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Influence of the depth of the anterior chamber on the resistance to flow of aqueous humour
E x p . E y e Res. (1962) 1, 2 2 9 - 2 3 3
I n f l u e n c e o f the D e p t h o f the A n t e r i o r C h a m b e r on the R e s i s t a n c e to F l o w o f A q u e o u s H u m o u r I ). iNT:I[HARD
Cliniffue Ophthalmologique de l' Universitd de Liege, B e l g i u m (.Received 30 November 1961) Some 50 enucleated h u m a n eyes were perfused t h r o u g h t h e anterior c h a m b e r while recording b o t h perfusion pressure a n d d e p t h of t h e a n t e r i o r chamber. The results showed t h a t t h e outflow resistance was ilxversely r e l a t e d to the d e p t h of t h e anterior chamber. The resistance came w i t h i n the pathological range, i.e. g r e a t e r t h a n 7, w h e n t h e d e p t h of the a n t e r i o r c h a m b e r was less t h a n 2.2 ram. 1. I n t r o d u c t i o n Several clinical observations indicate that the depth of the anterior chamber plays a role in the genesis of ocular hypertension. Eyes with angle-closure glaucoma have an abnormally narrow angle; this fact has been studied recently by ~reekers and G r i e t e n (unpublished) w i t h a v e r y p r e c i s e t e c h n i q u e . M y d r i a s i s c a u s e d b y d r u g s l e a d s t o a n o c u l a r h y p e r t e n s i o n i f t h e d e p t h o f t h e a n t e r i o r c h a m b e r i s l e s s t h a n 2.5 m m ( W e e k e r s a n d G r i e t e n , 1962). I n t h e p r e s e n t w o r k t h e r e l a t i o n b e t w e e n i ' e s i s t a n e e t o flow of aqueous humour and depth of the anterior chamber has been studied experimentally. 2. M e t h o d s T h e e n u c l e a t e d h u m a n e y e is c o n n e c t e d t o a p e r f u s i o n a p p a r a t u s b y w a y of a n e e d l e ; t h e l a t t e r is i n t o d u c e d l a t e r a l l y i n t o t h e a n t e r i o r c h a m b e r , t a k i n g care n o t to i n j u r e e i t h e r t h e l e n s or iris. D u r i n g t h e e x p e r i m e n t t h e flow of fluid D i n t o t h e e y e in u n i t t i m e is m e a s u r e d ; t h e p r e s s u r e P b e h i n d t h e p e r f u s i o n fluid is v a r i a b l e a n d m e a s u r e d w i t h a m a n o m e t e r . T h e r e s i s t a n c e R is c a l c u l a t e d f r o m t h e r e l a t i o n s h i p R -~ P / D a n d is exp r e s s e d i n u n i t s of m m H g / m m a nlin. I n a n e~rlier p u b l i c a t i f n ( N i h a r d , 1962) t h e d e t a i l s of t h e p e r f u s i o n t e c h n i q u e are g i v e n in m o r e detail.
Depth of anterior chamber T h e e y e p i e c e d e s c r i b e d b y G o l d m a n n (1932) for t h e s l i t - l a m p m i c r o s c o p e f o r t h e m e a s u r e m e n t o f t h e r e f r a c t i v e m e d i a w a s e m p l o y e d . T h e t h e o r y of its a p p l i c a t i o n t o t h e m e a s u r e m e n t o f t h e d e p t h o f t h e a n t e r i o r c h a m b e r w a s d e s c r i b e d b y G o l d m a n n et al. (1962) w h i l s t its a p p l i c a t i o n t o c l i n i c a l p r a c t i c e w a s d e s c r i b e d b y V(eekers, G r i e t e n a n d L a v e r g n e (1961), and this latter method was employed in the present work. T h e h u m a n e y e , e n u c l e a t e d i m m e d i a t e l y a f t e r d e a t h , w a s p l a c e d on a c o t t o n - w o o l p a d a n d t h e l i g h t f r o m t h e s l i t - l a m p w a s a r r a n g e d t o s t r i k e t h e a p e x of t h e cornea,, l~erfusion a t a p r e s s u r e of 20 m m H g w a s c a r r i e d o u t for 45 rain, t h e r e s i s t a n c e a n d d e p t h of t h e a n t e r i o r c h a m b e r b e i n g d e t e r m i n e d e v e r y 5 m i n . N e x t t h e p r e s s u r e - w a s r a i s e d t o 60 m m I{g. To a v o i d d r y i n g of t h e globe a n d t h e orifices of t h e d r a i n a g e c h a n n e l s , t h e globe w a s i r r i g a t e d b y d r o p p i n g saline o v e r its surface. 209
