Ординатура / Офтальмология / Английские материалы / Small Incision Cataract Surgery (Manual Phaco)_Singh_2002

Fig. 13.7: The corneal valve is closed by inflating the chamber with irrigating fluid, which pushes the corneal valve shut and seals the incision

lip of the incision should check the integrity of the incision. The most stable wound is created in case the length of the tunnel is equal to its width (Fig. 13.8).

If the incision is leaky, hydration of the corneal stroma may be tried at the extreme ends of the incision. The corneal edema pull: the tissues tight against each other and helps in a leak proof closure.

In case the incision still leaks, a single, horizontal 10-0 nylon or 10-0 vicryl suture should do the trick. Never let your ego come between the suture and safety.

Summing-up

In manual phaco, a good incision ensures sutureless and astigmatically neutral closure, which is actually half the surgical work. It is important to understand the relationship of the length of the incision and its distance from the limbus. Small incision can be made closer to the limbus and the longer incisions further away, with equivalent corneal stability. The internal corneal incision actually is the one, which affects corneal curvature. That is the

Fig. 13.8: The engineering aspects support the theory that maximum stability of the wound is achieved if length of tunnel is the same as the width

reason why even in cases where the lateral “horn” of the scleral lip gets incised during the process of extension of the incision, one may still not find any changes in keratometry. It is important to familiarise yourself with a set of “sharps” (blades) used for fashioning the phaco incision. Using the same design of keratomes, etc. should help you to standardize your incision making.

Get to feel the cutting properties of different blades with bevels on the front surface and the back surface. The bevel positions mentioned in the text are most recommended. It is true that diamond keratomes are very sharp and are probably the best for making the phaco incisions, but good quality steel keratomes carry out the job equally well and are economical at the same time. For the price of a single diamond blade, you can buy hundreds of steel keratomes.

One should never compromise on the sharpness of the blades (Fig. 13.9). Inspect every blade under the

microscope before you touch the eye. If you think it is blunt, change it immediately. Sometimes, the blade may look good on inspection but refuses to cut well; this warrants immediate change of the blade.

For best results, you have to learn how to make a good incision and then practice hard to get it right the first time, every time!

REFERENCES

1.Girrard LJ, Hoffman RF: Scleral tunnel to prevent induced astigmatism. Am. J Ophthalmol 97: 450-56, 1984.

2.Kratz RP, Colvard DM, Mazzoco TR, Davidson B: Clinical evaluation of terry surgical keratometer. Am Intraocular Implant Soc J 6: 249-51, 1990.

3.Jack A Singer: Frown incision for minimizing induced astigmatism after small incision cataract surgery with rigid

optic intraocular lens implantation. J. Cataract Refract Surg 17: 677-88, 1991.

4.Mishra P: Small incision cataract surgery (SICS) and IOL implantation. Cyberle4ctures, www.indmedica.com/ophthal 1-4, 2000.

5.Kapoor Sashi, Incisions: Emmetropia. J Intraocular Implant and Refract Society 2: 17-25, 1999.

6.Mishra P: Catract surgery and intraocular implantation in children. Cyberlectures www.indmedica.com/ophthal 1-5, 2000.

7.Mody Kirit, Singh Gagan J: Small incision non phaco cataract surgery. Emmetropia. J Intraocular Implant and Refract Society 2: 9-11, 1999.

8.Kumar Ravindra, Small incision cataract surgery without phaco–my experience. Emmetropia, J Intraocular and Refract Society 2: 53-55, 1999.

The Manual Small 14

Incision: Astigmatic

Considerations–II

Mahipal S Sachdev

Pradeep Venkatesh

Every cataract surgeon knows that preoperative and induced astigmatism is a deterrent to his aim of making his patients “emmetropic”. Over the years he has either consciously or subconsciously evolved from

doing just cataract surgery to planning astigmatic cataract surgery. The evolution of manual phaco is largely attributable to the relative immunity the procedure provides against large shifts in astigmatism. This immunity is not absolute though.

One important factor, which has kept most astigmatic cataract surgeons busy is the wound or the cataract incision. Several facts relating to incision and astigmatism are well-established but there possibly are several yet to be unraveled.

