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

12 THE ART OF PHACOEMULSIFICATION

Preparation of the Eye

The area around the eye and the eye itself are washed with 10 ml of 50 percent diluted Betadine 5 percent ( povidone-iodine) solution. A cotton bud soaked in full strength Betadine solution is swept along the lashes to make sure that they are well cleaned. Subsequently the eye is flushed out with distilled water or with Ringer lactate to remove all the impurities. There is never any need to cut lashes.

Draping the Eye

The area around the eye is dried thoroughly with a sterile towel. A sterile self-adhesive plastic drape, either individually, or as a part of a complete drape, must now be placed over the eye. The method of placement is fairly simple. The eyelids are kept widely open either by the surgeon’s left hand or kept open by the surgical assistant using cotton buds. The sterile drape is positioned over the opened eye, the tip of the index finger is allowed to press the drape in between the opened area, gradually letting the drape stick onto the lashes and then onto the area around the eye.

Using a blunt-tipped scissors, the plastic drape is tented and then incised down the middle being careful that the cornea is not accidentally touched. A soft wire speculum or a self-retaining speculum is then inserted in such a manner that the incised drape turns over the lashes, and then passes under the lids, held in place by the speculum, isolating them from the sterile field. Another big advantage of draping is that at no time is there any accidental touch at the time of insertion of the phacoemulsification probe or the implant in the eye.

Following the application of the drapes, a second cloth drape can be put over the site. It has three functions: (i) it acts as an additional sterile barrier, (ii) cuts down on reflections, and (iii) acts as an absorbent media.

Use of Lid Stitches

In the days of intracapsular and later extracapsular cataract surgery, the use of lid sutures or superior rectus sutures was almost a routine. In the phaco era, lid stitches are used extremely rarely and are quite unnecessary. The only time any sutures are used is a superior rectus suture placed if the surgeon requires more exposure as when he or she wishes to do a combined glaucoma and cataract procedure. By eliminating the use of a superior rectus stitch, postoperative ptosis incidence is markedly reduced, it is infinitely less traumatic, eliminates the hematomas, which occasionally accompanied the placing of the stitch, and reduces postoperative inflammation. Since more often than not, topical anesthesia is the technique of choice, the eye is kept stable enough by the patient and the use of the superior rectus stitch is thus redundant.

Suction Facilities

To maintain a dry field during surgery is important. It is very difficult to operate with a pool of liquid reflecting back the microscope light. Rather than repeatedly

COMMENCING PHACOEMULSIFICATION: THE BASICS 13

swabbing the area dry, which leads to conjunctival irritation and interferes with the surgeon, the best is to keep a small suction available. A good option is the use of self-retaining speculum with aspiration ports attached to a small dental suction which gives suction in the range of 5 to 7 mm Hg. An alternate method is to utilize a drainage device like a sterile plastic bag which can be attached on to the side of the eye to hold the excess fluid as it drains out, or to use an absorbent wick drape which permits easy leakage. Which ever device is used, it is important to

keep the floor dry. Dripping irrigating solution can be a source of great irritation to the surgeon when it falls on his or her feet, or wets his or her clothes. In addition

the dripping liquids tends to cause the phaco foot switch to become slippery and may even jam in time thanks to the dried salt crusts. In addition, the saline is electrically conductive and is thus an electrical hazard.

FURTHER READING

1.Mehta KR, Sathe SM, Karyekar SD: Computer Terminal Usage and Eye Fatigue, Xth Congress APAO. Soc Proc 2:946-48, 1985.

2.Mehta KR: Phacoemulsification cataract extraction with foldable IOLS-First 50 cases. All India Ophthl Soc Proc 56-60, 1989.

3.Mehta KR: Progressive corneal endothelial decompensation—extended wear contact lenses with aphakia.

All India Ophthl Soc Proc 109-14, 1989.

4.Mehta KR: Endocapsular phacoemulsification and posterior chamber IOL implantation. All India Ophthl Soc Proc 217-20, 1989.

5.Mehta KR: Post-cataract astigmatism: A comparison between phacoemulsification and ECCE procedure: cataract with and without intra-ocular implantation. All India Ophthl Soc Proc 226-29, 1989.