230
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3. Results
Influence of the duration of pe~:fusion on the depth of the anterior chamber Eyes at normal pressure (20 m m Hg) T h e d e p t h o f t h e a n t e r i o r c h a m b e r was m e a s u r e d a t t h e b e g i n n i n g a n d e n d o f a p e r f u s i o n a t a p r e s s u r e of 20 m m I-Ig l a s t i n g 45 r a i n . T h e f i r s t d e p t h (CA~) w a s m e a s u r e d a t t h e 5 t h m i n u t e a n d t h e l a s t (CA ~_) a t t h e 4 5 t h m i n u t e . CA2/CA1 g i v e s a m e a s u r e o f a n y c h a n g e in d e p t h d u r i n g t h e c o u r s e o f t h e p e r f u s i o n . F o r a g r o u p o f 30 eyes, t h e m e a n r a t i o w a s 1.003, w i t h a s t a n d a r d d e v i a t i o n o f 0.053 a n d a s t a n d a r d e r r o r o f t h e m e a n o f 0.0061. T h i s r a t i o was n o t s i g n i f i c a n t l y d i f f e r e n t f r o m u n i t y (t --~ 0.49; P :>0.60). I t m a y be c o n c l u d e d , t h e r e f o r e , t h a t t h e d e p t h o f t h e a n t e r i o r c h a m b e r i n m a n is n o t a l t e r e d d u r i n g p e r f u s i o n f o r 45 r a i n a t a p r e s s u r e o f 20 m m H g . 14 13 12
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CA (rnrn) F I G . 1. C o r r e l a t i o n b e t w e e n r e s i s t a n c e R t o f l o w a n d d e p t h C A o f t h e a n t e r i o r c h a m b e r e y e s p e l ~ u s e d a t a p r e s s u r e o f 20 m m H g .
for 50 human
Eyes at high pressure (60 m m Hg) As i n t h e p r e v i o u s series, t h e d e p t h was m e a s u r e d d u r i n g p e r f u s i o n f o r 45 ~ , but w i t h a p r e s s u r e o f 60 n l m H g . T h e m e a n v a l u e o f t h e r a t i o CA J C A 1 for 30 e y e s w a s 0.998, w i t h a s t a n d a r d d e v i a t i o n o f 0.033 a n d a s t a n d a r d e r r o r o f t h e m e a n o f 0.0061. T h e m e a n r a t i o is t h u s n o t s t a t i s t i c a l l y d i f f e r e n t f r o m u n i t y (t ~--- 0.49; P ~ 0 . 6 0 ) . I t m a y b e c o n c l u d e d t h a t a t 60 m m H g , too, t h e d e p t h of t h e a n t e r i o r c h a m b e r is unaffected by pe~usion.
Inj~uence of the pressure of the perfusion fluid on the depth of the anterior chamber F o r t y h u m a n eyes were p e r f u s e d f o r 45 rain a t a p r e s s u r e o f 20 m m H g , t h e d e p t h o f t h e a n t e r i o r c h a m b e r b e i n g m e a s u r e d e v e r y 5 m i n (CA1). T h e s a m e e y e s w e r e i m m e d i a t e l y p e r f u s e d a t a p r e s s u r e o f 60 m m H g f o r 45 rain. I n a n y g i v e n e y e t h e
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t r a n s i t i o n f r o m t h e low to t h e h i g h p r e s s u r e w a s i m m e d i a t e . T h e d e p t h of t h e a n t e r i o r c h a m b e r w a s m e a s u r e d e v e r y 5 r a i n a t t h e h i g h p r e s s u r e ( C A 2)- CA J C A ~ i n d i c a t e s t h e effect of p r e s s u r e on t h e d e p t h . T h e m e a n v a l u e w a s 1.03, w i t h a s t a n d a r d d e v i a t i o n of 0.051 a n d a s t a n d a r d e r r o r o f t h e m e a n o f 0.008. T h e m e a n r a t i o is t h u s s t a t i s t i c a l l y d i f f e r e n t f r o m u n i t y (t --~ 3.61; P <=0.01) a n d it m a y b e c o n c l u d e d t h a t t h e depth of the anterior chamber increases with increased pressure of perfusion.
