Ординатура / Офтальмология / Английские материалы / The Art of Phacoemulsification_Mehta, Alpar_2001

PHACOEMULSIFICATION IN DIFFICULT CASES 243

Technique

The placing of the incision is important in this situation and the placement should be avoided over the weak zonular area as the constant flow of fluid over this is usually maximal and also the constant placement of instruments into the eye can lead to further stretching and damage the zonules and cause vitreous prolapse.

A low flow technique should be used coupled with a high phaco energy to minimize the amount of fluid within the eye and also minimize the amount of

movement of the lens capsule complex in doing the phacoemulsification. A large capsulorhexis should be attempted again to minimize the amount of capsular movement during phacoemulsification. In all the situations it is advisable to use

a Morcher ring to stabilize the capsule. A two-handed phaco technique is advisable.

Capsulorrhexis

The capsulorhexis itself should be started toward the weak zonular zone. The initial capsular tear is usually the most stressful to the zonules. The circular portion of the capsulorrhexis causes the least amount of tension on the zonules

Phacoemulsification

Before phacoemulsification proper, hydrodissection of the nucleus and capsulorrhexis must be done and free rotation of the lens must be obtained.

Phacoemulsification is best done using a bimanual method in order that the cataract can be stabilized with a second instrument. The cataract itself is usually fairly soft and easy to phacoemulsify and requires very minimal amount of energy.

However, if it is a hard cataract a large capsulorrhexis must be done in order that the phacoemulsification can possibly be done at the iris plane rather than in the capsular bag. In all these circumstances a very retentive type of viscoelastic, e.g. Viscoat (Alcon, Fortworth, Texas) should be used (Fig. 22.28A).

Successful outcomes using this technique can be achieved even when there is more than 4 to 6 O’clock hours of zonular loss (Fig. 22.28B).

Miscellaneous Cases

High Myopia

Patients undergoing cataract surgery who are also highly myopic and have a large axial length present with a special problem of a very deep anterior chamber as soon as the phacoemulsification tip is put into the eye.

It is important that a short incisional tunnel to minimize the amount of striae. This should be done even if at the end of the procedure one has to use a suture to keep the incision water-tight. Low flow, high energy phaco is ideal in this situation. Of course in these patients there is also the possibility that there are weak zonules and again the use of a capsular tension ring, e.g. Morcher ring, should be considered. If the anterior chamber deepens excessively then it might be necessary to prolapse the nucleus into the anterior chamber and to phacoemulsify

244 THE ART OF PHACOEMULSIFICATION

Fig. 22.28A: Dense mature cataract with weak zonular region

Fig. 22.28B: Successful IOL implantation.

Note large area of absent zonules

in the anterior chamber. This should be done under good retentive viscoelastic, e.g. Viscoat, and also prior assessment of the corneal endothelium is important.

POSTVITRECTOMY PATIENTS

These patients present with very similar problems to the high myope patients and present with a deep anterior chamber, usually a very brunescent cataract and a small pupil. They also, not uncommonly have some damage to the zonules.

246 THE ART OF PHACOEMULSIFICATION

Keiki R Mehta

Cyres K Mehta

Irrigation and

Aspiration Following 23

Phacoemulsification

INTRODUCTION

The procedure of irrigation/aspiration refers to removal of the remaining soft cortical residue from the anterior chamber following nuclear removal. It is completed within the capsular bag at all times and is a closed chamber system.

If the hydrodissection procedure has been carried out properly, the quantum of cortical residual material will be very minimal. The cortical material lines the bag and care needs to be exercised that during the removal phase the capsule is not inadvertently sucked into the aspirating port.

Complete removal of the cortex leaves a perfectly clean chamber and minimizes the chances of postoperative inflammation on the day following the surgery. The functional recovery is much assisted and posterior capsulotomy is delayed.

Irrigation/aspiration is thought of as very simple procedure. The surgeon finishes the nuclear removal part of the phacoemulsification and then relaxes, thinking, that with the removal of the nucleus, his main work is complete. He then goes on to irrigation/aspiration to clean out the cortical residue and breaks the capsule. It is an unfortunately, widely known, but least acknowledged, fact, that more capsules are broken by the surgeon at this, so-called innocuous stage, than all the capsules broken at the nuclear removal ultrasound stage.

