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A Darkness Induced Eye Abnormality in the Domestic Chicken
A Darkness Induced Eye Abnormality in the Domestic Chicken R. L. JENKINS, W. D. IVEY, G. R. McDANIEL 1 , and R. A. ALBERT 2 Department of Zoology, Department of Poultry Science1, and Small Animal Veterinary Clinic2, Agricultural Experiment Station, Auburn University, Auburn, Alabama 36830 (Received for publication June 26, 1978) ABSTRACT Two-hundred broiler-type chickens were reared under either normal lighting or darkness for 16 weeks. Each week, birds were subjected to applanation tonometry for measurement of intraocular pressures (IOP). The birds were then weighed, eyes enucleated, and dimensions measured. All eyes were prepared for histological examination. Chickens reared in darkness for 4 to 6 weeks displayed an abnormal eye enlargement, accompanied by an increase in IOP in comparison to chickens reared under conventional management. From the 6th to the 16th week, the eyes of dark-reared chickens continued to enlarge while IOP decreased. The sclera, choroid, retina, and retinal layers of dark-reared chicks were not as thick as controls throughout the 16 weeks. Two principle retinal pathologies were induced by darkness. One appeared as darkened areas of the peripheral retina. In histological sections the darkened retinal areas had a thin choroid and thin retinal layers. The second retinal abnormality was one or more white, nonpigmented bands directed perpendicular to the pecten. Histologically, the depigmented bands were areas in which the vessels of the choroid, the pigmented epithelium, and the outer retinal layers were absent. The corneas of dark-reared chicks exhibited a reduction in their curvature and thickness compared to control corneas. INTRODUCTION
Each r o o m was adequately ventilated and air e x h a u s t e d by light-trapped ventilators. Darkcoil electric b r o o d e r s supplied h e a t a n d c o m mercial broiler ration and water were supplied ad libitum. Intraocular pressure (IOP) was d e t e r m i n e d weekly or biweekly on chickens of b o t h treatm e n t s by a p p l a n a t i o n t o n o m e t r y , using a Mackay Marg t o n o m e t e r . All pressures were measured b e t w e e n 1 3 0 0 and 1 4 0 0 hr t o prevent possible variation from diurnal IOP fluctuations. After pressures were recorded, t h e birds were weighed and t h e eyes were e n u c l e a t e d u n d e r general anesthesia. Extraorbital fatty tissues were t r i m m e d and t h e geometrical axis and trans d i a m e t e r were measured with calipers. Eyes were fixed in Zenker's fluid a n d emb e d d e d in Paraplast. Sections were c u t at 9 |U thickness and stained with either H e m a t o x y l i n a n d Eosin or G o m o r i Trichrome ( H u m a s o n , 1972). A calibrated ocular m i c r o m e t e r was used t o measure t h e cornea and t h e posterior, p o s t e r o peripheral, and peripheral thicknesses of t h e retina, choroid, and sclera. T h e retinal layers measured were (preceding from t h e inside t o t h e o u t ) t h e nerve fiber layer ( N F L ) , ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer, (INL), o u t e r plexiform layer (OPL), o u t e r nuclear layer ( O N L ) , r o d a n d cone layer (RC), and t h e p i g m e n t e p i t h e -
Eye enlargements have been induced in t h e growing domestic chicken b y the use of cont i n u o u s light (Jensen a n d Matson, 1 9 5 7 ; Lauber et al., 1 9 6 1 ) , b y diurnal low-intensity light (Harrison and McGinnis, 1 9 6 7 ) , and b y t o t a l darkness (Moore and McDaniel, 1 9 6 9 ; Chiu et al, 1975). T h e b u p h t h a l m i a s arising u n d e r t h e three lighting c o n d i t i o n s share c o m m o n eye enlargements and bird behaviors. T h e eye enlargem e n t p r o d u c e d b y c o n t i n u o u s light has been distinguished from t h e low-intensity light and darkness-induced b u p h t h a l m i a s by significant increases in t h e corneal thickness of t h e former (Chiu et al., 1 9 7 5 ) . Investigations on t h e various pathological features of t h e darknessinduced b u p h t h a l m i a in the domestic chicken have been u n d e r t a k e n by researchers at A u b u r n University. MATERIALS AND METHODS T w o - h u n d r e d male and female broiler-strain birds were conventionally reared t o one week of age, at which t i m e t h e y were r a n d o m l y divided i n t o t w o lighting regimes and maintained to 16 weeks. One t r e a t m e n t consisted of 12 hr light and 12 hr darkness ( 1 2 L : 1 2 D ) a n d t h e other consisted of t o t a l darkness ( O L : 2 4 D ) . All birds were reared in windowless r o o m s (1.82 m X 2 . 4 4 m ) , p a r t i t i o n e d by concrete block walls. 1979 Poultry Sci 58:55-59
55
56
JENKINS ET AL.
lium (PE). The total and cartilagenous thicknesses of the sclera were measured separately. Treatments were analzyed by an F-test analysis of variance in which sex was blocked. Statistical significance has been indicated at a .05 level of probability unless otherwise indicated.
