wool ball and to negotiate obstacles. Although
the owner had noted no change in vision, examination revealed
vision in the right eye and a blind left eye. Intraocular pressure
was measured by applanation tonometry using a Tonopen
(Mentor, USA). The IOP readings in both eyes were greater
than 25 mmHg, which was suggestive of a diagnosis of glau-
coma.11 As there was no evidence of inflammatory or neoplastic
lesions that could have contributed to the glaucoma, a clinical
diagnosis of primary glaucoma was made.
Gonioscopy was not initially performed in this cat, but was
performed 2 years and 4 months later for the purpose of this
study (Table 2). For this procedure, the cat was sedated with an
intravenous combination of diazepam and ketamine (1:1 at 1
mL/kg). The width of the ICA and the appearance of the pecti-
nate ligaments overlying the ciliary cleft were noted for 3600 in
each eye using an OG3MI three-mirror goniolens (Ocular
Instruments, USA) and a slit-lamp biomicroscope. Photographs
of the ICA were taken through the goniolens with a fundus
camera (Kowa Genesis, Japan) at maximum light setting. In
normal cats, the ICA and ciliary cleft consist of long, slender
and slightly branching pectinate ligaments that span across a
wide underlying pigmented trabecular meshwork (Figure 3 and
4). The pectinate ligaments are the same colour as the iris.2 The
ICA in both eyes in Case 1 were abnormal. The right eye had a
narrow ICA and the pectinate ligaments were fewer and shorter
(Figure 5). The left eye had a narrow to closed ICA with very
few and very short pectinate ligaments.
Figure 1. Affected eyes of a 9-year-old Burmese cat with primary
glaucoma (Case 1). The left eye shows buphthalmia and a dilated
pupil.
Both eyes were managed medically and surgically over 2 years
and 5 months during which 33 clinical examinations were made
(Figure 6). The aim of the medical and surgical management
was to maintain IOP below 25 mm Hg and preserve vision.
Consequently, re-examinations were conducted every 2 to 7
days until the IOP was below 25 mm Hg, and if maintained,
Figure 2. Injection of episcleral blood vessels over the dorsal sclera
of a 9-year-old Burmese cat with primary glaucoma (Case 1). This
clinical feature was present in all glaucomatous eyes.
Aust Vet J Vol 80, No 11, November 2002
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Clinical
Table 2. Details of clinical examination of six affected Burmese cats towards the end of the study period.
Case
Age
ICA status
Study period
Visual statusb
IOPb
Diagnosisb
a
(no)
(years)
c
1
11.0
13.0
OD: Narrow
OS: Narrow to closed
2Y 5M
4Y 5M
Poor OD
Blind OS
OD 17, OS 23
OD 23, OS 13
OU: Stable glaucoma, ODC
OU: Cataracts
2
OD: Closed
OS: Narrow to closed
Poor OD
Visual OS
OD: Stable glaucoma, ODC, RD
OU: Cataracts, iris atrophy &
pigmentation
3
4
5
13.5
10.5
7.5
OD: Narrow
OS: N/a
2Y 2M
2Y 2M
3M
Poor OD
N/a OS
OD 18, OS n/a
OD n/a, OS 21
OD 20, OS 15
OD 16, OS 41
OD: Stable glaucoma, RD
OS: Enucleated eye
OD: Narrowd
OS: Narrow
N/a OD
Visual OS
OD: Eye with intrascleral prosthesis
OS: Normal eye
OD: Narrow to open
OS: Narrow to open
Visual OD
Visual OS
OU: Stable glaucoma
c
6
7.0
OD: Narrow
OS: Closed
3M
Visual OD
Blind OS
OD: Normal eye
OS: Unstable glaucoma, ODC, RD
a
All cats were desexed females
ICA = Iridocorneal angle
M = Months
N/a = not applicable
ODC = Optic disc cupping
RD = Retinal degeneration
Y = Years
OD = Right eye
OS = Left eye
OU = Both eyes
b
c
Data from Cases 1-6 was collected at end of study period
These cats share the similar parentage
d
Gonioscopy prior evisceration revealed narrow ICA in both eyes
Control cats (numbered 7-12)
thereafter fortnightly, and then every 1 to 3 months. Both eyes
received 2% dorzolamide (Trusopt, Merck Sharp & Dohme), a
topical antiglaucoma drug, two to three times daily throughout
