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

Figure 39.4

Figure 39.5

Figures 39.4 and 39.5: : Insertion of CTR

capsule. The cortical fibers should be cleaned very gently in the area of dialysis. The cortical fibers should be stripped tangentially rather than radially in the area of dialysis so as to avoid further extension of dialysis. If the area of dialysis is more than 45° but less than 180°, then a capsular tension ring (CTR) should be used to stabilize the capsular bag. With bag inflated with good viscoelastic and the ring is inserted at one end inside the bag and the slowly pushed and dialed into the bag (Figures 39.4 and 39.5). Once the ring is inside the capsular bag, it will become stabilized. Now cortical cleaning can be done by stripping the cortical matter tangentially. Once the cortical cleaning is complete, the IOL is implanted in the bag. If the zonular dialysis is

more than 180° then the surgeon has to take the decision of further management. Depending on the expertise of the surgeon the best way to manage a case of zonular dialysis of more than 180° is to fixate the capsule with the help of Cioni’s capsular tension ring or with the help of Ahmed capsular segments. However if the surgeon feels that it is not possible to fixate the bag even with the help of these devices it is advisable to remove the bag and perform anterior vitrectomy and then either to implant a scleral fixated IOL or to implant an anterior chamber IOL.

Very rarely a nucleus can drop into the vitreous cavity while attempting to prolapse it into the anterior chamber. This usually happens during the learning phase or when the nucleus is very hard or the pupil is small, in pseudoexfoliation cases when the zonules are weak or if a posterior capsular rent is present at the time of prolapsing out the nucleus into the anterior chamber. If the nucleus is dropping through a posterior capsular rupture and a part is still in the bag, that is only a part of nucleus had dropped into the vitreous cavity than attempts could be made to recover the nucleus by posterior levitation with the help of viscoelastic. An opening is made in the pars plana and through this opening a canula mounted on 2 cc syringe filled with viscoelastic is inserted under the nucleus and viscoelastic is injected underneath the nucleus so as to levitate it to the level of anterior chamber from where it can be taken out through the tunnel. The surgeon should attempt this technique only if a part of the nucleus is still in the bag and has not fully dropped into the vitreous. The surgeon should also be well aware of the anatomy of the pars plana.

However if the nucleus has fully dropped into the vitreous it is best to do a good anterior vitrectomy and complete cortical clean up and then close the anterior chamber and refer the case to the vitreo retinal surgeon. Never ever try to take out a dropped nucleus with the help of wire vectis. Trying to fish out the nucleus with the help of wire vectis can lead to a retinal detachment with or without giant retinal tears which could be very difficult to manage as compared to taking out a dropped nucleus from the vitreous cavity. A decision to implant a lens can be taken on the amount of posterior capsule present. If good support is present, the lens can be implanted in the bag or in the sulcus.

Another important step during MSICS is delivering out the nucleus through sclero corneal tunnel. Again it is slightly difficult step to learn and many complications occur during this step. Since delivering out the nucleus most of the times involves insertion of an instrument

such as irrigating vectis or a canula or nucleus bisector into the anterior chamber which is already occupied by the nucleus, the complications are more common during this step. The complications seen most commonly during this step are rupture of posterior capsule and damage to corneal endothelial cells or sometimes detachment of Descemet’s membrane. Injecting copious amount of viscoelastic in between nucleus and posterior capsule and in between nucleus and corneal endothelium will usually prevent these complications. If posterior capsule rupture occurs or if Descemet’s membrane detachment occurs, they must be managed as described earlier in the chapter.

Iridodialysis is another complication which can occur while either prolapsing out the nucleus into the anterior chamber or can occur while delivering out the nucleus through the tunnel. Iridodialysis commonly occur while rotating out the nucleus through a small and rigid pupil. It also occurs while delivering out the nucleus out of the sclero corneal tunnel. The iris can get trapped in between the nucleus and the instrument like irrigating vectis while delivering out nucleus resulting in iridodialysis. This usually occurs at 12 O’clock position and if it is small does not require any treatment. If iridodialysis is large has to be managed by suturing it back to the sclera.