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RESULTS Chickens reared in darkness (OL:24D) for 16 weeks were more lethargic and appeared to socialize less than 12L:12D chickens. The social interaction of 12L:12D birds was demonstrated by their common aggregations while OL:24D birds were often dispersed throughout their rooms. Despite their lethargy, the body weights of OL:24D chickens showed no significant differences from that of 12L:12D birds. The enucleated eyes from OL:24D birds were larger on the geometrical axis and trans diameter than the eyes of 12L:12D birds. The mean axial depth of the eyes of OL:24D birds were significantly greater (P«.01) than controls after 5 weeks of age. The mean trans diameter of the eyes of OL:24D chickens were significantly greater than controls throughout the study (Fig. 1). Intraocular pressures (IOP) as measured by applanation tonometry were significantly greater in OL:24D chicks than 12L:12D chicks after 3, 5, and 6 weeks. Beyond the 6th week OL:24D pressures gradually decreased, becoming significantly less than control values after 12 weeks of age. Pressures decreased further from week 12 to week 16 (Fig. 2). Measurements of the thickness of the ocular tunics were taken posteriorly, postero-peripherally, and peripherally from sectioned eyes. The mean thickness of the total sclera of OL:24D eyes were less than 12L:12D eyes, the difference being most pronounced postero-peripherally. However, the mean thickness of the scleral cartilage was greater than controls after exposure to the lightless environment (Table 1). The thinning of the total sclera and thickening of the scleral cartilage reflects a pronounced reduction in the fibrous layer of the sclera. The choroid of OL:24D birds were generally thinner than those of controls with the largest differences occurring peripherally and posteroperipherally (Table 1). As the choroidal thickness decreased during dark treatmeant the vessels became flatter and fewer in number. The small vessels became less distinct and were often absent, leaving a poorly defined vascular
*/
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! • 1.6* it
T\
1.5** O /
1.41.3 1.2-
5
7
9
11
13
15
Age (weeks)
FIG. 1. Mean trans diameter (upper) and geometric axial length (lower) for OL:24D (A) and 12L:12D (0) reared chickens. *:P<.05 and **:P<.01.
plexus. The total retinal thickness progressively decreased throughout the globe the longer chickens were exposed to darkness. The greatest reduction of the retinal thickness of OL:24D eyes occurred peripherally. The posterior retina of OL:24D chickens was least affected while the postero-pheripheral retina was intermediately
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O
6 3 0
-3 -6
-9] -12 3
5
7 9 11 13 15 Age (weeks) FIG. 2. Percent deviation of mean IOP for OL:12D (A) and 12L:12D (0) reared chicks. *:P«.05 and **:P«.01.
DARKNESS INDUCED EYE ABNORMALITY IN DOMESTIC CHICKEN
57
TABLE 1. Mean and SEM of scleral, choroid, and retinal thickness (11) of 12L-.12D and OL-.24D reared chickens Sclera Site of measurement Posterior
Age (wk)
Retiila
OL:24D
12L:12D
OL:24D
12L:12D OL:24D
12L:12D
OL:24D
6
191.5 ±21.5
187.3 ±5.8
84.0 ±14.4
109.7 ±5.9
140.0 ±14.8
156.0 ±25.6
237.5 ±7.1
217.3 ±13.6
8
256.6 ±13.6
249.5 ±7.4
99.8 ±2.6
< 143.7
125.0 ±7.1
> 75.7
207.2 ±6.2
203.9 ±7.1
269.0 ±21.0
250.2 ±16.7
123.2 ±10.0
< 151.3
±4.9
140.7 ±14.6
> 65.5
±4.2
212.6 ±1.7
> 190.5
12
298.5 ±2.5
a > 263.0 ±7.1
107.5 ±3.2
157.0 ±1.4
141.0 ±18.8
>
41.3 ±4.4
206.0 ±1.7
171.5 ±6.7
6
164.5 ±25.0
141.3 ±3.3
96.0 ±2.5
< 115.3 ±5.2
165.0 ±6.0
> 89.6 ±8.1
197.5 ±22.2
147.9 ±5.0
253.2 ±19.6
> 188.0 ±9.6
122.8 ±6.7
141.0 ±9.4
133.7 ±17.5
> 76.7
±11.3
180.8 ±7.8
> 150.7
10
257.3 ±20.3
>
209.7 ±8.2
133.3 ±13.6
144.2 ±2.1
96.2 ±12.5
13.0 ±.8
181.5 ±10.25
>
12
313.5 ±15.9
> 240.0 ±14.1
130.0 ±10.6
< 163.5
±2.7
40.5 ±8.0
> 21.5
±.3
173.0 ±6.8
> 106.0
6
203.5 ±7.4
186.3 ±7.5
150.5 ± .3
> 137.7 ±3.7
79.5 ±3.8
> 50.3 ±4.0
128.5 ±23.7
> 66.7
8
183.6 ±1.8
180.2 ±4.0
156.0 ±1.0
170.0 ±1.3
35.8 ±2.9
>
16.7 ±3.4
101.8 ±5.0
> 78.2
10
194.7 ±17.4
180.7 ±8.9
159.3 ±7.8
165.0 ±9.4
39.3 ±5.4
>
7.2 ±.9
103.7 ±6.9
> 65.0
12
217.0 ±7.2
208.5 ±5.3
175.0 ±2.1
177.0 ±7.7
30.5 ±3.5
>
11.5 ±5.3
100.0 ±.1
> 65.1
8
Peripheral
Choroid
Cartilage
12L:12D
10
Postero-peripheral
Total
±5.3
<
<
±8.8
>
±1.2
>