the study period. However when used alone during the first 2
days, dorzolamide alone failed to reduce IOP. On the third day,
transscleral diode laser cyclophotocoagulation (Iris Medical
Diovet Diode Laser, USA) was performed in both eyes to reduce
the production of aqueous fluid by selective ablation of the
ciliary body. 12-13 For this procedure, the cat was sedated with
acepromazine and atropine, and anaesthesia was induced with
thiopentone and maintained with halothane in oxygen. Topical
0.05% prednisolone acetate (Sterofrin, Alcon) was used as post-
operative anti-inflammatory therapy. For 6 weeks after the first
surgery, IOP was controlled in both eyes. During the next 7
months, IOP increased whenever dorzolamide was applied
twice daily, but decreased when applied three times daily.
However by the tenth month, IOP had slowly increased again
and diode laser surgery was repeated in both eyes. An intra-
venous injection of 20 ng carprofen (Rimadyl, Pfizer) was used
as post-operative anti-inflammatory therapy. Subsequent to
both episodes of surgery, a superficial corneal ulcer developed in
the blind left eye. Once diagnosed, topical prednisolone was
withdrawn and eye drops containing fusidic acid (Conoptal,
Leo Pharmaceutical Products) were applied until the ulcer
healed. A short course of oral prednisolone (2.5 mg) was also
administered. During the last 17 months of the study, the IOP
was controlled and medical management consisted of 2%
dorzolamide applied to both eyes three times daily.
Case 2
A 9-year-old desexed female Burmese cat was referred in
September 1996. The cat had been vaccinated 1 week previ-
ously, at which time the referring veterinarian had noted a red
right eye and commenced antiglaucoma therapy with topical
2% pilocarpine (Pilopt 2%, Sigma Pharmaceuticals) three times
daily and oral acetazolamide (Diamox, Lederle) one-sixth 250
mg tablet twice daily. Ophthalmic examination revealed
injected episcleral blood vessels in the right eye and a normal
left eye (Table 1). The IOP readings in both eyes were less than
25 mm Hg and the difference in IOP between the two eyes was
less than 10 mm Hg. Although these readings were not sugges-
tive of glaucoma,11 intraocular hypertension in the right eye was
deemed to have responded to the concurrent antiglaucoma
therapy. One week after the withdrawal of medication, the IOP
in the right eye increased to 26 mm Hg.
Gonioscopy was performed in this cat at 4 years and 5months
after initial presentation (Table 2). The right eye had a closed
ICA with no or few pectinate ligaments and the left eye had a
narrow to closed ICA.
The right eye was managed medically and surgically for 4
years and 5 months during which 59 clinical examinations were
made. The right eye received topical 0.5% or 1.0% pred-
nisolone acetate (Prednerfrin forte, Allergan), as an anti-inflam-
matory drug, once to three times daily throughout the study
period. Initially, the right eye also received 0.5% timolol
(Timoptol, Merck Sharp & Dohme), a topical antiglaucoma
drug, twice daily. However, during the first month of medical
therapy, the IOP increased further and transscleral
cyclocryothermy using carbon dioxide (Keeler carbon dioxide
cryosurgery unit, USA, with a 2 mm cryoprobe) was performed
as a double freeze-thaw procedure on the right eye. Shortly
thereafter, timolol was replaced by 2% dorzolamide and the
IOP was controlled over the next 24 months. During the next
18 months, there were five IOP spikes (IOP >30 mm Hg)
which were managed consecutively by one treatment of diode
laser surgery, one treatment of transscleral cyclocryothermy
At the end of the treatment period, the response to antiglau-
coma therapy was assessed by visual status, IOP recordings and
ocular examination (Table 2). The right eye had poor vision and
a normal IOP. The left eye was blind, but also normotensive.
