Brown cataract phacoemulsification
Everything you ever wanted to know about brown cataract phacoemulsification - Part 1
Crater and chop technique of nuclear disassembly: A – A central crater has been created; B – Horizontal chop is performed for the rim of crater; C – The fragments are emulsified within the crater; D – First post-op day shows clear cornea
Brown cataracts can be associated with other ocular comorbidities in the form of loose zonules, low endothelial count, shallow anterior chamber, pseudoexfoliation and inadequate pupillary dilatation – all of which add on to difficulty in surgery as well as increase the likelihood of less than ideal outcomes. Brown cataracts can be associated with other ocular comorbidities in the form of loose zonules, low endothelial count, shallow anterior chamber, pseudoexfoliation and inadequate pupillary dilatation – all of which add on to difficulty in surgery as well as increase the likelihood of less than ideal outcomes. Preoperative evaluation should therefore look specifically for these conditions. The leathery non-compliant nature of the brown cataract per se also increases difficulty in surgery, and therefore phacoemulsification of the hard brown cataract should be taken up only by experienced surgeons, and even then with clear acceptance of the fact that conversion to either extracapsular cataract extraction (ECCE) or small incision cataract surgery (SICS) may be required. Patients who are not able to see well through the hard cataract may benefit more with immersion than with optical biometry. Specular microscopy should be done if possible. Surgery may be preferred under peribulbar anaesthesia rather than topical in order to more easily handle a longer surgical time and the possible eventuality of having to convert to ECCE/SICS or manage a posterior capsular rent or nucleus drop.
INCISION: Incision architecture should be ideal. Too long incisions cause oar locking, compression of phaco sleeve while manoeuvring and can also cause corneal burns. Too short incisions may lead to repeated iris prolapse and a small pupil, and therefore should be avoided.
RHEXIS: Lack of a good red reflex results in poor visualisation of the tearing edge of the rhexis. Coaxial light from good quality microscopes often overcomes this and give sufficiently good red reflex. Trypan blue capsular staining can be performed to enhance visualisation. Oblique light from an endoilluminator may also be used to improve the view. Small rhexis should be avoided to allow free rotation of the nucleus within the bag as well as conversion to SICS or ECCE if required. A large enough rhexis prevents capsular blowout and accidental damage to rhexis margins during chopping manoeuvres.
Trying to attain a complete cortical cleaving hydrodissection using a continuous fluid wave can result in a capsular blowout as the bulky hard endonucleus fills the capsular bag. Gentle multi-quadrant hydrodissection should be attempted. Further injection should immediately be stopped and the bag decompressed if elevation and contact of the endonucleus against the capsular bag is seen during hydrodissection. Hydrodelineation may not be able to effectively decrease the bulk of the central choppable core of cataract as there is very little epinucleus to separate. Nucleus rotation should be very gentle.
The large nucleus needs more phaco power for emulsification. The amount of phaco energy used, fluid turnover in the eye and the chances of endothelial damage are correspondingly more with brown cataracts. A dispersive ophthalmic viscosurgical device is preferred to coat the endothelium and this may be replenished multiple times during nuclear emulsification. Divide and conquer, stop and chop, crater and chop or a direct vertical chop may be used for nuclear disassembly. Sculpting should be performed using high power and low vacuum to avoid nuclear displacement and zonular stress. The phaco tip should be adequately exposed to go deep enough and to get sufficient purchase of the nucleus. For vertical chop, a sharp and long pointed chopper is preferred. While chopping, posterior pressure should not be applied. Instead, the dominant hand pulls the embedded phaco tip slightly forwards and the chopper separates laterally to create a vertical split. It is often difficult to get a complete crack through full thickness of the nucleus including the posterior leathery plate.In this scenario, the nucleus should be released and again embedded at a deeper plane to laterally separate the halves. This is more effective in cracking the posterior plate than extensive lateral separation of the nuclear halves with a superficial hold, which can cause stress to the zonules. The zonules in brown cataracts are loose and extra manipulation is often required. A capsular tension ring may therefore be considered, especially in case of pseudoexfoliation. Phaco power may be used in burst mode for embedding and chopping followed by pulse/hyperpulse mode for emulsifying the nuclear fragments. After chopping into smaller fragments, high vacuum and flow rate are used for faster emulsification. Bringing the first fragment out after chopping helps break the jigsaw puzzle arrangement of the nuclear pieces and subsequent fragments can be emulsified more easily. The phaco tip should point sideward and adequate distance should be maintained from the endothelium. Care should be taken not to aspirate the iris accidentally. Because of the lack of protective epinuclear shell, lax zonules and the thin fragile nature of the posterior capsule, the risk of a posterior capsular rent is higher. Using the air pump or pressurised air infusion allows maintenance of a deep anterior chamber and helps to protect both the endothelium and posterior capsule, as well as helping surgery to proceed faster. Towards the last pieces, phaco parameters should be brought down. Chatter is more commonly seen with brown cataracts and pulse mode helps to some extent to decrease this. Torsional ultrasound also helps faster and safer emulsification with less chatter. Small chips of the nucleus often break off and lodge themselves in the angle or sulcus, behind the iris or in the wound, and these should be looked for and removed after nuclear emulsification. BSS irrigation helps dislodge these pieces.
CORTEX ASPIRATION AND IOL IMPLANTATION:
Residual cortex is less as compared to soft cataracts and it is removed in the conventional manner. This is followed by viscoelastic injection and in-the-bag IOL implantation. Wound architecture should be carefully evaluated at the end of surgery for possible leakage secondary to mild wound burn or excessive distortion of the wound from the increased manoeuvring. Sutures may be applied if required. Postoperative care needs to be more intense because of a higher incidence of complications.
• Chop techniques for brown cataracts will be discussed in Part 2 of this series
Dr Soosan Jacob is Director and Chief of Dr Agarwal’s Refractive and Cornea Foundation at Dr Agarwal’s Eye Hospital, Chennai, India email@example.com