Ординатура / Офтальмология / Английские материалы / Master's Guide to Manual Small Incision Cataract Surgery (MSICS)_Garg_2009

Figure 3.2: High IOP in ECCE - High IOP, indicated by green arrows, pushes out the intraocular contents through the easiest escape route

Figure 3.3: Pressure on the globe from tight canthal tendon

– tight bridle suture and constricting canthal tendon increases external pressure on the globe indicated by blue arrows

with numerous sutures, which had its advantages as well as disadvantages.

With the advent of small incision cataract surgery, the designing of water tight, small, valve-like wounds, became very important. These surgeries had smaller incisions, minimum pressure fluctuations across the incision and a water tight chamber. Though the amount of fluid turbulence inside the anterior chamber was

more as compared to that in ECCE, these disadvantages were more or less offset by the speed of SICS surgery and the early visual recovery.

Let us now discuss, step by step, the various pressure vectors and the interplay between these during each step of SICS surgery.

STEPS OF SURGERY

Preparation of the Eye for Cataract Surgery

Though a little bit of hypotony is desirable in SICS, too much of it, as in ECCE and ICCE, would have a detrimental effect during the subsequent steps of the surgery. Lateral canthotomy may be done if the interpalpebral aperture is very narrow, though the constricting effect of a tight lateral canthal tendon may not be a significant factor in SICS as in ECCE or ICCE. Superior and interior rectus sutures assist the surgeon by applying traction-counter traction and thus immobilize and stabilize the eyeball. Also, since the direction of pull applied on the superior and inferior recti are not exactly at 180° to each other, the net effect of the pull is such that the eyeball is slightly jerked out of the socket making exposure better.

Incision

A key component of SICS is the incision, which, if not properly made, results in all the subsequent steps going awry. The incision may be of any shape, depending on the surgeon’s choice, but the underlying principle of each should be the construction of scleral or sclerocorneal tunnel which ensures a water-tight wound. The sclera is a relatively tougher structure than the cornea. Also, the corneal lamellae are more regularly arranged in parallel sheets as compared to the haphazard arrangement in sclera. The length of the scleral tunnel is more or less uniplanar in that it passes through the

Figure 3.4: Effect of bridle suture on eyeball—the superior and inferior sutures prop up the eyeball

Figure 3.5: Self-sealing wound in SICS—the valve like incision ensures a water tight wound even with a high IOP

same horizontal plane in sclera, without cutting across lamellar sheets and extends to the corneal side in the same plane too. But, there is a difference though. The degree of resistance encountered by the blade at the scleral side of the wound is much more than that on the corneal side, mainly attributed to the lamellar arrangement, as described above. So, the pressure exerted on the crescent blade while making the corneal side of the tunnel should be slightly less than that exerted while making the scleral side of the tunnel, or else a premature entry results.

Also, for designing a perfect tunnel, the eyeball should be somewhat firm and not totally hypotonic. The crescent blade moves forward and sideways by cutting as well as shearing movements and this is aided by the counter pressure/counter resistance offered by the tough and firm sclera.

The greater the length of the incision, the more water-tight it becomes. The incision in SICS is such that the higher the IOP, greater is the apposition between the wound margins. Therefore, a slight protrusion of the posterior lip of the scleral tunnel into the anterior chamber allows the intraocular pressure to be a potent force in wound closure.

Making the Side Port Incisions

The side port incisions can be made either by a 11 No. Band Parker blade or a lancet tipped blade or a flattened

Figure 3.7: Capsulorrhexis—delicate interplay between the forces across the anterior capsule

blade. With any of the blades mentioned above, the entry into the anterior chamber should be such that the posterior lip of the wound is never indented. Pressure on the posterior lip of the side port wound results in rapid egress of aqueous humour and collapse of the anterior chamber. If not careful, then the tip of the blade may hit the endothelium as well as cause Descemet’s membrane tear. Working through the sideport ensures that the anterior chamber is well formed throughout the surgery, allowing ample space for instrument maneuvering.