COMPLICATIONS DURING CORTICAL CLEAN UP

Cortical aspiration or clean up is a pretty easy step to master and very few complications occur during this step. The most common complication seen during this procedure is posterior capsular rupture or tear. Sometimes it is more commonly seen when cortical aspiration is done in small pupil or while cleaning up subincision cortex. If the pupil has become small during the maneuvers of nucleus prolapse and delivery, the pupil can be again dilated by injecting adrenaline into the irrigating fluid or directly injecting diluted adrenaline into the anterior chamber. This usually dilates the pupil which greatly facilitates the cortical aspiration.

Subincision cortex is difficult to aspirate with the help of normal irrigation aspiration canula. The best way to manage subincision cortex is to perform aspiration through a side port which is situated 90° away from the main incision. It can also be managed with the help of bimanual irrigation aspiration canula inserted through the side port (Figure 39.6) or using J shaped canula. After filling the anterior chamber the J shaped canula is inserted through the main incision and

Figure 39.6: Management of 12 O’clock cortex with bimanual irrigation and aspiration

Figure 39.7: Management of 12 O’clock cortex with J shaped irrigation aspiration canula

the subincision cortex is aspirated out. Care is taken not to aspirate too much of cortex in one go as it can lead to collapse of anterior chamber alternatively J shaped irrigation and aspiration canula can be used for subincision cortex aspiration (Figure 39.7).

If posterior capsular rupture or tear has occurred during the cortical clean up, the surgeon should train themselves to recognize this complication as soon as possible. Posterior capsular rupture can occur with or without vitreous prolapse into the anterior chamber. If there has not been any vitreous prolapse then the irrigation aspiration canula is taken out gently from the

Figure 39.8: Triamicinolone is being injected to stain the vitreous in anterior chamber

anterior chamber taking care to maintain the closed chamber and maintaining a positive pressure inside the anterior chamber. If irrigation aspiration canula is taken out suddenly or if a positive pressure is not maintained inside the anterior chamber, the vitreous can prolapse out through the capsular rupture into the anterior chamber. After the irrigation aspiration canula is taken out the anterior chamber is filled with viscoelastic and then dry aspiration of the cortex is carried out. That is just performing aspiration of cortical matter without irrigation and replacing the aspirated volume with viscoelastic. This procedure is repeated again and again till whole of the cortex has been removed. The dry aspiration of cortex is carried out only if there is no vitreous in the anterior chamber.

If vitreous has prolapsed through the capsular rupture then the management will consist of performing an anterior vitrectomy. Triamicinolone can be injected into the vitreous for visualization of vitreous in the anterior chamber (Figure 39.8). The vitreous cutter is inserted into the anterior chamber and through a separate port an irrigating canula is inserted (Figure 39.9). Vitrectomy is performed with the help of vitreous cutter till the anterior chamber is clear of all the vitreous and the capsule fall back freely and the margins of the torn capsule are moving freely. There should be no vitreous incarcerated inside the tunnel or it can lead to traction of vitreous and all the other complications associated with it. Care should be taken not to injure the capsule or iris while performing vitrectomy.

Figure 39.9: Anterior vitrectomy being performed

If the capsular rent is small than effort should be made to convert it into a capsulorrhexis and attempt should be made to implant an IOL inside the bag. If the rent is big and if there is sufficient amount of anterior capsule to support the IOL then it should be implanted in the sulcus.

