Download Animal model of closed angle glaucoma in albino mutant

Animal Model of Closed Angle Glaucoma
in Albino Mutant Quails
Koichi Takatsuji,* Yoshio 5ato,f Shuzo lizuka,t Hajime Nakatani,§ and Akira NakamuraH
The intraocular pressure of imperfect albino mutant quails with a sex-linked recessive gene was measured
by using a cannulating method, and morphological changes of the iridocorneal angle were observed with
a gonioprism. Albino mutant quails were characterized by an elevated intraocular pressure and lens
enlargement at 6 mo after hatching. Initially the iridocorneal angle opened and eventually closed. The
usefulness of the closed angle glaucoma as an animal model system for human diseases was discussed.
Invest Ophthalmol Vis Sci 27:396-400, 1986
Animal models have provided valuable information
for understanding human eye diseases. Spontaneous
buphthalmos or glaucoma model in animals has been
reported in rabbits and dogs.1"5 An imperfect albino
mutant quail with a sex-linked recessive gene exhibits
interesting ocular diseases, such as eye enlargement,
retinal ganglion cell degeneration, cupping of the optic
disc, and cataract.6"8 The histopathologicalfindingsin
the retina of albino mutant quails are similar to those
in animals with experimentally induced or spontaneous
glaucoma. Previously,7 we did not consider the albino
mutant quails as an avian glaucoma, because we had
not measured their intraocular pressure.
In this study, we measured intraocular pressure by
means of manometry and observed the morphological
changes of the iridocorneal angle in albino mutant quail
eyes at early, moderate, and advanced stages of avian
glaucoma to elucidate the primary defect responsible
for the development of the disease and its pathogenesis.
ing, under continuous 20-W incandescent bulbs for 4
wk. The animals were then exposed to a diurnal schedule, usually 16 hr of light per day. Animals were fed a
normal quail diet and water ad libitum.
The animals were anesthetized with sodium pentobarbital (2.5 mg/100 g i.p.), and their eyes were examined with a slit-lamp biomicroscope and Koeppe
type gonioprism modified for small animal eyes. To
measure intraocular pressure, the quails were anesthetized with sodium pentobarbital, and the head was immobilized by ear bars which were inserted into the external auditory meati. The eyes were cannulated with
27 G needles connected via short lengths of polyethylene tubing (outer diameter 1 mm) to Statham pressure transducer (Nihhon Koden; Tokyo, Japan). The
entire system was filled with heparin solution. Entry
through the cornea into the anterior chamber was made
from the temporal side of the eye, in order to minimize
irritation of the nictitating membrane. Care was taken
to prevent aqueous humor loss and not to strike the
iris. Continuous recording was done with an ink writing
oscillograph.
After the intraocular pressure was measured, the animals were killed by cervical dislocation. The one third
of the eyeball including the lens was carefully removed,
and fixed in 10% formalin solution. During this fixation, some lenses were removed from the anterior segment, and their dimensions were measured. Freshly
enucleated lenses of some quails were weighed. Animal
care and treatment in this investigation were in compliance with the ARVO Resolution on the Use of Animals in Research.
Materials and Methods
Imperfect albino mutant quails (Coturnix coturnix
japonica, gene symbol at) were used at 3 (n = 25), 6
(n = 25), and 12 (n = 15) mo of age, and normal wild
type quails at 3 (n = 15), 6 (n = 15) and 12 (n = 5)
mo of age. The quails become mature at 2 mo after
hatching. Animals were kept, from the time of hatchFrom the Departments of Anatomy,* Common Laboratory,! and
Ophthalmology,:}: Osaka University Medical School, Osaka, the Department of Ophthalmology,§ Osaka Welfare Pension Hospital,
Osaka, and Shizuoka Women's College,!! Hamamatsu.
This study was supported in part by Grant 59780056 for Scientific
Research from the Ministry of Education of Japan.
Submitted for publication: November 21, 1985.