The guidelines for safe and efficient removal of the cortical material is to progress in small steps, at a virtually constant rate. Start with aspirating the cortex in one quadrant and gradually go around till you reach the starting point. Evaluating the flow characteristics of the cortex controls the quantum of aspiration vacuum. As the aspiration vacuum is increased it reaches a level where the cortex seems to “flow” into the port. At this point, it becomes simple to remove the cortex, as one needs to only move the aspiration port gradually in a circular manner.

Sometimes the cortex is adherent to the posterior capsule especially when the hydrodissection has not been done properly. In these circumstances it becomes important to literally strip out the capsule piece by piece from the periphery to the center, using just adequate vacuum to hold the fragment. After a number of pieces have accumulated in the center, the vacuum is increased to aspirate them out together, all at one time.

It is important that the maneuvers in the anterior chamber are kept to a minimum. Irrigation/aspiration is always done at the end of the surgery and the pupil will have started to contract by this time, hence inordinate delay will lead to further

problems. Thus the irrigation/aspiration should be rapid while at the same time safety should not be compromised.

BASIC PARAMETERS FOR COMMENCING IRRIGATION/ASPIRATION

For aspiration to be performed correctly certain parameters need to be appropriately instituted

•Appropriate tip size

•Appropriate vacuum should be applied

•Equilibrium between inflow and outflow should be perfect

•Ability to alter suction to match the material and safety

•Variable progression of quantum of suction.

The vacuum to be generated at the aspirating tip is dependent upon the port size of the aspiration handpiece. The larger the port size, the lower should be the total vacuum limit and vice versa. The most common and widely used size is 0.3 mm. The standard operating parameters for an aspiration port of this size would be to keep the irrigation bottles at a height of 60 cm above the patient’s eye, and the vacuum set at 350 mm Hg in the “surgeon” mode (i.e. increasing with increased foot pedal depression) with a flow rate of 15 ml/min.

Irrigation/aspiration handpieces come in two types: one which is complete metal in which the tip of the irrigation/aspiration is a single piece of shining metal (usually titanium), or the second type in which the aspirating tube is metal while the irrigation fluid is conducted via a silicone sleeve. Though it is usually a surgeon’s personal preference, however silicone does have its advantages. The silicone sleeve occludes the phaco port better thus maintaining a better anterior chamber; being flexible it matches the contours of the opening and thus reduces leakage. In addition it reflects less light.

It has always been a point of debate on which is the ideal port size for the irrigation/aspiration technique. The diameter of the tips available is usually 0.2, 0.3, 0.5, or 0.7 mm. The former two tips are designed to be used with maximum vacuum limits (300 to 400 mm Hg), while the latter two tips need to be used with a minimum vacuum (100 to 200 mm Hg). With the larger size ports there is always a risk of anterior chamber collapse unless the irrigation/aspiration fluidics are perfectly balanced.

The 0.3 mm orifice is usually an ideal port size as there is a good balance between the inflow and outflow thus maintaining the chamber well. In addition a 0.3 mm

248 THE ART OF PHACOEMULSIFICATION

port would seem to be adequate for virtually all types of cortical debris. If the debris chokes the tip, a thin blade iris repositor inserted from the site port can either clean it or mash it into the port.

THE IDEAL CIRCUMSTANCES FOR IRRIGATION/ASPIRATION

The inflow and outflow must be balanced utilizing a flexible silicone test chamber prior to commencing surgery. The anterior chamber must remain formed and be kept deep. The pupil must be well dilated so that the I/A probe can have easy access to cortical material. There should be no source of pressure on the eye like an inappropriate lid clamp. The side and main ports should be of the appropriate size to minimize leakage. Adequate surge control facility must exist to prevent

barometric changes in the chamber.

The use of preservative free, intracardiac adrenaline (0.5 ml of 1/1000 adrenaline) injected into 500 ml of BSS has the ability to retain sufficient dilatation, and prevents the pupil from shutting down.

THE BASIC SURGICAL PRINCIPLES OF CONDUCTING PROPER IRRIGATION/ASPIRATION

Irrigation/aspiration can be conducted in many ways. However all the methods can be condensed into a simple basic technique, which is used at all times.