Correlation between depth of anterior chamber and resistance to f l o w Perfusion at normal pressure (20 m m Hg) I n Fig. 1 t h e r e s i s t a n c e to flow is p l o t t e d a s a f u n c t i o n of t h e d e p t h o f t h e a n t e r i o r c h a m b e r ; t h e r e s u l t s r e p r e s e n t p e r f u s i o n s of 50 e y e s a t a p r e s s u r e of 20 m m H g , t h e v a l u e s f o r r e s i s t a n c e b e i n g t h e m e a n s of 9 m e a s u r e m e n t s c a r r i e d o u t d u r i n g a p e r i o d o f 45 rain. T h e g r a p h r e v e a l s a n o b v i o u s d e p e n d e n c e o f t h e t w o v a r i a b l e s , w h i c h m a y be c o n f i r m e d s t a t i s t i c a l l y . T h u s t h e c o r r e l a t i o n coefficient is e q u a l t o - - 0 . 8 0 ; t h e n u m b e r o f p a i r e d m e a s u r e m e n t s b e i n g 50, t h i s coefficient is s i g n i f i c a n t ( P <:0.01). T h u s t h e r e s i s t a n c e t o flow i n c r e a s e s w i t h d e c r e a s e d d e p t h o f a n t e r i o r c h a m b e r . 14
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lWrQ. 2. C o r r e l a t i o n b e t w e e n r e s i s t a n c e R t o f l o w a n d e y e s p e r f u s e d a t a p r e s s u r e o f 6 0 m m ][=Ig,
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Pe~fusion at high pressure (60 m m Hg) T h e r e s u l t s o n 50 h u m a n e y e s p e r f u s e d a t 60 m m H g a r e s h o w n i n F i g . 2, w h e r e r e s i s t a n c e to flow is once a g a i n p l o t t e d as o r d i n a t e a g a i n s t d e p t h o f t h e a n t e r i o r c h a m b e r . T h e c o r r e l a t i o n coefficient is e q u a l t o - - 0 . 4 0 a n d , since t h e n u m b e r o f p a i r e d m e a s u r e m e n t s is 50, t h i s coefficient is s t a t i s t i c a l l y s i g n i f i c a n t ( P < 0 . 0 1 ) . T h u s r e s i s t a n c e to flow i n c r e a s e s w i t h d e c r e a s e d d e p t h of t h e a n t e r i o r c h a m b e r a t b o t h normal and high pressures.
232
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4. D i s c u s s i o n
T h e present experiments have s h o w n that, at constant pressure, the depth of the anterior chamber remains constant for the 45 rain during which the perfusion is maintained. If, on the other hand, the pressure is raised from 20 to 60 m m H g during the course of a given perfusion, the depth of the anterior c h a m b e r increases. In an earlier study (Nihard, 1962) it has been s h o w n that an increase in perfusion pressure from 20 to 60 _mn~ H g causes an increased resistance to i~ow of 44~/o. This increase in resistance to flow cannot be attributed to a decrease in depth of the anterior chamber; on the contrary, the depth actually increases a littlew h e n the pressure is raised. So far as the relationship between depth of anterior chamber and resistance to flow is concerned, the present finding, that the resistance increases with decreasing depth, is in general agreement with earlier studies. B A r A n y and W o o d i n (1955) studied the relationship between facility C of outflow (the reciprocal of the resistance) and t h e v o l n m e V of t h e a n t e r i o r c h a m b e r in p e r f u s e d e n u c l e a t e d r a b b i t s ' eyes. T h e r e l a t i o n s h i p w as linear, t h e ratio C / V b e i n g c o n s t a n t , w i t h a n a v e r a g e v a l u e of 1.7 for 17 eyes: T h i s l i n e a r r e l a t i o n s h i p b e t w e e n f a c i l i t y of outflow a n d d e p t h of a n t e r i o r c h a m b e r w a s c o n f i r m e d b y B e c k e t a n d C o n s t a n t (1956a) for d i f f e r e n t species (cat, g u i n e a - p i g a n d r a b b i t ) . T h e s a m e a u t h o r s (1956b) also m o d i f i e d t h e v o l u m e of t h e a n t e r i o r c h a m b e r e x p e r i m e n t a l l y , e i t h e r b y c o n s t r i c t i n g t h e sclera or b y i n j e c t i n g s e ~ l m into the vitreous body; t h e y observed an increase in resistance when the volume of t h e a n t e r i o r c h a m b e r dimini.