Fibrinolysis and Outflow Resistance in the Eye

FIBRINOLYSIS AND O U T F L O W RESISTANCE IN T H E EYE MAURIZIO PA TDOLFI, M.D.

Washing >n, D.C. Outflow of aqueous humor through the channels at the angle of the anterior cham­ ber of the eye is regulated by mechanisms which still remain only partially elucidated. In some animal species hyaluronic acid present in the trabecular meshwork is as­ sumed to be involved in the flow regulation, since application of hyaluronidase increases the outflow rate.1'2 In other species hyaluron­ idase has no effect.3 Histochemical studies have demonstrated a selective localization of fibrinolytic activity, caused by an activator of plasminogen, at the chamber angle of the eye of man and other primates.4'5 These findings suggest in these species an influence of fibrinolysis on the outflow of aqueous hu­ mor. Supporting evidence for this hypothesis is provided by the observation of Grant 6 that eyes from a glaucoma patient who had under­ gone fibrinolytic treatment showed an unex­ pected low outflow resistance, though in vitro perfusion of human eyes with streptokinaseactivated human globulin (containing chiefly an activator of plasminogen) gave inconsis­ tent results. Recently it was found that a por­ cine preparation of plasmin produced an un­ ambiguous lowering of the outflow resistance in the eye of the rhesus monkey.7 The pres­ ent paper attempts to elucidate the possible role of fibrinolysis in the regulation of outflow of aqueous humor. Eyes of monkey and rabbit were perfused in vitro with var­ ious fibrinolytic agents. MATERIAL AND METHOD

Eyes were obtained from young individ­ uals of rhesus monkey (Macaca mulatta) or vervet (Cercopithecus aethiops), weighing From the James F. Mitchell Foundation Insti­ tute for Medical Research. This study was sup­ ported by grant HE-0S020 from the United States Public Health Service, National Institutes of Health, National Heart Institute to Dr. Tage Astrup, Director of Research.

around 4.0 and 3.0 kg, respectively. The eyes were enucleated within 12 hours after death and used immediately. Care was taken to avoid strong traction during enucleation so as not to damage the resistance (massage effect of Bârâny 1 ). In the vervet, the outer wall of the orbit was first removed to facili­ tate sectioning of the optic nerve. Rabbit eyes (white New Zealand) were obtained from adult animals killed by Nembutal and used immediately. No regard was given to which eye of a pair was removed or cannulated first. Lyophilized trypsin-activated porcine plas­ min, labeled 25 Novo units ( N U ) per vial, was obtained from the Novo Laboratories, Copenhagen. The preparation used ( # 1 * 1 4 ) contained per vial 1.0 millimol lysine and 0.25 millimol phosphate buffer, pH 7.3. When tested with the urinary trypsin inhibitor,8 it was found not to be contami­ nated with trypsin (assays performed by Uwe Nissen, M.Se, of this Institute). Solu­ tions prepared in saline (0.15M NaCl) were used immediately or distributed in small vials and stored at —20°C for periods not exceeding one month. Glycerol-activated human plasmin in 5% glycerol was supplied by the American Red Cross from the Michigan Department of Health (courtesy of Dr. J. T. Sgouris). Di­ lution of this plasmin with saline produced a precipitate which was removed by centrifugation (2,500 rpm for 10 minutes). The su­ pernatant was assayed and used immediateiy· Human urokinase (Leo Pharmaceuticals, Copenhagen) was as a lyophilized powder in vials containing 5,000 Ploug units (ap­ proximately 6,500 C.T.A. units as defined by the Committee on Thrombolytic Agents, Advisory to the National Heart Institute). It was dissolved in saline and used immedi­ ately.

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1142

Trasylol® (a kallikrein inactivator and trypsin inhibitor isolated from bovine par­ otid gland) was obtained from FBA Phar­ maceutical Inc., New York, in vials contain­ ing 5,000 KIU (kallikrein inhibitor units) per ml. It was diluted in saline before use. All these solutions were adjusted to pH 7.0 before the perfusion. Crystalline trypsin (Novo Laboratories, Copenhagen) containing 27 Anson units per gm was dissolved in saline barbital buffer (0.05 M sodium barbital in 0.1 M NaCl, pH 7.75). The fibrinolytic activity of perfusion fluids was assayed by the fibrin plate method.9 Pairs of eyes from the same animal were simultaneously perfused by Bârâny's manu­ ally operated constant pressure method,1 using a 27-gauge needle attached to one-ml pipet graduated in 1/100 ml. The eyes, placed in 25-ml beakers, were supported and covered up to the limbus by cotton pads soaked in saline. Perfusion pressure was 27 cm of H 2 0 (20 mm H g ) . When­ ever possible each eye was perfused with at least 0.5 ml of liquid after a steady inflow rate had been reached two to three minutes after cannulation. The period of time re­ quired for each 50 μΐ to enter the eye was recorded. Flow resistance was expressed in mm Hg per μΐ per minute, which is the re­ ciprocal of the outflow facility (μΐ per min per mm H g ) . The corneas were kept moist 6 (

