Problem of Acute ocular hypotonia in modern ophthalmosurgery

ADVANCE COPY

Melyanchenko N.B.

Problem of Acute Ocular Hypotonia in Modern Ophthalmosurgery

2001

УДК 617.7

The monograph is dedicated to one of the most actual problems of modern ophthalmosurgery - syndrome of acute ocular hypotonia, that is complex of specific pathophysiological reactions, arising in response to traumatic depressurization and decompression of the eyeball.

Having systematised available scientific and practical data and also having made series of personal investigations, the author wants to draw the interest of scientists and specialists-practitioners to the problem of acute ocular hypotonia, to give possibility to look in other way at the nature and mechanisms of development of pathological processes which seem to be well-studied and well-known, to use the available methods of influence in order to prevent possible complications more effectively.

The book would be useful for teachers of medical institutes and also for clinical interns and young doctors grasping principles of eye microsurgery.

ISBN 5-900667-04-9

The publishing house apologizes for possible inexactitude of the English version of the monograph because while preparing this specimen edition technical translation of the text was performed without enlisting the services of the translator possessing special skills in the sphere of ophthalmology.

Melyanchenko N.B.,1999

From the author

Wide introduction of microsurgery into ophthalmosurgical practice has allowed significantly reduce frequency and heaviness of operative and postoperative complications, has improved quality of restoration and adaptation of tissues injured at treatment of penetrating wounds of the eye, has served as a powerful spur to development of transplantation and implantation. At the same time, diminution of the problem of mechanical trauma of the eye tissues has given possibility to pay more intent attention to the series of specific pathophysiological reactions developing as a sequence of depressurization and decompression of the eyeball inevitable in intraocular surgery, and also to evaluate significance of acute ocular hypotonia in pathogenesis of many complications.

Nevertheless from our point of view the problem of acute ocular hypotonia is studied not deep enough and not thoroughly at syndromal level.

Separate undoubtedly interesting but yet desultory data of significant impairments of haemo- and hydrodynamics, intertissular exchange, biochemical, humoral and neurophysiological reactions, topographic impairments caused by volume and linear deformation of tissues and intertissular spaces and so on, and also data of the factors influencing on deepness and duration of similar pathologic processes just proof the necessity of complex investigation of syndrome of acute ocular hypotonia with the usage of the most modern methods and technologies.

The aim of this work was seen in the following: to systematise available scientific and practical data conducting series of the most general and available investigations, to sharpen the interest of scientists and specialists-practitioners to the problem of acute ocular hypotonia, to give possibility to look in the other way at the nature and mechanisms of development of pathological processes which seem to be well-studied and well-known, to use the available methods of influence in order to prevent possible complications more effectively.

I hope that the book will be useful also for teachers of medical institutes, for clinical interns and young doctors grasping principles of eye microsurgery.

I would like to express special gratitude to my teacher professor Hatminskiy U.F., the author of original idea of controlled decompression of the eye, and also to the stuffs of department of ocular diseases of KSMA and Kemerovo regional ophthalmologic hospital for participation and great help in preparation of the present material.

Melyanchenko N.B.

Professor, M.D.,

Entitled by the President of Russian Federation

As “Honoured Physician of Russia”.

CHAPTER 1. CONCEPT “ACUTE OCULAR HYPOTONIA“

Term “ ocular hypotonia ” for the first time was proposed by Grefe in 1886 to define the sign of stable drop of intraocular pressure (IOP) after cavitary operations.

Later on the concept “ocular hypotonia” was connected, as a rule, with long-term non-recovery of ophthalmotonus after penetrating wounds or operations complicated by detachment of uveal tract [17,77]. Collins [32] used term “persisting hypotonia” for more exact clinic characteristic of syndrome of stable hypotonia of the eye. In later works [123] such condition was defined as “chronic ocular hypotonia”.

At present, term “chronic hypotonia” is generally accepted and widely used in ophthalmologic literature. In most cases chronic ocular hypotonia is understood as stable drop of ophthalmotonus caused by severe trauma or chronic disease leading to progressive decrease of visual functions and ending with eye subatrophy or atrophy [16,154].

Unlike chronic hypotonia, term “acute ocular hypotonia ” is met rather seldom and the essence of this term has not yet defined to the end. Most of the authors use term “acute hypotonia” to define condition of the eye which occurs immediately after penetrating wounds or hard contusions [154,117,141] or during cavitary ophthalmologic operations [38,71-75,81,128] and is accompanied by sharp drop of IOP to the level of hydrostatic.

In separate works condition of “acute ocular hypotonia” (AOH) is described in connection with temporal arteritis [135].

Thus, in accordance with literature data, the main reason of development of acute ocular hypotonia is traumatic depressurization of the eye, loss of a part of humor content and sharp decompression. In series cases acute ocular hypotonia develops also because of expressed impairment of intraocular blood circulation and production of intraocular humour (severe contusions, temporal arteritis). However, irrespective of the reason, common for all cases of acute ocular hypotonia is drop of ophthalmotonus to subnormal values during short period of time.