~hed. Fr a ngois, R a b a e y a n d l~eetens (1956a,b) a n d F r a n g o i s et al. (1958) s t u d i e d t h e ; n f l u e n c e of d e p t h of a n t e r i o r c h a m b e r on r e s i s t a n c e b y r e d u c i n g t h e v o l u m e of t h e posterior h a l f of t h e globe. T h e y p l a c e d a g u i l l o t i n e forceps w i t h a d j u s t a b l e s p a n a r o u n d t h e e qua tor . B y m e a n s of t h i s t h e y were a b l e to a l t e r t h e v o l u m e of t h e a n t e r i o r c h a m b e r a t will b y forcing t h e le ns a n d iris f o r w a r d . T h e y showed t h a t t h e r e s i s t a n c e i n c r e a s e d s t r o n g l y w i t h d i m i n i s h i n g d e p t h o f t h e a n t e r i o r c h a m b e r . T h e p r e s e n t e x p e r i m e n t s were c a r r ie d o u t w i t h o u t a n y s u c h artirice; t h e p e r f u s i o n fluid was n o t i n j e c t e d i n t o t h e v i t r e o u s b o d y b u t e n t e r e d t h e a n t e r i o r c h a m b e r l a t e r a l l y , a n d t h e v o l u m e of t h e a n t e r i o r c h a m b e r was n o t r e d u c e d b y e q u a t o r i a l compression. I t w a s e s s e n t i a l l y t h e large n u m b e r of eyes t h a t we were a b l e to s t u d y t h a t e n a b l e d us to o b t a i n v a l u e s of r e s i s t a n c e for d i f f e r e n t d e p t h s of a n t e r i o r c h a m b e r , to give t h e c u r v e of Fig. 1. T h e l a t t e r shows t h a t a d e p t h of 5 - 6 m m corresponds to a r e s i s t a n c e of 1.5, w h i l s t a d e p t h of 1.5 m m c or r e sponds to a resist a n c e of 13. B e t w e e n t h e two e x t r e m e s t h e i n t e r m e d i a t e v a l u e s m a y be r e a d o i l T h e s e r e s u l t s agree well w i t h those of F r a n g o i s et al. (1958). W h e n t h e p e r f u s i o n of t h e eyes is c a r r ie d o u t a t 60 m m Hg, t h e r e is a s i m i l a r corr e l a t i o n b e t w e e n d e p t h of a n t e r i o r c h a m b e r a n d outflow resistance, l~e ve r the le s s t h e s u p e r p o s i t i o n of t h e c u r v e s i n Figs. 1 a n d 2 shows t h a t t h e c u r v e is d i s p l a c e d to t h e r i g h t w h e n t h e pressure is i n c r e a s e d f r o m 20 to 60 r a m Hg. I n o t h e r words, t h e r e s u lts d e m o n s t r a t e once a g a i n t h a t t h e a n t e r i o r c h a m b e r d e e p e n s a l i t t l e w h e n t h e p r e s s u r e increases, a n d t h a t t h e r e s i s t a n c e increases w h e n the i n t r a o c u l a r p r e s s u r e rises. T h e records of t h e p r e s e n t studie s h a v e g i v e n a n a v e r a g e d e p t h of a n t e r i o r C h a m b e r of 2.92 m m for eyes p e r f u s e d a t 20 m m Hg. I f i t is c o n s i d e r e d t h a t t h e eyes were t a k e n f r o m s u b j e c t s aged m o r e t h a n 55 years, t h e figure is in good a g r e e m e n t w i t h t h e v a l u e o b t a i n e d b y W e e k e r s et al. (1961) on n o r m a l subjects. To repeat, t h e p e r f u s i o n of h u m a n eyes h a s s h o w n t h a t t h e r e s i s t a n c e to flow is g r e a t e r t h e s h a l l o w e r t h e a n t e r i o r c h a m b e r , a n d vice versa. T h e results show, also, t h a ~ the. r e a i s t a n c ~ a ~ t a i n s p a t h o l o g i c a l v a l u e s (greater t h a n 7) w h e n t h e d e p t h of t h e
ANTERIOI~ CHAMBER DEPTH AND AQUEOUS HUMOUR
233
anterior chamber is less than 2.2 ram. These experimental facts agree well with the clinical observations of Weekers and Grieten (1962) who fmmd that the average depth of eyes with angle-closure glaucoma was 2.30 ram; these authors found, moreover, that mydriasis induced by drugs induces a hypertension when the depth of the chamber is less than 2.5 ram. REFERENCES B~r~ny, E. and Woodin, A. M. (1955). Acta ~hysiol. scand. 33, 257. Becker, B. and Constant, M. (1956a). Arner. J. Ophthal. 42, 189. Becker, B. and Constant, M. (1956b). Arch. OphthaI., Chicago 55, 305. Franqois, J., Rabaey, M. and :Neetens, A. (1956a). Arch. Ophthal., Chicago 65, 488. Francois, J., Rabaey, M. and Nee~ens, A. (1956b). Arch. Ophthal., Chicago 55, 193. Franqois, J., Rabaey, M., Neetens, A. and Evens, L. (1958). Arch. Ophthal., Chicago 44, 204. Goldmann, H. (1932). Ber. dtsch, ophthal. Ges. 49, 435. Goldmann, H., Weekers, R., Grieten, J. and Lavergne, G. (1962). Ophthalmologica, Basel 143. Nihard, P. (1962). Acta ophthal. Kbh. 40, 42. Weekers, R., Grieten, J. and Lavergne, G. (1961). Ophthalmologica, Basel 142, 650. Weekers, R. and Grieten, J. {1962). Oph~halmologica, Basel 143, 56.