Both eyes had developed focal “spider web”-like anterior cortical
cataracts during the last 3 months of treatment. The optic discs
in both eyes were more deeply cupped, but the retinas still
showed no signs of retinal blood vessel attenuation or tapetal
hyperreflectivity.
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Clinical
Figure 4. Goniophotograph of normal ICA in right eye of a
control Burmese cat. The space between the peripheral margin
of the iris and the cornea characterises the ICA (arrowheads),
which in this eye is open. Note the long, thin and slightly
branching pectinate ligaments (arrows) that expand this space.
The pectinate ligaments are the same colour as the iris.
Figure 3. Diagrammatic representation of goniophotograph in
Figure 4, showing the normal ICA and ciliary cleft in a Burmese
cat. The pectinate ligaments (PL) are seen as strands bridging
from the peripheral iris to the sclera posterior to the limbus. CC
= Ciliary cleft, CSJ = Corneoscleral junction, I = Iris, ICA =
Iridocorneal angle, P = Pupil, S = Sclera.
using carbon dioxide and three treatments of transscleral
cyclocryothermy using nitrous oxide.12 Subsequent to the last
cryodestructive procedure, a superficial corneal ulcer developed
in the right eye. Two months later, another IOP spike was
recorded in the right eye and transscleral cyclocryothermy using
liquid nitrogen was performed.12,13 At this stage, 0.005%
latanoprost (Xalatan, Pharmacia & Upjohn) was commenced as
a once daily application to the right eye. During the last 7
months of treatment, the IOP was controlled and medical
management consisted of 2% dorzolamide applied to the right
eye three times daily and both 0.005% latanoprost and 1%
prednisolone applied to the right eye once daily.
At the end of the treatment period, the right eye had poor
vision, but was normotensive (Table 2). There were also signs of
optic disc cupping and retinal degeneration. The left eye had
normal vision and IOP. During the last 6 months of treatment,
a focal anterior cortical cataract was detected in the right eye
and fine linear lenticular opacities in the left eye. Although an
age-related darkening of iris colour was observed in both eyes,
the darkening was more marked in the right eye.
Figure 5. Goniophotograph of narrow ICA in the right eye of a 9-
year-old Burmese cat (Case 1). Note that the pectinate ligaments
(arrows) are fewer and shorter and the ICA is narrowed (arrow-
heads).
confirmed histologically. Ophthalmic examination revealed
injection of the episcleral blood vessels, a dilated pupil, a poor
PLR and tapetal hyperreflectivity in the right eye (Table 1). The
IOP was 45 mm Hg. As there was no clinical evidence of iris
melanosis or other neoplastic or inflammatory lesions, a diag-
nosis of primary glaucoma was made.
Case 3
Gonioscopy was performed in this cat 2 years and 2 months
after initial presentation (Table 2). The right eye had a narrow
ICA without any evidence of neoplastic lesions.
The right eye was managed medically and surgically for two
years and 3 months during which 13 clinical examinations were
A 10½-year-old desexed female Burmese cat was referred in
November 1998 with a history of vision loss and an abnormal
pupil in the right eye. Eight months previously, the left eye had
been enucleated as treatment for chronic glaucoma associated
with iris melanoma, a diagnosis which was subsequently
Aust Vet J Vol 80, No 11, November 2002
675

Clinical
Figure 6. Medical and surgical management of a 9-year-old Burmese cat with primary glaucoma (Case 1). Response of IOP for right eye
(red bars) and left eye (blue bars) to medical therapy (horizontal arrows and black asterisks) and surgical procedures (vertical arrows) with
respect to time (months) during the study. In this case, both eyes were treated. A clinical examination, including gonioscopy, was
performed one month before the end of the study as indicated by the red asterisk. Note: the time scale is not linear. C = intravenous
carprofen, CPC = diode laser cyclophotocoagulation, FA = eye drops containing fusidic acid, P = oral prednisolone.
