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

variance in the front and back bevel of the knife, it enters in smoothly, at the proper plane, and gives an excellent corneal valve. I normally utilize this 2.8 mm diamond, angled keratome (3-D Rhein).

In the two-plane entry system, the first incision is placed perpendicular to the corneal plane. I prefer to place the first plane of entry at 10.00 O’clock position. Rather than directly entering into the cornea I prefer to make a shallow groove with the sharp edge of the knife and equal in length to the blade’s width. Care is taken not to incise the conjunctiva, as this will result in conjunctival ballooning during phacoemulsification and during irrigation-aspiration, markedly reducing visibility.

The second plane, which essentially creates the cleavage in the corneal stroma and creates the corneal flap valve, is created by placing the shaft (the flat surface) of the blade in apposition with the conjunctiva and advancing in the plane of the cornea. When one had advanced by 2.0 to 2.5 mm, the tip of the diamond knife is turned forwards till it dimples the deeper layer of the cornea. The knife is then allowed to go its full depth creating a perfect rectangular and almost square incision. Dimpling is not required with the Rhein 3D knife with the anterior differential bevel as it automatically enters.

Removal of the knife from the eye is equally important. Many a good valve has been ruined by incising the edge during removal of the knife. It is important not to lift the knife during removal but to gradually slide it out in the same plane that it was inserted.

It is important to try and attain a perfect square inner entry zone. The characteristics of the flap valve stability depend more on the construction of the inner corneal valve and less on the total width or length of the incision as is commonly thought.

If premature tip entry takes place, do not let it continue. Remove the knife and change the position of the entry. Alternatively even the same site can be used but make the knife enter a corneal plane more superficial than the last one. The new incision will tamponade the old one. The incision when finally made, should be 2.8 mm in width and 2.00 mm in length which gives exceptionally good stability.

If a 5.25 mm width narrow profile phaco PMMA IOL lenses is to be used, ideally the incision should be a square, but a 5.25 by 4.00 mm length incision usually suffices.

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The position of the placement of the main phaco incisions is identical in both eyes, namely at the 10.00 O’clock position. If for any reason this site is not appropriate due to a very deep set eye or a prominent forehead or nose, I like to shift to a temporal approach. The big advantage of a fixed sitting position at the head of the patient is that the position of my surgical assistant, the microscope, anesthesiologist, and instruments lie in their fixed places and do not need to be shifted which often leads to confusion and slows down the pace of surgery.

I have found the use of an aspirating speculum (Liebermans) to be a great help. The aspirating speculum is connected to a small dental vacuum pump which gives

a low vacuum of 5 to 7 mm of Hg which is more than adequate.

THE CAPSULORRHEXIS

My personal preference is to utilize a sharp tipped forceps to do the rhexis in preference to a needle.(26 G, ¾” length) with its tip bent at a 45° angle (Figs 19.3 to 5). The sharp tipped needle, though it has the advantage that one can enter through a closed chamber, lacks control in hypermature cataracts, marbled cataracts (where the anterior capsule has a differentially thickened capsule, as typically occurs in old, neglected cataracts), or in eyes where the pupil is not fully dilated. On the other hand, where the capsule is thick and leathery, especially in young children, or is lax where there is doubt about zonular integrity, it would make more sense to do a needle rhexis.

Via the phaco corneal tunnel entry zone, the anterior chamber is re-formed with viscoelastic. I normally like to use methylcellulose which is frozen. Methylcellulose kept in the compartment just below the freezer increases its density by a factor of three. The frozen methylcellulose compresses the capsule making rhexis extremely easy. In addition frozen hydroxypropylmethylcellulose (HPMC) does not leak or ooze out easily, and is fantastic for use in children where even Healon does not stay in long. Methylcellulose is available as OccuCoat (Storz) in USA and other countries, and in India as Visilon, Hyprosol, Moisol and a host of others. AmVisc Plus (Alcon) is also a good viscoelastic which can be utilized, however it is quite

costly for the Indian situation. Healon, by itself has no place in phacoemulsification surgery as it promptly jumps out the moment the phaco tip goes in. However Healon 5, functions well, and is very useful, though prohibitively priced.

In doing a forceps capsulorrhexis, I prefer to make the incision in the capsule using the sharp pointed tips itself. The initial opening is made at 5.00 O’clock, about 2.5 mm inferior, measuring from the center of the lens simply opening a mm

in size. Closing the rhexis sharp pointed forceps makes a beautiful little nick in the capsule. Once the nick is made, the capsule is caught in the tips of rhexis forceps, which are then moved to the left in a counterclockwise direction, towards the 11.00 O’clock position. The forceps leaves the previous hold and takes a fresh hold at the tip of the rhexis tear, and the forceps is then swung to towards the 6.00 O’clock position, until it reaches the 8. 00 O’clock position when it is re-held and then gradually swung in such a way that it meets the previous rhexis opening from out, On an average three holds and re-holds are adequate for a good, well controlled rhexis peripherally. Doing a rhexis is like taking a dog for a walk. One needs to pull its direction at right angle to the prompt direction to change it to the new line.