±6.4
144.5 ±5.3 ±9.3
±8.4
±7.6 ±4.1 +8.0
> and < indicating significance (P<.05).
affected (Table 1). While all of the retinal layers were affected by the darkness the PE, RC, NFL, and INL of the retina were most drastically affected. The GCL showed the least reduction in thickness after exposure to darkness. The corneal thickness of OL:24D eyes increased between weeks 4 and 5 as did the corneas of 12L:12D eyes. After the fifth week the corneas of OL:24D eyes decreased in thickness and remained consistently thinner than control corneas (Fig. 3). Two principle retinal pathologies were induced by darkness. One appeared as darkened areas of the peripheral retina which was first seen in the 7 week-old OL:24D birds and was later seen to spread to the postero-peripheral retina. Histologically, the darkened retinal areas were seen to arise from a thinning of the retina
with the PE remaining unchanged. The second retinal abnormality which appeared only among OL:24D birds was one or more white bands directed perpendicular to the pecten. Histologically, these bands appeared as localized areas in which the vessels of the choroid, Bruch's Membrane, PE, RC, ONL, and OPL were absent. Non-collagenous fibers extended from the deformed choroid and infiltrated the remaining inner retinal layers. Large, multipolar cells which apparently were edematous Miiller cells appeared at the level of the abolished PE and in the existing IPL and GCL. These cells acquired a bluish tint after Gomori Trichrome staining. Their nuclei showed no affinity for hematoxylin. The retina immediately adjacent to the depigmented bands maintained its normal layering but was detached from the PE. The corneal curvature of OL:24D chickens
58
JENKINS ET AL. .30
.25 •
I .20
.15 • 4
6
8
10
12
Age (weeks) FIG. 3. Mean corneal thickness of OL:24D (A) and 12L:12D (0) reared chickens. ':P<.05. appeared to be reduced. This was evident after 10 and 12 weeks from the bisected hemispheres. By weeks 10 and 12 the irides of OL: 24D birds exhibited occasional lymphoid aggregations and reduced musculature. DISCUSSION Lethargic behavior appears to be a common feature among chickens reared in photoperiodic extremes. The listlessness seen in the OL:24D birds here has also been cited among 24L:OD birds (Schutz et al, 1960). Harrison et al. (1968) detected a hypothyroidism and reduced oxygen consumption among birds reared in diurnal dim light. The possibility of a systemic effect involved in 24L:OD buphthalmia has been discussed by Chiu et al. (1975). It seems likely that the lethargy which is produced by unnatural lighting may arise from a generalized metabolic stress. The buphthalmias induced by 24L:OD, OL: 24D, and diurnal dim light exhibit several common features. The onset of the three buphthalmias is chronologically similar. The 24L:OD buphthalmia occurs after 3 weeks of age (Lauber et al, 1970) while the OL:24D buphthalmia occurs after 4 weeks of treatment. The eye enlargement under dim light is delayed, becoming prominent after 7 weeks (Bercovitz et al., 1972). Another common feature of the three buphthalmias is a general thinning of the ocular tunics. However, the sclera has been reported to be unaffected by a 24L:OD regime (Lauber et al., 1961). Associated with a thinning of the choroid under the three photoperiodic extremes is a reduction in the number of blood vessels. This suggests a reduction in blood flow through the choroid. Because the
outer retinal layers depend upon the choroid for metabolic exchanges, some effect upon the physiology of these cells and vision may occur. The reduction of the retinal thickness under 24L:OD has been attributed to the distention of the eye ball and stretching of the retina (Lauber et al., 1961). The thinning of the retina in OL:24D buphthalmia may result in part from the distention of the globe but also from a lower rate of development. The greater reduction in the thickness of the peripheral retina compared to that of the posterior retina in OL: 24D buphthalmia indicates a retardation in the retinal development. Furthermore, while the PE and INL increased in thickness in 24L:OD buphthalmia (Lauber et al., 1961) they decreased in thickness in OL:24D buphthalmia. Thus PE and INL are two retinal layers of the growing chick which may be dependent upon light for their normal