& Dohme) one-half 50 mg tablet was administered daily before
made. Management consisted of diode laser surgery with topical
a second treatment of laser surgery. Thereafter, the IOP was
2% dorzolamide and 0.5% prednisolone acetate. Subsequently,
maintained for another 5 months until another IOP spike was
a superficial corneal ulcer developed in the right eye.
recorded. At this stage, a permanent solution was sought by the
Throughout the remaining study period, the IOP was
owners. The contents of the right eye were eviscerated and a sili-
controlled and all medication was withdrawn after 4 months.
cone prosthetic ball (Jardon Eye Prosthetics, USA) was
At the end of the treatment period, the right eye had poor
implanted intrasclerally.12, 14 A temporary tarsorrhaphy was
vision, but normal IOP (Table 2). The retinal degeneration in
maintained for 3 weeks to protect the eye during healing.
this eye had not progressed over the study period.
Postoperative medication included eye drops containing fusidic
acid applied twice daily for 10 days, oral amoxicillin and clavu-
lanic acid (Clavulox, Pfizer) at 10 mg/kg twice daily and keto-
profen (Ketofen, Merial) at 5 mg once daily for 7 days.
Examination of this eye prior to evisceration revealed a mid-
dilated and non-responsive pupil, an early posterior cortical
cataract, an anterior suture line cataract and tapetal hyperreflec-
tivity (Table 2). The vision was poor and the IOP elevated. The
left eye was normal.
Case 4
An 8½-year-old desexed female Burmese cat was referred in
December 1998 with a 6 week history of a red right eye. On
initial examination, the right eye had injected episcleral blood
vessels and an elevated IOP (Table 1). The left eye was normal.
Gonioscopy was performed in this cat 2 years and 2months
after initial presentation (Table 2). Both eyes had a narrow ICA.
The right eye was managed medically and surgically for 1year
and 3 months before it was eviscerated, and 16 clinical exami-
nations were made during this management period. The right
eye received 0.05% prednisolone acetate throughout the study
period. Medical therapy also commenced with 2% dorzo-
lamide, but after 3 weeks of therapy the IOP was still elevated
and diode laser surgery was performed. At this stage, dorzo-
lamide was withdrawn because the owners believed that the
drug irritated the eye. During the next 5 months the IOP was
controlled. At 9 months another IOP spike was recorded and a
short course of oral dichlorphenamide (Daranide, Merck Sharp
Case 5
A 7½-year-old desexed female Burmese cat was referred in
November 2000 with a 2 month history of red eyes. Initial
medication prescribed by the referring veterinarian consisted of
both 1% pilocarpine and drops containing fusidic acid applied
to both eyes twice daily. Oral dichlorphenamide was also
prescribed, but was immediately withdrawn because the drug
induced emesis. Ophthalmic examination revealed injected
episcleral blood vessels in both eyes, although only the right eye
was hypertensive (Table 1).
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Clinical
Gonioscopy was performed in this cat 3 weeks after initial
presentation (Table 2). Both eyes had a narrow to open ICA
with shorter pectinate ligaments (Figure 7).
Both eyes were managed medically for 3 months during
which seven clinical examinations were made. Both eyes
received 2% dorzolamide throughout the study period. Initially,
topical 1% prednisolone acetate was also used. However
following gonioscopy, a superficial corneal ulcer developed in
the left eye and prednisolone was withdrawn from both eyes.
Eye ointment containing framycetin sulphate (Soframycin,
Hoechst Marion Roussel) was applied until the ulcer healed.
