For certain difficult cases, bimanual phaco presents certain advantages as compared to the coaxial technique. These new benefits should encourage cataract surgeons to familiarise themselves with bimanual phaco in order to integrate this technique into their operative strategy, and can schematically be classified into two categories:
- The reduction in incision size is of obvious interest when confronted with a microphtalmic eye for which smaller surgical instruments are more appropriate, or with cataract following radial keratotomy in order to place the microincisions between the radial incisions while avoiding crossing incisions which weaken the mechanical resilience of the cornea;
- Closed eye surgery reduces complications in cases of hypermature dense nuclear cataract, with narrow anterior chambers with prolapse of the iris, and with zonular fragility. This chapter will examine these three complex cases.
Hyperdense Cataract
Incision size must be appropriate to the degree of difficulty presented by the cataract. Emulsifying a hard nucleus will require more time and US power. Incisions that are too narrow (1.2 mm) can promote thermal burns due to friction of the US probe in the incision. We recommend an incision of 1.4 mm that will help prevent irritation of the corneal tissue by the US and will ensure maintenance of its self-sealing characteristics through the end of the procedure.
To ensure safe capsulorhexis, visual control must be improved by means of capsular staining. Injecting trypan blue (BCC®) at the beginning of the procedure before the viscoelastic agent facilitates visualisation of the capsular incision. The advantage of a microincision combined with a high viscosity viscoelastic agent is that together they maintain sufficient pressure on the anterior capsule to prevent leakage from the capsulorhexis towards the equator of the crystalline lens as well as obstruction of the visualisation of the capsular incision by the egress of milky cortex. Better capsulorhexis control will be obtained by using a distal control forceps which will help better close the microincision than a cystotome.
Using an irrigating chopper with an appropriate infusion flow rate is a key element in the procedure. The Duet® vertical choppers with distal infusion opening provide an infusion flow rate of 50 ml/min with a bottle set at a height of 85 cm. This infusion flow rate enables the practitioner to maintain perioperative chamber stability. Using an aspiration flow reducer is advisable with peristaltic pumps in order to prevent occurrence of the “post occlusion surge” effect.
The best operative technique for very dense nuclei is Vertical Chop, which reduces US use when fracturing the nucleus. The number of nuclear fragments must be increased to at least 8 to enable easier emulsification of smaller fragments. To prevent dispersion of the nuclear fragments in the anterior chamber, infusion pressure should be reduced by 10 to 25 mm/Hg, or bottle height by 10 cm during aspiration of nuclear sections. Aspiration parameters should also be reduced in keeping with the new irrigation parameters.
The advantage of this surgical technique is that it reduces the risk of complications such as capsular rupture and endothelial cell loss during phacoemulsification of hard nuclei. Key elements in this are the size of the microincisions and adequate infusion pressure that maintains good cameral volume, keeping the instruments away from the endothelium and the posterior capsule throughout the procedure.
Narrow anterior chamber and prolapse of the iris.
A prolapse of the iris associated with anterior chamber effacement is a problem particularly affecting strongly hypermetropic eyes with a short axial length, microphtalmic or small eyes, and eyes with a large crystalline body or phacomorphic glaucoma. As soon as the capsulorhexis has been performed, a 1.2 mm microincision and a distal control forceps prevent viscoelastic reflux out of the anterior chamber while enabling better control of the capsulotomy procedure. These alternatives avoid the need to recur to vitrectomy through the pars plana to create greater depth for the anterior chamber, as this technique presents a risk of suprachoroidal effusion in microphtalmic eyes.
To avoid a prolapse of the iris by effacement of the anterior chamber, it is necessary to prevent cameral pressure from decreasing to zero during surgery. In such cases, the separate infusion option offered by the bimanual technique is a definite advantage. It enables the surgeon to leave the irrigating chopper in place in the anterior chamber and to exchange the US probe after phacoemulsification of the nucleus with the aspiration probe to clean the cortex. Following cortical aspiration, the irrigation probe is maintained in place until the chamber and the bag are completely filled with a viscoelastic agent. Maintaining positive intracameral pressure then enables withdrawal of the irrigation probe while avoiding a prolapse of the iris.
Partial zonular deficit
A partial zonular dialysis in post-traumatic cataracts, associated with a vitreous body prolapse, remains a difficult case in which bimanual phaco is an advantageous alternative. As irrigating choppers generally reduce the infusion flow as compared to coaxial infusion, bimanual phaco can be performed with low aspiration and vacuum rates. This is particularly useful in zonular deficit cases. High infusion flow rate choppers should therefore be avoided to prefer those having two side infusion openings, while simultaneously reducing bottle height, infusion pressure and aspiration power. This helps minimise the risk of vitreous body collapse with partial zonular rupture. The bimanual approach enables the surgeon not to infuse into the sensitive area by keeping the irrigation probe above the plane of the iris in a direction opposite to that of the zonular defect. It is thus possible to maintain a dispersive viscoelastic substance in place to protect the area of the zonular deficit and minimise the risk of extension of the zonular rupture. Bimanual phaco combined with the use of a capsular tension ring finally makes it possible effectively to manage these delicate cases.
