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|Year : 1969 | Volume
| Issue : 6 | Page : 231-241
Experiences in cryosurgical extraction of cataract
Sir Cowasji Jehangir Ophthalmic Hospital, Bombay, India
P B Banaji
Sir Cowasji Jehangir Ophthalmic Hospital, Bombay
|How to cite this article:|
Banaji P B. Experiences in cryosurgical extraction of cataract. Indian J Ophthalmol 1969;17:231-41
Intracapsular removal of the lens began gaining popularity in the first quarter of this century through the work and advocacy of Arruga, Kalt Elschning and Sinclair all of whom employed a forceps of their own design for the operation. Barraquer's suction cup although described in about 1917 did not gain universal acceptance till about twenty years later.
A third method though not entirely new in its principles was described by Kawawitz  in 1961 who used a metal probe cooled to about-70° in a mixture of carbon dioxide snow and alcohol to remove the lens. The cooled probe adheres to lens in the same manner that a moist finger adheres to the metal of the deep freeze compartment of a refrigerator.
The purpose of this paper is to compare Cryoextraction with the more orthodox methods of intra-capsular extraction, to determine its advantages, and to decide whether it should entirely replace the usual methods or be used in certain cases only.
Two hundred and fourteen, cryoextractions were done and the results as regards capsule breakage, vitreous loss and other less important operative and post-operative complications were compared with those of 1000 most recent extractions with the forceps and erysiphake.
In the last few years many new and refined instruments have been described with different methods of obtaining a temperature low enough for the probe to adhere to the lens, all of which consist essentially of a handle, to the end of which is attached a metal probe about one inch long and about 3 mm. in diameter ending in a rounded or flat tip.
Whatever be the design of the instrument, and there are many, it should possess the following features , -
1) It should be of a size and shape approximately of other ophthalmic instruments to which the surgeon is accustomed.
2) It should attain and maintain a temperature of between -25° to -40° C for at least 5 minutes.
3) It should possess a heating mechanism (usually electrical) that can instantly defrost the probe if it inadvertently touches and adheres to any tissue besides the lens.
4) The probe should be insulated usually by rubber, plastic or tefIon except for the last 2 mm. ,
There are several methods of cooling the tip :-
a) Direct immersion of the solid probe into a cooling mixture of dry ice and alcohol (temperature about -80°C) or in liquid nitrogen (-196°C). This was the method originally described by Kawawitz but hardly ever used now.
b) Change of state of the coolant. When solid Carbon dioxide or liquid nitrogen become gaseous, cooling takes place. (Rubenstein,  Kelman and Cooper.  ).
c) By sudden expansion of gas. The gas, usually Carbon dioxide is passed from acylinder under high pressure through an 'open ended' capillary tubing enclosed in the cooling tip of a hollow probe. This sudden expansion cools the probe to a temperature of -80°C. This principle is used in the Amoils Apparatus (manufactured by Keeler) and is one of the instruments used for the operations described below.
d) Thermo-electric effect of Peltier. When a direct current is passed through a junction of two different metals the juncture is cooled. This is the principle of the Kelman and Cooper instrument. However, the instrument is rather bulky, of a girth similar to that of a tennis racket handle. Cooling is effected by using only electricity and water, the latter conducting away the heat.
e) Freon gas ampoules are ready packed in the handle of certain instruments and when allowed to expand via the tip by pressing a plunger produce the necessary cooling. Such an instrument is ready for instant use when needed during the course of an operation where Cryosurgery was not planned.
Two instruments were used in this study, the Pierse cryo-pencil and the Amoils apparatus made by Keeler.
The former which is much simpler and which works with solid carbondioxide snow is shown in an expanded view in [Figure - 2] and ready for use in [Figure - 1]. Its body consists of a hollow steel tube (B) to one end of which is screwed and interchangeable probe (A).
Through the opposite end of the cylinder is passed another plastic cylinder (C) filled with carbon-dioxide snow which is kept rammed down in place by a spring loaded plunger (D). There is a small hole in the distal end of the hollow plastic cylinder into which fits the proximal end of the probe. This end of the probe is in contact with the ice within the plastic cylinder and the cold travels down its length to reach the tip.