COMPLICATIONS DURING IOL INSERTION

The IOL needs to travel through the tunnel during insertion into anterior chamber in a case MSCIS so it needs to be held firmly with the forceps. The plane of insertion of IOL is not the same as the plane in which it has to be implanted. So the IOL needs to be tilted once it is inside the anterior chamber to be implanted in the bag. If the posterior capsule is intact there are barely any complications related to its implantation in the bag. Sometimes when the tunnel is long and the pupil is small the IOL may be need to be tilted much more for insertion into the posterior chamber and finally into the bag. This maneuver can lead to breakage of the haptic if the lens is held by haptic. It is best advisable to hold the IOL with the optic so it can be tilted easily. Once the IOL is in the bag it can be left as such and then dialed into position with the help of lens manipulator. Some times while inserting an IOL into the bag with posterior capsular rupture can result into slippage of the IOL into the vitreous cavity. It is best avoidable to insert an IOL into the bag with large posterior capsular tear (Figures 39.10 and 39.11). After implantation of an IOL in a case of posterior capsular tear one must determine

Figure 39.10: Posteriorly subluxated IOL in a case of posterior capsular rupture

Figure 39.11: Same IOL after being put into the sulcus

that the IOL is held firmly. If the IOL is not held firmly it can lead to posterior subluxation or sometime dislocation of IOL into the posterior vitreous cavity. This may not happen until in the early postoperative period. If subluxation of an IOL is noted in the immediate postoperative period it should be promptly repositioned into the sulcus where it is held more firmly. However if there is posterior dislocation of IOL into the vitreous cavity then the anterior chamber must be cleared of any vitreous and the anterior chamber closed and the patient referred to a surgeon with expertise in posterior segment surgery.

SUMMARY

Intra ocular complications do occur with every body. There is nothing wrong if a complication has occurred but what is bad is not managing the complication properly. If a complication is managed properly and meticulously, the patient will get a good or near normal vision even on the first postoperative day. It is important to recognize and treat a complication for the best results.

DO’S

1.Do a good preoperative evaluation.

2.Get a good dilatation of pupil before surgery.

3.Stick to strict aseptic technique for best postoperative results.

4.Use sharp and new blades and keratome to get good tunnel.

5.When ever required use trypan blue to stain the capsule.

6.Use good viscoelastic during capsulorrhexis especially in white mature cataracts.

7.Try to maintain a close chamber while performing capsulorrhexis.

8.Make adequate sized capsular opening.

9.Whenever in doubt do not hesitate to give relaxing incision or to enlarge the capsulorrhexis opening.

10.Always keep the chamber inflated with viscoelastic.

11.Before prolapsing out the nucleus into the anterior chamber inject copious amount of viscoelastic in between the nucleus and the posterior capsule.

12.Perform a good and complete cortical clean up.

13.Perform a good and complete vitrectomy if the vitreous has prolapsed into the anterior chamber.

14.Secure the incision with suture whenever in doubt about the integrity of the tunnel.

15.Ensure that IOL is held firmly either in bag or in sulcus in a case of posterior capsular rupture.

16.Close the conjunctiva so as to cover the tunnel completely.

DON’TS

1.Do not go to the next step without taking proper care of the complication occurred earlier.

2.Do not continue with the surgery if retrobulbar hemorrhage has occurred and the eye ball is tense and proptosed.

3.Do not continue if there has been a premature entry of the incision. Make a new tunnel.

4.Do not use blunt blades and keratome to make tunnel.

5.Do not try to pull on the capsular margin that has gone underneath the iris, it might have gone upto the equator.

6.Do not try to prolapse out a large sized nucleus through a small capsulorrhexis opening.

7.Do not pull on the capsule while performing aspiration of the cortex as this might lead to disinsertion of zonules.

8.Never ever go for fishing out of a dropped nucleus or dropped IOL

9.In case of vitreous prolapse, do not pull on the vitreous instead perform vitrectomy with the help of vitreous cutter.

10.Do not leave any vitreous in the anterior chamber or in tunnel.

11.Do not leave any cortex in the bag.

12.Do not leave any part of tunnel exposed at the end of surgery.

13.Do not leave any part of tenon’s capsule exposed.