During this period, the IOP was maintained between 25 and 30
mm Hg. One month later, an IOP spike was recorded and the
frequency of application of dorzolamide was increased from
three to four times daily. Within 1 week, the IOP was
controlled. Topical 0.005% latanoprost was tried twice, but
appeared to have no added benefit. During the last 2 months of
treatment, the IOP was controlled and medical management
consisted of 2% dorzolamide applied three times daily to both
eyes.
At the end of the treatment period, both eyes had vision and
normotensive. Despite the presence of slightly injected epis-
cleral blood vessels in both eyes, no other abnormalities were
detected.
Figure 7. Goniophotograph of narrow to open ICA in the right eye
of Case 5. The pectinate ligaments, (arrows) although numerous,
are shorter and the ICA (arrowheads) is narrowed.
Case 6
A 7-year-old desexed female Burmese cat was referred in
November 2000 with a 3-week history of an enlarged left eye
with ocular discharge, poor vision and an abnormal pupil. On
ophthalmic examination, the left eye was buphthalmic, had
injected episcleral blood vessels, a poor PLR and an IOP
reading greater than 50 mm Hg (Table 1). On funduscopy,
both eyes had small multifocal areas of hyperreflectivity
surrounded by zones of hyporeflectivity in the nasal tapetum.
These lesions were not associated with signs of previous anterior
segment inflammation and consequently were not believed to
be related to the pathogenesis of glaucoma in the left eye. The
right eye had a normal tapetum, normal optic disc and retinal
blood vessels (Figure 8), but the left eye had a hyperreflective
tapetum, cupped optic disc, and attenuated retinal blood vessels
(Figure 9).
Gonioscopy was performed in this cat 1 week after initial
presentation (Table 2). The right eye had a narrow ICA and the
left eye had a closed ICA (Figure 10).
The left eye was managed medically and surgically for 3
months during which six clinical examinations were made. The
left eye received 2% dorzolamide throughout this period.
Within 3 weeks of presentation, the left eye received two treat-
ments with cyclocryothermy: once using nitrous oxide and once
with liquid nitrogen. However, despite combined medical and
surgical therapy, IOP remained elevated. Topical 0.005%
latanoprost was also used on two occasions, but did not reduce
IOP.
Figure 8. Photograph of normal fundus of right eye of Case 6.
This eye was clinically normal. Note the optic disc (long arrow) is
surrounded by little myelin. (short arrow) Subsequent
gonioscopy of this eye revealed a narrow ICA.
At the end of the treatment, IOP in this blind, left eye was
still elevated (Table 2). While optic disc cupping and retinal
degeneration were features in the left eye, the right eye remained
normal.
coma in the Burmese cat, and provides details of clinical find-
ings and medical and surgical management of primary glau-
coma in these cats. Such detail in cats with primary glaucoma
has not been reported in earlier clinical studies of feline glau-
coma.4, 6, 9
Primary glaucoma occurs in the absence of an underlying
primary ocular lesion.3, 4 Although no lesions were detected
clinically in this study, verification by histologic examination of
the affected eyes was not possible, and it is hoped that these
Discussion
Although feline primary glaucoma has been reported previ-
ously in the Siamese, Persian and European Short Hair breeds,5-
this study reports for the first time primary narrow-angle glau-
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Aust Vet J Vol 80, No 11, November 2002
677

Clinical
required to demonstrate if the Burmese cat is genetically predis-
posed to primary glaucoma.
Primary glaucoma is usually classified by the appearance of
the ICA and ciliary cleft. The ICA is an anatomical feature that
can be examined by gonioscopy and histology. Because of its
large size in the cat, the ICA can also be viewed directly. Grossly,
as illustrated in Figure 3, the ICA spans the internal region of
the eye between the peripheral cornea/sclera and the peripheral
iris/ciliary body musculature.16 Microscopically, the ICA
consists of a meshwork of connective tissue beams or trabeculae,
that are lined by phagocytic-like trabecular cells. As a functional
unit, the ICA permits the drainage and filtering of aqueous
fluid from the anterior chamber of the eye.