If a needle rhexis is desired, I prefer to make the initial capsular opening with a 26 G, ¾ inch needle, performing the initial capsular opening at the 6. 00 O’clock position about 3.00 mm peripherally to the center. The initial opening is made by impaling the needle tip and pulling down, to the 12.00 O’clock position for about a mm and then swinging it to the right to the 3.00 O’clock position, in one smooth maneuver. This simple arc-shaped movement will give rise to a well-positioned flap.

The next step is to lay the flap onto the capsule. The point of the needle must be used to move the detached flap in a plane with the residual capsule. Try not to dig it in the capsule. The whole secret is to nudge the capsule along. Since the flap lies in apposition there is no chances of a sudden breakout and often control is better. Be sure to turn the flap, around till it reaches more peripheral to the place where it began and turn it in the meet the origin of the rhexis. The correct shape after completion would, thus resembles an apple.

Ideally rhexis is best done under a viscoelastic though it can also be done under BSS and even under air. Viscoelastic has the advantage that it keeps the chamber well formed and tamponades the capsule. If HPMC is used as a viscoelastic substance, it works even better as frozen methylcellulose (kept in the last shelf, below the freezer compartment) as it does not flow out easily, and tamponades the capsule perfectly, maintaining the chamber deep, even in a tight eye.

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Both airand BSS-based rhexis can only done with the needle. Using a forceps and opening up the chamber lead to a disastrous collapse of the chamber and even inadvertent contact of the delicate endothelium and the rhexis instrument. In both BSS and an air-based rhexis, the rhexis has to be done before the phaco corneal tunnel is made, so that it is complicated in a totally sealed chamber.

If the phaco entry incision has been made prior rhexis, it is safer and better, to use a third incision site for doing the rhexis. Using BSS-filled chamber during

rhexis is easy, provided a third port is made with a continuous infusion of BSS (Bluementhal cannula), while the procedure is being done. The only problem is

that often the flaps floats around and makes it difficult to carry out the procedure. Though, in theory, air is better in an overmature cataract, and the use of BSS based rhexis avoids the use of the viscoelastic, it is always a bit dicey. I always use frozen methylcellulose-assisted forceps-based rhexis.

HYDRODISSECTION AND HYDRODELAMINATION

Hydrodissection is done utilising a fine, 2426 G flattened cannula with rounded edges (Fig. 19.6), mounted on a Luer Lock 3.00 ml plastic disposable syringe. I always specify Luer Lock since the time I shot a blocked needle in the eye. Fortunately only the capsule broke with no other problems and the patient retained full vision, but it was an experience, difficult to forget.

Hydrodissection should be commenced at a point just below the edge of the capsulorrhexis. The tip of the hydrodissection cannula should go just under the edge of

the rhexis, slightly lift it up, and then inject. This technique is termed as cortical cleaving hydrodissection (Fine 1992). Hydrodissection should be commenced first at 4.00 O’clock position and subsequently at the 7.00 O’clock and finally at 2. 00 O’clock position. Usually by this time the lens seems to move slightly upwards, indicating that the nuclear zone has been hydrodissected off. It is important after every injection to gently compress the center of the nucleus to enable better hydrodissection and prevent central pooling of the liquid and allow the excess liquid to flow out again.

It is important to appreciate that hydrodissection in a hard cataract can sometimes give trouble. The surgeon injects, and the moment the fluid is injected, the chamber shallows and, the intraocular pressure (IOP) rises sharply. What has happened is that the fluid has pooled at the back of the lens, as it has no way to exit, and is now pushing the nucleus forward. Any pressure on the lens in an effort to push it back and deepen the chamber will lead to a posterior capsule rupture. At this stage the correct management is to utilize a thin blade iris repositor and insert

it under the capsular edge at 4.00 O’clock (the site of the primary injection) and sweep it sideways to 8.00 O’clock on the right and to 2.00 O’clock on the left side.. Immediately the fluid will gush out and the eye becomes soft and the chamber automatically deepens.