It is well-established that the following induce greater astigmatism:

l. Longer incision

2.A corneal incision

3.A limbus parallel incision

4.A uniplanar incision

5.A sutured incision

An obvious approach to reduce the chance of astigmatic shift would therefore be to shift to an incision that is small (3 mm in length if corneal incision desired); that is away from the cornea either straight or frown shaped (to stay within the astigmatically neutral funnel); multiplanar and one that can be “safely” left un-sutured. Also, wounds with a square configuration (i.e. wherein the length and width are small and equal) are considered more.

Achieving Emmetropia

The astigmatic cataract surgeon can modify his wound parameters to undo any undesirable preoperative astigmatism. Preoperative astigmatism could be low (0-1.0 D), moderate (1.0 to 2.0 D) or high (>2.0 D).

When the preoperative astigmatism is low, the ideal small incision wound construction would be a straight, clear corneal, 3 mm incision (possibly in the temporal region). By this the surgeon aims at retaining the preoperative sphericity. A “frown” incision 3 mm behind the cornea can also achieve this goal by being within the astigmatically neutral funnel (Fig. 14.1).

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.

When moderate preoperative astigmatism is encountered (1.0 to 2.0 D), the small incision, surgeon in an endeavor to regain sphericity should construct a wound that is centered along the steep meridian, about 6 mm with a thin scleral flap and straight in relation to the limbus.

A combination of spherical small incision profile with astigmatic keratotomy is needed when the aim is to reduce preoperative sphericity that is high (>2.0 D). Spherical small incision profile is as described under “low” preoperative astigmatism. This however, is constructed only after completing astigmatic keratotomy. A 7mm optic zone is maintained during astigmatic keratotomy. The depth of the incision should be 90 per cent thickness. The length of the incision is dependent on the correction necessary. An incision of 45° rectifies 1 D; of 60°, 1.5 D and of 90°, 2.0 D. Any additional incisions made will increase this effect by 20-30 per cent.

When preoperative astigmatism exceeds 4D, the implant power has to be modified to counter the effect of coupling.

In constructing the incision, the surgeon has to “tailor” wound parameters to suit individual cases with one

important caveat, i.e. to center the wound along the meridian in which against the rule change is desired.

Thus the incision being amenable to modification as desired by the surgeon enables him/her to achieve emmetropia. In some patients astigmatic keratotomy may be needed for the same in addition to the tailored incision.

SUGGESTED READING

1.Buzard KA, Shearing SP: Comparison of postoperative astigmatism with incisions of varying length closed with horizontal sutures and with no sutures. J Cataract RefractSurg. 17(Suppl): 734-39, 1991.

2.Davison JA: Keratometric comparison of 4.0 mm and 5.5 mm scleral tunnel cataract incision. J Cataract Refract Surg. 19(1): 3-8, 1993.

3.Feil SH, Crandell AS, Olson RJ: Astigmatic decay following small incision, self sealing cataract surgery. J Cataract Refract Surg 20(1): 403-09, 1994.

4.Fine I Howard: The infinity suture for closing phacoemulsification incision. Symposium: In Cataract IOL and refractive surgery. American Society of Cataract and Refractive Surgery, 1990.

5.Gimbel HV, Sun R: Postoperative astigmatism following phacoemulsification with sutured Vs un-sutured wounds. Can J Ophthalmol 28(6): 258-62, 1993.

6.Masket S: Comparison of suture materials for closure of the scleral pocket incision. J Cataract Refract Surg. 14(5): 54851, 1988.

7.Nielsen J: Induced astigmatism and its decay with a frown incision. J Cataract Refract Surg. 19(3): 375-79, 1993.

8.Suzuki R, Tanaka K: Outcome of preoperative against the rule astigmatism after phacoemulsification; Characteristic change over time Part II Ophthalmologica, 204(4): 184-91, 1992.