Because of absence of special investigations of the present topic in ophthalmologic literature the question of differentiation of the terms “acute” and “chronic” hypotonia is practically left open. Till the present moment the difference between these terms is rather conditional and can be defined only by classical characteristic of pathological process caused condition of hypotonia [154,155]. Experimental work of Rykov V.A. [141] apparently is an exception. The author gives pathologicoanatomic characteristic of hypotonic conditions of rabbit's eyes depending on duration of hypotonia. So, in accordance with the data given by Rykov V.A. acute hypotonia of the eye is characterised by disorder of blood circulation, edema and swelling of tissue with rising of content of glycosaminoglycanes, expansion of spaces of iridocorneal angle cells of trabecular and ciliary fundiform net. In chronic ocular hypotonia rough fibroplastic processes in drainage system and adjacent tissues prevail. Rough sclerosis of drainage system with cicatrization of ciliary body points out to transition of chronic ocular hypotonia to subatrophy of the eyeball.

In spite of the fact that the term “acute hypotonia of the eye” is not widely spread in ophthalmologic literature, the problem of fighting with consequences of sharp drop of ophthalmotonus attracts attention of ophthalmologists for a long time.

Especially it concerns the questions of ophthalmosurgery, because in everyday practice ophthalmologists meet the condition of acute ocular hypotonia exactly while making intraocular operations [63,108,115]. Such type of acute hypotonia we conventionally define as hypotonia of the operated eye (HOE).

Chapter 2. Pathophysiological changes in the eye tissues in its acute hypotonia

As it was mentioned above condition of acute ocular hypotonia, as a rule, is caused by traumatic depressurization and decompression of the eyeball. Two factors influence on intraocular tissues in conditions of HOE: mechanical trauma in the area of surgical intervention and very low hydrostatic pressure. Compound combination of these factors on the one hand causes large variations of possible pathophysiological reactions in the eye tissues, on the other hand makes the defining of true role of acute hypotonia in their formation in each concrete case more difficult. Evidently by this fact comparatively small amount of works dedicated to studying of concrete pathophysiological changes in the eye tissues caused by acute hypotonia can be explained, the most part of such investigations is of applied character and concerns concrete intra- and postoperative complications.

Meanwhile, in our opinion broadening of conceptions of the character and degree of pathophysiological reactions and possibilities of eye adaptation to drop of intraocular pressure will define in many respects development of microsurgery of the eye and the brain in the nearest future. Evidently, in conditions when many surgical interventions will be made at microtissular and even cellular level looking for effective methods of the eye adaptation to condition of acute hypotonia, reduction of time of its influence and, if possible, making interventions while keeping natural intraocular or intracranial pressure will be more actual in prophylaxis of possible complications (Hatminskiy U.F.1975), [70].

Changes in intraocular blood circulation

Even at the beginning of the XXth century leading ophthalmologists such as Fucks [59], Hudson [77] and others pointed out to the leading role of hemodynamic disorders in pathogenesis of many complications of cataract extraction. Russian ophthalmologists such as Samoylov A.Y. [144], Filatov V.P., Kalfa S.P. [53] were of the same opinion.

Astahov U.S. [10] during experiments on cats has found drop of pressure in posterior long ciliary arteries by 4-5 mm. of mercury column (m.c.) in sharp drop of ophthalmotonus to the level of atmospheric pressure, it pointed out to widening of intraocular vessels and in particular, choroid vessels and also speeding-up of blood flow in them. In drop of IOP to zero the author observed also hyperemia of ciliary vessels during 6-9 minutes, for all this blood flow was sometimes tripled and then gradually it came back to initial level.

Similar reaction in the vessels of drainage system of the eye after aspiration of large amounts of the vitreous and sharp drop of IOP was described by Rykov V.A. [141] in the experiments on rabbits. Immediately after decompression of the eye expressed disorders of blood circulation in the form of irregular and sharp plethora of vessels, extravasates and strip-like perivascular haemorrhages.

In accordance with the data of Bunin A.Y. [24] in drop of ophthalmotonus to 10 mm. of m.c. and lower microcirculation in the vessels of conjunctiva is sharply intensified.

Jalkh and co-authors [81] having applied an original method of A- and B-scanning have found diffuse thickening of the choroid in 108 patients after intraocular operations. The authors connect hyperemia of the choroid with acute hypotonia of the eye.

Krol D.S. and Sheludchenko V.M. [99] in experiment on the rabbits' eyes simulated heavy contusion of intraocular tissues presenting one of the reasons of acute hypotonia. During the period to 1,5 hour the authors observed sharp increase in diameter of conjunctival and episcleral vessels, significant increase of their permeability with formation of many extravasates. In the iris parallel changes were marked.

Many authors attach importance to the influence of reactive syndrome arising during the first hours after cavitary operations and becoming apparent by prostoglandinous reaction and increase in blood filling of uveal tract on hemodynamics of the eye [161,122,133,144,146,148].

Dmitrovskaya I.P. [36] in the experiment on rabbits simulated penetrating linear injury of cornea 4mm wide accompanying by loss of part of humoral content of the eye. With the help of tono- and rheoophthalmography changes in hydro- and hemodynamics of the eye were studied. The author had found that dynamics of IOP had three consecutive phases: in the first minutes after cornea perforation ophthalmotonus was very low, then gradually it increased to supernormal values and having reached maximum level it again dropped to the initial level. Final normalisation of IOP occurred on the 90th minute (at an average) from beginning of the eye decompression. In accordance with the author's data dynamics of rheoophthalmography and tonography coincided.