The Amoils apparatus which is much more complicated consists of a main box about 15"x8"x8" [Figure - 3] which is connected to the electric mains and to a carbon-dioxide cylinder and also to the cryopencil by electric wires for the heating element and a thin tube transmitting the gas under pressure. On depressing a foot switch carbon-dioxide passes at a pressure of 700 lbs per square inch from the apparatus into the cryopencil and suddenly expands through a very thin capillary tubing inside the metal probe which reaches its operative temperature (-30°C) in a few seconds. There is also an electrical heating appliance incorporated in the probe to produce rapid defrosting. The outer plastic tube enclosing the electric wires and the carbondioxide tube from the cryopencil to the main apparatus does not interfere with the movements of the cryoprobe held in the surgeon's hand. The size and shape of a cryo instrument is similar to an ordinary lead pencil. The diameter of the probe at the end is about 2 mm. [Figure - 4] shows cryopencils with straight and curvey tips. Probe C is for retinal detachment operations.
The probes are sterilized by ethylene oxide gas, formalin vapor or autoclaving. The outer casing and probe of the Pierse instrument can also be boiled. When more than one cataract is to be removed by the Amoils apparatus, the outside of the cryopencil is wiped with spirit care being taken to remove any excess from the end of the probe with distilled water.
| Mode of Action of the Cryoprobe|| |
When the cooled probe touches the lens capsule not only does an adhesion form between the two but the cooling process extends into the lens matter itself for about 2 mm forming an ice-ball which is in direct continuity with the tip of the instrument. The intralenticular ice then becomes an extension of the cryoprobe and any traction on the instrument acts as if it came from the ice-ball inside the lens. The traction not being via the capsule it is much less likely to rupture during the process of extraction. It is as if a small steel ball was fixed inside of the lens and the latter was removed with a magnet applied to the capsule.
The ice-ball is about 2 or 3 mm in diameter and is too small to interfere with plasticity or flexibility of the lens. The rest of the lens acts as an insulator and prevents the cold passing to the vitreous or ciliary body.
| Method of Using the Cryoprobe for Lens Extraction|| |
The preliminary stages of the operations are exactly similar to those of any other extraction except that it is important to make the section at least 180° and slightly (by ½ mm) beyond the limbus.
Iridectomy :-For the first two or three opeaations when commencing cryosurgery, it is advisable to do a full iridectomy. Not only is removal easier but the operator can see better what is actually happening, although extraction through a round pupil is not difficult provided it is well dilated and retracted upwards.
Application of the cryoprobe:- Whichever instrument is used one must be certain that the probe has attained the proper temperature (-20° to -30°) before applying it to the lens. Most probes have no temperature recording mechanism but the surgeon knows by the amount of frost that accumulates on the probe when the correct temperature has been reached.
The tip of the probe should be rubbed free of frost since ice is bad conductor and will impede passage of cold from the probe to the lens. A useful method to prevent the probe from adhering to structures such as the cornea or iris is to wipe the sides with alcohol, glycol or liquid silicone. All three have a very low freezing point and form a capillary thin layer between the probe and the adjacent tissue. A probe the sides of which have been wiped with alcohol, does not form nearly as thick a layer of frost on its surface as it would do otherwise. This prevents or greatly reduces the risk of adhesion to any tissue it may inadvertently touch.
The cornea is held up by an assistant. The iris (if no iridectomy has been done) is retracted upwards to expose the upper portion of the lens surface. Various forms of retractors have been devised but I prefer to hold the iris at the pupillary edge at 12 o'clock with a toothless Jayles forceps. This has the advantages that the iris can be moved from side to side as the lens is rocked during extraction and also, if the case so demands, the iris can be pushed back over the equator as the lens emerges through the pupil.