Any kind of ammetropia—myopia, hypermetropia or astigmatism present after the surgery gives rise to doubts in the mind of patient. In present age patients desire for a postoperative result that can give them a vision without glasses, not only for near but for distance also. Therefore, our endeavor should be to examine the patient thoroughly before the patient is taken to the operation theater. The surgeon should know the preoperative keratometry and his precataract refractive status. Postoperative astigmatism is annoying to the patient, especially if the astigmatism is more than 2.5 D. Because astigmatism of this order, even when fully corrected, causes blurring of the image, leads to field distortion and produces monoocular diplopia. All these problems cause asthenopia, and the patient remains unsatisfied.

Therefore, it should be very clear in our mind as to what we wish to achieve after the surgery. Our goal is customer’s full satisfaction. He wants and deservesvision for both near and distance. In order to achieve this, we must aim for a postoperative refraction of –1.5D cylinder at 180 degrees. This gives two point foci rather than one point focus. He can easily read 6/12 for distance and N6 for near. Patients are happiest with this kind of result, because they can do their routine activity without glasses. They can watch TV in their room and can also read the newspaper.

WITH THE RULE AND AGAINST

THE RULE ASTIGMATISM

The rule is that cornea is more curved in vertical meridian than in the horizontal meridian. So far as our discussion is concerned there are two kinds of

astigmatism— with-the-rule (WTR) and against-the- rule (ATR).

WTR astigmatism is said to be present, when on keratometry the cornea is more curved vertically than horizontally. In contrast, ATR astigmatism is said to be present, when cornea is less curved vertically than horizontally. This can be understood by the following example.

Suppose, on keratometry, vertical K reading is 48D and horizontal K reading is 43D. This means that the vertical meridian of cornea is more curved, or steeper. This is, therefore, an example of WTR astigmatism. On the other hand, if vertical K reading is 43D and horizontal K reading is 48D. ATR astigmatism, which means cornea is steeper in horizontal meridian, is said to be there.

THE EFFECT OF SURGERY

In a study conducted by Merriam change on the horizontal and vertical meridians of the cornea after cataract surgery was observed in 5 different incisions for cataract : extracapsular cataract extraction (ECCE), 6 mm superior scleral tunnel (6 Sup), 3 mm superior scleral tunnel (3 Sup), 3 mm temporal scleral tunnel (3 Temp), and 3 mm temporal corneal incision (3 Cor). After each superior incision, the steepness and length of the transition from the initial to final plateau for each meridian depend on incision length. Considering the uncertainty of measuring K, the corneal meridians stabilized 4.5 months after ECCE, 1.2 months after 6 Sup, and 0.3 months after 3 Sup. No significant change was detected on the horizontal and vertical meridians after 3 Temp and 3 Cor.

In another study conducted by Huang to compare the corneal astigmatic changes induced by clear corneal incisions with those induced by scleral tunnel frown incisions, both from a temporal approach, in sutureless cataract surgery. Corneal stability was achieved with minimal astigmatic change 1 week after scleral frown incisions, while clear corneal incisions induced greater WTR astigmatism with delayed stabilization 1 to 3 months postoperatively.

In a study conducted by Zheng, the change in induced astigmatism was calculated for 8 years after ECCE (n = 144), for 3 years after 6 mm superior incisions (6 Sup) (n = 93), for 2 years after 3 mm superior incisions (3 Sup) (n = 120), and for 18 months after 3 mm temporal incisions (3 Temp) (n = 65). Two weeks after ECCE the mean induced cylinder was +3.47 D, which decayed to about –1.25 D after 6 months. Induced cylinder increased gradually to about -1.6 D after 8 years, although this further change was not significantly different than that at 6 months after surgery. For the phako groups, the net induced cylinder on the first postoperative day was +1.23 D (6 Sup), +0.49 D (3 Sup), and –0.19 D (3 Temp). After 6 Sup the wound was astigmatically stable after approximately 3 months, and 3 years after surgery net induced cylinder was -0.66 D; after 3 Sup the wound was astigmatically stable after about 6 weeks, and after 18 months net induced cylinder was -0.35 D. Maximum visual acuity was reached after a mean of approximately 6 weeks after ECCE, 2 weeks after 6 Sup, and between 1 day and 1 week after 3 Sup and 3 Temp.

