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

142 THE ART OF PHACOEMULSIFICATION

iii.The next quadrant is moved into position by the manipulator, tilted up and emulsified as already described. The remaining two quadrants are dealt with similarly.

Note With the higher levels of vacuum currently being used, care must be exercised to avoid anterior chamber collapse when occlusion breaks. A number of methods are available on modern machines to mitigate against this eventuality. Firstly continuous irrigation, here even in position 0 the chamber will always be filled so that the postocclusion break surge is neutralized. The use of non-compliant tubing as used in all the machines the author currently uses will help to minimize the effect of any residual line vacuum. On the AMO Prestige phaco machine a mechanical model of events in the anterior chamber exists in relation to the pump mechanism. This allows the pump speed to slow to 0 after occlusion and maximum vacuum has been achieved. As the piece of nucleus being removed clears the tip and occlusion breaks, instead of the pump accelerating to its predetermined speed it reaches it after a pause. The anterior chamber can thus equilibrate without any risk of collapse. This is particularly important with harder cataracts. The Aspiration Bypass System tips on the Legacy approach chamber fluidics in a different way. Here there is a small hole drilled in the phaco tip near to its base. This means that there is a constant flow of fluid through the needle even when in full occlusion. Thus occlusion break response is thus considerably lessened and much higher vacuum levels can then be used efficiently and safely. The Sovereign has even more monitoring of the anterior chamber than the Prestige, with the sampling of the pressures in the anterior chamber many times per second. The machine can be programmed to respond to a whole range of predetermined thresholds during phaco, which may vary between occluded and unoccluded modes. However where these mechanical aids are not present, surgeon anticipation of the likelihood of this event has to suffice. The foot pedal has to be lifted immediately prior to the clearing of the port in the phaco tip.

The hard nucleus presents the phaco surgeon with one of his greatest challenges. The ability of the tip to penetrate the nucleus, often in the face of weak zonules and combined with controlling sharp nuclear fragments so as to avoid damaging capsule or endothelium need special skills to avoid problems.

•Sculpting: In order to minimize the movement of the nucleus away from the phaco tip which might put the zonules on the stretch, high ultrasonic power settings are necessary. The use of maximum power on panel control means the greatest possible acceleration of the tip into the hard nucleus, thus it is more efficient and ultimately less power is used. Since adopting this approach phaco times in hard nuclei have been reduced and nuclear movement largely eliminated. The Kelman tip with its high cavitation also helps considerably. Note In hard cataracts the cut edge of the nucleus produces (Fig. 14.25) a characteristic white tramline. This will alert the surgeon when a good red reflex suggested only a moderately hard nucleus.

•Cracking: In hard cataracts cracking may be relatively easy as the nuclei are some times quite brittle. However the plates of the nucleus (Fig. 14.26) often do not part cleanly, therefore it is essential to make sure that the grooves in the nucleus are of adequate depth. The most common cause of cracking difficulties with hard nuclei is due to insufficient depth of the grooves. If problems arise return to each groove and gently redeepen it. This may be facilitated by lengthening the amount of the phaco trip protruding from the sleeve (Fig. 14.27). Make sure that all quadrants are well separated before starting to remove them.

•Quadrant removal: Hard nuclei are also large nuclei, it is often sensible once the quadrant has been well engaged by the phaco tip to take a chopper and reduce the size. This is done by pulling the chopper from the periphery of the quadrant towards the phaco tip. Maintaining occlusion of the tip is vital

146 THE ART OF PHACOEMULSIFICATION

existing fibrous tissue but should not damage the sphincter so that the pupil often is functional postoperatively. When viscoelastic is then introduced the pupil will be found to be satisfactorily large.

Combined Glaucoma and Cataract Surgery

Small incision cataract surgery lends itself very well to combination with glaucoma filtering surgery to produce a safe effective operation, which has little effect on astigmatism. It works particularly well with foldable intraocular lenses, as the

wound requires minimal modification.

Instruments for the trabeculectomy Vannas scissors, St Martins toothed forceps, bipolar cautery wand, Colibri toothed microsurgical forceps, Alcon angled 3.2 mm phaco slit blade, Crozafon sclerotomy punch, 8/0 Vicryl stitch, micro needle holder.

Technique

i.A conjunctival flap based on the fornix is formed with St Martins forceps and the Vannas scissors. The conjunctiva is dissected off Tenon’s capsule. This is then dissected from the sclera and removed from the area of the trabeculectomy wound.

ii.The scleral vessels are gently cauterised using the bipolar wand.

iii.A 4 mm vertical groove is prepared using the slit knife as already described 2 mm behind the anterior limbus. The knife is then turned back to its usual position and a tunnel formed as already

described. Phacoemulsification now proceeds normally.

iv.After the lens has been inserted and before the viscoelastic has been removed from the eye the Crozafon punch is inserted through the wound. The distal end of the cutter hooks over the edge of the internal part of the tunnel and the punch is closed (Fig. 14.31).

be required to produce an adequate opening, this is usually two. The sclerotomy should be about 1mm from the proximal lip of the wound and should leak aqueous gently when it touched with a dry sponge.

vi.A small iridectomy is then made and the viscoelastic removed with the I/A.

vii.For closure of the wound use 8/0 Vicryl stitches at each end of the conjunctival wound.

viii.Inject BSS through the side port and observe the bleb forming.