Enter the anterior chamber using only irrigation, so that the chamber deepens, the capsular bag opens up, and the cortical remnants are easily available, and accessible, for removal. The aspirating port is then taken close to the material to be aspirated, only at this stage the suction is activated by the foot switch, which raises the vacuum so that the orifice becomes obstructed by the cortical material. The tip is moved towards the center of the chamber gently separating the cortex fragments. In the center of the anterior chamber, vacuum is enhanced so as to quickly aspirate the larger cortical clumps, which are free floating in the chamber.

Each time aspiration is turned on and off with irrigation running, there are fluidic chamber changes. There is an alteration in the fluid balance of the anterior chamber in this process. When the cortical piece is attracted to the tip, the piece adheres to it, and then as the suction builds up, it is suddenly sucked in, producing surge. Unless the inflow is adequate the chamber is likely to collapse with dire consequences. Many phacoemulsification instruments have computerized surge controls (Alcon Legacy, Storz Millennium. Allergan Sovereign), automatically alter the speed of suction (by altering the speed of the peristaltic pump, in the Alcon and Allergan unit and the speed of the rotor in the Storz unit) to diminish or even eliminate this surge. In some instruments (Like the Opticon and the Mentor units) the use of the flexible diaphragm compensates effectively for the variation.

As one analyzes the depth variants of the anterior chamber it becomes obvious that a great deal depends on two inputs, namely, the quantum of inflow and the quantum of fluid outflow. Inflow is dependent upon the diameter of the tube leading into the anterior chamber, the diameter of the connections and the size of the inflow

ports. It is equally dependent upon the pressure, which is generated by the height of the bottle.

The outflow is naturally dependent upon the size of the outflow port in the irrigation/aspiration handpiece, the quantum of vacuum or suction applied to the tip, the diameter of the vacuum tubing, and the firmness or stability of the walls of the tubing. There is also a certain amount of fluid loss, which occurs from leakage from the sides of the main and side port incisions.

One always has to remember that the basic rule of aspiration namely that cortical material should be captured from the periphery and then subsequently drawn to

the middle of the anterior chamber and then, and only then, by a burst of vacuum power, aspirated. The novice often tries to maintain a constant vacuum level which may at times lead to accidental aspiration of the capsule in the aspirating port leading to a capsular tear.

There is another important rule that the aspirating orifice of the instrument must always be visible to the surgeon. This prevents accidental snagging and tearing of posterior capsule. In the event of an accidental miosis, though it is in order to go under the iris in a blind maneuver to hold the cortical fragments. However the fragments should be gently pulled outwards to the center of the pupil, at the same time visualizing the posterior capsule to be sure that no striae appear which would indicate that the capsule has been snagged.

RECOGNITION OF POSTERIOR CAPSULE CAPTURE

It is imperative during irrigation/aspiration that the surgeon recognizes immediately when the capsule inadvertently, has been captured in the aspirating port. It is important that when irrigation/aspiration is commenced, the focus of the microscope is changed so as to produce a sharp focus onto the posterior capsule, and the position of the eye with relation to the coaxial tube of the microscope be so adjusted so as to achieve the best possible red glow. If the focus is fixed on the posterior capsule the surgeon will realize immediately that the capsule is sucked into the port (captured) when thin and fine lines of folds, termed striae start from the point of capture with radial extensions. The appearance is very suggestive of a sunray appearance. If the capsule is caught in the middle it is easy to note that it has taken place, however if it is caught in the periphery, identification may prove difficult.

The accidental capture of the posterior capsule is much easier and more frequent with the larger size ports like the 0.5 or the 0.7 mm size but comparatively less frequent with the smaller 0.2 or 0.3 mm ports. It is important that the moment capture is recognized the surgeon should immediately reverse fluid outflow to release the capture without moving the aspirating tip. Capturing the posterior capsule does not break the capsule (provided the port is smooth and well polished). It is the movement of the aspirating tip once the capture has occurred which breaks the capsule. Thus care should be taken that once the capture is detected, to freeze movement, stop aspiration and break the suction.

Some of the better phacoemulsification machines are fitted with active venting capability, which permits an immediate break of vacuum with a positive outflow,

which literally sweeps the posterior capsule away from the aspirating port. It is important that the surgeon is familiar with the controls and adapts himself to it so that at the critical time he does not fumble with the foot controls. Another quick technique to release the adhesion is to simply squeeze on the aspirating plastic/ silicone tube with the thumb and the forefinger, which also acts as an active venting technique. Care should however be taken to note that this technique will not work with the high vacuum tubing is available in such machines like the Alcon Legacy

and the AMO Diplomax as the thickness of the tube is such that it simply does not get squeezed.

