Local use of Heparin in the Eye*

LOCAL USE O F H E P A R I N IN T H E EYE* PELLET IMPLANTATION AT A N EXPERIMENTAL FILTERING SITE MALCOLM

W.

BICK,

M.D.

Springfield, Massachusetts AND ROBERT W .

HAINES,

M.D.

Baltimore, Maryland

The desirability of using heparin to prevent postoperative fibrosis after glaucoma surgery was mentioned in a previous paper.1 Methods of heparinization of the eye were investigated and it was shown that heparin did not enter the primary aqueous. It was concluded that direct local introduction of heparin would be the most efficient and practical means of heparinizing the eye. This study concerns the local use of heparin in the form of pellets and the results obtained from the implantation of such pellets at the site of an experimental filtering operation. Observations on the local absorption of heparin are made. PREPARATION OF PELLETS

The preparation of pellets of sodium heparin for local use was undertaken to provide a readily controllable mass of heparin to remain at a local site for a longer period of time than the heparin powder or the heparin solution. The following technique was employed for the preparation of heparin pellets. Powdered sodium heparin was loaded into one end of a cellophane soda straw for a distance of about 1 cm. The open end was moistened with a few drops of distilled water until the heparin powder melted. A mosquito clamp was placed distal to the heparin mass to prevent it from running down the cellophane tube. The segment of tube containing the wet heparin was placed in a vacuum dry* From the Wilmer Ophthalmological Institute of The Johns Hopkins Hospital and University. This study was supported in part by the Chalfont Fund. The heparin used in this work has been generously donated by the Abbott Research Laboratories, North Chicago, Illinois.

ing jar for 24 hours. The cellophane was then easily peeled off and the pellet of fused heparin was removed, weighed, and placed in absolute alcohol for storage. Pellets remaining in absolute alcohol lost no weight in three months. The pellets were cylindrical in shape with tapered ends and were quite brittle. They varied in weight from 60 to 34 mg. each, with an average weight of about 45 mg. Before use, the pellets were air dried on a sterile towel to remove the alcohol. ABSORPTION OF HEPARIN PELLETS

TWO experiments using heparin pellets were undertaken to determine the rate of solution of heparin in the intraocular fluid of the rabbit. An anterior-chamber implant of a 41-mg. pellet dissolved completely in 21 minutes, while 66 mg. of sodium heparin dissolved in 41 minutes. In order to insert a pellet of the latter size, it was necessary to dislocate the lens backward slightly. Subconjunctival implants of 43- and 55-mg. pellets dissolved in an hour and an hour and 15 minutes, respectively. In these experiments, there was no local inflammatory reaction. In Figure 1, a comparison is made between an intravenous dose of heparin of 25 mg. per kilogram and a similar dose in the form of a subconjunctival pellet implantation. When the heparin is given intravenously, the anticoagulant effect reaches a maximum immediately and is almost dissipated at six hours. In the case of the subconjunctival pellet, six hours are required for the maximal anticoagulant effect. Heparinization of the blood stream per-

774

LOCAL USE OF HEPARIN IN T H E EYE

775

* Kafcbi*

Pillet 2S™lM'

~g

si

E—a—Î"—J2—n~

H o u « follevî-ng H e ? » f i n

T

-ΓΓ

Aim'ir\!s*r<>+;«n

Fig. 1 (Bick and Haines). Anticoagulant effect of intravenous heparin and a subconjunctival heparin pellet implant.

sists for 18 to 24 hours after pellet implantation. If a similar pellet is implanted at the site of a filtering operation (fig. 2 ) , there is a delay in the appearance of heparin in the blood stream and a maximal clotting time is reached in two hours.

The anticoagulant effect of a pellet of 34 mg. (15 mg./kg.) implanted at a filtering site is also plotted in Figure 2. Both curves represent heparin which is released from the local site in excess of the capacity of the tissues to hold heparin. With pellets smaller

.acx Mim.

« £5-m 3 /K

Pellet

-

Pelle*

JSmj/K

JCTO planted

U"nder

IridencleislsFlap

fcUui

nPtev

Heparin

"ISr^T

Fig. 2 (Bick and Haines). Anticoagulant activity of heparin pellets placed at the site of an iris inclusion operation. The lower curve indicates tissue saturation with a slight excess of heparin. The upper curve shows a considerable excess of heparin.