development. Diminished 0-waves of the electroretinogram has been observed in 12-week-old dark-reared chickens (Jenkins et al., 1978). A correlation between the loss of electrophysiological properties of the j3-wave producing cells of the INL with cellular degeneration and thinning of the INL remains to be seen. The IOP has been measured in the three buphthalmias either by applanation tonometry or manometries. In the present study tonometric IOP decreased after the sixth week under darkness. Under dim blue light manometric studies have shown that mean IOP were lower than controls after 5 and 10 weeks, although not significantly (Bercovitz et al., 1972). After 12 weeks under 24L:OD, tonometries and manometries has determined that IOP of chicks increased above normal values (Smith et al, 1969; Lauber et al, 1970). Whether a tonometric or manometric method is used to measure IOP does not camouflage the general tendency. Pressures increase in 24L:OD and decrease in dim light and OL:24D buphthalmia. Whatever the cause of the differences in IOP among the three buphthalmic conditions, it does indicate the occurrence of different sequences of events in the developing glaucoma. The pressure differences between OL:24D and dim light buphthalmia could be a matter of degree with the same causative factor producing a more pronounced effect in darkness. In this study the corneal thickness in OL: 24D buphthalmia was found to be less than that of normal corneas from week 5 to 12. In
DARKNESS INDUCED EYE ABNORMALITY IN DOMESTIC CHICKEN 2 4 L : O D b u p h t h a l m i a t h e c o n t r a r y has b e e n t r u e with increases in corneal thickness after 4 weeks. T h e corneal thickness of diurnal dim light b u p h t h a l m i a has been u n c h a n g e d b y their t r e a t m e n t (Chiu etal, 1 9 7 5 ) . Corneal thickness apparently correlates with t h e a m o u n t of light e x p o s e d t o t h e eye. T h e less t h e length of exposure t h e t h i n n e r t h e cornea; t h e greater t h e e x p o s u r e t h e t h i c k e r t h e cornea. T h e retinal p a t h o l o g y which appeared as darkened peripheral retinal areas has been prod u c e d in O L : 2 4 D a n d dim light b u p h t h a l m i a s . Differences exist as t o t h e length t o e x p o s u r e required t o p r o d u c e t h e established defect. Forty-six weeks were required in dim light (Harrison et al., 1968) while less t h a n 10 weeks were required in darkness.
REFERENCES Bercovitz, A. B., P. C. Harrison, and G. A. Leary, 1972. Light induced alterations in growth pattern of the avian eye. Vision Res. 12:1253-1259. Chiu, Peter S. L., Jean K. Lauber, and Adrianne Kinnear, 1975. Dimensional and physiological lesions in the chicken eye as influenced by the light environment. Proc. Soc. Exp. Biol. Med. 148:12231228. Harrison, P. C , and J. McGinnis, 1967. Light induced
59
exophathalmos in the domestic fowl. Proc. Soc. Exp. Biol. Med. 126:308-312. Harrison, P. C , J. McGinnis, A. B. Bercovitz, and G. A. Leary, 1968. Development of eye enlargement of domestic fowl subjected to low intensity light. J. Biometeor. 12:351-358. Humason, Gretchen L., 1972. Page 183-185 in Animal tissue techniques. W. H. Freeman and Company, San Francisco. Jenkins, R. L., W. D. Ivey, R. W. Redding, and G. R. McDaniel, 1978. Effects of darkness on the maturation of the electroretinogram in the chicken. Paper presented at the 75th Annu. Meeting Southern Ass. Agr. Sci. Jensen, Leo S., and Walter E. Matson, 1957. Enlargement of avian eye by subjecting chicks to continuous incadescent illumination. Science 125:741. Lauber, Jean K., J. V. Schutz, and James McGinnis, 1961. Effects of exposure to continuous light on the eye of the growing chick. Proc. Soc. Exp. Biol. Med. 106:871-872. Lauber, Jean K., James Boyd, and T. A. S. Boyd, 1970. Intraocular pressure and aqueous outflow in light-induced avian buphthalmos. Exp. Eye Res. 9: 181-187. Moore, C. H., and G. R. McDaniel, 1969. Unpublished observation. Schutz, J. V., L. S. Jensen, J. S. Carver, and W. E. Watson, 1960. Influence of various lighting regimes on the performance of growing chickens. Washington Agr. Exp. Sta. Tech. Bull. 36:9. Smith, Morton E., Bernard Becker, and Steven Podos, 1969. Light-induced angle-closure glaucoma in the domestic fowl. Invest. Ophthalmol. 8 : 2 1 3 - 2 2 1 .