Capsulotomy for 15 Small Incision

Cataract Surgery

AK Grover

Pankaj Puri

Harprit Singh

Capsulotomy plays a vital role in the further progress of the surgical procedure of cataract extraction by any technique. The most commonly used

techniques are (1) Can opener technique, (2) Envelope technique, (3) Capsulorhexis. However, with a greater appreciation of the role of symmetrical placement and long-term maintenance of the intraocular lens, continuous curvilinear capsulorhexis has acquired the widest acceptance.

Can Opener Technique

In it, an irrigating cystitome or simply 26 G needle, bent at the tip is introduced into anterior chamber and multiple small radial cuts are made in the anterior capsule for 360 degree. The technique is same as for the conventional extracapsular cataract extraction. It however, has the following disadvantages:

1.Possibility of posterior extension of capsulotomy tear during surgery.

2.Difficulty in ensuring in the bag placement of intraocular lens.

3.Escape of the haptic from the bag during IOL insertion.

4.Asymmetric fibrosis of the bag with long-term decentration of the lens.

Envelope Technique (Linear Capsulotomy)

Envelope technique became increasingly popular in extracapsular cataract extraction as its advantage of endothelial protection during surgery and greater surety of ‘in the bag’ placement of IOL were recognised.

Here a straight incision is made in the anterior capsule in the upper part from two to ten O’clock position. The rest of the capsulotomy is completed in the end after removal of nucleus and cortex.

However, it shares the disadvantages of possibility of posterior extension of the tear, escape of IOL from the bag and decentration due to long-term fibrosis.

Capsulorhexis

Continuous, curvilinear capsulorthexis (CCC) developed by Gimbel, Neuhann and Schimizu independent of each other in 1980’s is the most preferred technique. The CCC technique has significantly improved the safety of cataract extraction and in the bag intraocular lens implantation. Before we begin with discussion on capsulorhexis, a basic understanding of the anatomy of the lens capsule is a pre-requisite.

Anatomy of the Lens Capsule

Capsule of the lens forms a transparent homogeneous highly elastic covering of the lens. Ultra structurally the capsule has a laminated appearance. When out or ruptured its edges roll out and then curl up. It is much thicker in the front than behind and the anterior and posterior portions are thinner towards the periphery (equator) just within the attachment of the suspensor ligament than at the poles (Figs 15.1 and 15.2).

The pattern of insertion of zonular fibres has an important bearing on the size of the capsulorhexis.

Zonular fibres arise from the ciliary body and would be divided into two groups.

First those that pass from the ciliary process to the lens, most of which attach to the anterior or posterior lens capsule than the equator and do not seem to cross each other, while those that form a mesh work across the ciliary body or extend from the pars plana to the vitreous body to form part of the vitreous base form the second group. As a whole the zonule forms a ring which

Fig. 15.2: A schematic view of the lens of the eye

is roughly triangular on meridinal section. The base of triangle is concave and occupies the equator and portions of the anterior and posterior surface of the lens.

Technique: Sheer Versus RIP

The red fundus reflex produced by coaxial light of the microscope is essential to visualise the capsule while performing capsulorhexis. Also, high magnification, horizontally placed eyeball and putting viscoelastic on the wet cornea improves visibility of the anterior capsule.

Capsulorhexis can be performed by either a sheer technique (Fig. 15.3) or by a ripping technique (Fig. 15.4). Propagators of both the techniques have shown distinct advantages and disadvantages of the same. However, in our experience we feel that the sheering technique

Fig. 15.3: Demonstrating the sheer technique for initiating capsulorhexis

Fig. 15.4: Demonstrating the rip technique for initiating capsulorhexis

provides us with an advantage of an ultimate control on the initiation and performance. Ripping the capsule is

less desirable than sheering because the tear tends to extend uncontrollably even when the grasp is held stationery. Secondly more force is generally needed to begin a tear with ripping as opposed to that with sheering as the force is distributed over a larger area in ripping.

This entails that a capsulorhexis performed by sheering technique is much more under control and requires much less energy then that performed with the ripping.

A complex physical basis of two techniques and distribution of the force vectors in both the techniques are being shown in Figures 15.3 and 15.4. A combination of a sheer and rip technique can also be used to perform a safe capsulorhexis.