Capsulorhexis

The interplay between the intraocular and extraocular forces are best demonstrated during the process of capsulorrhexis. A close understanding and monitoring of the pressures acting on the surface of the anterior lens capsule is crucial for the successful completion of capsulorrhexis. The intralenticular pressure as well as the intraocular pressure exerts an upthrust on the anterior lens capsule from below. This has to be countered exactly in the opposite direction and opposite

magnitude by increasing the pressure in the anterior chamber, i.e. by injecting a good quality, dispersive viscoelastic. This results in canceling the upward and downward thrusts on the anterior capsule, leaving a plane of zero resultant pressure, where, first, the centrifugal force exerted by the capsulorrhexis forceps and subsequently the centripetal pull on the rhexis margin by the same forceps results in a continuous circular tear of the capsule. This tear in the horizontal plane happens because there is no resultant vertical pressure component.

In a situation when the upthrust on the anterior capsule from below is more than the down thrust on its surface (as is very commonly encountered), then the place of zero resultant pressure is non-existent and the excess of the vertically acting pressure component changes the centripetal pull on the capsular margin into a centrifugal tear, extending towards the periphery of lens capsule.

In contrast to this, if the down thrust on the anterior capsule over weighs the upthrust, then again tearing the anterior capsule in the horizontal direction becomes very difficult. This situation is very clearly seen in moderate to severe subluxation of cataractous lens. Any attempts at tearing the anterior capsule shifts the balance between the pressure vectors leading to more pull and tear of the remaining zonules.

Hydrodissection and Hydrodelineation

The lens is formed in the embryonic life by laying down of the successive layers of cortex. Thus, there exists planes of cleavage between the lens capsule and the cortex and between the cortex and lens nucleus. All such cleavage

planes can be opened up by pushing fluid under pressure in between the different layers. This principle is the basis for hydrodissection and hydrodelineation, wherein the nucleus is freed from its cortical adhesions and the cortex in also loosened from the lens capsule. Once the fluid is pushed through the equator of the lens, inside the capsulorrhexis margin, initially it flows towards the bottom of the lens, separating the epinucleus from the capsule in its path and subsequently the cushion of fluid beneath the lens nucleus pushes up the nucleus to close the rhexis opening. This movement of fluid inside the now closed bag rotates the nucleus inside it, or sometimes, if the rhexis is big, even prolapses the nucleus into the anterior chamber. Thus, a second pair of instruments can be avoided to prolapse the nucleus into the anterior chamber.

Nucleus Prolapse Out of the Wound

Since the anterior chamber is a water tight compartment, enough viscoelastic or fluid (Blumenthal

Figure 3.10: Nucleus prolapse out of the wound. Fluid pressure inside the capsular bag pushes out the nucleus through a large rhexis

Figure 3.9: Hydrodissection and hydro-delineation—the jet of fluid sheers the epinucleus from the capsule

Figure 3.11: Tapping the posterior lip of the scleral tunnel provides the exit route to the nucleus

Figure 3.12: Cortical clean up

technique) is pushed in so as to raise the anterior chamber pressure many folds above the atmospheric pressure. Then a slight indentation over the posterior lip of the scleral tunnel results in sudden release of pressure from higher towards lower gradient, dragging with it the nucleus too, sometimes helped along the way by a second instrument. Once, the nucleus moves out, the anterior chamber collapses which should be quickly reformed with viscoelastic or fluid, lest endothelial damage happens.

Cortical Clean Up

The best technique is to work in a fully formed, closed anterior chamber. So that there is ample space to maneuver the instruments and to minimize tissue damage. The main SICS wound should be least disturbed, as being of wider dimensions, the pressure escape and chamber collapse is faster than can be compensated for by the irrigation system. Cortical

clean up done through the side ports, whether by manual or automated methods, should be so regulated that the aspiration rate is equal to or less than the irrigation. This ensures minimal turbulence inside the anterior chamber and easy tissue demarcation. Too much use of the main port during irrigation-aspiration shifts the pressure gradient to that side with likely damage to the capsulo-zonular assembly.