6.Mehta KR: Posterior capsular capsulorrhexis with shallow core vitrectomy following implantation in paediatric cataracts. All India Ophthl Soc Proc 207-10, 1995.

7.Mehta KR: The loop tri suction nonphaco technique of small incision cataract surgery. All India Ophthl Soc Proc 210-12, 1995.

8.Mehta KR: The clear corneal phacoemulsification with injectable silicone lenses. All India Ophthl Soc Proc 218-22, 1995.

9.Mehta KR: An Advanced but simple keratometer for control of postoperative astigmatism. All India Ophthl Soc Proc 122-23, 1990.

10.Mehta KR: Posterior chamber implantation. All India Ophthl Soc Proc 143-44, 1990.

11.Mehta KR: YAG laser damage to intraocular implants—an evaluation. All India Ophthl Soc Proc 14750, 1990.

12.Mehta KR: Phacoemulsification—is it the true III world answer for eye camps. All India Ophthl Soc Proc 301-303. 1990.

13.Mehta KR: An analysis of causative factor leading to eye strain caused by computer monitor screens.

All India Ophthl Soc Proc 334-36, 1990.

14.Mehta KR: Single stitch elliptical funnel incision for cataract surgery. All India Ophthl Soc Proc 25354, 1991.

15.Mehta KR: Bifocal intraocular implants—a functional evaluation based on 425 cases. All India Ophthl Soc Proc 271-74, 1991.

16.Mehta KR: Phacoemulsification with flexible PC IOL—is it really a step forward. All India Ophthl Soc Proc 287-88, 1991.

17.Mehta KR: The new phaco cleave technique for hard cataracts. J Intraocular Implant and Refractive Society, India 1(1): 74-75, 1996.

18.Mehta KR, Sathe SN, Karyekar SD: The new soft intraocular lens implant. Am Intraocular Implant Society J4(4):200-05, 1978.

19.Mehta KR, Sathe SN, Karyekar SD: New soft posterior chamber implant, X Congress of the AsiaPacific Academy of Ophthalmology. New Delhi,1985.

20.Mehta KR: Clear corneal phaco with injectable silicone IOL proc. All India Ophthl Soc Proc (Mumbai) 1995.

14 THE ART OF PHACOEMULSIFICATION

21.Mehta KR: Phaco with flexible IOL—is it a step forward. All India Ophthl Soc Proc (Bangalore) 1991.

22.Mehta KR: The tripod posterior chamber flexible acrylic implant —the answer to better stability. APIIA Conference, 1997.

23.Mehta KR: Intralenticular “hubbing” technique for simple eye camp phacoemulsification—a simple technique. APIIA Conference, 1997.

24.Mehta KR: Newer techniques for eye camp safe phaco techniques. APIIA Conference, 1997.

25.Mehta KR: Intralenticular “hubbing” phaco technique for safe phaco. Proc of SAARC Conference, Nepal, 1994.

26.Mehta KR: The New Multiport Phaco Tip for Safer, More Effective Phacoemulsification, with Virtually

Zero Capsular Damage. Proc of SAARC Conference, Nepal, 1994.

of electrical energy into ultrasound is at the handpiece level. The body of the machine thus basically has controls which modulate every key requirements, be it diathermy, irrigation-aspiration control, ultrasound energy stability, or even the height of the irrigation bottle, etc. The fine-tuning is done by the foot switch which gives the surgeon more flexibility.

Every phacoemulsifier has five basic functions; diathermy, irrigation, irrigation- aspiration, ultrasonic fragmentation and vitrectomy. Each of these functions has

a handpiece to match them.

Irrigation Handpiece

The irrigation handpiece is used when only irrigation is required. It is connected to an irrigating cystitome for anterior capsulotomy, or to an irrigating loop for hydrodissection. Many machines have the ability to preset controls so that when only irrigation is required, the foot switch functions purely as an on-off mechanism.

Irrigation-Aspiration (I-A) Handpiece

The infusion liquid is sent to the anterior chamber through the connected tubes. The basic function of the I-A handpiece is to aspirate liquid and cortical material through the aspiration port, at the same time infusing chamber-maintaining liquid into the anterior chamber. Essentially the irrigation-aspiration (I-A) handpiece, has a either single piece metal (stainless steel or titanium) irrigation-aspiration sleeve or has an aspiration sleeve with a silicone sleeve that fits snuggly around the aspirating tip.