Markova T.L. and co-authors [113] had investigated intercommunications between the character of volumetric pulse (ophthalmosphygmogram - OSG) in the patients having cataract before the operation and number of operational and postoperational complications. The authors had marked that in the patients with increased OSG amplitude (as a rule they are young persons) hemorrhagic complications at the operational table had appeared 2,5 times more often, but in the postoperational period there were practically no haemophthalmuses. In the patients who had decreased amplitude of OSG (they were old people with the signs of atherosclerosis) during the postoperational period hyphemas developed more often (two times) and detachments of uveal tract (by 11,8 %), hernia of the vitreous body (two times). The authors came to a conclusion that when perfusion pressure in the eye vessels was increased as well as when permeability and rigidness of their walls were increased, intraocular vessels became more sensitive to the influence of acute hypotonia.

On the whole analysis of the literature shows that till the present moment ophthalmologists could accumulate rather large factual material concerning changes in tissues and structures of the eye in its acute hypotonia. Sharp drop of ophthalmotonus to the level of atmospheric pressure leads to deep disorders of functional conditions of the eye and especially of its hemo- and hydrodynamics. Decompression of the eyeball promotes increase of perfusion pressure and hyperemia of intraocular vessels, increase of their permeability, transsudative reaction and intensification of production of intraocular humor.

However we can not but pay attention to the largest disconnection of investigations carried out. Practically there were no investigations of acute ocular hypotonia “in the pure form” when influence of mechanical trauma (operation) was absent or minimised. In connection with this we have conducted a series of personal independent experimental and clinical investigations.

Changes of blood circulation in the vessels of uveal tract of rabbits after eye decompression (independent investigation).

During the experiments on the rabbits with the help of methods of rheo- and sphygmography we have investigated disorders of intraocular blood circulation, arising at the first minutes after drop of ophthalmotonus, connected with depressurization of eye chambers and loss of its part of humor (more detailed in publications 117,120).

Dependence of rheographic coefficient (RQ) on time passed from the moment of eye decompression (t), is represented on the scheme (pic. 1).

Pic 1. Dependence of Rq on time passed from the moment of decompression.

As it is seen on the scheme, in sharp drop of ophthalmotonus to the level of hydrostatic pressure two-phase character of changes in uveal bloodstream was observed. During the first 6-9 minutes sharp increase of Rq to 228% +/- 26% (p<0,01) was observed. Later on bloodstream began to decrease and to the 11th-14th minutes bloodstream in majority of animals dropped below the initial level, this tendency maintained till the end of investigations (66% +/- 4%, p<0,001).

The results of investigations have shown that quick eye decompression leads to sharp disorders of intraocular blood circulation, which become apparent just after drop of ophthalmotonus. Increase of volumetric bloodstream in the vessels of uveal tract at the first minutes after decompression, is obviously connected with their widening resulting from drop of extravasal pressure [104] and appearance of misbalance between pressure in extraocular (afferent) and intraocular vessels.

As far as volume of blood deposited in the choroid is increased, pressure in its vessels again begins to increase, speed of choroidal bloodstream drops and Rq lowers. Evidently, irritation of baroreceptors of choroidal vessels resulting from their out-tension at the first minutes after eye decompression calls reflex vasoconstrictive reaction in the posterior period and, as far as normalisation of ophthalmotonus takes place, Rq is reduced lower than initial level.

Changes of blood circulation in orbital artery after eye decompression (independent investigation)

Results of our investigations concerning changes in linear speed of bloodstream (LSB) in orbital artery of rabbits after simulation of condition of acute hypotonia turned to be very interesting. Dependence of LSB in orbital artery (S) on time passed from the moment of eye decompression (t) is shown on the diagram ( pic. 2)



Pic. 2. Dependence of LSB in orbital artery on time

passed from the moment of decompression

As it is seen from the diagram, amplitude of ODG- wave after drop of ophthalmotonus had sharply increased, had reached the maximum (145 +/- 21%) at the first minute and was maintained above the norm during 4 minutes. Then decrease of amplitude below initial level was observed: to 50% +/- 18% at the first 10th-11th minutes with posterior increase to 85-87% +/- 13% at the 15th-18th minutes.

Such reaction is well conformed to increase in that period of volumetric bloodstream in uveal vessels (pic. 1) found by us with the help of rheograph. Periods of maximal (the first minute) and minimal (the 11th - 12th minutes) bloodstream in the orbital artery and uveal vessels are practically coincide. However we should pay attention to the fact that in accordance with our data, LSB in the orbital artery came down below the initial level already from the fifth minutes, whereas volumetric bloodstream of the choroid was increased during several minutes yet. It's evidently that high level of volumetric bloodstream of the choroid can not be supported at low level of hemodynamics in the afferent vessel.

Probably the reason of this disparity is in the following: in decrease of the eye turgor conditions for spreading of ultrasonic wave in its cavity become more worse, energy of reflected signal is diminished, value of the signal equally with frequency modulation (Doppler's effect) also influences on amplitude of ODG- wave and results of changes in LSB are underestimated slightly.

