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

392 THE ART OF PHACOEMULSIFICATION

CONCLUSION

Cataract surgery continues to undergo improvements and refinements making it safer and faster. Although most patients with COPD can undergo phacoemulsification without regards to their respiratory disease, patients with severe pulmonary disease often present challenges to the cataract surgeon.

Coughing will usually present itself as more of a nuisance than a threat to surgical outcome now that incision architecture has allowed for small self-sealing wounds.

Despite this, there are measures that can be taken preoperatively to help reduce the incidence of coughing allowing for safer uninterrupted phacoemulsification.

Probably the greatest obstacle and challenge for performing surgery in these patients are those individuals who are unable to fully recline for the operation. Phacoemulsification can be performed in the standing position to accommodate patients who are intolerant to the supine position, however we feel that new surgical tables and/or surgical chairs will allow patients with severe COPD to undergo phacoemulsification under safer and more comfortable conditions in the future.

REFERENCES

1.Rimmer S, Miller KM: Phacoemulsification in the standing position with loupe magnification and head lamp illumination. J Cataract Refract Surg 20:353-54, 1994.

2.Hunter LH: Standing while performing phacoemulsification. J Cataract Refract Surg 21:111, 1995.

3.Liu C: Phacoemulsification in a patient with torticollis. J Cataract Refract Surg 21:364, 1995.

INTRODUCTION

Phacoemulsification is an excellent procedure however, it needs to be done with care and caution. In the hands of a skilled surgeon, phacoemulsification can give exceptional vision, rapid rehabilitation, in a virtually painless procedure.

For the less experienced surgeon, if the selection of cases is not appropriate, there is always a possibility of having problems. In phacoemulsification every single step commencing from the preparation and positioning of the instrument, to the proper construction of the corneal tunnel, the capsulorrhexis, and the completion of the procedure, have to be accurate and well completed. A mistake in one step will snowball into problems, which will complicate the steps to follow.

In this chapter, let us take problems as they arise. Some of them may seem very small and steps to prevent them would seem to be insignificant, but experience has taught that the smallest steps, if ignored can precipitate situations, which are best avoided.

PREVENTIVE ASPECTS PRIOR COMMENCING PHACOEMULSIFICATION Positioning of the Patient

Proper positioning of the patient is very important as it permits stability with adequate access to the eye. The brow and the chin of the patient should be on the same horizontal plane and at right angles to the operating microscope. It is important to keep a number of small rubber pillows, of different thickness, (1/2 inch, 1 inch, 2 inch, 3 inch, 4 inch) which can be added to get the best possible position of the forehead. It is important that a rubber ring be inserted under the head on the

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final rubber pillow, which will prevent the rolling of the head during surgery stabilizing it further. The premade trough pillows (a section cut into them to fit the head) are quite inadequate. Either they are too large, permitting excessive rotation, or too small, in which case the head sits on the edges and does not fit into the groove, making it very unstable.

Checking the Intraocular Pressure

It is mandatory prior commencing surgery, whether a retrobulbar, a peribulbar, or topical anesthesia is being utilized, that the intraocular pressure (IOP) be checked with a Schiotz tonometer on the table. Many surgeons will check the pressure digitally (using the digits of two fingers) after giving a retrobulbar, or a peribulbar block. The block merely relaxes the muscles and a digital check-up merely indicates the softness of the retro-orbital tissues and does not reflect the softness of the eye. Immediate preoperative checking IOP with a Schiotz tonometer routinely is important. Often surprises will occur when an eye, thought to be soft digitally, will turn out to have a high pressure with the tonometer.

In topical anesthesia, what must be remembered is that the eyes are being maximally dilated, using a combination of NeoSynephrine 5 percent with homatropine 2 percent. Thus, there is always the chance of an angle-closure glaucoma (ACG) developing, even more so considering that the cataract, being advanced, is likely to have swollen. A pressure up to 21 mm Hg would be taken as acceptable, while the surgery may need to be put off for some time and an effort made to reduce the IOP by I/V Mannitol or pressure with a Honan’s balloon or Buy’s bag or the balancing balls. Ideal pressure for phacoemulsification is 15 mm Hg or below. Doing phaco surgery with a high IOP is asking for trouble. The chamber will tend to collapse and will remain shallow. There is always the likelihood of endothelial damage. The chances of capsular break are significantly increased, and God forbid, if the capsule breaks, vitreous loss is virtually inevitable.