I n f l u e n c e o f the D e p t h o f the A n t e r i o r C h a m b e r on the R e s i s t a n c e to F l o w o f A q u e o u s H u m o u r I ). iNT:I[HARD
Cliniffue Ophthalmologique de l' Universitd de Liege, B e l g i u m (.Received 30 November 1961) Some 50 enucleated h u m a n eyes were perfused t h r o u g h t h e anterior c h a m b e r while recording b o t h perfusion pressure a n d d e p t h of t h e a n t e r i o r chamber. The results showed t h a t t h e outflow resistance was ilxversely r e l a t e d to the d e p t h of t h e anterior chamber. The resistance came w i t h i n the pathological range, i.e. g r e a t e r t h a n 7, w h e n t h e d e p t h of the a n t e r i o r c h a m b e r was less t h a n 2.2 ram. 1. I n t r o d u c t i o n Several clinical observations indicate that the depth of the anterior chamber plays a role in the genesis of ocular hypertension. Eyes with angle-closure glaucoma have an abnormally narrow angle; this fact has been studied recently by ~reekers and G r i e t e n (unpublished) w i t h a v e r y p r e c i s e t e c h n i q u e . M y d r i a s i s c a u s e d b y d r u g s l e a d s t o a n o c u l a r h y p e r t e n s i o n i f t h e d e p t h o f t h e a n t e r i o r c h a m b e r i s l e s s t h a n 2.5 m m ( W e e k e r s a n d G r i e t e n , 1962). I n t h e p r e s e n t w o r k t h e r e l a t i o n b e t w e e n i ' e s i s t a n e e t o flow of aqueous humour and depth of the anterior chamber has been studied experimentally. 2. M e t h o d s T h e e n u c l e a t e d h u m a n e y e is c o n n e c t e d t o a p e r f u s i o n a p p a r a t u s b y w a y of a n e e d l e ; t h e l a t t e r is i n t o d u c e d l a t e r a l l y i n t o t h e a n t e r i o r c h a m b e r , t a k i n g care n o t to i n j u r e e i t h e r t h e l e n s or iris. D u r i n g t h e e x p e r i m e n t t h e flow of fluid D i n t o t h e e y e in u n i t t i m e is m e a s u r e d ; t h e p r e s s u r e P b e h i n d t h e p e r f u s i o n fluid is v a r i a b l e a n d m e a s u r e d w i t h a m a n o m e t e r . T h e r e s i s t a n c e R is c a l c u l a t e d f r o m t h e r e l a t i o n s h i p R -~ P / D a n d is exp r e s s e d i n u n i t s of m m H g / m m a nlin. I n a n e~rlier p u b l i c a t i f n ( N i h a r d , 1962) t h e d e t a i l s of t h e p e r f u s i o n t e c h n i q u e are g i v e n in m o r e detail.
Depth of anterior chamber T h e e y e p i e c e d e s c r i b e d b y G o l d m a n n (1932) for t h e s l i t - l a m p m i c r o s c o p e f o r t h e m e a s u r e m e n t o f t h e r e f r a c t i v e m e d i a w a s e m p l o y e d . T h e t h e o r y of its a p p l i c a t i o n t o t h e m e a s u r e m e n t o f t h e d e p t h o f t h e a n t e r i o r c h a m b e r w a s d e s c r i b e d b y G o l d m a n n et al. (1962) w h i l s t its a p p l i c a t i o n t o c l i n i c a l p r a c t i c e w a s d e s c r i b e d b y V(eekers, G r i e t e n a n d L a v e r g n e (1961), and this latter method was employed in the present work. T h e h u m a n e y e , e n u c l e a t e d i m m e d i a t e l y a f t e r d e a t h , w a s p l a c e d on a c o t t o n - w o o l p a d a n d t h e l i g h t f r o m t h e s l i t - l a m p w a s a r r a n g e d t o s t r i k e t h e a p e x of t h e cornea,, l~erfusion a t a p r e s s u r e of 20 m m H g w a s c a r r i e d o u t for 45 rain, t h e r e s i s t a n c e a n d d e p t h of t h e a n t e r i o r c h a m b e r b e i n g d e t e r m i n e d e v e r y 5 m i n . N e x t t h e p r e s s u r e - w a s r a i s e d t o 60 m m I{g. To a v o i d d r y i n g of t h e globe a n d t h e orifices of t h e d r a i n a g e c h a n n e l s , t h e globe w a s i r r i g a t e d b y d r o p p i n g saline o v e r its surface. 209