Dependence of changes of blood circulation in the vessels of uveal tract on the speed of drop of ophthalmotonus (independent investigation)

In making intraocular operations accompanied by drop of ophthalmotonus (cataract extraction, antiglaucomatous and so on) in order to prevent hemorrhagic and other complications many authors suggest before the opening of the eye cavity to make compression ( massage) of the eyeball for relieve of initial intraocular pressure [50], and also to relieve ophthalmotonus in slow regime preventing by this or that method quick emptying of anterior chamber [41,71,75,151]. However in available literature we did not find any concrete data describing the way how eye tissues actually react to slowing the speed of decompression or to decompression with preliminary compression.

In order to specify reaction of eye vessels to the speed of decompression and to study possibilities of usage of personal methods of eye adaptation to condition of acute hypotonia in making intraocular operations (idea of Hatminskiy U.F.), in the experiments on the rabbits with the help of rheograph we have tested four regimes of speed of eye decompression, (more detailed description you can find in the monograph “Acute ocular hypotonia”. InSEPZ.1996): 0,222gPa/sec (0,167 mm. of m.c./sec); 0,111 gPa/sec (0,084 mm. of m.c./sec); 0,055 gPa/sec (0,042 mm. of m.c./sec) and 0,028 gPa/sec (0,021 mm. of m.c./sec). Guided dosed decompression of the eye was made with the help of special device [120].

We have managed to conduct rheographic control in all the animals for 17 minutes. Results of investigations in accordance with each regime of speed of the eye decompression including speed 7,0 gPa/sec. (was described in the previous chapter) are shown in picture 3.

As it is seen from picture 3, there is distinct direct dependence between speed of drop of ophthalmotonus and value of reactive hyperemia of the vessels of uveal tract. So, when the most slow speed of decompression equal to 0,028gPa/sec. was used, the level of maximal hyperemia turned to be the smallest - 161% +/- 4,3% (p<0,001). However it's necessary to underline that if lowering of speed of decompression to 0,222 and 0,111 gPa/sec has diminished reactive hyperemia of the uvea accordingly by 32% and 23% that further lowering of decompression to 0,055 and 0,028 gPa/sec would not be so significant - 12% and 2% accordingly.

7,000 gPa/sec

0,222 gPa/sec

0,111 gPa/sec

0,055 gPa/sec

0,028 gPa/sec

Pic.3. Dependence of changes of Rq on the speed of decompression

We can not also but pay attention to direct link between degree of hyperemia of uveal tract at the first minutes after decompression and value of reactive spasm of its vessels later on (correlation coefficient 0,70+/-0,14). It points out to presence of mechanism of adaptation of vascular system of the eye to disorder of intraocular blood stream and in particular to available system of reflex neuroregulation of vascular tonus in reply to irritation of baroreceptors of vascular wall.

Also it seems to be interesting relations between time spent for decompression and time of maximal increase of blood stream (table # 1. Page 10). As it seen from the table when speed of drop of ophthalmotonus was 7,0-0,222-0,111 gPa/sec maximal increase of blood stream in the vessels of ciliary body occurred 1-3 minutes after eye decompression; when speed was 0,055 gPa/sec. these showings practically coincided; when subsequent slowing down of decompression took place to 0,028 gPa/sec blood stream in uveal vessels reached the maximum for 4,5 minutes before its termination (!).

Simple calculations showed that intraocular pressure to this moment was 13,4 gPa. Consequently animals of this group beginning from the 9^th minute had tendency to normalisation of intraocular blood stream in spite of the fact that ophthalmotonus still continued to drop during 4,5 minutes.

Table # 1

Relations between the time spent on eye decompression and the time of development of maximal hyperemia of the uvea depending on the speed of drop of ophthalmotonus.

Space of time	Speed of drop of ophthalmotonus
	7,000	0,222	0,111	0,055	0,028
Time spent on the eye decompression (in minutes)	0,05	1,58	3,15	6,30	12,50
Time of development of maximal hyperemia of uveal tract (in minutes)	1,66 +/-0,19 * p<0,001	4,00 +/- 1,18 * p<0,05	6,20 +/-1,75 * p<0,05	6,40 +/- 1,83 * p<0,05	8,40 +/-2,35 * p<0,05
Difference between the time of termination of decompression and the time of maximal hyperemia of the uvea	-1,61	-2,42	-3,05	-0,10	+4,10

* - reliability of difference with initial level of Rq

This fact also shows presence of mechanism of adaptation of ocular vascular system to changes of intraocular pressure.

Changes of blood circulation in the vessels of uveal tract in dosed decompression of the eye with preliminary hydraulic compression (independent research)

As our experimental investigation shows when ophthalmotonus is dropped during the first 6-9 minutes sharp increase of blood stream in the vessels of uveal tract occurs (look at picture 3). When speed of eye decompression is slowed down to 0,055-0,028 gPa per second level of choroidal hyperemia diminishes being nevertheless rather high (164%-161% from the initial). In connection with it search for methods of influence on the vessels of uveal tract aiming to diminish their reactive hyperemia in the first minutes after decompression is actual.

In the present work we tried to study how well known peculiarity of uveal vessels to respond for short-term increase of ophthalmotonus by expressed vasoconstrictive reaction [140] influences on hemodynamic displacements connected with drop of ophthalmotonus.