Each r o o m was adequately ventilated and air e x h a u s t e d by light-trapped ventilators. Darkcoil electric b r o o d e r s supplied h e a t a n d c o m mercial broiler ration and water were supplied ad libitum. Intraocular pressure (IOP) was d e t e r m i n e d weekly or biweekly on chickens of b o t h treatm e n t s by a p p l a n a t i o n t o n o m e t r y , using a Mackay Marg t o n o m e t e r . All pressures were measured b e t w e e n 1 3 0 0 and 1 4 0 0 hr t o prevent possible variation from diurnal IOP fluctuations. After pressures were recorded, t h e birds were weighed and t h e eyes were e n u c l e a t e d u n d e r general anesthesia. Extraorbital fatty tissues were t r i m m e d and t h e geometrical axis and trans d i a m e t e r were measured with calipers. Eyes were fixed in Zenker's fluid a n d emb e d d e d in Paraplast. Sections were c u t at 9 |U thickness and stained with either H e m a t o x y l i n a n d Eosin or G o m o r i Trichrome ( H u m a s o n , 1972). A calibrated ocular m i c r o m e t e r was used t o measure t h e cornea and t h e posterior, p o s t e r o peripheral, and peripheral thicknesses of t h e retina, choroid, and sclera. T h e retinal layers measured were (preceding from t h e inside t o t h e o u t ) t h e nerve fiber layer ( N F L ) , ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer, (INL), o u t e r plexiform layer (OPL), o u t e r nuclear layer ( O N L ) , r o d a n d cone layer (RC), and t h e p i g m e n t e p i t h e -
Eye enlargements have been induced in t h e growing domestic chicken b y the use of cont i n u o u s light (Jensen a n d Matson, 1 9 5 7 ; Lauber et al., 1 9 6 1 ) , b y diurnal low-intensity light (Harrison and McGinnis, 1 9 6 7 ) , and b y t o t a l darkness (Moore and McDaniel, 1 9 6 9 ; Chiu et al, 1975). T h e b u p h t h a l m i a s arising u n d e r t h e three lighting c o n d i t i o n s share c o m m o n eye enlargements and bird behaviors. T h e eye enlargem e n t p r o d u c e d b y c o n t i n u o u s light has been distinguished from t h e low-intensity light and darkness-induced b u p h t h a l m i a s by significant increases in t h e corneal thickness of t h e former (Chiu et al., 1 9 7 5 ) . Investigations on t h e various pathological features of t h e darknessinduced b u p h t h a l m i a in the domestic chicken have been u n d e r t a k e n by researchers at A u b u r n University. MATERIALS AND METHODS T w o - h u n d r e d male and female broiler-strain birds were conventionally reared t o one week of age, at which t i m e t h e y were r a n d o m l y divided i n t o t w o lighting regimes and maintained to 16 weeks. One t r e a t m e n t consisted of 12 hr light and 12 hr darkness ( 1 2 L : 1 2 D ) a n d t h e other consisted of t o t a l darkness ( O L : 2 4 D ) . All birds were reared in windowless r o o m s (1.82 m X 2 . 4 4 m ) , p a r t i t i o n e d by concrete block walls. 1979 Poultry Sci 58:55-59
55
56
JENKINS ET AL.
lium (PE). The total and cartilagenous thicknesses of the sclera were measured separately. Treatments were analzyed by an F-test analysis of variance in which sex was blocked. Statistical significance has been indicated at a .05 level of probability unless otherwise indicated.