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1

1

1

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by frequent dripping of saline. In view of the deteriorating effect of saline on filter resistance,3-10 it was thought more appropri­ ate to relate the perfusion to the volume of liquid perfused rather than to the time elapsed. For this reason, outflow resistances were compared at points where equal vol­ umes of perfusion fluid had entered the eye. All perfusions were performed at room temperature. Most of the experiments were performed between March and June when the room temperature varied about 5°C. Data obtained from a perfusion of human plasmin in a rhesus eye are shown in Figure 1. RESULTS

Several experiments were interrupted be­ cause of leakage or defective cannulation, or by occlusion of the needle. The corneal tis­ sue of the monkey was more consistent and resilient than that of the rabbit, in which leakage at the needle entrance occasionally occurred. PERFUSIONS

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I ol 0

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I 0.3 ML

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SALINE

1

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3-

WITH

Cercopithecus. As controls, 20 pairs of vervet eyes were perfused with saline. The calculated average values of outflow resis­ tance, with range and standard deviation, are presented in Table 1. The resistance de­ creased less during saline perfusion in Cer­ copithecus than in the rhesus monkey pre­ viously studied.7 The washing-out effect is noticed only at the end of the perfusion pe-

-

|

DECEMBER, 1967

0.5

Fig. 1 (Pandolfi). Influence of human plasmin on flow resistance in rhesus eyes. Abscissa. Volume of perfusion fluid in ml entering the eye. Ordinate. Resistance expressed as time in minutes required for 0.05 ml of perfusion fluid to enter the eye. Eye 1 (full circles) perfused with human plasmin. Eye 2 (empty circles) perfused with saline alone.

VOL. 64, NO. 6

1143

FIBRINOLYSIS AND OUTFLOW RESISTANCE TABLE 1 CERCOPITHECUS EYES (20 PAIRS) PERFUSED WITH ISOTONIC SALINE

Mean outflow resistance (mm Hg per pIXmin -1 ). At 0.50 ml the mean was calculated from 17 values. Ml Fluid Infused

0.05

0.10

0.25

0.50

Eye 1 (Saline)

1.43±0.51* 0.44-2.20f

1.73 + 0.66 0.50-2.90

1.73 + 0.61 0.66-2.66

1.50 + 0.43 0.86-2.40

Eye 2 (Saline)

1.46 + 0.59 0.40-2.96

1.64±0.61 0.50-2.96

1.69 + 0.63 0.73-2.86

1.56 + 0.56 0.81-2.76

Ratio of average: Eye 2 Eyel * Mean + S.D. t Range.

1.02

riod. Differences in resistance were greater between eyes of different individuals than between eyes of the same individual. The ratio of the averages did not change signifi­ cantly during perfusion. Rabbit. Similarly, five pairs of rabbit eyes were perfused with saline (table 2 ) . There is marked decrease in outflow resistance during perfusion. The ratios of the averages fluctuated slightly. This could be due to the few samples assayed, for which reason stan­ dard deviations were not calculated. PERFUSIONS

WITH

PORCINE

0.98

0.95

PLASMIN

Rhesus. In 20 pairs one eye was perfused with porcine plasmin and the other with sa­ line. In eight eyes the perfusion fluid con­ tained 1.0 NU of plasmin per ml. In three

1.04

other groups, each of four eyes, the solu­ tions contained 0.5, 0.25, and 0.12 NU/ml, respectively. Table 3 shows the average val­ ues of the resistance with range. The por­ cine plasmin produced an increased flow rate as shown by the increase in ratio be­ tween the averages of controls and the plasmin-perfused eyes. The effect decreases with progressive dilution of plasmin, but it is still noticeable at a concentration of 0.12 NU/ml. The results confirm our previous observations on rhesus eyes.7 Cercopithecus. Similarly, 14 pairs of eyes were perfused with porcine plasmin and sa­ line. In six eyes the perfusion fluid con­ tained 2.0 NU/ml, and in eight eyes the concentration was 1.0 NU/ml. As before, the contralateral eyes were perfused with