Investigation was carried on the rabbits' eyes with usage of method of ROG. After suturing of electrodes to the sclera anterior chamber was punctured and with the help of special device ophthalmotonus was stabilised at the level 21gPa. Three minutes after control record of rheogram was taken (initial level). Then ophthalmotonus was increased to 60gPa and repeated record of ROG was taken. One minute after initialisation of hydraulic compression of the eye, dosed drop of ophthalmotonus with speed 0,111gPa per second was began.

Results of investigations are shown on the diagram (pic.4).

As it is seen on the diagram, immediately after beginning of hydraulic compression of the eye sharp drop of rheographic coefficient to 45% +/-16%, p<0,01 occurred. Such tendency kept even after drop of ophthalmotonus right up to 6-7 minutes. Only on the 8^th minute from beginning of decompression (the 9^th minute from the beginning of investigations) level of Rq exceeded the initial level and continued to increase during 3-4 minutes yet after its termination.



Picture 4. Changes of Rq in dosed decompression of the eye

after its preliminary compression.

In the next minutes tendency to diminishing of uveal blood stream again appeared.

Reduction of the level of reactive hyperemia of uvea after eye decompression in these series of tests lets us suppose that resulting from preliminary short-term hydraulic compression Rq decreases not only at the expense of mechanical squeezing of choroidal vessels, but also because of influence of reflex contraction of their walls. This tendency is maintained in the first minutes after initialisation of drop of ophthalmotonus also because during this period its level is still higher than initial level. One peculiarity shown in the process of investigation and consisting in the following also proves this supposition.

In the process of eye decompression the initial level of ophthalmotonus in 21gPa was reached only on the 6^th minute from its initialisation (7^th minute from the beginning of the investigation), whereas volumetric blood stream in the vessels of uvea came to the initial level only on the 8^th minute of decompression, when intraocular pressure dropped on the average up to 7gPa. In our opinion hydraulic compression of the choroid preceding to drop of ophthalmotonus starts up as though beforehand the mechanism of adaptation of the vessels to changes in extravasal pressure, and their wall on the background of reactive spasm becomes more stable to the following decompression of the eye.

On the whole analysis of experimental investigations of hemodynamics on rabbits' eye lets us make the following conclusions:

In relieving of ophthalmotonus to the level of atmospheric pressure expressed changes in blood circulation in the vessels of uveal tract occur.

Curve of hemodynamics change in uveal vessels under conditions of eye decompression has be-phase character: during the first 6-9 minutes sharp increase of volumetric bloodstream to 161%-228% occurs, further bloodstream decreases lower than initial level. Changes of linear speed of bloodstream in the orbital artery are of similar character.

The first 6-9 minutes from initialisation of the eye decompression are the most dangerous, from point of view of possible hemorrhagic complications.

There is direct link between speed of drop of ophthalmotonus and degree of arising of vascularomotor reactions at this time.

Vascular system of the eye has mechanisms of adaptation to drop of intraocular pressure, which arise several minutes after the eye decompression.

Preliminary short-term hydraulic compression of vascular membrane before drop of ophthalmotonus provides more valuable adaptation of its vessels to drop of extravasal pressure.

Changes of blood circulation in the choroid during intraocular decompressive operations (independent research)

In world literature there are large amount of evidences, pointing out to important role of essential hemodynamic disorders arising in the eye tissues during operations after drop of ophthalmotonus in operational and postoperational complications [10,24, 81,141 and others]. However most of such suppositions are based on the facts received empirically or as a result of laboratory or experimentally simulation of separate conditions.

As a result of serious technical difficulties till the recent times there was no possibility to follow in conditions of real surgical interference how for example intraocular vessels react to section of cornea and emptying of the anterior chamber, removal of lens, cauterization of episcleral vessels, introduction of mydriatics and so on. After working out methods of intraoperational rheo- and dopplerography [73,118-120] we have managed to get interesting data concerning character of hemodynamic changes, arising in the eyeball under real conditions of cavitary operations, accompanied by the eye decompression.

As it is known, particularity of such operations is that during these operations besides mechanical trauma, pathologic influence on the eye tissues makes itself the condition of acute hypotonia. In connection with this, in the process of investigations we were interested first of all in the character of mutual influence of condition of acute ocular hypotonia and mechanical trauma in dependence on peculiarities of techniques and technologies of making operational intervention, and also the role of acute hypotonia in pathogenesis of operational and postoperational complications.

As an object of investigations we have taken operation on extraction of senile cataract. This operation has attracted our attention because of series of reasons.

First of all, intraocular tissues of the patients having senile cataract are pathologically changed in significantly less degree than, for example, of the patients operated on glaucoma; consequences of trauma or inflammation process and pathophysiological reactions, arising in reply to the eye decompression, are less perverted and are of more typical and stable character. Consequently, these reactions will be more compared with results of our experimental investigations.

In the second, while making operation on cataract extraction fibrous capsule of the eye is opened for a long extent, disorders of hydrostatics are of expressed and long-term character, so as a result pathophysiological changes are displayed rather clear.

In the third, operation on cataract extraction is the most typical operation in intraocular surgery.

Results of investigations are presented on the diagrams (pic. 5, 6) where values of Rq in percentage from initial are shown at all main stages of cataract extraction in accordance with intracapsular (ICCE) and extracapsular (ECCE) methods (average indices for each group).