Reprint requests: Koichi Takatsuji DMsc, Department of Anatomy
(2nd Div.), Osaka University Medical School, Nakanoshima 4, Kitaku, Osaka 530, Japan.
Results
General Morphology of Quail Eyes
The eye organization in the quails was similar to
that in other vertebrates. However, the sphincter pu-
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CLOSED ANGLE GLAUCOMA IN ALDINO QUAILS / Tokorsuji er ol.
pillae in avian eyes is composed of striated muscle
rather than smooth muscle.9 There were many pigment
granules in the pigment epithelium, choroid, ciliary
processes, ora serrata, and iris in normal quails. In al
mutant quails, there were few pigment granules in the
pigment epithelium and choroid, while some pigment
granules could be observed in the ciliary processes, ora
serrata and iris. Therefore, al mutant quails have a
ruby eye color instead of brown. The corneas in at
mutant quails were flatter than those in normal quails
at 3 mo of age (Figs. 1A-B). At 12 mo of age the corneas
in some al mutant quails protruded forward and were
milk white. The cornea of normal quails had not
changed at 12 mo.
Intraocular Pressure (IOP)
Figure 2 shows the IOP of normal and al mutant
quails determined by the cannulating method. The
mean IOP of the normal quails at 3 and 6 mo of age
was 16.3 mm ± 1.4 mm Hg and 17.3 mm ± 1.7 mm
Hg. The mean IOP of al mutant quails at 3 mo of age
was 19.6 mm ± 1.6 mm Hg. At this age, there was no
significant difference between the mean IOP of normal
and al mutant quails. However, the mean IOP (25.2
mm ± 2 . 2 mm Hg) of al mutant quails at 6 mo of age
was significantly higher than the mean IOP of normal
quails. Some al mutant quails showed markedly elevated IOP (over 35 mm Hg) at 12 mo.
Lens Dimensions
The mean lens dimensions of normal quails at 3 or
12 mo of age were 4.2 X 4.1 X 2.7 mm. No anomalous
appearances were observed in normal quail lenses at 3
or 12 mo after hatching. The mean lens dimensions
(4.4 X 4.3 X 3.1 mm) of al mutant quails at 3 mo of
age were slightly larger than those of normal quails. At
6 mo of age, many lenses had become opaque, and the
mean lens dimensions (4.7 X 4.5 X 3.5 mm) of the al
mutant quails were larger than those of the normal
quails (Fig. 3). The lens was particularly enlarged in
the antero-posterior direction. The mean lens dimensions of al mutant quails were 4.8 X 4.7 X 3.5 mm at
12 mo of age. The whole lens was opaque, and lens
atrophy was observed in severe cases at this age group.
The lens weight at 3 mo of age was 23.6 mg ± 1.6
mg in normal quails and 24.8 mg ± 2.2 mg in al mutant
quails. At 6 mo of age, the lens of the al mutant quails
(33.2 mg ± 3.5 mg) was heavier than that of the normal
quails (23.8 mg ± 1.4 mg).
Fig. 1. Dorsal views of normal (A) and al mutant (B) quail eyes
at 3 mo of age. The color difference of the posterior two thirds of
the eyeballs is due to the pigment granules that exist in the choroid
and pigment epithelium. Note that the eye of the at mutant quail
shows reduced corneal curvature. Bar, 10 mm.
angles in normal quails were open (Fig. 4A). At 3 mo
of age, when glaucoma was in the early stage, the iridocorneal angles in most al mutant quails opened (Fig.
4B). The corneal curvature in al mutant quails was flat
compared with that in normal quails (Figs. 1A and
IB). Although the iridocorneal angles in al mutant
quails at 3 mo of age were open, the anterior chambers
were shallow. At 6 mo of age, the iridocorneal angles
in 13 of the 20 eyes of the al mutant quails were closed
(Fig. 4C). At 6 mo of age, when glaucoma was in an
advanced stage, the whole iris was attached to the posterior cornea. This suggests anterior synechia. Under
this condition, the pupil was not reflexed by light. At
12 mo of age, the iridocorneal angles in most al mutant
quails were usually closed, and many congested vessels
mm.