776

MALCOLM W. BICK AND ROBERT W. HAINES

than 30 mg., no anticoagulant effect is noted. Consequently, the tissue saturation dose for a pellet implantation is about 30 mg. For purposes of tissue saturation, pellets in excess of this may be regarded as wasted heparin. It is interesting to study the rapidity with which the heparin enters the blood stream

Fig. 3 (Bick and Haines). Heparin implant at site of filtering operation. The conjunctiva is sutured well behind the implant.

according to the site of implantation. If heparin is placed directly into the anterior chamber by injection of a saturated solution, a maximal effect is noted in the peripheral blood in one hour. 1 With pellet implantation at a filtering site (fig. 2), the time is lengthened to two hours; whereas, a simple subconjunctival implant (fig. 1) delays the maximal effect to six hours. It would appear, therefore, that the wash of aqueous through the filtering operation is instrumental in carrying heparin through the channels by which it is absorbed into the blood stream. This wash of aqueous saturated with heparin is sufficient to prevent the local formation of fibrin in the absorbing channels for at least 18 hours and probably for several hours after the anticoagulant effect

of the heparin is no longer apparent in the circulating blood. EXPERIMENTAL USE OF HEPARIN PELLETS

An experiment was undertaken to determine what effect, if any, the local use of heparin had on the development of postoperative fibrosis and filtration in the normal rabbit eye following a filtering operation. Heparin pellets manufactured and stored as described above were used throughout. Albino rabbits were shaved closely about the lids with an electric clipper and were anesthetized with 300 mg. of nembutal per kilogram of weight by the intravenous route. The skin of the lids was painted with 3.5percent iodine. Pontocaine was instilled into the conjunctival sac and, under sterile conditions, an iris inclusion operation was performed through a keratome incision. A large flap of conjunctiva extending well back to the equator was employed in each case. The optimal site for such a procedure was found to be the superior portion of the globe next to the lateral muscle. A fine running silk suture was used to close the flaps. In some cases, the sphincter of the iris was cut; in others, the iris was included without cutting. In those eyes in which heparin implants were used, a milligram of heparin in 0.1 cc. solution was introduced into the anterior chamber as soon as the keratome incision was made. A heparin pellet was then placed at the site of the inclusion or right adjacent to it and the flap was closed (fig. 3). Sutures were removed during the second week under topical pontocaine. The eyes operated upon fall into three groups: (1) Those in which heparin was implanted directly; (2) those in which no heparin was implanted and where the animal received no heparin; and (3) those in which no heparin was used directly, but where a heparin pellet had been placed under the conjunctival flap in the opposite eye within a half hour. In this way we were able to observe the effect of varying uncontrolled degrees of systemic heparinization and in-

LOCAL USE OF HEPARIN IN THE EYE

Fig. 4 (Bick and Haines). Appearance of rabbit eye prior to injection of trypan blue.

tense, well-controlled local heparinization. The weight of the heparin implant employed varied from 60 to 34 mg. and averaged about 45 mg. The average weight of the rabbits employed was 2.5 kilograms. The smallest dose used was sufficient to have some effect on the clotting time for 5 hours and the largest for 18 hours. Every pellet used exceeded the tissue saturation level. The animals were observed for 6 weeks to 2 months and, after the eyes had whitened completely, the sizes of the blebs were compared, and filtration was observed. Filtration was estimated by puncturing the cornea with a hypodermic needle, allowing most of the aqueous to escape, and then injecting 0.1 cc. of 1-percent solution of trypan blue. The rapidity of filling of the conjunctival bleb, the amount of filling, and the spread of the dye under the conjunctiva were observed for 15 minutes. Filtration was classified in three groups : (1) Absent, (2) poor, or (3) good. If the bleb filled slowly and incompletely during the period of observation, the filtration was considered to be poor (figs. 4 and 5). If the bleb filled rapidly and the dye spread out under the conjunctiva around the bleb, filtration was considered to be good (fig. 6). The

777

Fig. 5 (Bick and Haines). When the dye was confined to, the bleb, filtration was considered to be poor.

size of the bleb in general corresponded to the degree of filtration present. There were exceptions, however, and grading was made solely on the basis of the spread of the dye. After the filtration experiment, the rabbit was killed, and the eyes were fixed in Zenker's solution for histologie study. RESULTS

The results of the filtration experiments in the three groups are summarized in Table 1. If the absent and poor filtration are

Fig. 6 (Bick and Haines). When the dye spread under the conjunctiva outside the bleb, filtration was graded as good.

MALCOLM W. BICK AND ROBERT W. HAINES

778

Fig. 7 (Bick and Haines). Section taken from the control eye in which no filtration was observed. The heavy episcleral layer of fibroblasts (a) arising from normal sciera (b) which bridges over the iris (c) impeded the spread of trypan blue to the subconjunctival space (d).

grouped together, a statistically significant diflPerence exists between Groups 1 and 3 which gives x 2 = 5.49. Since P = 2 at 5.412, there are only 2 chances in 100 that the observations are a matter of chance. The differences observed indicate that intense local heparinization with saturation of the tissues is of benefit in promoting filtration.

test, one is impressed that there are two critical points which determine the success or failure of filtration. These are: (1) The channels from the anterior chamber between the iris and the cornea on one side and sciera on the other, and (2) the organization and thickness of the fibroblastic layer overlying the iris under the conjunctiva. This fibrous layer bridges the iris from the cornea to the sciera. In Figure 7, the normal sciera is seen in the lower right corner. The iris is in the lower left corner and, above this, is the very heavy layer of fibroblasts which bridges over the iris. Overlying this is the subconjunctival tissue. This heavy fibrous capsule impeded the spread of trypan blue so that no filtration was possible. This section was taken from one of the control eyes in which no filtration was observed. In Figure 8, the channel between anterior chamber and subconjunctival space is closed by organization of the iris with episcleral fibrous tissue so that a free channel from the anterior chamber does not exist. Even though the iris is well incarcerated and the fibrous subconjunctival layer is not excessivelv thick, no filtration was observed.