While making ICCE in series of cases we used diathermocoagulation of episcleral vessels, which had significant influence on condition of uveal blood stream in all next stages of operation, that is why on picture 5. curves of change of Rq with thermo- (A) and diathermocoagulation (B) of the vessels are shown separately.

While making ECCE in some cases we have registered paradoxical reaction of pupil on bringing into anterior chamber of 1% solution of phenylephine hydrochloride, accompanied by expressed general vasoconstrictive effect on the vessels of ciliary body. In connection with this on picture 6 curves of changes of Rq of the patients with usual (A) and paradoxical (B) reaction are also shown separately.

It should be noted that there is particular difficulty in interpretation of data of hemodynamics in the vessels of uveal tract, received by method of rheoophthalmography. In particular, the question is discussed concerning the following: what is the leading factor in disorder of volumetric bloodstream - change of blood filling of the vessels or change of linear bloodstream speed? Kolinko A.N. and Zilikson B.B. [88] point out that in the eye, full with non-compressive liquid content, change of pulse volume of blood in comparison with other tissues, is possible mainly because of change of linear bloodstream speed.

In conditions of traumatic depressurization and hypotonia of the eye disorder of blood stream, in our opinion takes place mainly because of change of clear spaces in the vessels lack of hydraulic compression.



Pic. 5. Changes of Rq in different stages of operation on ICCE made under local anaesthesia.

Stages of the operation:

1-initial stage:

2- incision of conjunctive;

3- thermo- (A) and diathermocoagulation (B) of episcleral vessels (immediately and 2 minutes after);

4- incision of cornea (immediately and 2 minutes after);

5-basal iridectomy;

6- cryoextraction of lens (immediately and 2 minutes after);

7- suturing of 1/2 of corneal wound;

8- full suturing of corneal wound;

9- restoration of anterior chamber and ophthalmotonus (immediately and 2 minutes after);

10-suturing of conjunctiva.

Picture 6. Changes of Rq in different stages of operation on ECCE,

made under local anaesthesia.

Stages of the operation:

initial level;

incision of conjunctiva;

thermocoagulation of episcleral vessels ( immediately and 2 minutes after);

puncturing of cornea and injection of 1% solution of phenylephine hydrochloride into anterior chamber A-B ( immediately and 2 minutes after);

capsulotomia;

incision of cornea (immediately and 2 minutes after);

basal iridectomy;

removal of the core of the lens ( immediately and 2 minutes after);

washing of cataract mass;

injection of solution of Acetylcholinum chloridum;

suturing of 1/2 of corneal wound;

full suturing of corneal wound;

restoration of anterior wound and ophthalmotonus (immediately and 2 minutes after);

suturing of conjunctiva.

Intracapsule cataract extraction (ICCE)

As it is seen from the Diagram on pic. 5, section of conjunctiva did not lead to changes of intraocular bloodstream. Immediately after coagulation of episcleral vessels in all the cases there is clear tendency to spasming of the vessels of ciliary body. Diathermocoagulation caused more strong reaction in comparison with thermocoagulation (accordingly 33% +/110%, p<0,1 and 65% +/-7,5%, p<0,05 from the previous level).

Section of cornea and sharp decompression of the eye during the first 4-6 minutes caused increasing of intraocular bloodstream by 55% +/- 8%, p<0,01(A) -68%+/-4,6%, p<0,1(B). Degree of reactive hyperemia after drop of ophthalmotonus turned out to be lower the level which was previously marked in the experiments on rabbits (228%). We connect it with vasoconstrictive effect of thermo- and diathermocoagulation of the vessels, on the background of which an opening of anterior chamber was made. During the experiment such coagulation was not made.

Iridectomy did not influence significantly on the character of rheographic (ROG) wave but stopping of growth of hyperemia of the vessels of ciliary body after it probably connected with additional irritation of receptor organs of the iris.

The greatest change of the level of hemodynamics in the vessels of ciliary body in the direction of enlargement was marked in the vessels after cryoextraction of the lens: : 102% +/- 29,1%, p<0,05 (A) - 68% +/- 17,4%, p<0,1(B). Absence of such strong reaction of the patients with ECCE (pic.8) points out to the great role of traction mechanisms in its formation. In particular, in ECCE tension of zone ciliaire, and also arising of discharge behind the lens in the moment of its passing through the pupil (especially if basal coloboma of the iris is absent or if there is its pressing by irisretractor and it's impossible to depressurise posterior chamber in the proper time) provide the following: pressure in the eye cavity sharply drops, probably in some cases even below the level of atmospheric (sticking effect of extraction).

The following fact also attracts attention: 4-6 minutes after cryofakia in all cases we have marked the tendency to graduate decrease of intraocular bloodstream. It was the most expressive in the patients who passed through diathermocoagulation of episcleral vessels at the initial stage of the operation.

Immediately after restoration of anterior chamber and ophthalmotonus there was sharp drop of intraocular circulation by 30% +/- 2,5%, p<0,001. In our opinion short-term character of this reaction is connected with mechanical compression of uveal tract when additional volume of liquid is brought into the eye cavity. While excessive quantity of liquid was filtered through corneal wound the level of uveal bloodstream again increased.