TABLE 2 RABBIT EYES (FIVE PAIRS) PERFUSED WITH ISOTONIC SALINE

Mean outflow resistance (mm Hg per /ulXmin-1). Ml Fluid Infused

0.05

0.10

0.25

0.50

Eye 1 (Saline)

4.16* 2.10-7.60f

4.54 1.92-7.00

3.53 1.87-5.92

3.12 1.60-5.70

Eye 2 (Saline)

3.84 2.22-5.76

4.17 2.20-6.80

3.45 2.17-5.62

2.56 1.68-4.48

Ratio of average: Eye 2 Eye 1 * Mean. t Range.

0.92

0.92

0.98

0.82

1144

AMERICAN JOURNAL OF OPHTHALMOLOGY

DECEMBER, 1967

TABLE 3 PERFUSION OF RHESUS EYES WITH PORCINE PLASMIN -1

Mean outflow resistance (mm Hg per fjIXmin ).

Ml Fluid Infused

0.05

0.10

0.25

0.50

Eyel (Plasmin 1 U/ml)

1.66* 1.34-1.94f

1.56 1.16-1.94

1.23 1.00-1.44

1.04 0.84-1.06

Eye 2 (Saline)

2.12 1.50-2.84

2.38 1.76-3.10

1.85 1.70-2.76

1.72 1.26-2.40

1.27

1.52

1.50

1.65

Eyel (Plasmin 0.5 U/ml)

1.67 1.00-2.10

1.49 1.16-1.90

1.47 1.14-1.66

1.11 0.94-1.40

Eye 2 (Saline)

2.12 1.56-2.56

2.08 1.60-2.60

1.73 1.24-2.22

1.41 1.14-1.70

1.27

1.39

1.18

1.27

Eyel (Plasmin 0.25 U/ml)

1.96 1.18-3.16

2.21 1.50-3.34

1.64 1.16-2.06

1.25 0.90-1.56

Eye 2 (Saline)

2.32 1.86-3.26

2.50 1.64-3.64

1.85 1.44-2.90

1.67 1.04-2.60

1.18

1.13

1.13

1.34

Eyel (Plasmin 0.12 U/ml)

1.85 1.30-2.46

1.92 1.20-2.44

1.75 1.00-2.10

1.55 0.90-2.00

Eye 2 (Saline)

2.08 1.50-2.86

2.32 1.40-3.34

1.79 1.10-2.54

1.64 1.04-2.20

1.12

1.21

1.02

1.06

Ratio: Eye 2 ,„ . , (8pa.rs) E y e l

Ratio: Eye 2 ,„ Eye 1 ( 4

Ratio: Eye 2 Eyel

. s palrs)

. , lA (4palrs)

Ratio: E

Ve2

Eyel

u( 4

■ \

Pairs)

* Mean. t Range. saline alone. Again, porcine plasmin pro­ duced an immediate and marked lowering effect on the outflow resistance in both con­ centrations (table 4 ) . Rabbit. In each of eight pairs, one eye was perfused with a solution containing 2.0 NU/ml of porcine plasmin. The contralater­ al eye was perfused with saline. The mean outflow resistances with range are reported in Table 5. It is evident that plasmin does not decrease the outflow resistance in the rabbit eye. The agreement between the two

groups is as if both series had been perfused with saline (table 2). PERFUSIONS

WITH

HUMAN

PLASMIN

Six perfusions were carried out on rhesus eyes using human plasmin. Dilution of the stock solution with an equal volume of sa­ line gave, after centrifugation, a superna­ tant having on fibrin plates a fibrinolytic ac­ tivity comparable to a solution containing 2.0 NU/ml of porcine plasmin. As controls, the contralateral eyes were perfused with

TABLE 4 P E R F U S I O N OF CERCOPITHECUS E Y E S WITH PORCINE PLASMIN -1

Mean outflow resistance (mm Hg per μΐΧπΰη ). At 0.50 ml the mean was calculated from five values. 0.05

0.10

0.25

0.50

Eye 1 (Plasmin 2 U/ml)

