STRATEGIES FOR ACHIEVING CLEAR CORNEA IN BROWN CATARACTS

Dr. Pankaj Sharma

Associate Professor of Ophthalmology

SMS Medical College & Hospital, JAIPUR

"Challenges are what make life interesting; overcoming them is what makes life meaningful." -Joshua J. Marine

The modern era of medicine has seen exponential growth in diagnostics and therapeutics. Still we know in our hearts that we have crossed maybe a few yards in a million mile race ! Overcoming each challenge brings us face to face with an even bigger and daunting challenge. Just when we were sitting smug in the glory of modern era of cataract surgery, the list of contraindications for phacoemulsification started haunting us.

The paradigm shift can be appreciated by the fact that these contraindications have now become real indications for phaco. Brown, subluxated, morgagnian cataracts; small pupil; unco-operative patients; patients with postural problems, to name a few, are better dealt with phaco.

Seeing from the patient’s perspective, each one has to be perfect in giving results. Cataract surgery is still in its infancy and till the time we can give emmetropia in all the cases with the power to accommodate, we cannot sit idle and gloat in our achievement of sutureless surgery.

Brown and morgagnian cataracts are the most frequently seen difficult cases, especially in the Indian subcontinent. Until one is proficient in dealing with them, one’s armamentarium would be really lacking. Just reassuring the patient that his vision will remain blurred for a few days to weeks due to post-operative corneal edema will not absolve any of us from the crime committed against the corneal endothelium and wound.

 To effectively deal with these cataracts, the following strategies can be adopted:

1. Minimal use of intraocular ultrasound. Focus on mechanical disassembly of the cataract rather than actual emulsification.
2. Minimal delivery of intraocular ultrasound. Focus on new technology of burst, hyperpulse, torsional phaco.
3. Effective and safe delivery of intraocular ultrasound. Focus on stable chamber and minimal surge with emulsification in the capsular bag.
4. Minimizing intraocular damage: Focus on good OVDs and intraocular fluids.

DISASSEMBLY OF BROWN CATARACTS

Hardness of any cataract is directly proportional to its brown discolouration. The human lens normally undergoes changes with age. It slowly increases in size as new lens fibers develop throughout life; older lens fibers in the center of the lens become dehydrated and compacted. The cross linking of proteins in the nucleus increases its optical density and decreases the transparency. This crosslinking is somewhat similar to those of aging collagen or keratin. Three types of cross links are identified in senile cataracts

1. Disulfide crosslinks (S-S)
2. Lysine modification
3. Dityrosine crosslinks

These crosslinked compounds are particularly susceptible to oxidative damage, leading to progressive colour change of the lens.

In essence, the central most part of the lens is the most affected leading to formation of a dense “core” surrounded by the less dense epinucleus. Brown cataracts form a special group where this process has gone to the extent that the central core forms a significant bulk of the lens.

Thus dealing with hard lens is basically dealing with the dense central core. Not only is it very hard to crack or chop, it also prevents the epinuclear shell to be cracked and prolapsed anteriorly (Fig. 1).

As if that was not enough, the capsule is usually thin and inelastic with degeneration of the zonular elements. Thus we are presented with a rock hard lens with little zonular, capsular or epinuclear support

The various modalities which have been described for such cataracts are:

1. Debulking of the central core followed by chop
2. Divide and conquer
3. Stop and chop
4. The two step chop
5. The Direct chop

The first three are beset with significant problems:

1. Unpredictability of sculpting the core (when to stop ?)
2. High phaco energy used for the same
3. Needle dependence: It has to be sharp
4. Excessive forces used for separation

The two step chop has been described by Dr. Vasavada where an initial superficial direct chop is made, followed by re-grasping the deeper nuclear layers with the phaco needle and completing the deeper chop.

The direct chop in brown cataracts is technically difficult due to lack of capsular tension and elasticity and little epinuclear support. Holding the center of the cataract and initiating a classical Nagahara or karate chop  requires the two forces, one of the nucleus held with the phaco needle at high vacuum, and the other, of the chopper, to be exactly equal and opposite. Even the slightest disparity leads to formation of a ‘couple’ of forces which either just rotates the nucleus or, more dangerously, tilts it, leading to zonular dehiscence (Fig. 3 ). In black cataracts, the central core of the cataract is literally unchoppable

Fig.3  Unequal forces leading to tilt and rotation. Peripheral placement of the chop reduces the rotational vector forces

Fig 4

Fig 5

Fig 6

DIRECT CHOP FOR BROWN CATARACTS: THE “CORE” TECHNIQUE (multiple peripheral nucleotomies with central core enucleation)

 Pre-requisites:

Apart from an advanced experience with the direct chop technique, the following are desirable pre-requisites:

1. High end phaco machine with facility for burst mode, hyperpulse (cold phaco) and an effective surge suppressor
2. Sharp tipped, cutting chopper (Fig. 7)
3. Good OVD for chamber maintenance and endothelial protection.
4. A mechanical bent of mind with understanding of the behavior of lenticular fibres.