Extracapsule Cataract Extraction (ECCE)

As it is seen from the diagram on picture 6 (page 14) in ECCE many stages of operation similar to ECCE (conjunctiva incisions, cornea incision, basal iridectomy, restoration of anterior chamber and ophthalmotonus) caused similar reaction of the vessels of uveal tract. Vasoconstrictive effect of such manipulations as injection of 1% solution of Phenylephine Hydrochloride into anterior chamber and washing out of cortical mass and also weak reaction of the choroid to removal of nucleus of the lens are specific for ECCE.

We'd like to draw special attention to reaction of uveal tract of the eye. In the most cases after injection of 50-100mm of 1% solution of Phenylephine Hydrochloride the pupil was quickly enlarged to 7-8mm. Under these circumstances we have registered slight decrease of volumetric bloodstream in the vessels of ciliary body (curve A).

The pupils of some patients after injection of Phenylephine Hydrochloride (the same quantity) were enlarged to 5-6mm. When injection of Phenylephine Hydrochloride was repeated paradoxal reaction of pupil developed, its diameter reduced to 4-5mm. At the same time the record of rheogram showed sharp drop of hemodynamics in the vessels of ciliary body at an average by 37% +/-7,0%, p<0,05 (curve B), and such tendency was clearly traced during some minutes, till the moment of suturing of corneal wound.

We have supposed that expressed general vasoconstrictive effect of Phenylephine Hydrochloride on intraocular vessels is connected with its hit into uveal tract through fibres of ciliary body. In order to prove this hypothesis during three operations on ICCE before the opening of anterior chamber we injected 100mm of Phenylephine Hydrochloride into posterior chamber and once again we had registered decrease of Rq at an average by 55% +/0 -17,1%.

In our opinion, such reaction of the uveal tract to injection of Phenylephine Hydrochloride can be explained in the following way: When the surface of iris is irrigated with 1% solution of Phenylephine Hydrochloride at first its local effect on dilatator is expressed, as a result the pupil is widened. When the larger quantity of Phenylephine Hydrochloride is injected, it flows into posterior chamber and being soaked in by the fibres of ciliary body, provides expressed general sympathomimetic effect on the whole uveal tract. Arising of general reaction of uvea in some patients to intrachamberal injection of small quantity of Phenylephine Hydrochloride shows that evidently 1% concentration of Phenylephine Hydrochloride is too large for ophthalmosurgical practice. When we used 0,25% solution of Phenylephine Hydrochloride during ECCE we did not register cases of parodoxal reaction of the pupil, however this question should be investigated.

Short-term increase of Rq after injection of solution of Acetylcholinum Chloridum into the anterior chamber probably can be explained by some expansion of uveal vessels under the effect of the drug and by inflow of additional volume of blood into them.

On the whole comparative analysis of two basic methods of extraction of senile cataract shows that ECCE calls less expressed disorders of intraocular circulation than ICCE and consequently it has smaller possibility of complications from the part of the uveal tract.

The results of conducted investigations let us make the following conclusions:

1. Operation on extraction of senile cataract is accompanied by expressed changes of intraocular circulation during all its stages.

2. Reaction of the vessels of human uveal tract to the opening of anterior chamber and drop of ophthalmotonus is comparable with the results of similar investigations during the experiments on animals.

3. The most dangerous from the point of view of possible hemorrhagic complications are the first minutes after the eye decompression and especially after removal of the lens at the expense of traction.

4. Diathermocoagulation of episcleral vessels (in comparison with thermocoagulation) has more expressed vasoconstrictive effect on the vessels of uveal tract, that should be taken into consideration while using this technique in ophthalmosurgical practice.

5. When solution of Phenylephine Hydrochloride is injected intrachamberly, possibility of its general influence on the vessels of uveal tract should be taken into consideration.

6. Technique of extracapsular cataract extraction is more physiological for vascular system of the eye.

Influence of acute hypotonia on the other tissues of the eyeball

The works devoted to the influence of acute hypotonia not only on the vascular system of the eye but also on the other tissues of the eyeball began to appear in the literature during the last years.

So, Grehn, Prost [66] making experiments on monkeys had detected disorders in carrying out of neuraxonal impulses in the retina when ophthalmotonus was relieved. There are data that when ophthalmotonus is dropped to the level of atmospheric pressure, loss of 3%-7% of cells of posterior epitelium of cornea takes place. Sicelman, Coleman [150] described the case of spontaneous destroy of the lens after vitrectomy through flat part of ciliary body under the conditions of expressed postoperative hypotonia of the eyeball.

Forofonova T.I. [55] while making densitometrical scanning of fluorescent angiograms of the patients' eyes after depressive operations has observed increase in intensity of bloodstream into microvessels of disc of optic nerve in 8 cases of 11.

Large amount of works is dedicated to investigations of hydrodynamic deviations in the eye after cavitary operations accompanied by its acute hypotonia and in particular by reactive hypertension of early postoperative period [23,28,86,100,121,129,138,152]. After cataract extraction ophthalmotonus is increased in 3% to 50% cases [34,102].