0.91* 0.60-1.20f

1.10 0.70-1.46

1.02 0.60-1.66

0.98 0.72-1.14

Eye 2 (Saline)

1.43 0.84-2.20

1.67 0.86-2.64

1.85 0.84-3.04

1.45 0.76-2.00

1.57

1.50

1.81

1.46

Eye 1 (Plasmin 1 U/ml)

1.45 0.66-2.84

1.47 0.84-2.86

1.52 0.70-2.74

1.52 1.04-2.60

Eye 2 (Saline)

1.82 0.90-3.16

2 18 0.86-3.10

1.85 0.94-2.90

1.82 1.10-2.60

1.26

1.47

1.22

1.20

Ml Fluid Perfused

Ratio: Eye 2 ,£ . N Eyel ( 6 p a , r s )

Ratio: Eyel

(8pmrs)

* Mean.

t Range.

saline containing 2.5% glycerol. Like por­ cine plasmin, though less marked, human plasmin showed an immediate lowering effect on the outflow resistance in all experi­ ments (table 6). An example of perfusion with human plasmin is shown in Figure 1 which resembles curves produced previously with porcine plasmin.7 PERFUSIONS

WITH

UROKINASE

Three perfusions were made on rhesus eyes with solutions of urokinase containing

1,250, 2,500, and 5,000 Ploug units/ml respec­ tively. In all experiments urokinase failed to influence the outflow resistance. The differ­ ences observed were larger than in the series perfused with saline alone. PERFUSIONS W I T H PLASMIN AND

TRASYLOL®

When Trasylol® was added to plasmin in amounts sufficient to inhibit fibrinolytic ac­ tivity, the mixture did not lower the outflow resistance of rhesus eyes. Thus, in two ex­ periments one eye was perfused with a mix-

TABLE 5 P E R F U S I O N OF RABBIT EYES WITH PORCINE PLASMIN -1

Mean outflow resistance (mm Hg per μΐχπύη ).

Ml Fluid Infused

0.05

0.10

0.25

0.50

Eyel (Plasmin 2 U/ml)

3.34* 2.10-4.14f

3.29 2.60-4.05

2.62 2.06-3.44

2.32 2.00-3.20

Eye 2 (Saline)

3.04 1.86-4.00

3.41 2.56-3.60

2.72 2.34-3.20

2.52 2.18-3.11

Ratio: Eye 2 (8 pairs) Eyel * Mean.

t Range.

0.91

1.04

1.04

1.09

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DECEMBER, 1967

TABLE 6 P E R F U S I O N O F R H E S U S E Y E S (SIX P A I R S ) W I T H H U M A N PLASMIN IN A C O N C E N T R A T I O N

FIBRINOLYTICALLY EQUIVALENT TO 2 U / M L OF PORCINE PLASMIN

Mean outflow resistance (mm Hg per μ\Xmin-1). At 0.50 ml the mean was calculated from four values. 0.05

0.10

0.25

0.50

Eyel (Plasmin)

1.54* 1.00-2.14f

1.52 1.14-1.96

1.50 0.94-1.70

1.14 0.94-1.26

Eye 2 (Saline)

1.97 1.16-2.94

2.22 1.40-2.80

1.87 1.34-2.74

1.58 1.26-1.76

Ml Fluid Infused

Ratio: Eye 2 Eyel * Mean. t Range.

1.46

1.28

ture of equal volumes of porcine plasmin (2.0 NU/ml) and of Trasylol® solution (1,000 K I U / m l ) . Tested on fibrin plates this mixture showed only a trace of fibrinolytic activity. The other eye was perfused with porcine plasmin at a concentration of 1.0 NU/ml. The outflow resistance was markedly decreased in the eye perfused with plasmin, while with the mixture the resis­ tance decreased after the pattern observed with saline alone. In three other perfusion experiments one eye of each pair was first injected with 0.01 ml saline containing 5,000 KIU/ml of Trasylol,® while the contralateral eye re­ ceived 0.01 ml of saline. After injection, the needle was pushed through the opposite side of the cornea, the syringe removed and the needle left in situ. For these experiments

1.43

1.39

hypotonie eyes were enucleated from ani­ mals which had been dead several hours. This precaution was taken to avoid a rise in the intraocular pressure with damage to the resistance resulting from the injection. After injection the eyes were left at room temperature for five minutes and then per­ fused with porcine plasmin (2.0 NU/ml). The lowering effect of plasmin on the outflow resistance was observed only in the eyes pretreated with saline. In the eyes pretreated with Trasylol® the resistance de­ creased as if the eyes were being perfused with saline (fig. 2). Finally, three pairs were perfused solely with Trasylol,® in con­ centrations of 1,000, 2,000, and 5,000 K I U / ml, respectively, and with saline. Trasylol® alone had no influence on the outflow re­ sistance.