230
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3. Results
Influence of the duration of pe~:fusion on the depth of the anterior chamber Eyes at normal pressure (20 m m Hg) T h e d e p t h o f t h e a n t e r i o r c h a m b e r was m e a s u r e d a t t h e b e g i n n i n g a n d e n d o f a p e r f u s i o n a t a p r e s s u r e of 20 m m I-Ig l a s t i n g 45 r a i n . T h e f i r s t d e p t h (CA~) w a s m e a s u r e d a t t h e 5 t h m i n u t e a n d t h e l a s t (CA ~_) a t t h e 4 5 t h m i n u t e . CA2/CA1 g i v e s a m e a s u r e o f a n y c h a n g e in d e p t h d u r i n g t h e c o u r s e o f t h e p e r f u s i o n . F o r a g r o u p o f 30 eyes, t h e m e a n r a t i o w a s 1.003, w i t h a s t a n d a r d d e v i a t i o n o f 0.053 a n d a s t a n d a r d e r r o r o f t h e m e a n o f 0.0061. T h i s r a t i o was n o t s i g n i f i c a n t l y d i f f e r e n t f r o m u n i t y (t --~ 0.49; P :>0.60). I t m a y be c o n c l u d e d , t h e r e f o r e , t h a t t h e d e p t h o f t h e a n t e r i o r c h a m b e r i n m a n is n o t a l t e r e d d u r i n g p e r f u s i o n f o r 45 r a i n a t a p r e s s u r e o f 20 m m H g . 14 13 12
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for 50 human
Eyes at high pressure (60 m m Hg) As i n t h e p r e v i o u s series, t h e d e p t h was m e a s u r e d d u r i n g p e r f u s i o n f o r 45 ~ , but w i t h a p r e s s u r e o f 60 n l m H g . T h e m e a n v a l u e o f t h e r a t i o CA J C A 1 for 30 e y e s w a s 0.998, w i t h a s t a n d a r d d e v i a t i o n o f 0.033 a n d a s t a n d a r d e r r o r o f t h e m e a n o f 0.0061. T h e m e a n r a t i o is t h u s n o t s t a t i s t i c a l l y d i f f e r e n t f r o m u n i t y (t ~--- 0.49; P ~ 0 . 6 0 ) . I t m a y b e c o n c l u d e d t h a t a t 60 m m H g , too, t h e d e p t h of t h e a n t e r i o r c h a m b e r is unaffected by pe~usion.
Inj~uence of the pressure of the perfusion fluid on the depth of the anterior chamber F o r t y h u m a n eyes were p e r f u s e d f o r 45 rain a t a p r e s s u r e o f 20 m m H g , t h e d e p t h o f t h e a n t e r i o r c h a m b e r b e i n g m e a s u r e d e v e r y 5 m i n (CA1). T h e s a m e e y e s w e r e i m m e d i a t e l y p e r f u s e d a t a p r e s s u r e o f 60 m m H g f o r 45 rain. I n a n y g i v e n e y e t h e
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t r a n s i t i o n f r o m t h e low to t h e h i g h p r e s s u r e w a s i m m e d i a t e . T h e d e p t h of t h e a n t e r i o r c h a m b e r w a s m e a s u r e d e v e r y 5 r a i n a t t h e h i g h p r e s s u r e ( C A 2)- CA J C A ~ i n d i c a t e s t h e effect of p r e s s u r e on t h e d e p t h . T h e m e a n v a l u e w a s 1.03, w i t h a s t a n d a r d d e v i a t i o n of 0.051 a n d a s t a n d a r d e r r o r o f t h e m e a n o f 0.008. T h e m e a n r a t i o is t h u s s t a t i s t i c a l l y d i f f e r e n t f r o m u n i t y (t --~ 3.61; P <=0.01) a n d it m a y b e c o n c l u d e d t h a t t h e depth of the anterior chamber increases with increased pressure of perfusion.