The majority of the authors call close among themselves temporary parameters as reactive hypertension, that is from 3-5 hours to 1-3 days after operation. However the difference in interpretation of the reasons of hypertension development attracts attention. The main pathogenetic factors leading to reactive hypertension are: disorder of circulation and increase of permeability of the vessels with strengthening of ultrafiltration of humour [89], edema of drainage system in the area of cornea section [138], functional or organic block of the pupil, prostaglandine reaction [46], vitreous swelling [90,152].

Chapter 3. Topographic changes in the eye in its acute Hypotonia

In this chapter we shall dwell on disorders of normal topographic relationships between eye tissues arising at decompression of the eyeball, and also on the factors causing them. Thus during the discussion we whenever possible have excluded those changes which develop as a result of tissue injury because of mechanical trauma.

Topographic changes consequent to acute hypotonia of the eye, arise in general in the form of tissue deformation and only at a last resort of their injury. Concept “deformation of the eye tissues” in this case reflects specific of topographic changes. We have used this term also because last time it is more widely used by ophthalmologists [9,12,35,142].

In connection with that hypotonia of the operated eye is a consequence of surgical intervention, deforming factors are also of interest- deforming factors connected with specific technology of making intraocular operations which influence on the eyeball in conditions of its acute hypotonia, and if not take them into consideration analysis of anatomic changes would be impossible.

In order to recite the material more consequently we conventionally have divided the factors influencing on the eyeball in conditions of acute hypotonia to intraocular (that is shown immediately in tissues and structures of the eye) and extraocular (influencing on the eyeball from the outside).

Intraocular factors

There is an opinion that when ophthalmotonus is relieved, humor exchange in the intraocular tissues sharply infringes. This leads to changes of their natural anatomic configuration. In accordance with Gloor [63], opening of the eyeball during the operation causes quick drop of ophthalmotonus to zero. It leads to changes of ratio between hydrostatic, osmotic and colloidosmotic pressure in the capillaries of choroid and surrounding tissues. On the one hand because of depressurization the eye looses a part of liquid from cavities and on the other hand - conditions are created for liquid part of blood to flow out of capillaries into surrounding tissues. Edematization occurs, exudation of liquid part of blood into suprachoroidal space causes enlargement of the volume of posterior eye segment, pushing irido-lens diaphragm and the vitreous forward.

Egorov V.V. [41] draws attention to ambiguity of reaction of the eye content to acute hypotonia of different patients. After humor removal from anterior chamber different position of irido-lens diaphragm is possible, in the author's opinion it depends on the pressure in the vitreous. In those cases when pressure in the vitreous is higher than in the anterior chamber, sharp deviation of the diaphragm forward takes place. Many other authors are of the same opinion [20,80,91]. However Glomaud and co-authors [62] during the experiment on the rabbits did not detect any correlation between indices of general IOP and pressure in posterior segment of the eyeball.

Some of the authors point out to the importance of disorders of hemodynamics in pathogenesis of topographic changes. In accordance with suppositions of Posagennikov A.P. [133] at the time of the ocular operations after depressurization of the eyeball increase of the volume of vascular tract occurs and that influences on the changes in position of the vitreous and other tissues. As it was mentioned above thickening of the choroid of series of the patients passed through intraocular operations is maintained in early postoperative period also [81]. However this point of view does not yet have sufficient pathogenetic ground because of absence of true data about changes of volumetric blood stream in the eye cavity just during surgical intervention (besides our observations).

Many of the authors think that initial condition and next volumetric changes of the vitreous in reply to decompression are of importance.

In accordance with observations of Pisetskaya S.F. [128] position of anterior hyaloid membrane during the operation depends on the quantity of bound water (volume of albuminous micelles) in the vitreous. So, during the operations on the patients who passed through dehydrational therapy before the operation we have found expressed hypotonia with collapse of scleral capsule and deepening of anterior chamber. In the control group of the patients in more than half cases putting of the vitreous forward into anterior chamber was marked.

Sydorenko E.I. [152] supposes that during cavitary operations on the eye on the background of low hydrostatic pressure swelling of the vitreous and enlargement of its volume take place. Koretskaya U.M. and co-authors [90] also mention the edema of the vitreous after intraocular depressive operations.

Egorova E.V. with co-authors [42] describe 41 cases of paradoxal reaction of the eye contents to the opening and emptying of anterior chamber of the patients with complicated traumatic cataracts. This reaction consists in development of expressed collapse of the eyeball after incision of the cornea. As the authors think the reason of such reaction is derangement in the structure of the vitreous in the form of its dilution,, disintegration of fibrillar stroma, formation of cavities filled with free fluid. When operational depressurization and decompression of the eye take place liquid goes out of the vitreous cavities and it leads to collapse of membranes of the eyeball.

Arising of cavities in the vitreous (in accordance with data of Kartashova E.A. and Rosenfeld E.F. [84]) is one of the reasons of prolapse of the vitreous into anterior chamber on aphakic eye in postoperative period.

* * *

So, in accordance with literature data, the main intraocular factors of deformation of intraocular tissues in the period of its acute hypotonia are: disorders of hydrostatics and hydrodynamics; enlargement of the choroid's volume; exudation of humor through vascular wall and tissue edema; accumulation of transsudate into intermembraneous spaces; swelling of the vitreous; and in the period of its destruction vice versa - emptying of intravitreous cavities and retraction of fibrillar stroma.