6 5 4 If)

ω z 2

-

·

·

·

o -

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·

·

#

o O

o

° °

2 I 0.1

·

0.2

0.3 ML

° 0.4

o

0

0.5

_

Fig. 2 (Pandolfi). Prevention of the plasmin effect on outflow re­ sistance by means of Trasylol®. Abscissa and ordinate as in Figure 1. Both eyes (rhesus) perfused with porcine plasmin. Eye 1 (full circles) pretreated with Trasylol®. Eye 2 (empty circles) pretreated with saline.

VOL. 64, NO. 6 PERFUSIONS

FIBRINOLYSIS AND OUTFLOW RESISTANCE

WITH

1147

TRYPSIN

Five pairs of rhesus eyes were perfused with trypsin dissolved in buffer and with buffer alone. The trypsin concentration (20 μ§/ηι1) was approximately equivalent to 2.0 NU/ml of porcine plasmin. In three of the five experiments trypsin lowered the outflow resistance, but in the other two it had only a slight influence. The mean values with range are reported in Table 7. DISCUSSION

When the anterior chamber of the eye is perfused with saline there is a progressive reduction of the outflow resistance, the socalled "washing-out" effect.3 This effect is observed in several animal species, including primates. In some species it can be enhanced when hyaluronidase is added to the perfu­ sion fluid.1-3 The cause of the washing-out effect is not fully understood. It is believed that a substance, presumably hyaluronic acid, coats the outflow pathways, thus con­ tributing to the total outflow resistance. It is assumed that during perfusion with saline this resistance progressively drops because the substance is mechanically removed by the perfusion liquid.3 When hyaluronidase is present, the effect of this enzyme is added to the mechanical action of the liquid and the resistance drops faster. However, in man and monkey, the effect of hyaluroni­ dase is controversial. While François, Rabaey and Neetens 11 found a reduction of the

outflow resistance in the human eye in the presence of hyaluronidase, although more slight and more variable than in the rabbit, Pedler 12 and Grant 6 could find no clear effect. In monkey eyes, Abraham 13 and Becker14 observed only a weak effect of hy­ aluronidase. In contrast, porcine plasmin was found to have an unequivocal lowering effect on the resistance of rhesus eyes,7 sug­ gesting the existence in the eye of the pri­ mate of a plasmin-sensitive barrier to the outflow of aqueous humor. The effect of porcine plasmin on the outflow resistance of rhesus eyes decreased by dilution and was barely noticeable at a concentration of 0.12 NU/ml (table 3). Human plasmin was also active (table 6 ) . Plasmin was active in the vervet (table 4) but failed to influence the outflow resis­ tance in the rabbit (table 5). This finding is significant because perfusion of hyaluroni­ dase has been reported in particular to de­ crease the resistance in the rabbit eye. These observations suggest the existence of bar­ riers which vary in type from one species to another. Tissues of the anterior chamber, and especially the aqueous outflow path­ ways, are rich in plasminogen activator,4'5 and in man and monkey the aqueous humor contains plasminogen and plasminogen ac­ tivator.5'15 The finding that plasmin decreases the outflow resistance provides further sup­ porting evidence that fibrinolysis is involved

TABLE 7 P E R F U S I O N OF RHESUS EYES (five PAIRS) WITH TRYPSIN

Mean outflow resistance (mm Hg per /ilXmin -1 ). At 0.50 ml mean of only four values. 0.05

0.10

0.25

0.50

Eye 1 (Trypsin)

1 S3* 1.36-3.00f

1.57 1.34-2.40

1.37 1.00-2.10

1.21 0.84-1.16

Eye 2 (SBB)

2.47 1.46-3.50

2.22 1.54-2.66

2.08 1.24-2.00

1.33 0.86-1.60

Ml Fluid Infused

Ratio: Eye 2 Eyel * Mean.

t Range.