Gonioscopy in the present study revealed narrow ICA in both
glaucomatous and non-glaucomatous eyes in all affected cats,
with the exception of two eyes in which the ICA may have
changed from the narrow to a closed state during the progres-
sion of glaucoma. Interestingly, a narrow ICA was also found in
the non-glaucomatous eyes of two control Burmese cats. One of
these control cats was only 4-years-old, and may be at risk of
developing primary glaucoma when older. Although IOP does
not vary significantly with age in normal cats,17 our study
suggests that older cats with a narrow ICA may be at risk for
developing primary glaucoma. It is possible that the age-related
microscopic changes documented in the canine ICA16 also
occur in the older cat, thereby making them more susceptible to
glaucoma. Nevertheless, not all affected cats in this study devel-
oped bilateral glaucoma, in contrast to canine primary glau-
coma which appears to be a bilateral disease.13 The benefits of
prophylactic therapy in delaying or preventing the onset of
glaucoma in the second eye of dogs with primary glaucoma18
are unlikely to be found in cases of feline primary glaucoma.
In humans, visual field testing and assessment of optic nerve
cupping and IOP are used to make a diagnosis of primary
chronic glaucoma. In cats, the diagnosis is more difficult to
establish due to the subtlety of clinical signs2. Furthermore,
visual field testing is not possible clinically and optic disc
cupping is not usually observed in the cat because the optic disc
lacks the extensive myelination seen in dogs.2 Consequently, the
diagnosis of glaucoma in this study was made on history,
ophthalmic signs and applanation tonometry.
Figure 9. Fundus photograph of left eye of affected Burmese Cat 6
.
This eye was clinically a blind, end-stage globe with an elevated
IOP. Note the cupped optic disc characterised by an enlarged
pale optic nerve head with a surrounding halo of pigmentation
(long arrow). The blood vessels originate deep within this
depressed optic disc. There is also retinal degeneration charac-
terised by attenuated retinal blood vessels in the peripheral
retina (arrowhead) and hyperreflectivity of the tapetal region of
the retina (short arrow). Subsequent gonioscopy of this eye
revealed a closed ICA (Figure 10).
Clinical signs of primary glaucoma in these Burmese cats
included: injected episcleral vessels due to venous congestion
from a hypertensive globe, a mid-dilated and poorly light-
responsive pupil due to direct pressure-induced changes to the
iris sphincter muscle itself and its neural supply, and buph-
thalmia due to stretching of the scleral coat by elevated IOP.19
This latter finding is often not noticed in cats due to the large
orbits which house the globes.2,11 One feature of glaucoma
commonly seen in canine primary glaucoma, but not seen in
this study, was corneal oedema. It would appear that the corneal
endothelial pump that controls water movement from the
corneal stroma into the anterior chamber is less susceptible to
damage with increased IOP in the cat compared with the dog.2, 11
Fundic changes associated with glaucoma in cats are difficult
to appreciate, possibly because the feline retina is less susceptible
to the effects of increased IOP.11 However in this study, retinal
degeneration was a feature characterised by tapetal hyperreflec-
tivity in four eyes (including the eviscerated eye in Case 4) and
by the attenuation of retinal blood vessels in one eye. In addi-
tion, optic disc cupping was evident in three eyes with IOP
greater than 40 mm Hg. Despite these changes, most of the
Figure 10. Gonioscopy of closed ICA in the left eye of Case 6.
Note the absence of pectinate ligaments. The iris base abuts the
corneoscleral junction (arrow).
globes will become available for histologic studies in the future.
Compared with the dog, primary glaucoma is rare in the cat.