Correlation between depth of anterior chamber and resistance to f l o w Perfusion at normal pressure (20 m m Hg) I n Fig. 1 t h e r e s i s t a n c e to flow is p l o t t e d a s a f u n c t i o n of t h e d e p t h o f t h e a n t e r i o r c h a m b e r ; t h e r e s u l t s r e p r e s e n t p e r f u s i o n s of 50 e y e s a t a p r e s s u r e of 20 m m H g , t h e v a l u e s f o r r e s i s t a n c e b e i n g t h e m e a n s of 9 m e a s u r e m e n t s c a r r i e d o u t d u r i n g a p e r i o d o f 45 rain. T h e g r a p h r e v e a l s a n o b v i o u s d e p e n d e n c e o f t h e t w o v a r i a b l e s , w h i c h m a y be c o n f i r m e d s t a t i s t i c a l l y . T h u s t h e c o r r e l a t i o n coefficient is e q u a l t o - - 0 . 8 0 ; t h e n u m b e r o f p a i r e d m e a s u r e m e n t s b e i n g 50, t h i s coefficient is s i g n i f i c a n t ( P <:0.01). T h u s t h e r e s i s t a n c e t o flow i n c r e a s e s w i t h d e c r e a s e d d e p t h o f a n t e r i o r c h a m b e r . 14
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Pe~fusion at high pressure (60 m m Hg) T h e r e s u l t s o n 50 h u m a n e y e s p e r f u s e d a t 60 m m H g a r e s h o w n i n F i g . 2, w h e r e r e s i s t a n c e to flow is once a g a i n p l o t t e d as o r d i n a t e a g a i n s t d e p t h o f t h e a n t e r i o r c h a m b e r . T h e c o r r e l a t i o n coefficient is e q u a l t o - - 0 . 4 0 a n d , since t h e n u m b e r o f p a i r e d m e a s u r e m e n t s is 50, t h i s coefficient is s t a t i s t i c a l l y s i g n i f i c a n t ( P < 0 . 0 1 ) . T h u s r e s i s t a n c e to flow i n c r e a s e s w i t h d e c r e a s e d d e p t h of t h e a n t e r i o r c h a m b e r a t b o t h normal and high pressures.
232
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4. D i s c u s s i o n
T h e present experiments have s h o w n that, at constant pressure, the depth of the anterior chamber remains constant for the 45 rain during which the perfusion is maintained. If, on the other hand, the pressure is raised from 20 to 60 m m H g during the course of a given perfusion, the depth of the anterior c h a m b e r increases. In an earlier study (Nihard, 1962) it has been s h o w n that an increase in perfusion pressure from 20 to 60 _mn~ H g causes an increased resistance to i~ow of 44~/o. This increase in resistance to flow cannot be attributed to a decrease in depth of the anterior chamber; on the contrary, the depth actually increases a littlew h e n the pressure is raised. So far as the relationship between depth of anterior chamber and resistance to flow is concerned, the present finding, that the resistance increases with decreasing depth, is in general agreement with earlier studies. B A r A n y and W o o d i n (1955) studied the relationship between facility C of outflow (the reciprocal of the resistance) and t h e v o l n m e V of t h e a n t e r i o r c h a m b e r in p e r f u s e d e n u c l e a t e d r a b b i t s ' eyes. T h e r e l a t i o n s h i p w as linear, t h e ratio C / V b e i n g c o n s t a n t , w i t h a n a v e r a g e v a l u e of 1.7 for 17 eyes: T h i s l i n e a r r e l a t i o n s h i p b e t w e e n f a c i l i t y of outflow a n d d e p t h of a n t e r i o r c h a m b e r w a s c o n f i r m e d b y B e c k e t a n d C o n s t a n t (1956a) for d i f f e r e n t species (cat, g u i n e a - p i g a n d r a b b i t ) . T h e s a m e a u t h o r s (1956b) also m o d i f i e d t h e v o l u m e of t h e a n t e r i o r c h a m b e r e x p e r i m e n t a l l y , e i t h e r b y c o n s t r i c t i n g t h e sclera or b y i n j e c t i n g s e ~ l m into the vitreous body; t h e y observed an increase in resistance when the volume of t h e a n t e r i o r c h a m b e r dimini.