The I-A tip differs from the phaco tip in being smooth and rounded with a single aspiration port on the side of the tip and not at the end. The sleeve may be turned to orient the irrigation port in any direction. The irrigation ports in the silicone sleeve should be kept perpendicular to the metallic aspiration port as this helps direct the infusion fluid along the iris plane. This reduces iris flutter during the surgery.

Typically the I-A handpiece has a rounded tip with the aspirating port at one side usually 0.75 mm to 1.5 mm away from the tip. The opening can be in a diameter of 0.2, 0.3, 0.4, or 0.5 mm. The overall diameter of the I-A handpiece usually varies from 2.5 to 3.0 mm depending on whether the aspiration sleeve is metal, or of silicone. The angulations of the I-A handpiece can be straight, 45° bent, or has a 90° bend. Most surgeons prefer to utilize the curved I-A tip. Recently Alcon in its Legacy phaco machine has taken out a tip which can be varied as desired termed a “steerable tip”.

The commonly used I-A port is a 0.3 nun port. It has the safety feature that it will aspirate the cortex and not the capsule. It is however wise to keep on one’s table a 0.5 port so that at times when you wish to aspirate larger particles it is available. The larger port is also useful when doing a direct aspiration, as is often done in a congenital cataract.

Irrigation/aspiration handpieces corne with metal or silicone sleeves, each having their own advantages.

Metal Sleeves

Metal sleeves allow a more regular inflow since they neither are compressed by the incision edges nor are they compressed if the tip is moved in a tunnel obliquely when oar-locking can obstruct the flow. Having smoother edges they are easier to introduce into the phaco tunnel. They also do not snag on the edges of the iris. Naturally being metal, they last much longer (Fig. 2.2).

Fig. 2.2: Irrigation/aspiration metal sleeved handpiece curved, and 90 degrees bent

Silicone Sleeves

Silicone sleeves have greater flexibility and by molding themselves to the walls of the tunnel (basically, once a tunnel is opened, it is no longer a slit but elliptical in shape) give a better fit, thus diminishing the leakage from the chamber. This is important especially if the eye pressure is a bit high, chamber is shallow, or in children (Fig. 2.3).

Fig. 2.3: Silicone-sleeved bent for irrigation/aspiration bent

The Diathermy Handpiece

In diathermy handpiece is a very essential adjunct and is ideal when a blood-free field is required typically in preparation of squared or smile (chexron) scleral or semiscleral incision.

Diathermy handpieces can be coaxial (Erasertm) or of the forceps type. The coaxial type is excellent in preparing and having a bloodless scleral area. The forceps on the other hand can also be used for sealing the edges of the conjunctiva together (coaptation) at the end of the surgery.

It is essential that the minimum quantum of diathermy be utilized. In most modern machines the control of the quantum of diathermy is linear, i.e. it is controlled by depressing the foot pedal. The maximum and minimum values can be preset on the console.

Anterior Vitrectomy Handpiece

The unit can be either of the guillotine type or of the rotating type with a triangular tip. In the earlier days most machines had the rotating vitrectomy tip, but it was soon recognized that the moment the unit got a little older it tended to entrap and tug on the vitreous and hence the guillotine vitrector has now become a standard in most machines.

For anterior vitrectomy, the tip usually comes with a perfusion sleeve which can be removed if so desired. On the console, the essential values of flow rate, cut rate and vacuum can be set to suit individual requirements.

Ultrasonic Handpiece

Bimanual

It has become customary for many surgeons to use separate handpieces for irrigation and aspiration. This helps immensely in cortical removal (Fig. 2.4).

Fig. 2.4: Bimanual hand pieces, separate for irrigation/aspiration

Phacoemulsification of a lens nucleus depends upon ultrasonic power which is the function of the acoustic vibrator that has been incorporated into the ultrasonic handpiece. Attached to this vibrator is a hollow titanium needle or the phaco tip. The acoustic energy produced along the ultrasonic handpiece is then transmitted onto the phaco tip (Fig. 2.5).