Point of application of the Probe:-- Some authors recommend applying the probe to the centre of the anterior surface and dislocating the lens by pulling directly forwards (i.e. towards the roof) claiming that such a movement places an equal strain on the zonules all round. This method has many disadvantages. Firstly, the further down the lens one applies the probe the nearer it is to the cornea and pulling the lens forward brings the cold probe dangerously close to touching the endothelium. Secondly, there is a capillary suction between the posterior lens surface and the patellar zone of the vitreous and it is far easier to slide the lens from the hollow in the vitreous than to pull it off. Lastly, if there are vitreo-lenticular adhesions they are more easily broken by sliding the lens and if need be separated with a brush or a straight iris repositer.
Saline or aqueous in the anterior chamber is swabbed out and the lens capsule very gently "dried" with a sponge; it is of course impossible and undesirable to get it completely dry.
The probe is applied as close to the upper pole as the retracted iris allows without risking contact with the latter. A full iridectomy will allow an even higher hold. It is held against the capsule 5-10 seconds before starting traction depending on the type of instrument and the amount of frost already on the probe.
By gentle pulling one makes sure the probe has adhered completely before commencing the traction, otherwise the capsule might tear. The first movement is directly forward to break the zonule at the 12 o'clock position. (Some surgeons advocate that once the upper pole of the lens is pulled forward and the zonule stretched, its fibres be broken at 12 o'clock by a zonule stripper which is something like a very blunt cystitome. 
This is unnecessary, and can be done satisfactorily only after an iridectomy. The use of zonulysin is a far better method of weakening the suspensory ligament and is preferred to any mechanical separation of the zonule). After the zonue at 12 o'clock position is broken the direction of traction is changed to forward and upward, at the same time rocking the lens gently from side to side to help break the zonules from above downwards on both the inner and outer sides of the lens. Once the initial break is made in the zonule enlarging this in both directions downwards requires much less effort just as it becomes simpler to tear a sheet of cardboard after the edge has been nicked.
Pressure with the blunt hook at the six o'clock position on the limbus is unnecessary for it needlessly increases the intraocular pressure on all structures of the eye and may even predispose to vitreous escape if the latter is fluid.
The lens can be removed only by sliding: tumbling is not possible. The lens should ideally emerge with its equatorial plane at an angle not much greater than 30° to the coronal plane of the head. This angle often depends on how the probe attaches itself to the lens. If the angle is too great and the lens tends to emerge almost vertically, the probe is released by heating (which takes 3 seconds) and re-applied at a more satisfactory angle.
Once the lens is out the operation is completed like any other intracapsular extraction.
Zonlysis with cryoextraction. The majority of lenses were removed with chemotrypsin but that is because I have always used it for most of my cataract operations.
Generally speaking chemotrypsin is used when one feels that the capsule may rupture without it. Capsules which are most liable to break are those of mature cataracts with sector like water clefts in the cortex. The next most easily broken are the capsules of Morganian cataracts and the capsules of some black or brown cataracts. The capsules least likely to break are of immature nuclear cataracts.
Although an iceball exerts traction from within the lens instead of via the capsule, it must still overcome the pull of the zonule before the latter gives way, and this pull can tear a fragile capsule. Zonulysin is very helpful in preventing this type of rupture.
| Indications for and Advantages of Cryoextraction|| |
After using the cryoprobe for about a year it is concluded that it is a simpler safer and surer method of extraction than with the forceps or erysiphake. The manifold and often perplexing choice of manoeuvres when using the forces-to slide or tumble, to hold tangentially or radially, to take a large or small bite, how much to press backwards whilst taking the bite, how much pressure to apply with the hook, how much to pull with the forceps and whether the forceps is more likely to slip or grip-are all eliminated and replaced by a single routine and dependable procedure.