2.2-
****rf
2.0' #
1.9 •
RESULTS Chickens reared in darkness (OL:24D) for 16 weeks were more lethargic and appeared to socialize less than 12L:12D chickens. The social interaction of 12L:12D birds was demonstrated by their common aggregations while OL:24D birds were often dispersed throughout their rooms. Despite their lethargy, the body weights of OL:24D chickens showed no significant differences from that of 12L:12D birds. The enucleated eyes from OL:24D birds were larger on the geometrical axis and trans diameter than the eyes of 12L:12D birds. The mean axial depth of the eyes of OL:24D birds were significantly greater (P«.01) than controls after 5 weeks of age. The mean trans diameter of the eyes of OL:24D chickens were significantly greater than controls throughout the study (Fig. 1). Intraocular pressures (IOP) as measured by applanation tonometry were significantly greater in OL:24D chicks than 12L:12D chicks after 3, 5, and 6 weeks. Beyond the 6th week OL:24D pressures gradually decreased, becoming significantly less than control values after 12 weeks of age. Pressures decreased further from week 12 to week 16 (Fig. 2). Measurements of the thickness of the ocular tunics were taken posteriorly, postero-peripherally, and peripherally from sectioned eyes. The mean thickness of the total sclera of OL:24D eyes were less than 12L:12D eyes, the difference being most pronounced postero-peripherally. However, the mean thickness of the scleral cartilage was greater than controls after exposure to the lightless environment (Table 1). The thinning of the total sclera and thickening of the scleral cartilage reflects a pronounced reduction in the fibrous layer of the sclera. The choroid of OL:24D birds were generally thinner than those of controls with the largest differences occurring peripherally and posteroperipherally (Table 1). As the choroidal thickness decreased during dark treatmeant the vessels became flatter and fewer in number. The small vessels became less distinct and were often absent, leaving a poorly defined vascular
*/
2.1-
*#^>^ *
1.8##
Sl.7-
*/ /
! • 1.6* it
T\
1.5** O /
1.41.3 1.2-
5
7
9
11
13
15
Age (weeks)
FIG. 1. Mean trans diameter (upper) and geometric axial length (lower) for OL:24D (A) and 12L:12D (0) reared chickens. *:P<.05 and **:P<.01.
plexus. The total retinal thickness progressively decreased throughout the globe the longer chickens were exposed to darkness. The greatest reduction of the retinal thickness of OL:24D eyes occurred peripherally. The posterior retina of OL:24D chickens was least affected while the postero-pheripheral retina was intermediately
9\ Q.
O
6 3 0
-3 -6
-9] -12 3
5
7 9 11 13 15 Age (weeks) FIG. 2. Percent deviation of mean IOP for OL:12D (A) and 12L:12D (0) reared chicks. *:P«.05 and **:P«.01.
DARKNESS INDUCED EYE ABNORMALITY IN DOMESTIC CHICKEN
57
TABLE 1. Mean and SEM of scleral, choroid, and retinal thickness (11) of 12L-.12D and OL-.24D reared chickens Sclera Site of measurement Posterior
Age (wk)
Retiila
OL:24D
12L:12D
OL:24D
12L:12D OL:24D
12L:12D
OL:24D
6
191.5 ±21.5
187.3 ±5.8
84.0 ±14.4
109.7 ±5.9
140.0 ±14.8
156.0 ±25.6
237.5 ±7.1
217.3 ±13.6
8
256.6 ±13.6
249.5 ±7.4
99.8 ±2.6
< 143.7
125.0 ±7.1
> 75.7
207.2 ±6.2
203.9 ±7.1
269.0 ±21.0
250.2 ±16.7
123.2 ±10.0
< 151.3
±4.9
140.7 ±14.6
> 65.5
±4.2
212.6 ±1.7
> 190.5
12
298.5 ±2.5
a > 263.0 ±7.1
107.5 ±3.2
157.0 ±1.4
141.0 ±18.8
>
41.3 ±4.4
206.0 ±1.7
171.5 ±6.7
6
164.5 ±25.0
141.3 ±3.3
96.0 ±2.5
< 115.3 ±5.2
165.0 ±6.0
> 89.6 ±8.1
197.5 ±22.2
147.9 ±5.0
253.2 ±19.6
> 188.0 ±9.6
122.8 ±6.7
141.0 ±9.4
133.7 ±17.5
> 76.7
±11.3
180.8 ±7.8
> 150.7
10
257.3 ±20.3
>
209.7 ±8.2
133.3 ±13.6
144.2 ±2.1
96.2 ±12.5
13.0 ±.8
181.5 ±10.25
>
12
313.5 ±15.9
> 240.0 ±14.1
130.0 ±10.6
< 163.5
±2.7
40.5 ±8.0
> 21.5
±.3
173.0 ±6.8
> 106.0
6
203.5 ±7.4
186.3 ±7.5
150.5 ± .3
> 137.7 ±3.7
79.5 ±3.8
> 50.3 ±4.0
128.5 ±23.7
> 66.7
8
183.6 ±1.8
180.2 ±4.0
156.0 ±1.0
170.0 ±1.3
35.8 ±2.9
>
16.7 ±3.4
101.8 ±5.0
> 78.2
10
194.7 ±17.4
180.7 ±8.9
159.3 ±7.8
165.0 ±9.4
39.3 ±5.4
>
7.2 ±.9
103.7 ±6.9
> 65.0
12
217.0 ±7.2
208.5 ±5.3
175.0 ±2.1
177.0 ±7.7
30.5 ±3.5
>
11.5 ±5.3
100.0 ±.1
> 65.1
8
Peripheral
Choroid
Cartilage
12L:12D
10
Postero-peripheral
Total
±5.3
<
<
±8.8
>
±1.2
>
±6.4
144.5 ±5.3 ±9.3
±8.4
±7.6 ±4.1 +8.0
> and < indicating significance (P<.05).