HlSTOLOGIC OBSERVATIONS

I n a correlation of the histologie picture with the degree of filtration recorded on our

· # -

TABLE 1 FUNCTION OF FILTERING OPERATIONS IN HEPARINIZED AND NONHEPARINIZED RABBIT EYES

Filtration

Group 1 Heparin Implant (Locally)

Group 2 Hepannized (Remotely)

Absent Poor Good

0 10 7

2 7 4

3 8 1

17

13

12

3 G nC o n tJ*. ro1 Fig. 8 (Bick and Haines). Section from control eye in which no filtration was observed. There is no free channel from the anterior chamber. The episcleral fibrous layer is not excessively dense, (a) Sciera, (b) cornea, (c) iris, (d) episcleral fibrous layer.

LOCAL USE OF HEPARIN IN THE EYE In Figure 9, taken from one of the eyes in which a heparin pellet was directly placed, we observe a free channel over the anterior but not the posterior surface of the iris. The fibrous layer extending from the episcleral tissue is of sufficient thickness to impede filtration. Filtration was rated as poor in this eye. In Figure 10 one is able to see a free channel of flow from the anterior chamber. The fibrous layer is loosely organized and allows the formation of cystic spaces. Bath of these sections represent eyes in which filtration was rated as good, and in which heparin implants were placed at the time of surgery. DISCUSSION AND CONCLUSIONS

A heparin pellet dissolves somewhat more rapidly in the aqueous than under the conjunctiva. The high solubility of heparin in tissue fluids and its relatively slow appearance in the blood stream indicate that it remains locally in high concentrations even though the pellet has dissolved. This would seem to fit in with the known facts that heparin is nondialyzable and forms dissociable complexes with proteins.2 We were able to follow the release of heparin into the

779

Fig. 9 (Bick and Haines). Filtration was rated poor. Despite a free channel over the anterior surface of the iris, a dense episcleral layer of fibrous tissue impeded filtration to the subconjunctival space, (a) Cornea, (b) sciera, (c) iris, (d) episcleral fibrous layer.

blood stream for almost 24 hours following local implantation. A pellet of 30 mg. is sufficient to saturate an implantation site and have a slight excess detectable in the blood stream of the rabbit. How long heparin remains effective locally is still to be determined. From the present study, it would appear that heparin remains for a sufficient period of time locally to

Fig. 10 (Bick and Haines). Sections taken from eyes in which heparin implants were used. The episcleral fibrous layer is loosely organized and permits the formation of cystic spaces (a). There are open channels between the anterior chamber (b) and the subconjunctival space (c).

780

MALCOLM W. BICK AND ROBERT W. HAINES

modify in some manner the normal process of tissue repair. There is enough heparin present to prevent fibrin formation for at least a day, and this may be all that is required to improve filtration in the normal rabbit eye. Heparin pellets implanted at the site of filtering operations caused no undue reaction and histologie observations made during the first week after subconjunctival implantation substantiated this gross observation. There is no reason why heparin cannot be used locally in the human being in the same manner as in the rabbit. A pellet of 30 to 60 mg. should have little or no effect on the blood coagulation time in the human. On theoretical and experimental grounds, such implantation of heparin might be of

value in those cases where fibrin formation and secondary fibrosis are to be avoided. It should be borne in mind that the eyes used in our animal study were not inflamed or congested, conditions where heparin might show its full usefulness. SUMMARY

The preparation of heparin pellets was briefly described. The local absorption of heparin pellets placed in ocular tissues was observed. The experimental use of heparin pellets at a filtering site indicates that intense local heparinization is of benefit in promoting filtration in the normal rabbit eye. Heparin causes no undue local reaction. 292 Worthington Street. The Johns Hopkins Hospital (5).

REFERENCES

1. Bick, M. W. : Heparinization of the eye. Am. J. Ophth., 32:663,1949. 2. Mason, F. F. : Heparin : A review of its history, chemistry, physiology, and clinical application. Surgery, 5 :451-4S6, 618-634, 1938.

O P H T H A L M I C MINIATURE There are four varieties of protuberance of the iris. The first, resulting from rupture of the cornea, resembles the head of an ant, so that it may be mistaken for a pustule. I will in a short time speak of the difference between the two. The second variety of prolapse is larger and more prominent than the first. It is called "fly's head." The third sort is still larger and may protrude so far as to come in contact with the eyelashes. This condition is a very serious bar to vision. Its appearance gives it the (vulgar) name of "berry," and it certainly has a grapelike shape. The fourth variety bears the vernacular name "nail-head." It is found in chronic cases, where the cornea has grown over the protrusion, thus giving the swelling the likeness attributed to it. Paulus calls it simply "finger nail." Memorandum Book of a Tenth Century Oculist Translated by Casey A. Wood.