Oxygen or Fresh Air under the Drapes

It makes sense to use a digital oxygen saturation monitor in all cases. Fresh air provided under the drapes (fresh air, since oxygen is not truly required, though preferable) washes out the carbon dioxide, which induces air hunger and makes a patient extremely restive. Patients, in the older age group, already have compromised pulmonary function and go into oxygen deprivation extremely quickly. The presence of fresh air whistling under the nose gives the patient a comfortable feeling. If the surgery is being done under topical anesthesia, adequate oxygenation is vitally important for a peaceful patient, which would lead to peaceful surgery by a peaceful surgeon. The ideal technique of introducing the air/oxygen is by using soft silicone nasal prongs, which enables the air to whistle comfortably in the nostrils. The plastic tube should be fixed so it does not move and irritate the patient during surgery. The ideal technique is to loop the plastic tube around the ears and then fix them under the chin. Fixed in this manner, the tube remains stable no matter how the patient moves. This particular technique is termed as the Santa Barbara method.

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Placement of the Lid Retractor

The lid retractor should be able to properly open the eye to achieve good access without causing any discomfort. Essentially retractors can be divided into two categories.

•Fixed retractors can be opened and fixed at a required lid retraction or opening, using a ratchet arrangement or a screw attachment. The advantage of the fixed

retractors is that the quantum of the opening can be varied as per requirement.

On the other hand, the disadvantage is that the patient often tries to fight the offending retractor, which causes pain, leads to an uncooperative patient.

•Spring retractors utilize a spring mechanism to keep the eye open. The spring retractors only open to the level at which the tension of the lid is offset by the tensile strength of the spring. Thus the quantum pf opening is dependent on the tension of the lids vis-a-vis the spring elasticity. The big advantage is that as the patient tries to forcibly close the eye the spring retractor automatically closes and then reopens. After some time of this closing and opening cycles, the orbicularis tires and the eye remains open. However, the advantage is that the patient is comfortable and the cooperation of the patient is assured.

Aspiration of Excess Fluid

In a deep-set eye or in one that has prominent bony configuration the BSS and secretions tends to accumulate in the eye and reflect like a mirror back into the operating microscope literally blurring the surgeon’s vision. It is thus important that the fluid be aspirated or drained off. There are many types of drains available. Merocell is a close mesh plastic which allows the fluid to flow out of the eye. Builtin aspirator is a benefit with retractors. Usually the suction line is in-built and the openings in the tines of the retractors suffice to suck out the excess BSS and secretion from the eye. This is an ideal type and is to be recommended. Connect the aspirating retractor to a small suction unit. Usually the suction units available in the hospital are much too powerful and tend to suck in not only the fluid but also the conjunctiva. A small gentle dental suction unit that has a suction of 2 to 4 mm Hg is ideal. This little suction unit should be connected via a silicone, autoclavable tube to the aspirating retractor or alternatively, a small hand suction tip so the assistant can do the suction. It keeps the field dry, prevents Merocell or cotton swabs from being used continuously near the fornices. This continuous swabbing predispose to redness and small subconjunctival hemorrhages the next day. It also increases the possibility of accidental pressure on the eye, especially after the attendant becomes inattentive, after long list of surgical cases, typically at the end of the day.

COMPLICATIONS AT VARIOUS PHASES OF PHACOEMULSIFICATION SURGERY

The incision is the most important part of the phacoemulsification surgery.

To be a self-sealing incision, the tunnel must be of an adequate length. The incision at the entry point on the cornea and the exit point at the Descemet’s membrane should be a straight line if the valve is to really function well. The ideal instrument is a diamond knife where there is a differential bevel between the front and the back. This type of a diamond knife, conceived by Dr Fine, made by Rheim, called a 3D blade, gives almost perfect tunnel formation time after time. However, a metal

keratome or knife would also work well but would need a lot more experience to achieve perfect tunnels. The diamond knife does it effortlessly. Many surgeons prefer to use a round beveled blade to dissect a pocket, and then use a 15-degree sharp knife to enter into the anterior chamber. Though in the hands of an expert this technique would seem to be adequate, its ability to do consistent corneal tunnels is limited.