H
NORMAL
30
ALBINO
20 -
i
10 -
Iridocorneal Angle
No differences were detected in the iridocorneal angles between the 3- and 6-mo-old normal quails. The
3M
6M
Fig. 2. IOP in normal and al mutant quails at 3 and 6 mo of age.
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INVESTIGATIVE OPHTHALMOLOGY 6 VISUAL SCIENCE / March 1986
Vol. 27
largement, shallowed anterior chamber, reduced corneal curvature, closed iridocorneal angles and elevated
IOP.13~16 Anterior synechia eventually develops in the
late stage oflight-induced avian glaucoma. Lauber and
McGinnis reported that eye enlargement does not de-
Fig. 3. Anterior views of normal (A) and al mutant (B) quail lenses
at 6 mo of age. Lenses removed from the anterior one third segment
of the eyeball were immersed in 0.9% NaCI solution for photography.
Iris was removed. The white color in the albino quail lens is due to
cataract. Note that the lens of the al mutant quail is larger than the
normal quail lens. Bar, 2 mm.
were present on the anterior surface of the iris. Corneal
edema and a fixed pupil were also observed.
Discussion
Lauber was the first to find sex-linked albinism in
the Japanese quail.10 He crossed the Fl offsprings with
each other, and found that most albino quails died
within 3 to 4 days after hatching and that the albino
gene itself was semi-lethal. However, avian species are
easily killed by inbreeding. Nakamura and Kaneko also
found a spontaneous sex-linked recessive albino mutation in a Japanese quail.6 The female albino quail
was mated with unrelated normal quails, and then Fl
males were mated with their mother and sisters. However, the mating was unsuccessful. Most of the albino
quail chicks died. Subsequently, they mated Fl males
with unrelated female normal quails and paid special
attention to the suitable temperature for broodings. In
that case, the viability and hatchability of the albino
quails have markedly increased.
Accurate measurement of IOP in the glaucomatous
animals is essential. We measured IOP by means of
manometry following cannulation. A noninvasive
method of IOP measurement would be valuable. However, common instruments for measurement of IOP
(Schiotz tonometer, Winters; Hamburg, West Germany, applanation tonometer of Goldmann, Haagstreit; Bern, Switzerland, or pneumatic applanation
tonometer) could not be used in the present study, because quail corneas were too small. IOP in avian species
has been reported by several investigators.11"14 The
mean IOP values for normal quails were similar to
those for domestic fowl reported by Sears and Seaman
and Himelfarb."' 12 Because the al mutant quails at 6
mo of age had showed significantly higher IOP, they
were considered to have avian glaucoma.
Chickens reared from hatching in continuous incandescent light have been reported to develop eye en-
Mg. 4. uomophotographs oi the indocorneal angle in the normal
quail (A) at 6 mo of age, al mutant quail at 3 mo of age (B) and al
mutant quail at 6 mo of age (C). Arrows in 4A and 4B indicate open
iridocorneal angle. Figure 4C shows closed iridocorneal angle. S, sclera.
1, iris.
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CLOSED ANGLE GLAUCOMA IN ALBINO QUAILS / Tokorsuji er ol.
velop in Japanese quails reared under continuous light,
but that corneal curvature is reduced and corneal diameter small in the quails.16 We used normal quails
which were kept from the time of hatching, under continuous 20-W incandescent bulbs for 4 wk. Therefore,
the normal quails may not serve as a baseline control.
However, neither eye enlargement nor degeneration of
retinal ganglion cells has been observed in normal
quails.7 In al mutant quails, we had found eye enlargement, retinal ganglion cell loss and cupping of the optic
disc. In the present study, we detected reduced corneal
curvature and elevated IOP in al mutant quails. If the
corneal curvature of al mutant quails was compared
with that of normal quails kept under truly diurnal
conditions, the differences in corneal curvature might
have been greater.