(1) Whilst the cryoprobe can be used for any type of cataract it is preeminently useful in mature cataracts with a sector-like anterior surface, and a very thin fragile capsule. The forceps would merely slip on this surface or hold such a small pinch of capsule that it would surely tear. The erysiphake may bite through the capsule. Tumbling with the erysiphake will need counter pressure which may increase the intralenticular pressure and burst the capsule; sliding with the erysiphake, unless the zonule is extremely weak, may again tear the capsule. Smith's tumbling method is unreliable and should not be used with these cataracts. The cryoprobe is uniquely suited for such cases, the pull being from inside the lens the chances of rupture are minimised. The only threat to rupture is the firm attachment of a strong zonule and hence chernotrypsin is used in nearly all such cases. The capsule casualty in this type of cataract is so high by the usual intracapsular methods that many surgeons prefer to use the cystitome. Cryosurgery reduces the breakage rate by over 50%.
(2) Cataracts whose capsules have been injured at operation by the knife, keratome, razor blade, sicissors, iris forceps, Arruga forceps or erysiphake can often be removed without further tearing of the capsule of and spilling out of cortex provided the rupture is small, detected immediately, and is on the upper half of the anterior surface of the lens. The cold probe is placed on the rupture and freezes the capsule and cortex into a solid sphere of ice and enables the lens to be removed more or less intact. One has to pull rather less forcibly in such a case and therefore it would help if Quemotrase is used.
(3) In the very rare instance of the capsule breaking during cryoextraction (usually due to applying a probe not cold enough or not long enough), the probe can be reapplied to almost the same spot and the lens carefully and slowly slid out. I have applied a probe as many as four times on what was actually bare cortex after the capsule broke and have been able to ease out the lens together with the capsule without any; part of either remaining behind. This extraction was helped by ""he prior injection of zonulysin.
(4) Some traumatic cataracts where there ias not been excessive capsule damage can be similarly removed. The type which lends itself most readily to extraction is a cataract due to a small intralenticular foreign body and where the capsule tear is minute or has healed.
(5) Most authors who have used cryosurgery are of opinion that it is easier to remove a dislocated lens by this method than fishing about for it with a loop.
Three such lenses were removed. The first was a senile mature cataract lying obliquely covered with a thin layer of vitreous. This presented no difficulty the insulated sides of the probe did not adhere to the vitreous. The second, also a senile cataract, lay deeper and its localisation was helped by the ultraviolet lamp. The sides of the probe of the Amoils apparatus were rubbed with alcohol, and the freezing was turned on only after contact was made with the capsule. Although no ice-ball could be seen forming we hopefully assumed its presence : this turned out to be correct and the lens was slowly withdrawn through the vitreous. The third case was one of Marfans syndrome in a young patient where the remaining zonule was particularly tough. I think the capsule would have ruptured by any other method.
When removing dislocated lenses, it is advisable to do an iridectomy. It should be remembered that since the lens is usually tilted we cannot apply the probe to the point of our choice but only to the uppermost (i.e. most forward) part of the lens. Hence it may emerge obliquely, flat, or with its long axis at right angles to the wound. Attempting to twist it around to make it emerge parallel to the wound may break the contact between probe and lens.
The smearing of the probe except the tip with alcohol or glycol prevents the vitreous adhering to the sides of the instrument. A teflon sleeve would also act well.
(6) The cryoprobe is useful in removing the transparent or opaque lens (when required) after cutting out the corneal disc in a total or sub-total penetrating keratoplasty. Zonlysin should be used and the probe applied to the centre of the lens, pulling it straight forwards (i.e. towards the roof).
(7) When the cornea collapses or cups after the sections, extraction is difficult because pressure with the hook used in connection with the forceps or erysiphake is often ineffective since the vitreous wedge cannot be made to push against the lower zonules and rupture them. When the cryoprobe is used the hook is unnecessary and the lens is simply pulled out with the probe.
(8) The great advantage of the cryoprobe in all cases is the very firm union between the extracting instrument and the lens and the deep sense of security that the surgeon enjoys in the near certainty that the lens will be extracted intact.
Disadvantages. These are few. The apparatus is complicated and expensive, and in this country its availability is limited.
As regards the operation we need one more hand to hold up the cornea as the surgeon holds back the iris and extracts the lens. The large bulky handles of certain types of apparatus are unwieldy but the slim modern cryopencils feel like any other ophthalmic instrument.