CURRENT PHACOEMULSIFICATION TECHNIQUES 147

White Cataracts

These cases are, as already stated in the discussion of capsulorrhexis, very challenging. However even if the rhexis has been satisfactorily accomplished there are still a few points worth noting.

When Removing the Nucleus

•The nuclei in these cases are often not only hard but very mobile. In order to maximize control during emulsification introduce the manipulator early on to stabilize the nucleus. This is particularly important when sculpting.

Note Use of a chopping technique is not recommended in these cases because the capsule can be difficult to see when the chopper is passed to the equator and it is thus easily damaged.

•There is little if any epinucleus or cortex to protect the posterior capsule in the presence of sharp nuclear fragments. Use the same precautions as mentioned in relation to hard cataracts.

EPINUCLEUS REMOVAL

The main points in relation to persistent epinucleus have already been discussed under the section on soft cataracts. However if there is a bowl of epinucleus as sometimes occurs with no break in the edge it can present the surgeon with some difficulty. Here are some suggestions:

•Use the nucleus manipulator to go out to the equator of the capsular bag to pull the epinucleus centrally

•If this does not work the manipulator can be used to divide the edge and allow the phaco tip to occlude on one side

•Finally if all else fails and the epinucleus refuses to cooperate use viscoelastic to get under the edge and lift it centrally for aspiration.

IRRIGATION/ASPIRATION

I/A Handpieces

The bimanual irrigation/aspiration handpieces considerably facilitate cortical removal, particularly that found subincisionally. The advantage of cortical cleaving hydrodissection is that there is relatively little cortex left to aspirate.

Machine settings Both Alcon Legacy and AMO Prestige—Maximum vacuum 400+ mmHg, linear aspiration flow 24 ml/min.

Technique Occlusion of the aspiration port is all important to achieve efficient cortical removal. Once this has happened the cortex can be dragged centrally for aspiration.

i.Begin the cortical removal with the irrigation in the left hand and the aspiration in the right. The deep chamber produced by the closed wounds will help considerably the removal from the fornices of the capsular bag. Aspirate

150 THE ART OF PHACOEMULSIFICATION

will allow easy placement of the IOL and its unfolding with minimum trauma to the ocular contents.

Wound Sizing

In small incision cataract surgery there is now a bewildering array of lenses available in a variety of materials. Some folding lenses can be implanted through unenlarged wounds, often however some adjustment of the wound will be necessary. The folding lens, which I currently use, is the Alcon MA60 or MA30 Acrysof. The former will pass easily through a 3.5 mm opening, the latter through 3.2 mm. The phaco slit knife can be used to ease the edge of the wound and

thus enlarge it sufficiently.

Lens Implant

At present I use only Alcon AcrySof for all cataracts except high myopes where the dioptric range is not available. I have stopped using PMMA because it does not fold and therefore denies my taking an advantage of small incision. Silicone I will no longer use because although on the whole my results were good, the capsular effects and occasional foreign body reaction in the eye are not satisfactory. PolyHEMA I like as a material and have been involved in trials of a new design of lens made of this material. However it is as good as Acrysof in terms of capsular opacity and YAG laser rates. My own experience of acrylic is now 8 years, the results in visual terms as well as the very low capsulotomy rate are impressive. This material also works very well in compromised eyes with uveitis, glaucoma, diabetes, etc. The size of the MA60 and three-piece design mean that it can be used also as a backup lens and the gentle unfolding of acrylic allows insertion folded even with a capsular break. The lack of capsular contraction that this IOL produces permits me to insert it safely into the bag in the presence of a capsulorrhexis break with little risk of decentration.

Implantation

Instruments Angled McPherson forceps, Seibel folding paddles, Duckworth and Kent (Buratto) insertion forceps, Colibri microsurgical forceps, lens dialing hook.

Technique

i.Open the wagon wheel container for the lens and ask the nurse to squirt BSS on to the lens.

Note This material is affected by temperature in that if the lens is too cold it is harder to fold. It is best if available to place it in a warming cabinet.

ii.Move the microscope away from the eye and reduce the magnification. With the McPherson forceps place the lens on the back of the wagon wheel case.

iii.Take the Seibel paddles and open them press down on the edge of the lens to make sure their is no meniscus of BSS underneath it and fold the lens. This done by closing the paddle forceps having placed the lens in the