Fig 7

The outermost shell of the cataract is almost never black and always choppable. Instead of holding the nucleus from the centre, hold it near the CCC edge and initiate a small peripheral nucleotomy with lateral separation. This is repeated after about 20 to 30 degrees of nucleus rotation so that 10-12 such multiple peripheral nucleotomies are created. No attempt must be made at this point to dislodge these small elements or to extend the cracks posteriorly. Since the forces are applied away from the centre:

1. The nucleus does not rotate during the chop
2. It never tilts
3. The central core gets mechanically separated from the peripheral nuclear fibres.

The number of peripheral nucleotomies required to achieve the separation of the central core is directly proportional to the size and hardness of the core.

Once the central loosening is achieved, the phaco needle is buried face down into the central core and, with the aid of high vacuum, it is brought up. The second hand can be used to separate any remaining adhesions between the centre and periphery. This ‘nucleolus’ can then be easily jackhammered with the chopper against the phaco needle and easily emulsified (Figs. 2,4,5,6). Once this is completed, majority of the problems are over since:

1. Space is created in the capsular bag which assists in future chops and separations.
2. The incomplete peripheral nucleotomies can now be completed under direct visualization.
3. These peripheral nuclear fragments thus created easily prolapse anteriorly.

 90 percent of the procedure is thus completed with one phaco setting (high flow, high vacuum, hyperpulse or burst mode) and the last few fragments are then with the step-down technique (low vacuum and flow rate). This is to avoid damage to the posterior capsule which is more exposed at this stage.

 The preferred settings are :

1.    Vacuum : 250-350 mm Hg. Working at high vacuum requires a particularly thick (non-collapsible) tubing with efficient surge-suppressor mechanisms in the machine

2.    Asp. Flow Rare : 26-40 ml/min

3.    Phaco Power : 10-50 % (foot controlled) . Burst mode and hyperpulse mode are both desirable for this technique. The burst mode is useful for embedding the needle into the nucleus and to release the occlusion when a hard piece is impaled into the needle. The pulse and/or hyperpulse are particularly useful for dealing with the fragments with as little heat generation as possible. Torsional phaco is also a good alternative to reduce heat generation and repulsion.

It would not be out of place here to mention the qualities of a good phaco needle:

1. Micro needle: 0.9 mm
2. Flared or miniflared tip: for better holding
3. 30 degress: for good trade-off between holding and cutting abilities
4. Kelman bent: for efficient cutting
5. ABS system: The small aspiration bypass hole in the shaft minimizes surge with more emphasis on phaco-assisted aspiration rather than actual emulsification. (Fig. 8)

The advantages of this technique are:

1. Predictability and reproducibility: The size of the central core need not be titrated as the peripheral chops just bring out this core, whatever be its size. The problem with sculpting was finding out when it was enough.
2. Phaco power: The average effective phaco time for even the hardest nuclei is less than 20 seconds since minimal phaco power is used to eat up the central core.
3. The chance of would burn is minimal.
4. The procedure is not dependant on the sharpness of the needle since mechanical forces are used to break the nucleus rather than ultrasound.

MORGAGNIAN CATARACTS

 Cataracts crossing the stage of maturity finally develop liquefaction of their cortex leading to freely floating nucleus core in a sea of milky cortex. Such cataracts are still being dealt with ECCE or SICS. The main bug bear for such cases is a very poor zonular support, not to mention the occasional surprise of being greeted with a rock hard brown nucleus once the milk is released.

 Evidently, any type of sculpting or dividing of such nuclei is next to impossible. The direct chop is the only method which can be adopted with such cataracts. The lollipop chop or the tangential chop is ideal for such situations.

The nucleus is impaled with a burst of phaco power and held like a “lollipop” making its equatorial diameter vertical. The chopper is then used to split the nucleus from periphery to the center (Fig. 9). Releasing the nucleus from the capsular bag completely obviates the risk of further stretching the zonules. A capsular tension ring is a good way of further ensuring the same. The mechanics of such a chop are a bit different from the conventional chop as it is not in the iris plane but perpendicular to it.

 The various modalities of decreasing phaco power delivery, decreasing surge and proper use of OVDs have been dealt with in my previous articles in this Journal.

 To end, a famous quote which is very dear to my heart:

"Adversity has the effect of eliciting talents, which in prosperous circumstances would have lain dormant."       -Horace