It may be pertinent at this point to explain the principle of the flow rate setting on the phacoemulsification machine. Despite the volumes that have been written on the subject, a simple way of remembering is that flow rate settings controls the speed at which you work in the chamber. A slow flow rate (10 to 20 ml/min) means that it takes a much longer time to develop the level of vacuum you desire, while a fast flow rate (20-40 ml/min) indicates a very rapid onset of the suction. A good medium flow rate is 15 ml/minute. Whenever in doubt, slow down the flow rate and you will rarely get into trouble.

ASPIRATION VARIABILITY FOR SUBINCISIONAL CORTEX REMOVAL

One of the problems faced by both the novice and the experienced surgeon is the problem of removal of subincisional cortex. Customarily it tends to occur as the surgeon has, as one would say, “painted himself into the corner”, by removing the larger, easier to reach pieces first, leaving the removal of the subincisional cortex to the end. Usually the small clump left strenuously resists any efforts for its removal.

Techniques for Subincisional Cortex Removal

As a primary requirement the irrigation bottle should be raised a little higher so as to deepen the anterior chamber.

The Ice-cream Scoop Maneuver

The irrigation/aspiration handpiece should be inserted with only the irrigation on. The handpiece is then lifted 30 degrees vertically in an arc. The aspiration is energized, keeping a sharp lookout on the posterior capsule; the aspiration is gradually increased till the subincisional cortex pieces simply float out.

The Bimanual Technique

Go from the side port incision in a bimanual (two-handed) technique. Here we use two handpieces each with an individual, single function, either irrigation or aspiration. Hold the irrigation handpiece in the right hand, and the aspiration handpiece in the left hand. Enter via the side port and then gradually insinuate the aspirating needle under the capsule and simply draw out the offending cortical material. Alternate techniques such as the bent cannula (Binkhorst) are not as

IRRIGATION AND ASPIRATION FOLLOWING PHACOEMULSIFICATION 251

convenient. Various shaped cannulas have been developed with bends at strategic locations but the bimanual technique is the simplest and works exceptionally well. Many reputed surgeons do bimanual irrigation/aspiration as a routine technique with all their cases.

The IOL Sweep Technique

Place the intraocular implant in the eye and insert it in the bag. Fill the bag with viscoelastic and using a lens rotator, spin the IOL in the bag a few times. Very often the IOL loops will either clean the subincisional cortex out or make it so

loose that it aspirates out fairly easily.

IOL Compression Aspiration Technique

Here after placing the IOL in the bag, simply rotate the loops away from the site of the subincisional cortex, fill the bag with viscoelastic, press on the surface of the implant with the irrigation/aspiration handpiece to deepen the chamber and push the posterior capsule backwards, energize the aspiration and the subincisional cortex will easily come out. The posterior capsule is not at risk as the IOL comes between the capsule and the I/A probe.

Sometimes, in a difficult situation, the subincisional cortex simply refuses to come out, then the surgeon is left with the option that he can leave the piece behind and risk it reappearing later (usually between the 3rd and 7th postoperative days), in the visual axis, lying under or over the implant, appearing as soft, white, flocculent material appropriately termed as “cortical rain”. In this circumstance, the surgeon should re-enter the chamber through the previous phaco incision and using low suction aspirate the cortical “rain” out.

It is always a fallacy to tell the patient that it will absorb by itself. It may, but by that time the patient is quite apprehensive and unhappy at the outcome of the surgery, in addition its presence leads to an irritable eye, and its absorption will invariably lead to early capsular thickening. With the present day litigious atmosphere in India, it makes more sense to simply aspirate it out. It leaves behind a happy patient and a relieved surgeon.

MANAGING THE VITREOUS IN THE ANTERIOR CHAMBER

Despite the best efforts of the surgeon an occasional capsular break will take place. It is important to learn how to handle this break, as its appropriate management will govern the quality of vision one will achieve. It is important that at the first sign of the break, the irrigation/aspiration handpiece be removed from the eye. If most of the cortical material has been removed it is important that first the intraocular implant be placed in the bag prior to removing the cortical residue. The logic behind this procedure is that while the bag has been unharmed the implant can easily be put in (bag fixation). In case the bag tears excessively, the implant can be put in the sulcus, i.e. on the anterior capsule (sulcus fixation).