IOL Insertion

The IOL, whether foldable or rigid, has to be inserted through the main port and in doing so, some degree of chamber collapse ensues. Once enough viscoelastic is pushed into the capsular bag and the trailing IOL haptic is pushed into the bag, the IOL, most of the time, settles down with a little rotational movement, the haptics coming to lie at a position farthest from the point of maximum pressure fluctuation, i.e. at the main entry wound. This rotatory movement is in part due to the inherent plasticity of the haptic material and partly due to the centripetal recoil of the capsulo-zonular assembly.

On conclusion of the surgery, the wound is checked for any leakage and the corneal dome is tapped with a blunt instrument to assess the intraocular pressure. If the eyeball is felt as hard, then a little fluid from anterior chamber is released by pressing gently on the posterior lip of the side port.

Thus, in conclusion, it can be said that a thorough knowledge of various pressure parameters at work during the course of SICS helps the surgeon to pre-empt and prevent complications and to use the pressure vectors to his or her advantage for an optimal surgical outcome.

INTRODUCTION

In this chapter, I would like to describe a small incision manual technique which I have used since 1985. It involves “sandwiching” the nucleus out between a lens loop and spatula. This technique uses an incision of 7.0 mm. It can be used with capsulorhexis or with any other type of capsulotomy, such as can-opener. This 7.0 mm “frown” incision is self-sealing in the majority of cases, and does not require a suture. This larger incision does give more astigmatic shift than a 3.0 mm phaco incision, however, this can be of benefit if one operates on the steep axis of K.

This technique works as well with rock-hard nuclei as with soft nuclei. It can be done with inexpensive reusable instruments, and may be more appropriate than phaco in situations where finances are limited. It might also be helpful for the phaco surgeon to use for the occasional very hard nucleus. My endothelial cell loss for the procedure is around 2 percent (Fry LL Yee, RW: Healon GV® in extracapsular cataract extraction

with intraocular lens implantation. J Cataract Refractive Surg 19(3): 409-12, 1993). This is less than my loss with phaco, and certainly less than the loss when I emulsify a very hard nucleus.

This is my present technique (Please note that I am left handed).

Topical anesthesia with intracameral lidocaine is used. I presently prefer 2 percent lidocaine gel. The 1 percent nonpreserved intracameral lidocaine seems to sting less if it is made-up by diluting 2 percent nonpreserved lidocaine 50/50 with BSS (We did, on one occasion, inadvertently use preserved 1 percent lidocaine for 12 cases until the error was discovered. Although I would not recommend this, these corneas all looked fine the next day).

INCISION

A side-port is made with a 15° blade. A few tenths cc of 1 percent nonpreserved lidocaine are instilled (Figures 4.1 and 4.2). The eye is filled with viscoelastic

through the side-port (Healon GV® is presently my preferred viscoelastic).

An 8.0 mm peritomy is made with scissors and bleeding is cleared up with wet-field cautery (under topical anesthesia, this may cause a slight sting. This, and the cauterization closure of conjunctiva at the end are normally the only times the patient feels anything. The discomfort is minor, and not a problem if the patient is forewarned). A superior rectus suture is not used. The incision site is on steep axis of “K” for cylinder 1.0 diopter or greater. For less than 1.0 diopter cylinder, temporal approach is preferred. Deep set eyes are also approached temporally. A limbal relaxing incision opposite the incision is added for cylinder greater than 2 diopters (Figures 4.3 to 4.5).

A “frown” incision is made with a guarded diamond knife set at 0.25 mm. The incision is dissected forward into clear cornea with a bevel-up crescent blade (Figures 4.6 and 4.7). Superior incisions are dissected about

1.0 mm into clear cornea and temporal about 1½ mm into clear cornea (the initial groove can also be freehanded with either the crescent blade or other blade, I feel the guarded diamond gives a better and more reproducible groove).

The anterior chamber is entered with a 3.2 mm keratome at the depth of this scleral flap, giving a selfsealing internal flap. Additional viscoelastic is placed (Figures 4.8 and 4.9).

SMALL PUPILS

Small pupils are managed by stretching them out with two Kuglen hooks. One stretch, limbus-to-limbus, is all that is necessary. Additional stretches give little additional effect. Stretching slowly may help to avoid rupturing the sphincter. Hold for a second or two at maximal stretch. Then expand the iris out with viscoelastic (Figures 4.10 to 4.13).