1.35

1.41

1.52

1.11

in the regulation of the outflow of aqueous humor in man and other primates. The experiments with the protease inhibi­ tor Trasylol® indicate that the effect of plasmin is due to its enzymatic action and could not be caused by impurities contained in the plasmin preparations. The ambiguous re­ sults with trypsin could possibly be attrib­ uted to the sensitivity of trypsin to protease inhibitors, which could make the trypsin de­ pend on contaminating inhibitors, possibly present in the eye, to a higher extent than is plasmin. Perfusion with urokinase had no in­ fluence on the flow resistance. This obser­ vation could appear to contradict the as­ sumption of a plasmin-resistant barrier, since urokinase produces plasmin by activa­ tion of plasminogen. However, since strong solutions of plasmin were needed to produce the in vitro effect, it is quite possible that the amount of plasminogen available in the eye is insufficient to cause a noticeable re­ duction of flow resistance. In the physiolog­ ic regulation of flow resistance a regulated production of small amounts of plasmin would be required, for which the plasmino­ gen available in the aqueous humor5 might be sufficient. Hence, the urokinase experi­ ments do not contradict the suggestion that a plasmin-resistant barrier participates in the regulation of outflow of aqueous humor in the eye of man and other primates. SUMMARY

The effect of fibrinolysis on outflow resis­ tance in the eye was studied by means of in vitro perfusions. Porcine and human plas­ min markedly decreased the outflow resis­ tance in rhesus and vervet eyes. This effect was caused by the proteolytic action of the enzyme, since no reduction in resistance was noticed if plasmin was neutralized by a pro­ tease inhibitor (Trasylol®). In some experi­ ments, trypsin decreased the resistance in

rhesus eyes but its effect was variable. Urokinase had no effect. Plasmin failed to influence outflow resistance in the rabbit. It is suggested that intraocular fibrinolysis plays a role in the regulation of outflow of aqueous humor in man and primates. 5401 Western Avenue, N.W. (20015) REFERENCES

1. Bârâny, E. H., and Scotchbrook, S. : Influ­ ence of testicular hyaluronidase on the resistance to flow through the angle of anterior chamber. Acta Physiol. Scand. 30:240, 1954. 2. Bârâny, E. H. : In vitro studies of the re­ sistance to flow through the angle of the anterior chamber. Acta See. Med. Uppsala, 59:260, 1953. 3. Melton, C. E. and DeVille, W. B. : Perfusion studies on eyes of four species. Am. J. Ophth. 50:302,1960. 4. Kwaan, H. C. and Astrup, T.: Localization of fibrinolytic activity in the eye. Arch. Path. 76:595,1963. 5. Pandolfi, M. and Kwaan, H. C. : Fibrinolysis in the anterior segment of the eye. Arch. Ophth. 77:99, 1967. 6. Grant, W. M. : Experimental aqueous perfu­ sions in enucleated human eyes. Arch. Ophth. 69:783,1963. 7. Pandolfi, M. and Astrup, T. : Effect of plas­ min on outflow resistance in the primate eye. Proc. Soc. Exp. Biol. Med. 121:139, 1966. 8. Nissen, U. : Estimation of trypsin in pres­ ence of plasmin and their separation by gel filtra­ tion. Ann. Biochem. 14:480, 1966. 9. Astrup, T. and Müllertz, S.: The fibrin plate method for estimating fibrinolytic activity. Arch. Biochem. Biophys. 40:346, 1952. 10. Bârâny, E. H. : The mode of action of pilocarpine on outflow resistance in the eye of a primate (Cercopithecus ethiops). Invest Ophth. 1:712, 1962. 11. François, J., Rabaey, M. and Neetens, A. : Perfusion studies -on the outflow of the aque­ ous humor in human eyes. Arch. Ophth. 55:193, 1956. 12. Pedler, C. : The relationship of hyaluroni­ dase to aqueous outflow resistance. Tr. Ophth. Soc. U.K. 76:51, 1956. 13. Abraham, quoted by Perkins, E. S. : Tr. Ophth. Soc. U. K. 76:62,1956. 14. Becker, B. : In Newell, F. W. (ed) : Glauco­ ma. Transactions of the fourth conference spon­ sored by Josiah Macy Jr. Foundation. Princeton, 1959, p. 80. 15. Franceschetti, A. and Eichenberger, E. : Fibrinolyse im Kammerwasser menschlicher und tierischer Augen. Experientia, 15:130, 1959.