Cryoextraction is contraindicated in patients under 30 years even in conjunction with chemotrypsin for the vitreous in such persons is often adherent to the rear of the lens and tends to follow it into the anterior chamber and even out of the wound. An extracapsular extraction preceded if necessary by a needling is here the method of choice.
| Complications|| |
Capsule breakage. In my last thousand intracapsular extractions done by the forceps and erysiphake the capsule breakage rate was 6.2%. Various authors give their figures as between 3% and 10%. These statements, however, present an incomplete picture unless it is mentioned what percentage of all cataracts are attempted by the intracapsular method, for surgeons who remove only immature lenses in older persons in relaxed easy eyes will have a far lower figure than another group of operators who attempt to remove all (or almost all) lenses intracapsularly irrespective of the maturity or type of the cataract, the fragility of the capsule, age of the patient and the tenseness of the eye.
An analysis of the writer's figures show that practically all cataracts in persons over 30 years were planned intracapsular extractions with the forceps or erysiphake. Of the 62 capsules which broke in the last 1000 operations only 21 were of immature cataracts and 35 of mature cataracts although the former far outnumbered the latter.
I started using the cryoprobe about a year ago and have done to date 214 extractions of which 170 were done with the Pierse cryopencil and the remainder with the Amoils apparatus. The number of extractions done so far is admittedly small, but so is the rate of capsule rupture. The cryoprobe was used in all types of cataracts in the beginning to acquire proficiency but was latterly employed only where the capsule appeared likely to break by other methods; and in these cases the results have been most gratifying. The breakage rate of thin capsuled and Morgagnian lenses was reduced from 8% with forceps and erysiphake to less than 3% with the cryoprobe. Chemotrypsin was almost always used for the removal of cataracts with fragile capsules for one can never be certain of the strength of the zonule, and if the latter is unexpectedly tough and firmly adherent to the capsule chances of breakage are increased.
Four of the six capsules which broke with the cryoprobe were of mature cataracts. The first broke in the beginning of the series before we learnt to tell when the probe was cold enough. The tip had only half adhered, and on traction a punched out area of capsule came off with the probe. It was allowed to cool further and reapplied below the same point. Gentle traction removed almost the entire lens and capsule, only a little cortex remaining in the anterior chamber which was then washed out.
Two capsules burst well away from the probe. This happened after the lenses were half out. We could not ascertain just where or why the capsules had ruptured. Perhaps the posterior part of the capsule was excessively fragile or possibly the cold brought about much shrinkage of the capsule at the point of application which was then unable to withstand the internal pressure and consequently burst. The lenses were removed by pressure and counter pressure, the capsule with an Arruga forceps, and the cortex by irrigation.
In the most interesting case the capsule broke at the point of application of the probe. The probe was reapplied to the capsule further down but again after some upward movement of the lens it came unstuck. This happened a third time, the lens again moving out a little. It was then applied to what was virtually bare cortex, and an ice-ball allowed to form for 20 seconds before pulling, after which the lens mvoed out of the eye with the probe.
Some lenses with fragile looking capsules were deliberately removed without zonulysin just to test the adherence of the probe and the effectiveness of the method. None broke but this may be more due to luck than efficiency of the probe. On the whole, considering all types of lenses, the breakage rate with the probe is about half that with the forceps and erysiphake.
| Other Complications|| |
1. Vitreous loss occured six times in 214 cases. In three instances the eye was tense, the patient not completely sedated and general anaesthesia was unavailable. In two cases the vitreous was definitely adherent to the rear surface of the lens. In the last case a completely liquid vitreous filled the anterior chamber after the lens was out and the three preplaced sutures were tied. A drop escaped from the wound whilst inserting additional stitches.
As in all sliding procedures vitreous escaped from behind the lens when the extraction was nearly completed.
The vitreous loss with forceps and erysiphake extraction occurs in about the same proportion as with the cryoprobe.
2. No immediate or late complications have been encountered due to low temperature. The cold is not transferred to the ciliary body or vitreous. The probe inadvertently adhered only twice to other structures, once when the assistant accidentally dropped the cornea on the probe and once when it touched the iris. Each time a few drops of saline from the irrigator freed the probe which was reapplied after a few seconds and the lenses removed uneventfully.