THE PHACOEMULSIFIER 19

Fig. 2.5: Phacoemulsification handpiece with four crystals (Alcon Legacy)

The acoustic vibrator is of two types: magnetostrictive or piezoelectric device. The acoustic vibrator converts electrical energy into mechanical energy under the influence of an electrical signal. The acoustic vibrator oscillates longitudinally at a frequency between 30,000 and 60,000 Hz. This imparts a linear motion to the ultrasonic tip. The stroke amplitude of the linear movement is 3.1000 of an inch and the acceleration 80,000 to 2,40,000 G.

Magnetostrictive Handpiece

Magnetostrictive handpiece was the first in use, and has now been phased out. It uses an electric current to induce a magnetic field which results in the linear movements of the ultrasonic tip. The electromagnetic field is generated by a coil of wires wrapped around the handpiece.

Advantages and Disadvantages of Magnetostrictive Handpiece

•Can be autoclaved repeatedly with no risk to the handpiece

•Much sturdier. Does not break if dropped

•Can be repaired easily

•The handpiece is larger (almost the width of the base of a billiard cue)

•It is much heavier

•Needs to be water-cooled

•The greatest problem is that power delivery is inadequate and often at peak powers tends to be erratic, more so as the handpiece gets older.

Piezoelectric Handpiece

Piezoelectric handpiece uses electric energy to reorient the piezoelectric crystal which in turn is translated into linear movement. The piezoelectric transducer requires a direct electrical contact to be made with the crystal.

20 THE ART OF PHACOEMULSIFICATION

Advantages and Disadvantages of Piezoelectric Handpiece

•Has a more efficient power delivery. With the use of multiple crystals the full range of delivery can be made very smooth even at very small increments.

•It is air-cooled

•Is very much lighter, almost featherweight as compared to the magnetostrictive handpieces

• It is however very fragile and can break on being dropped

•Costly to repair. Some handpieces may need to be calibrated every 1500 phaco procedures for optimal output.

THE PHACOEMULSIFIER 21

Tuning the Phaco Tip

The phaco tip is screwed into the handpiece directly using a wrench. The handpiece is then tuned so as to synchronize the mechanical movement of each tip with the handpiece. Autotuning also allows the handpiece to maintain its frequency irrespective of change in the density of the medium. A loose or a heavily used needle will not tune. It is also customary to tune every time a needle is changed. Some of

the newer machine (Sovereign Allergan) can retune the needle in few seconds. The irrigation fluid is made to flow through the two side ports on the silicone

sleeve. The silicone hub threads the sleeve onto the outer casing of the handpiece. In some instruments (Alcon), an internal rigid sleeve has also been designed to separate the aspiration and the irrigation fluids. This is also supposed to reduce the bubble formation that is often encountered during the phaco procedure.

Phaco Power Settings

There is no predetermined “correct” power. Initially the manufacturer’s recommended settings are used. With experience, each surgeon “fine-tunes” his settings.

Power variables are adjusted intraoperatively depending on

•Density of nucleus where phaco tip is engaged

•Amount of tip engaged

•Linear velocity of the tip during emulsification.

When the power is inadequate, the tip will fail to cut the nucleus, and tend

the push excessively on the nucleus which lead to zonular stress and can be dangerous. When the power is too much, rather than holding the nucleus it will cause the nucleus to flyaway from the ultrasound tip, termed chatter. Too much power can also accidentally pierce the nucleus, making a hole in the capsule and leading to

a dropped lens, a catastrophe, best avoided.

Thus setting a safe power setting prior commencing is important. A safe “standard” setting is as under.

The ultrasound power is set to 50 to 70 percent. If the lens is soft, it is decreased to about 30 percent and if it is hard, the power is increased to 80 percent or 90 percent. Power is reduced if the nucleus chatters. At this stage, the linear ultrasound mode is changed to pulse mode, which tends to hold the nucleus better against the tip and by giving a break between each pulse enables the fragments to corne to the tip easier.

The third-generation machines, having four crystals per handpiece, have far better fragmentation control and rarely need the power to be turned up above 70 percent. It is best to consult each individual manufacturer regarding their safe “recommended” settings and only after experience is derived on that machine gradually change the values to suit ones individual style of phaco.

Ultrasound is inaudible. The buzzing audible sound often mistaken for ultrasound, is simply the harmonic overtones of the handpiece and phaco tip.