Maintenance of the Anterior Chamber Depth

A deep anterior chamber which is ensured with the generous use of a viscoelastic provides us with a safe atmosphere for initiation and propagation of capsulorhexis. a shallow anterior chamber, an indicator of a high vitreous pressure results in the anterior displacement of lens and zonular stress. It also leads to a more convex position of the lens. Therefore, any stress at the sight of the capsulorhexis whilst initiation or propagation will tend to extend towards the perphery as the force vectors then act in two directions (Figs 15.5a and 15.5b). When the anterior chamber is deep and viscoelastic is used to counteract the vitreous pressure, the stress on the zonules is neutralised (Fig. 15.5c). Thereafter, the capsular forces work only in the direction desired. Maintaining a deep anterior chamber during capsulorhexis is therefore highly recommended. Learning a capsulorhexis, using a cystitome on a visco-elastic syringe may help to compensate for any decrease in the anterior chamber depth.

Initiation of Capsulorhexis

We tend to perform the capsulorhexis with the use of a sheering technique and the technique described herewith will follow the principle.

Capsulorhexis is often initiated with formation of a flap. A puncture wound at the centre of the lens and the cut is extended to a point B (Fig. 15.6). At point B cystitome is pulled towards point C as shown in Figure 15.7. This lead to creation of a capsular flap which is then folded over to lie on top of the intact capsule. The direction of the horizontal cut can be towards the nasal or temporal side of the lens or towards the site of the incision depending on personal preference. It can then be extended either in the clockwise or anticlockwise direction. We prefer to perform capsulorhexis and

Figs15.5a to c: (a) Demonstrating the upward direction of force of vector when the anterior chamber is shallow, (b) Showing how this force vector acts in extending the tear to the periphery, and (c) Deepening of the anterior chamber by viscoelastic neutralises the force vector

Fig. 15.6: Showing initiation of capsulorhexis starting from the centre and going to the mid-periphery

continue it in an anticlockwise direction. A slight variant of the continuous capsulotomy as popularised by Charles Kelman may be performed by engaging the lens capsule in the centre of the lens and then pulling the capsule towards the incision site (Fig. 15.8). This leads to creation of a triangular flap described as a Christmas tree flap by Kelman.

Fig. 15.7: Showing progression of capsulorhexis using shear technique

Fig. 15.8: Showing a variant of continuous capsulotomy known as “Christmas Tree Flap” creation

Important Factors while Initiating Capsulorhexis

1.Incision should be superficial and should involve only the capsule.

2.Incision should be extended for just about 2 mm on either side depending on the personal preference.

3.Aim for minimal disturbance of the lens cortical material as this will hinder visualisation.

4.A deep anterior chamber is a pre-requisite and should be maintained by a generous use of viscoelastics.

Propagation of Capsulorhexis

After initiation, as described earlier, the capsular flap is folded upon itself. The flap is then engaged with either a cystitome or a capsulorhexis forceps at point C and the flap pulled in the desired direction of capsulorhexis (Fig. 15.7). While using a cystitome one has to be very cautions that very minimum pressure is applied to engage the capsule as too much pressure may penetrate the flap. Also the capsule should be held or engaged somewhat inside the peripheral edge of the flap in order to provide a safety margin against the cystitome slipping peripherally and damaging the intact capsule. The direction of the force ensures correct position and extension of the capsulorhexis. It can be seen that point of engagement of the instrument is adjusted to stay two to three clock hours away from the point of sheering. If the instrument is placed closer, an artificial stress line is created which could compromise the predictability of the capsulorhexis and direction of sheer propagation. The direction of capsulorhexis can be altered by changing the direction of force as shown in Figure 15.9. The changes in direction may be required when the capsulorhexis tends to extend peripherally. One should be aware of the fact that if a change in direction of the capsulorhexis is abrupt it can induce modification of the force vectors converting sheer to a modified rip which has a potential of peripheral extension. A deep anterior chamber during any of these manipulations is highly desirable for a high predictability.