However, since there is a genetic predisposition underlying most
primary glaucomas in animals, 15 an increase in the incidence of
feline primary glaucoma is likely to occur with selective
breeding. Although it is known that some of the cats in this
study shared common parentage, further studies would be
678
Aust Vet J Vol 80, No 11, November 2002

Clinical
ciliary muscle.33 In the current study, latanoprost did not lower
IOP. The drug was discontinued in three glaucomatous eyes,
but continued in conjunction with topical dorzolamide and
prednisolone in one glaucomatous eye (Case 2). The develop-
ment of iris pigmentation in this case suggested an age-related
phenomenon, however, the markedly darker iris in the treated
eye may have been the result of a drug-induced pigmentation,
which has been reported to occur in humans.34
affected eyes maintained vision for 2 to 4 years when appropri-
ately managed. Evidence of poorer vision and “tunnel-like
vision”, as described by owners, only became apparent in some
cats during the last 6 months of the study. Thus, primary glau-
coma in these cats was an insidious, chronic, progressive optic
neuropathy in which visual field damage was delayed. A similar
presentation has been reported for canine primary glaucoma in
the Norwegian Elkhound and Chow Chow breeds, in which
vision is maintained despite elevated IOP, buphthalmos and
obvious extensive optic nerve head degeneration.13
Optic nerve cupping indicates a weakening of the scleral
lamina cribosa, a porous structure through which optic nerve
axons pass at the optic nerve head region. Increased IOP pushes
this area posteriorly, thereby causing mechanical compression of
axons and microcirculatory abnormalities.13,20 The ganglion
cells and inner retinal neurons, especially in the peripheral
retina, are particularly sensitive to elevated IOP and a cascade of
tissue and vascular events leads to their death.13, 20 The under-
lying mechanisms for the retinal and optic disc changes are due
only in part to increased IOP; other factors include the release
of glutamate and other neuroexcitatory chemicals.21 Despite
current research into the role of anti-inflammatory and cryopro-
tective agents in reversing or preventing these mechanisms,
there are currently no controlled clinical studies to support the
use of these agents.21
All cats in this study received topical prednisolone either as
0.5% or 1.0% solution. This drug is frequently used in cases of
secondary glaucoma to reduce intraocular inflammation. In this
study, it was used to reduce the inflammatory changes associ-
ated with glaucoma. It is thought by one author (RS) that a low
grade inflammation is present in all glaucomas. Longterm
control of inflammation may prevent or delay repeat pressure
spikes and help maintain vision, however, the use of longterm
topical steroids has also been associated with elevated IOP in
35
normal cats. The development of cataracts may have also
been caused by the longterm use of topical steroids35 or by the
well-known side effects of diode laser therapy.12
Surgery was frequently required in this study to regain
normotension in eyes in which IOP was greater than 30 mm
Hg. However, comparison of the efficacy in lowering IOP
between the different cyclocryothermy techniques was not
possible in this study. Cyclocryothermy with liquid nitrogen has
been reported to give the best results due to its rapid freeze and
slow thaw of tissues, which is advantageous in cryodestruc-
tion.36 Diode laser surgery in the present study produced fewer
traumatic side effects, although corneal ulceration was a
problem, especially if topical prednisolone was used concur-
rently. Histologic studies have revealed that transscleral diode
laser cyclophotocoagulation in the normal canine eye produces
focal coagulative ciliary body necrosis.37 However, the success of
diode laser surgery depends on the amount of melanin in the
tissue and cats with a lightly pigmented iris may not absorb
sufficient laser energy for adequate cyclodestruction.12
In conclusion, the findings in this study support several
recommendations for the diagnosis and management of feline
primary narrow-angle glaucoma. Firstly, injected episcleral
blood vessels should be recognised as an early marker for glau-
coma, which then can be confirmed with tonometry. Secondly,
medical treatment should be commenced early with topical 2%
dorzolamide at three times daily and if the IOP is not respon-
sive to this drug alone, the addition of cyclodestructive surgery
is required. Finally, good client communication and compliance
with regular monitoring is manditory in the management of
these patients, as this condition is progressive and, while it can
be controlled, it cannot be cured.