~hed. Fr a ngois, R a b a e y a n d l~eetens (1956a,b) a n d F r a n g o i s et al. (1958) s t u d i e d t h e ; n f l u e n c e of d e p t h of a n t e r i o r c h a m b e r on r e s i s t a n c e b y r e d u c i n g t h e v o l u m e of t h e posterior h a l f of t h e globe. T h e y p l a c e d a g u i l l o t i n e forceps w i t h a d j u s t a b l e s p a n a r o u n d t h e e qua tor . B y m e a n s of t h i s t h e y were a b l e to a l t e r t h e v o l u m e of t h e a n t e r i o r c h a m b e r a t will b y forcing t h e le ns a n d iris f o r w a r d . T h e y showed t h a t t h e r e s i s t a n c e i n c r e a s e d s t r o n g l y w i t h d i m i n i s h i n g d e p t h o f t h e a n t e r i o r c h a m b e r . T h e p r e s e n t e x p e r i m e n t s were c a r r ie d o u t w i t h o u t a n y s u c h artirice; t h e p e r f u s i o n fluid was n o t i n j e c t e d i n t o t h e v i t r e o u s b o d y b u t e n t e r e d t h e a n t e r i o r c h a m b e r l a t e r a l l y , a n d t h e v o l u m e of t h e a n t e r i o r c h a m b e r was n o t r e d u c e d b y e q u a t o r i a l compression. I t w a s e s s e n t i a l l y t h e large n u m b e r of eyes t h a t we were a b l e to s t u d y t h a t e n a b l e d us to o b t a i n v a l u e s of r e s i s t a n c e for d i f f e r e n t d e p t h s of a n t e r i o r c h a m b e r , to give t h e c u r v e of Fig. 1. T h e l a t t e r shows t h a t a d e p t h of 5 - 6 m m corresponds to a r e s i s t a n c e of 1.5, w h i l s t a d e p t h of 1.5 m m c or r e sponds to a resist a n c e of 13. B e t w e e n t h e two e x t r e m e s t h e i n t e r m e d i a t e v a l u e s m a y be r e a d o i l T h e s e r e s u l t s agree well w i t h those of F r a n g o i s et al. (1958). W h e n t h e p e r f u s i o n of t h e eyes is c a r r ie d o u t a t 60 m m Hg, t h e r e is a s i m i l a r corr e l a t i o n b e t w e e n d e p t h of a n t e r i o r c h a m b e r a n d outflow resistance, l~e ve r the le s s t h e s u p e r p o s i t i o n of t h e c u r v e s i n Figs. 1 a n d 2 shows t h a t t h e c u r v e is d i s p l a c e d to t h e r i g h t w h e n t h e pressure is i n c r e a s e d f r o m 20 to 60 r a m Hg. I n o t h e r words, t h e r e s u lts d e m o n s t r a t e once a g a i n t h a t t h e a n t e r i o r c h a m b e r d e e p e n s a l i t t l e w h e n t h e p r e s s u r e increases, a n d t h a t t h e r e s i s t a n c e increases w h e n the i n t r a o c u l a r p r e s s u r e rises. T h e records of t h e p r e s e n t studie s h a v e g i v e n a n a v e r a g e d e p t h of a n t e r i o r C h a m b e r of 2.92 m m for eyes p e r f u s e d a t 20 m m Hg. I f i t is c o n s i d e r e d t h a t t h e eyes were t a k e n f r o m s u b j e c t s aged m o r e t h a n 55 years, t h e figure is in good a g r e e m e n t w i t h t h e v a l u e o b t a i n e d b y W e e k e r s et al. (1961) on n o r m a l subjects. To repeat, t h e p e r f u s i o n of h u m a n eyes h a s s h o w n t h a t t h e r e s i s t a n c e to flow is g r e a t e r t h e s h a l l o w e r t h e a n t e r i o r c h a m b e r , a n d vice versa. T h e results show, also, t h a ~ the. r e a i s t a n c ~ a ~ t a i n s p a t h o l o g i c a l v a l u e s (greater t h a n 7) w h e n t h e d e p t h of t h e
ANTERIOI~ CHAMBER DEPTH AND AQUEOUS HUMOUR
233
anterior chamber is less than 2.2 ram. These experimental facts agree well with the clinical observations of Weekers and Grieten (1962) who fmmd that the average depth of eyes with angle-closure glaucoma was 2.30 ram; these authors found, moreover, that mydriasis induced by drugs induces a hypertension when the depth of the chamber is less than 2.5 ram. REFERENCES B~r~ny, E. and Woodin, A. M. (1955). Acta ~hysiol. scand. 33, 257. Becker, B. and Constant, M. (1956a). Arner. J. Ophthal. 42, 189. Becker, B. and Constant, M. (1956b). Arch. OphthaI., Chicago 55, 305. Franqois, J., Rabaey, M. and :Neetens, A. (1956a). Arch. Ophthal., Chicago 65, 488. Francois, J., Rabaey, M. and Nee~ens, A. (1956b). Arch. Ophthal., Chicago 55, 193. Franqois, J., Rabaey, M., Neetens, A. and Evens, L. (1958). Arch. Ophthal., Chicago 44, 204. Goldmann, H. (1932). Ber. dtsch, ophthal. Ges. 49, 435. Goldmann, H., Weekers, R., Grieten, J. and Lavergne, G. (1962). Ophthalmologica, Basel 143. Nihard, P. (1962). Acta ophthal. Kbh. 40, 42. Weekers, R., Grieten, J. and Lavergne, G. (1961). Ophthalmologica, Basel 142, 650. Weekers, R. and Grieten, J. {1962). Oph~halmologica, Basel 143, 56.