With phacoemulsification, it is important that the width of the incision must exactly mimic the width of the phaco tip used. Some machines require 3.00 mm for the phaco tip introduction in the anterior chamber while in others 2.8 mm may be ideal. In the author’s machine, an Alcon Legacy with the 0.9 mm diameter tips, a 2.8 mm incision is required. If incision is too narrow, it is difficult to insert the phaco tip, which is liable to brush against the Descemet’s and even detach the Descemet’s is as the phaco tip enters the anterior chamber. The other problem being that if it is too narrow the sleeve tends to get compressed in the lips of the tunnel, choking off the inflow of irrigating solution. A phaco tip remains cool by the flow of irrigating solution over the phaco tip under the sleeve and by the outflow of aspirating solution through the needle. It is however the irrigation flow which does the main work. If the sleeve is too tight in the incision, it chokes off the irrigation flow allowing the temperature of the phaco tip to build up which is liable to produce corneal burns. The biggest disadvantage of corneal burns is that it makes the cornea at the burnt area shrink slightly, which retracts creating a bridge over the incision, no longer functioning as a self-sealing incision and even requiring sutures to close the incision adequately on completion of the surgery.

The problem of a proper size incision can be solved by using the appropriate blade, calibrated precisely for that incision’s requirement. One of the advantages of a diamond blade is that a 2.8 mm blade will give you an exact 2.8 mm incision. Since no pressure needs to be applied on a diamond blade during entry, the width of the incision remains a constant.

If on the other hand the incision is too wide, fluid tends to escape from the sides, disproportionately, with the result that the chamber depth tends to fluctuate and is even liable to collapse. If the IOP of the patient is high, more so if the vitreous pressure is also high as occurs in myopes, a fluctuant chamber is liable to lead to a break in the posterior capsule. In addition the outflow from the leakage sites coupled with the outflow from the bore of the needle would mean that during phaco one can be saddled with an unstable, ever changing anterior chamber depth with a bouncing (trampoline) posterior capsule. A single mistake will lead to a rupture of the posterior capsule with a vitreous break.

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viscous (icing makes the methylcellulose increase by in viscosity by a factor of three), does not readily come out of the chamber, keeping it well inflated at all times.

Problems with the capsulorrhexis Among the problems, which can occur during a capsulorrhexis, the most frequent is a rhexis, which escapes off into the periphery. The reason is not hard to see. The anterior zonular fibers fan inserts onto the anterior capsule usually at 8.5 to 9.00 mm from the lens center, however some aberrant fibrils will extend anteriorly up to the 7.0 mm from the lens center (Eisner, 1975).

If a rhexis extends out to this level and reaches the zonular insertion on the anterior capsular membrane, rather than turning smoothly the rhexis will be deflected along

the zonular path, literally, running off into the periphery.

It is possible to shift it again, using a forceps, but be sure to use a repositor to sweep the anterior capsule free of zonular adhesions prior continuing the rhexis. With the rhexis forceps, grasp the edge of the capsule and swing it sharply inwards. Usually it is more than adequate to get the rhexis going again around.

Another easy way to tame a rhexis, which has run away from you, is to redirect it using a fine scissors, (a long-bladed Vannas scissors is ideal). Make a small fresh cut in the direction you want the rhexis to go and, holding the edge of the freshly cut capsule, complete the rhexis. Be very certain not to exert stress at the place where you have reverted the flap, as the initial extension is likely to go to the periphery with problematical consequences.

Another method is to place a repositor under the edge of the rhexis where you wish it to go, use a sharp pointed needle and nick the capsule, Holding the inner nicked part of the capsule, complete the rhexis, bringing the advancing flap over the initial cut edge from the out, in. This will once again restore the capsular bag integrity.

Prevention of Complications with Hydrodissection

To prevent complications occurring it is important to use a proper technique. The technique involves injecting a small amount of fluid (Ringer lactate or BSS)

under the anterior capsule with a fine blunt cannula connected to a 3.00 ml syringe. Because of the fluid pressure and the dissecting ability of the fluid to take the path of least resistance, the fluid separates the cortex and the epinucleus and partly separates the capsule and the cortex.