Earlier clinical studies of feline glaucoma report a poor
6, 9
response to medical or surgical therapy,
possibly because of
the late presentation of these cases and the use of less efficacious
drugs. A recent clinical study reports greater success in main-
taining vision and controlling IOP with the use of topical
ophthalmic medications such as dorzolamide and latanoprost,
when used alone or with other antiglaucoma medications.4 In
the present study, antiglaucoma drugs were selected for their
efficacy in lowering IOP and for being non-irritant in cats.
Thus topical pilocarpine, an effective drug for lowering IOP in
normotensive cats,22 was not used because it was considered too
irritant. Initially, timolol maleate, a non-selective β-adrenergic
blocker that lowers aqueous humour production,23 was selected.
The use of timolol in lowering IOP in normal cats has been
previously described,24 but did not appear efficacious in our
study. Dorzolamide, a topical carbonic anhydrase inhibitor
which in humans decreases the production of aqueous produc-
tion without systemic side effects,25,26 has also been shown to
lower IOP in normal and glaucomatous dogs when applied
three times daily.27,28 Whereas dorzolamide was used in all
affected cats in this study, it is not possible to comment on the
efficacy of this drug alone, because surgical cyclodestructive
procedures were also required to control IOP. In the present
study, one cat could not tolerate dorzolamide, and, possibly as a
consequence of its withdrawal, IOP in this cat was not well
controlled. Similar side-effects of dorzolamide in cats have been
described elsewhere.4
Acknowledgments
Financial support was provided by the Brisbane Veterinary
Practitioners Group and VPS-IDEXX. We acknowledge the
following veterinarians for the referral of cases: Drs C Caesar, F
Galloway, M Gunew, V Menrath, M Ryan, S Steiner-Bakker
and C Stewart. Special thanks are given to the cats and their
owners who have made this study possible.
Latanoprost, a recently introduced prostaglandin agonist, was
also used topically on four glaucomatous eyes in the present
study. This drug increases the outflow of aqueous fluid through
the uveoscleral pathway, an alternative to the usual drainage site,
in humans,29 monkeys and rabbits.30 Although latanoprost is
widely and successfully used in canine primary glaucoma, its
clinical efficacy in cats is controversial,4,31 especially since only
3% of aqueous drainage in the cat occurs through the
uveoscleral pathway.32 Futhermore, the FP receptor, the site by
which IOP is lowered by latanoprost, is absent in the feline
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(Accepted for publication 9 September 2002)
Challenges of pain assessment in domestic animals
n response to a perceived lack of study in the area of pain management in veterinary medicine the authors attempt to provide an
overview of the current concept of pain and evaluate the current methodologies available for assessment of pain in domestic animals.
As pain sensation and assessment are subjective, the difficulties of human recognition and evaluation in animals are formidable.
Whereas tissue damage in sentient creatures is widely accepted as resulting in pain, the mere sighting of a predator may result in
distress, suffering and stress, terms often associated with pain in the literature.
I
The types of pain are listed as superficial, deep, acute and chronic and all are examined. It is assumed that when in pain animals are
emotionally affected and express this by behavioural and hormonal responses; these responses are obvious with acute pain but often
not perceptible in chronic pain.
The process of nociception and subsequent recognition of pain is associated with the pre-fontal cortex in humans; those who have
undergone pre-frontal lobotomy still physically re-act to noxious stimuli but no longer consider them unpleasant. As domestic animals
have relatively smaller pre-tonal areas it has been postulated that their capacity for pain perception may be reduced.
A variety of responses to pain are listed: appearance, gait, posture, appetite, handling response. Changes in behavioural patterns
are the most striking; knowledge of normal species patterns is essential.
The measurement and limitations of pain assessment in animals is the major portion of the paper and again stresses the need for
appreciation of species-specific behaviour. The authors urge more research to identify the species-specific indicators of pain in both
individual animals in the clinical setting and in herds under farm conditions.
Anil SS, Anil L, Deen J. J Am Vet Med Assoc 2002;220:313-319.
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