In SICS we make basically 3 kind of incisionsparallel to limbus, straight and frown. The postoperative astigmatism depends upon the type of incision made, whether the incision has been made within the astigmatically neutral funnel, the length of incision and the distance from the cornea. Here, we have to understand that the frown incision gives minimum astigmatism. If the incision is within the astigmatically neutral funnel, the astigmatism is least, smaller the incision less is the astigmatism and finally farther is the distance from cornea smaller is the astigmatism.

INCISION TYPE

When the incision is made parallel to limbus, the inferior edge of the incision may fall back, which flattens the cornea in this meridian. If the incision is made at 12 o’clock this incision flattens the vertical meridian of the cornea, causing against the rule astigmatism. When straight incision is fashioned, there are no chances of

inferior edge falling back. Whatever astigmatism is produced by the straight incision is because of the instability of the central portion of the wound, which is much less than the smile incision. Least astigmatism is produced by the frown incision, because the edges of this incision are further away from the cornea. These edges become stable much earlier. Therefore, this incision produces minimum possible astigmatism.

LENGTH OF THE INCISION

Many studies have documented beyond doubt that the longer the incision more is the astigmatism. Usually, the incision size in SICS is between 6 and 7 mm. This causes astigmatism up to 1.0 D. If the incision is larger than this, the induced astigmatism may increase to 3D, because the approximation of the wound is not good causing sagging of inferior edge of the wound. These edges must be sutured in order to get less astigmatism.

ASTIGMATICALLY NEUTRAL FUNNEL

The concept of astigmatic funnel arose from two mathematical relationships; firstly, that corneal astigmatism is directly proportional to the cube of the length of the incision and the second, that, it is inversely related to the distance from the limbus. Incisions made within this funnel will be for all practical purposes, astigmatism equivalent. Curvilinear limbus parallel incisions fall outside this funnel and are hence unstable. Therefore, any incision within this funnel causes almost negligible astigmatism.

DISTANCE FROM CORNEA

More is the distance from cornea less are the chances of astigmatism because the wound at the sclera has little effect on the corneal curvature.

THE ENTRY POINT AT CORNEA

The wound of entry in SICS is much larger than the external scleral wound. This also results in considerable astigmatism. Opening in the anterior chamber, the edges of which are straight cause much less astigmatism than the ragged edges of the corneal wound.

MANAGING PREEXISTING ASTIGMATISM

We make an incision at 12 o’clock if the preoperative keratometry shows with-the-rule astigmatism. In presence of against-the-rule astigmatism the incision is

made on the temporal site. If the astigmatism is high, the incision goes close to the limbus, becomes paralimbal and long. If no or small degree of astigmatism is present, the small, frown and away from the limbus is fashioned. There are many other ways and means like keratotomy and LASIK for which reader is referred to appropriate book on the subject.

BIBLIOGRAPHY

1.Huang FC, Tseng SH. Comparison of surgically induced astigmatism after sutureless temporal clear corneal and scleral frown incisions. J Cataract Refract Surg 1998; 24(4):477-81.

2.Merriam JC, Zheng L, Urbanowicz J, Zaider M. Change on the horizontal and vertical meridians of the cornea

after cataract surgery Trans Am Ophthalmol Soc. 1997;95:387-410; Discussion 410-15.

3.Percival P, Thornton S. The plan for ametropia and astigmatism in A Colour Atlas of Lens Implantation Percival Piers (Ed). Wolfe Publishing Ltd: England 1991;164-7.

4.Sachdev Mahipal, Mishra P, Thanikachalam S. The manual small incision: Surgical aspects-I in Small Incision Cataract Surgery (manual Phaco) Kamaljeet Singh (Ed): Jaypee Brothers: New Delhi, India 2002;7583.