In the postnatal growing period, some animals have
a regulatory mechanism which directs the growth of
the eye toward emmetropia.17 In al mutant quails, a
low corneal refraction due to reduced corneal curvature
might give rise to elongation of the eye in order to
improve the visual image. However, eye dimensions
of al mutant quails at 3 mo of age were similar to those
of normal quails. The quails are mature at 2 mo after
hatching. The eye enlargement of al mutant quails was
observed during 6-12 mo after hatching.7 Therefore,
eye enlargement in al mutant quails is not due to the
elongation of the eye to improve the visual image. Albinism in humans is often associated with myopia. The
al mutant quails have weak eyes and are photophobic.
It appears that al mutant quail eyes are useful only for
near vision, on the basis of behavioral observation.
Gonioscopic examination of al mutant quail eyes
indicated an open iridocorneal angle at 3 mo of age,
an early stage of glaucoma. In moderate and advanced
glaucomatous stages at 6 mo of age, the iridocorneal
angles of al mutant quail eyes were closed due to anterior synechia. This suggests that al mutant quails are
closed angle type of glaucoma. Closed iridocorneal angle in al mutant quails may be associated with reduced
corneal curvature and lens enlargement. Smith et al
suggested that reduced corneal curvature and narrowed
iridocorneal angle were related to the angle-closure
glaucoma that later developed,13 but Frankelson et al
reported that iridectomies performed on newly hatched
chicks that were subsequently reared under continuous
light failed to alter the course of development of the
characteristic glaucoma.18 Therefore, Lauber et al concluded that increased inflow may be the primary lesion
in light induced avian glaucoma, but not impaired
aqueous outflow facility.14 The IOP of al mutant quails
at 3 mo of age was slightly higher than that of normal
quails at the same age, although eye enlargement could
not be detected in al mutant quails. Eye enlargement
399
could be observed in al mutant quails at 6 mo of age.7
In this age group, elevated IOP and lens enlargement
were discernible. Narrowed iridocorneal angle due to
reduced corneal curvature and lens enlargement may
cause an obstacle of drainage in the aqueous humor.
In human senile cataract, an intumescent cataract
pushes the iris forwards forcing the anterior chamber
to become shallow and block the iridocorneal angle.19
Although lens enlargement was not reported in lightinduced avian glaucoma, it may play an important role
in the pathogenesis of albino avian glaucoma. However,
studies on aqueous flow, iridectomy, and extraction of
lens must be performed in the future to elucidate the
pathogenesis of this albino avian glaucoma.
Spontaneous buphthalmos or glaucoma as an animal
model has been reported in rabbits and dogs. Recessive
buphthalmos in the rabbits was linked to a semilethal
trait accompanied by other congenital malformations.1
Spontaneous glaucoma has been investigated in three
breeds of dogs: American cocker spaniel, basset hound,
and the beagle.5'20'21 It appeared that beagle glaucoma
was a simple autosomal inheritance. It takes over 12
mo before the dogs suffer from glaucoma. The al mutant quails described here are an imperfect albino mutation with a sex-linked recessive gene. The al mutant
quails as a glaucoma model exhibit a predictable clinical course over a period of at least 3 to 6 mo after
hatching and show no congenital anomalies except for
the pigmentation. It is easy to maintain and to handle
al mutant quails in a laboratory. Although the primary
pathologic event is still obscure, albino avian glaucoma
in experimental animals presents a unique opportunity
in the study of the etiology and pathogenesis of the
disease. The ocular changes, such as lens enlargement,
lens opacity, or reduced corneal curvature, in al mutant
quails may be associated with the recessive albino gene
itself, or be a secondary effect caused by illumination
or other environmental factors.
Key words: avian glaucoma, animal model, albino quails,
closed iridocorneal angle, elevated intraocular pressure, lens
enlargement
Acknowledgments
We thank Professor Dr. Hideo Masai, who passed away
in February, 1985, for his valuable comments. We will never
forget his warm and gentle character. We wish to thank Dr.
Teh-Ching Chu (The Mount Sinai School of Medicine) for
critical reading of the manuscript.
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