The ideal technique of cannula placement for effective hydrodissection is to place the cannula just within the capsulorrhexis edge, slightly tenting it or lifting it upwards. This technique termed as “cortical cleaning hydrodissection” was originally conceived by Dr Howard Fine. Injecting the fluid along the rhexis edge permits the fluid wave, literally to shear close to the capsule, thus significantly diminishing the quantum of cortical remnants which will need to be aspirated after the primary nucleus is removed by phacoemulsification.During the hydrodissection, unless it is a very hard cataract or an opaque one, the fluid wave can be seen clearly to separate the cortex from the nucleus, and is indicative of a successful hydrodissection. Hydrodissection

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is usually carried out in three sites commencing with the 4.00 O’clock position followed by the 2.00 O’clock position and finally followed by hydrodissection at 8.00 O’clock position. It is important that small aliquots of fluid be utilized, as excess fluid especially in a hard brown cataract is liable to balloon the capsule posteriorly, rather than spreading as a wave, and may, if more fluidic pressure is applied, rupture the capsule.

It is important to visualize while injecting the fluid diffusion wave. The ideal syringe is a Luer-Lock, plastic, disposable, Teflon-coated or siliconized, of 3.00 ml capacity. This type of a syringe permits a better control, prevents application of too much pressure. Being Teflon coated, or siliconised, the piston moves very smoothly, and does not stick. Too thin a cannula, (ideal is 24-26G, flat cannula), even if blunt is liable to puncture the capsule if accidentally inserted too far into the periphery.

In addition, a thin cannula permits the fluid to emerge in a sharp jet, at high velocity, which is not required. The one way to be sure the hydrodissection is complete is to check whether the nucleus rotates freely in the bag.

In all cases, hydrodissection should be followed by mechanical rotation of the nucleus to be sure the nucleus rotates freely and that all adhesions have broken down. It is important to appreciate that the lens does not rotate freely one must do hydrodissection again, and again, and again, until smooth rotation is achieved.

It is important that after every injection of fluid the lens should be gently pressed backwards. This technique is termed as “compression hydrodissection” and works by causing the fluid to disperse and spread out as a flat lamellar zone at the back of the nucleus and thereby enhance the hydrodissection. This technique should compress gently following each injection of fluid under the capsular flap. Compression hydrodissection thus decompresses a filled capsular bag, and at the same time shears off any adhesions.

Managing complications in hydrodissection It is imperative that the quantity of BSS injected under the capsule should never exceed 0.5 ml at a time. In addition, to prevent the risk of inadvertent perforation of the anterior capsule, always use a 24 to 26 G blunt cannula. Always lift up the edge of the capsule. Besides doing a good fluid wave, this technique also prevents accidental puncture of the capsule, which will nick and weaken the rhexis.

It is important to always press on the nucleus after every injection to be sure that the fluid is dispersing well and not accumulating below the nucleus, which may lead to a rupture of the distended posterior capsule.

Impending Rupture of the Posterior Capsule

Every surgeon, at some time or the other is liable to break the posterior capsule during hydrodissection. If one learns to identify the signs of an impending rupture, it can be handled safely. In case rupture does occur, it is important to identify it early, as soon as it occurs, so that the problem can be managed smoothly with minimal complications.

The earliest signs of an impending rupture is to have the iris/lens diaphragm move forwards reducing the anterior chamber to a thin chink. At this stage, if the

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Fig. 37.11: Rupture of capsule during phaco

Fig. 37.13: Showing subconjunctival swelling due to poor position sclerocorneal incision

surgeon panics and tries to force the reformation of the anterior chamber by injecting viscoelastic under pressure or, worse still, tries to push on the nucleus, in a backward direction, it will immediately lead to a rupture of the posterior capsule.

The method of handling it at this stage is simple. All one needs to do is to take a thin blade iris repositor and introduce it under the capsule in the 5.00 O’clock position and then sweep in, under the capsule to 3.00 O’clock position and then

to the 7.00 O’clock position. Almost immediately, the surgeon will be rewarded with a gush of fluid indicating that the block has broken

Managing the ruptured capsule after hydrodissection Rupture is detected by the tight eye suddenly going soft, and the iris and the nucleus moving backwards with the chamber deepening. At this stage though the posterior capsule has ruptured,