3. Post operative clouding of the cornea described by other authors was not encountered.
4. It is said that if the probe temperature is much cooler than its normal -30° C it does not adhere and hold to the lens. A few cataracts were removed with the detachment probe of the Amoil's apparatus which reaches -70° C and no lack of adhesion due to the lower temperature was encountered.
5. Inadequate cooling of the probe is a complication which occurs oftener than one would expect especially with the Pierse instrument. Feeble adhesion to the capsule and separation of the probe usually with a broken capsule may occur if the cooling is inadequate, if the anterior chamber and lens surface are not dried, if the tip of the probe is not wiped free of frost, or inadequate time is allowed for the ice-hall to form.
| Assessment of the Usefulness of Cryosurgery|| |
When cryoextraction first appeared on the scene in 1961 it was regarded skeptically by some, looked upon as just another method by most, and adopted enthusiastically by a few. In recent years it is deservedly becoming increasingly popular. It can be used with equal facility for all types of cataracts which is more than can be said for other methods. I have found it neat, easy, sure and safe, more so than the forceps or suction cup and the fact that the lens cannot be tumbled does not make the delivery any more difficult or unsafe.
However, the overwhelming advantage of the cryoprobe is that it extends the number of cataracts which can be removed intracapsularly without unduly risking capsule breakage. The large group of mature, Morganian or semi-Morganian cataracts and delicate capsuled cataracts can be now removed as safely as immature or nuclear cataracts.
| Summary|| |
With the cryoprobe all types of adult cataracts can be removed with equal facility although it is especially useful in removing taut capsuled lenses which cannot be held with the forceps and very fragile capsuled cataracts which readily break with the forceps or erysiphake. The thinner the capsule the greater the indication for Zonulysin. They are removed by sliding not by tumbling.
The cryoprobe acts by freezing to the capsule at the point of application and freezing the adjacent lens matter into an "ice-ball" for about 3 mm. around the tip of the probe. This iceball becomes so as to speak an extension of the instrument and traction acts as if it were coming from within the lens rather than via the capsule. Hence the capsule breakage rate is greatly reduced to approximately half that of the forces or erysiphake.
The only operative complications are accidental touching and sticking of the probe to the cornea or iris which is easily separated by heating the probe.
Cryoextraction is a safe and easy method of removing cataracts especially mature cataracts and may to a great extent replace the forceps or erysiphake in the near future.
| References|| |
|1.||Amoils, S P.: Technique for cryothermic round-pupil cataract extractions. Am. J. Ophth. 60: 846, 1965. |
|2.||Bellows. J. G.: Indications and Techque of Cryoextraction of CataractsArch. of Ophthal. (Chicago) 73, 1965. |
|3.||Conway J.: Preliminary report of Cataract Extraction by freezing. Brit. J. of Ophth. 49: 141, 1965. |
|4.||Kelman. C. D. and Cooper, 1. S.: Cryogenic Ophthalmic Surgery. Am. J. Ophth. 56: 731. 1963. |
|5.||Kelman C. D.: Atlas of Cryosurgical techniques in Ophthalmology, 1966 (C. V. Moseby Co.). |
|6.||Krwawicz T.: Intracapsular extraction of intumescent cataract by application of low temperature, Brit. J. Ophthal. 45: 279, 1961. |
|7.||Rubinstein, K.: A report on development of a cryosurgical unit for controlled used of very low temperatures in ophthalmic surgery Tr. Ophth. Sec. U.K. 85: 555: 1965. |
|8.||Taylor and Dalburg, Corneal Complication from Cryocxtraction of Cataracts Aych. of Ophth. (Chicago) 79: 1 (Jan. 1968). |
|9.||Worst J. C. F.: New Instruments & Technique for Cataract CryosurgeryAmer. J. of Ophthal. 65: 587 Apr. 1969. |
[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4]
[Table - 1], [Table - 2]