Hydrodelamination as a procedure is now rarely utilized. It was originally conceived as the technique of delineating the hard nucleus and the peripheral epinuclear material. It was in vogue during the four-quadrant grooving technique and was utilized as a method to know how far one could groove in the periphery without accidentally touching the capsule. Since the advent of Nagahara’s chopping techniques, and its multiple variants, hydrodelamination is no longer required. It is, however, still utilized as a means of inducing a soft nucleus to break it into its component parts and permit it to be aspirated easily, especially in young adults.

Once the hydrodissection has been done, the nucleus is rotated utilizing a lens rotator. It should rotate freely with no hesitation. If it does not rotate, it is important that you hydrodissect once again.

The next step depends on whether the surgeon wishes to either flip the lens out of the bag on its front side (supracapsular tumble) or enable the lens to stand vertically (vertical phacoemulsification), or float the entire lens out (anterior chamber phacoemulsification) (Visco-levitation) (Fig. 19.7) Mehta (1995) Kelman (1997). All three techniques are done by injecting viscoelastic under the lens capsule, at 9.00 O’clock, irrespective of whether it is the right or left eye. Injecting at this site leads the 3.00 O’clock position of the lens

(temporal in the left eye, nasal in the right eye) to tip forwards. Using the same cannula which is being used to inject the viscoelastic, gently nudge the inferior pole of the lens,. A small nudge will make it stand up vertically (Lens salute, Mehta 1997.), if more is injected, the lens will flip over and can be rotated out of the bag supracapsularly (Maloney 1997). If one injects without tipping the inferior pole, it will, if the rhexis is 7.00 mm or more in size, float vertically upwards or viscolevitate (Mehta/Kelman).

PHACOEMULSIFICATION TECHNIQUE (Figs 19.8 to 31)

There are two methods which I use: the first is the tangential phaco chopping technique—a method which was popularized in 1996 (Mehta), and the second which I prefer is the vertical nuclear ‘hubbing’ phacoemulsification.

In 1996 I developed the tangential chopping technique whereby the chop rather than going vertically through the substance of the lens, would go obliquely. One had merely to tip an edge of the nucleus out, impact the nucleus in the middle with a phaco tip and using a sharp-edged but blunt-tipped chopper obliquely the

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The technique involves a 6.00 mm rhexis, following a full hydrodissection placing the nucleus vertical viscodissection at the 9.00 O’clock position with the nucleus at 3.00 O’clock position standing out of the capsule bag (Lens salute).

The steps of the surgery are as under:

Nuclear stabilization Viscoelastic is injected from the side port incision. This manages to stabilize the nucleus and prevent it flopping back. From the side port,

enter with the blunt-tipped, but sharp-sided chopper and support the nucleus.

Coring the nucleus The next step is to core out the center of the lens. In this technique termed “hubbing”, I like to use the Kelman bent 0.9 dia phaco tip as it penetrate easily in the nuclear matter. The phaco settings are now altered to 70% phaco power, vacuum is reduced to the minimum. Thus, when energized, the phaco tip can penetrate, and move out of the nucleus without displacing it since no suction is involved.

Supporting the nucleus from the left with the phaco chopper held flat against the nuclear surface to stabilize it, the phaco tip is placed squarely in the middle of the lens and literally allowed to penetrate virtually all the way through. The first core, made in the middle of the nucleus is called the primary core. Subsequently make three, one secondary core just above, and two, one at each side of the primary core. The next step is to rotate the nucleus by 90° and make the final core. In any lens up to grade 4 in density, a total of five cores (one central primary and four secondary cores) will literally, eliminate the hard central nuclear matter. If it is harder cataract, another set of four cores (termed tertiary cores)are placed a little peripherally and in between the previous four secondary cores.

Snapping the periphery The lens is now converted into a doughnut. To aspirate the final rim, it needs to be snapped. The chopper, which till the present was only supporting the nucleus for the coring is now allowed to slip in-between the cored nucleus. Using a phaco in the right hand, the ring is split open using the sharp inner curve of the chopper. After snapping the ring, it is slightly widened.

Pulse aspiration of the ring The open end of the doughnut ring is allowed to impact onto the phaco tip. The settings now change, ultrasound power is kept at 20 to 30% depending in the density of the lens, set pulse at 8 pulses per second. Vacuum is set at 400 mm Hg, Flow rate at 18 ml/min, energizing the tip will lead the entire rim of the lens to rotate (carrousel) till it is fully removed.

An average phacoemulsification, from beginning to end, done with no haste, in a medium dense grade 4 cataract, with this technique can be completed easily in 6 minutes.

Indications

Though it is an exceptional technique and can be used in virtually any type of density of nucleus, it, however, does require a little care. It is difficult to tumble the lens through a rhexis smaller than 6.00 mm in size. It is possible to enlarge