Fig.15.9: Showing the direction of force used for progression of a capsulorhexis by sheer technique

The capsulorhexis is progressed gradually, the capsular flap is engaged repeatedly and capsulotomy progressed for about two to three clock hours at a time. Figure 15.10 shows the capsulotomy three quarters of the way through. When coming to the end of the capsulorhexis, problems are often entailed as there is a lot of capsule lying free,

impending visualisation of the capsulotomy edge. Viscoelastic are used here to flatten the capsular flap and to ensure good visualisation of the tear (Figs 15.11 and 15.12a and b). Also when coming to the end of the capsulotomy an attempt should be there to bring the capsule from outwards in, as shown in Figure 15.13. The direction of the force is slightly modified to increase the diameter of the capsulorhexis and then to bring the capsular flap from out in. This modification of the technique helps in prevention of any radial extensions of the capsulorhexis during phacoemulsificaton.

Figs15.12a and b: A flat anterior capsule with the help of viscoelastic enhances visualisation. Courtesy: Alcon (India)

Fig.15.11: Shows wrinking of the anterior capsule creating problems in visualisation

Fig.15.12a

Salient Features of Capsulorhexis with the Cystitome Using the Sheer Technique

Fig.15.13: Showing the direction of the capsulorhexis when coming to the completion (coming from outwards to in)

2.Radial extension of the capsulorhexis should be only for about 2 mm.

3.The direction of the force should be in the desired direction and shape of capsulorhexis.

4.The capsule should be grasped with the cystitome using gentle pressure to avoid any tears or inadvertent rupture of the capsule.

5.The point of engagement of the capsule should be kept slightly away from the margin of the lens.

6.The capsulotomy should be progressed slowly moving two to three clock hours at a time.

7.When nearing the end the capsule flap should be spread evenly using a viscoelastic to enable completion of rhexis and to visualise the end of the tear.

8.Capsulorhexis should be finished from an outward in movement of the capsule.

9.A deep anterior chamber should be maintained at all times.

Capsulorhexis with the Ripping Technique

1.Initiate the capsulorhexis straight in the centre puncturing just the capsule avoiding inadvertent disturbance of the cortical matter.

Performing a capsulorhexis with a ripping technique differs from the sheering technique in the following aspects:

1.Direction of the pull is much more towards the centre of the capsule (Fig. 15.14).

2.The flap is engaged by pulling the instrument at a point which is much closer to the tear.

3.A larger amount of force is required to initiate and propagate capsulorhexis.

4.The direction of the force has to be constantly changed to direct and propagate the capsulorhexis in a circular manner( Fig. 15.15).

Fig.15.14: Showing the direction of the force when you are creating a capsulorhexis with the ripping technique

Fig.15.15: Shows the changing direction of force needed to propagate the capsulorhexis in a circular manner with the ripping technique

Shear v/s Rip

In our experience, the ripping techniques have been shown to be more difficult to control and more likely to inadvertently extend peripherally relative to the sheering techniques. However, they can be combined with the sheering technique when a change of direction of the capsulorhexis is desirable.

Capsulorhexis Using Forceps

points at the tip directed downward to grab the anterior capsule are now available to perform capsulotomy. Initiation of capsulotomy in these cases is begun with a needle puncturing the capsule in the centre making a horizontal movement 2 mm towards the lateral side, creating a capsular flap. The capsular flap thus created is grasped with the forceps and the capsulorhexis may be performed by ripping the capsule in the direction of desired capsulorhexis. Capsulorhexis using a Utrata’s forceps has been reported by some investigators to be much easier and provides more control over the capsulorhexis then with the cystitome. However, in our experience we feel that either of the two techniques is quite safe and predictable and use of either of the instruments is entirely a personal preference. However, the use of a forceps requires AC maintenance by more dense viscoelastic and methyl cellulose alone may not always suffice (Figs 15.17 to 15.19a and b show the use of a Utrata’s forceps in performing a capsulorhexis). We still prefer the use of sheer technique in performing a capsulorhexis even when using the Utrata’s forceps.

Fig.15.16: Showing the use of an external light source for visualisation of the anterior capsular flap

A number of capsulotomy forceps based on the wonderful design of Utrata, long handled forceps with 2

Fig.15.17: Showing a “Christmas Tree Flap” as

advocated by Kellman