affected (Table 1). While all of the retinal layers were affected by the darkness the PE, RC, NFL, and INL of the retina were most drastically affected. The GCL showed the least reduction in thickness after exposure to darkness. The corneal thickness of OL:24D eyes increased between weeks 4 and 5 as did the corneas of 12L:12D eyes. After the fifth week the corneas of OL:24D eyes decreased in thickness and remained consistently thinner than control corneas (Fig. 3). Two principle retinal pathologies were induced by darkness. One appeared as darkened areas of the peripheral retina which was first seen in the 7 week-old OL:24D birds and was later seen to spread to the postero-peripheral retina. Histologically, the darkened retinal areas were seen to arise from a thinning of the retina
with the PE remaining unchanged. The second retinal abnormality which appeared only among OL:24D birds was one or more white bands directed perpendicular to the pecten. Histologically, these bands appeared as localized areas in which the vessels of the choroid, Bruch's Membrane, PE, RC, ONL, and OPL were absent. Non-collagenous fibers extended from the deformed choroid and infiltrated the remaining inner retinal layers. Large, multipolar cells which apparently were edematous Miiller cells appeared at the level of the abolished PE and in the existing IPL and GCL. These cells acquired a bluish tint after Gomori Trichrome staining. Their nuclei showed no affinity for hematoxylin. The retina immediately adjacent to the depigmented bands maintained its normal layering but was detached from the PE. The corneal curvature of OL:24D chickens
58
JENKINS ET AL. .30
.25 •
I .20
.15 • 4
6
8
10
12
Age (weeks) FIG. 3. Mean corneal thickness of OL:24D (A) and 12L:12D (0) reared chickens. ':P<.05. appeared to be reduced. This was evident after 10 and 12 weeks from the bisected hemispheres. By weeks 10 and 12 the irides of OL: 24D birds exhibited occasional lymphoid aggregations and reduced musculature. DISCUSSION Lethargic behavior appears to be a common feature among chickens reared in photoperiodic extremes. The listlessness seen in the OL:24D birds here has also been cited among 24L:OD birds (Schutz et al, 1960). Harrison et al. (1968) detected a hypothyroidism and reduced oxygen consumption among birds reared in diurnal dim light. The possibility of a systemic effect involved in 24L:OD buphthalmia has been discussed by Chiu et al. (1975). It seems likely that the lethargy which is produced by unnatural lighting may arise from a generalized metabolic stress. The buphthalmias induced by 24L:OD, OL: 24D, and diurnal dim light exhibit several common features. The onset of the three buphthalmias is chronologically similar. The 24L:OD buphthalmia occurs after 3 weeks of age (Lauber et al, 1970) while the OL:24D buphthalmia occurs after 4 weeks of treatment. The eye enlargement under dim light is delayed, becoming prominent after 7 weeks (Bercovitz et al., 1972). Another common feature of the three buphthalmias is a general thinning of the ocular tunics. However, the sclera has been reported to be unaffected by a 24L:OD regime (Lauber et al., 1961). Associated with a thinning of the choroid under the three photoperiodic extremes is a reduction in the number of blood vessels. This suggests a reduction in blood flow through the choroid. Because the
outer retinal layers depend upon the choroid for metabolic exchanges, some effect upon the physiology of these cells and vision may occur. The reduction of the retinal thickness under 24L:OD has been attributed to the distention of the eye ball and stretching of the retina (Lauber et al., 1961). The thinning of the retina in OL:24D buphthalmia may result in part from the distention of the globe but also from a lower rate of development. The greater reduction in the thickness of the peripheral retina compared to that of the posterior retina in OL: 24D buphthalmia indicates a retardation in the retinal development. Furthermore, while the PE and INL increased in thickness in 24L:OD buphthalmia (Lauber et al., 1961) they decreased in thickness in OL:24D buphthalmia. Thus PE and INL are two retinal layers of the growing chick which may be dependent upon light for their normal development. Diminished 0-waves of the