5.Zheng L, Merriam JC, Zaider M. Astigmatism and visual recovery after ‘large incision’ extracapsular cataract surgery and ‘small’ incisions for phakoemulsification. Trans Am Ophthalmol Soc 2001;99:187-95; Discussion 195-7.

AIMS: ASTIGMATISM NEUTRILITY AND SELF-SEALING INCISIONS (FIGURE 41.1)

Incision

Scleral flap incision has three dimensions.

1.Depth: Thickness of the flap.

2.Width: Perpendicular distance from scleral groove to the line of entry into the anterior chamber.

3.Length: The distance between the length of the incision measured along the contour of the incision.

Depth

Scleral flap can be dissected to virtually any predetermined depth. Sclera 2 mm posterior to the limbus is roughly 0.60 mm thick (600 microns).

In order to avoid very thin flap or perforation of the globe about 0.20 mm (200 microns) can be a optimal incision depth or about 1/3 the thickness of sclera.

Width

The distance between the external groove and the internal entry into the anterior chamber is the width of the incision. Wider the flap, the less astigmatic effect, because the lateral pillars of the wound help in supporting the existing shape (As the eye is a round structure, there is a practical limit as to how far back one can go [limit is about 4.00 mm] fear of bleeding is always there during dissection of the flap).

More posteriorly one proceeds, the more bleeding one will encounter.

Length

It depends upon the size of the IOL to be employed. Incision of 3 mm or less does not produce against the rule astigmatism.

WOUND ARCHITECTURE (FIGURE 41.2)

Importance of wound architecture is highlighted by the ability of a properly constructed internal incision to seal

itself without the aid of suture, while improving corneal stability.

There are two incisions:

i.External, i.e. scleral groove

ii.Internal, i.e. site of entry into the eye

—External incision taken with care really does not produce any astigmatism. The scleral tunnel is also astigmatically neutral.

—Internal incision plays major role in producing astigmatism.

Corneal Lip Incision/Corneal Valve— 3 Step Procedure

External incision then tunnels through sclera into the cornea and enters the AC 1.5 mm into clear cornea, through a beveled wound—this process creates an internal corneal flap or lip that acts as a valve.

When the eye is pressurized with BSS through a side port incision to a normal palpable IOP, the internal corneal flap is forced up against the intracorneal portion of the incision, sealing the wound and making it watertight without sutures. As the intracorneal pressure increases, the corneal valve becomes tighter.

Strength of the wound: Studies of cadaver eyes by Ernest. Hydrostatic pressure exceeding 400 mm Hg and compressed air pressure exceeding 2000 mm Hg resisted leakage and iris prolapse.

Wound strength is maximised in “square wound”.

Advantages

Surgical

1.An expulsive choroidal hemorrhage can be managed by simply removing the instrument, thus closing the eye.

2.An acute respiratory or cardiac incident intraoperatively can be dealt with by removing the instrument, resuscitating the patient then continuing the surgery when the patient is stable.

Patient’s advantages

1.Stronger wound that permits a greater range of postoperative activities such as bending, lifting, resuming sports, and even rubbing of the eyes on the first postoperative day.

2.Lower incidence of hyphaemas.

3.No suture induce FB sensation.

4.No contraindication to anticoagulants including sodium warfarin.

5.Decreased incidence of iris prolapse.

6.Avoidance of hypotony.

7.Decreased incidence of peripheral synechiae.

External Incision

Effects of the External Incision (Figures 41.3A to D)

Corneal astigmatism is directly proportional to the length of the incision and is inversely proportional to the distance from the limbus. Short incisions can be made close to the limbus and longer ones further away.

Figure 41.3A: External incision

Figure 41.3B: Suturing in leaking wound

Figure 41.3C: Tunnel suture methods

Figure 41.3D: Undermining directions for external incision