electroretinogram has been observed in 12-week-old dark-reared chickens (Jenkins et al., 1978). A correlation between the loss of electrophysiological properties of the j3-wave producing cells of the INL with cellular degeneration and thinning of the INL remains to be seen. The IOP has been measured in the three buphthalmias either by applanation tonometry or manometries. In the present study tonometric IOP decreased after the sixth week under darkness. Under dim blue light manometric studies have shown that mean IOP were lower than controls after 5 and 10 weeks, although not significantly (Bercovitz et al., 1972). After 12 weeks under 24L:OD, tonometries and manometries has determined that IOP of chicks increased above normal values (Smith et al, 1969; Lauber et al, 1970). Whether a tonometric or manometric method is used to measure IOP does not camouflage the general tendency. Pressures increase in 24L:OD and decrease in dim light and OL:24D buphthalmia. Whatever the cause of the differences in IOP among the three buphthalmic conditions, it does indicate the occurrence of different sequences of events in the developing glaucoma. The pressure differences between OL:24D and dim light buphthalmia could be a matter of degree with the same causative factor producing a more pronounced effect in darkness. In this study the corneal thickness in OL: 24D buphthalmia was found to be less than that of normal corneas from week 5 to 12. In
DARKNESS INDUCED EYE ABNORMALITY IN DOMESTIC CHICKEN 2 4 L : O D b u p h t h a l m i a t h e c o n t r a r y has b e e n t r u e with increases in corneal thickness after 4 weeks. T h e corneal thickness of diurnal dim light b u p h t h a l m i a has been u n c h a n g e d b y their t r e a t m e n t (Chiu etal, 1 9 7 5 ) . Corneal thickness apparently correlates with t h e a m o u n t of light e x p o s e d t o t h e eye. T h e less t h e length of exposure t h e t h i n n e r t h e cornea; t h e greater t h e e x p o s u r e t h e t h i c k e r t h e cornea. T h e retinal p a t h o l o g y which appeared as darkened peripheral retinal areas has been prod u c e d in O L : 2 4 D a n d dim light b u p h t h a l m i a s . Differences exist as t o t h e length t o e x p o s u r e required t o p r o d u c e t h e established defect. Forty-six weeks were required in dim light (Harrison et al., 1968) while less t h a n 10 weeks were required in darkness.
REFERENCES Bercovitz, A. B., P. C. Harrison, and G. A. Leary, 1972. Light induced alterations in growth pattern of the avian eye. Vision Res. 12:1253-1259. Chiu, Peter S. L., Jean K. Lauber, and Adrianne Kinnear, 1975. Dimensional and physiological lesions in the chicken eye as influenced by the light environment. Proc. Soc. Exp. Biol. Med. 148:12231228. Harrison, P. C , and J. McGinnis, 1967. Light induced
59
exophathalmos in the domestic fowl. Proc. Soc. Exp. Biol. Med. 126:308-312. Harrison, P. C , J. McGinnis, A. B. Bercovitz, and G. A. Leary, 1968. Development of eye enlargement of domestic fowl subjected to low intensity light. J. Biometeor. 12:351-358. Humason, Gretchen L., 1972. Page 183-185 in Animal tissue techniques. W. H. Freeman and Company, San Francisco. Jenkins, R. L., W. D. Ivey, R. W. Redding, and G. R. McDaniel, 1978. Effects of darkness on the maturation of the electroretinogram in the chicken. Paper presented at the 75th Annu. Meeting Southern Ass. Agr. Sci. Jensen, Leo S., and Walter E. Matson, 1957. Enlargement of avian eye by subjecting chicks to continuous incadescent illumination. Science 125:741. Lauber, Jean K., J. V. Schutz, and James McGinnis, 1961. Effects of exposure to continuous light on the eye of the growing chick. Proc. Soc. Exp. Biol. Med. 106:871-872. Lauber, Jean K., James Boyd, and T. A. S. Boyd, 1970. Intraocular pressure and aqueous outflow in light-induced avian buphthalmos. Exp. Eye Res. 9: 181-187. Moore, C. H., and G. R. McDaniel, 1969. Unpublished observation. Schutz, J. V., L. S. Jensen, J. S. Carver, and W. E. Watson, 1960. Influence of various lighting regimes on the performance of growing chickens. Washington Agr. Exp. Sta. Tech. Bull. 36:9. Smith, Morton E., Bernard Becker, and Steven Podos, 1969. Light-induced angle-closure glaucoma in the domestic fowl. Invest. Ophthalmol. 8 : 2 1 3 - 2 2 1 .