Effect of Minimising Ultrasound Power to 1% During Cataract Surgery on Corneal Endothelium.

Corneal endothelial damage and posterior capsular rupture are two most undesirable complications of cataract surgery, infact significant loss of endothelium can lead to corneal decompensation and loss of corneal clarity. However, some degree of endothelial cell loss is inevitable after any cataract surgery. A loss of 3.2%-23.2% has been shown in various studies since 1967. It is well known that during cataract surgery many different factors can generate endothelial damages, these include the impact of the nuclear fragments, the turbulence generated in anterior chamber and the volume of liquid. It is also related to the amount of ultrasonic energy used and the subsequent temperature rise, the contact with surgical instruments and the IOL during implantation. It also depends on the release of free radicals the length and features of incision,the surgical technique used . The risk of endothelial cell density loss is further enhanced when surgeons have to deal with high density cataract, shallow anterior chamber and old age.

Since the time Kelman introduced his technique of phacoemulsification, there has been constant and conscious effort on the part of phaco surgeons to reduce their phaco time by bringing some alteration or innovation in their personal technique or introducing new technologies for the procedure of phacoemulsification. Development of Laser emulsifier, SONAAR machines, introduction of cold phaco with modulations of ultrasound in the form of pulse, micropulse and bursts were achievements towards attaining this end and goal.

Coaxial microphacoemulsification is the standard phacoemulsification technique being practised globally for cataract extraction and on many occasions we intentionally do not use the phaco power either at all or fully as per the pre set limit. In fact the use of efficient fluidic controls and a chopper minimizes the use of phaco energy. If we could assess a zero/minimal ultrasound technique in a scientific setting we might achieve the desired goal without resorting to major modifications of instrumentation and machine. Coaxial MICS fully utilizes the advantages of small incision and provides the most comfortable platform for the surgeons using conventional phacoemulsification.

We imagined that most ideal setting would be introducing zero phaco power in the anterior chamber for emulsifying the nucleus as has been done already in case of Aqualase using warm fluid based system and Howard Fines new technique of mechanically emulsifying the lens with rotators(under investigation). For that we undertook a pilot study in 10 patients and performed coaxial microincision phacoemulsification, introducing the ultrasound power in incremental fashion during the surgery in each of the 10 patients till we could achieve the adequate aspiration of fluid and fragments .

At zero power the phacotip and tubing experienced repeated blockages with associated prolongation of surgical time,thus increment to one percent was made during the same sitting. To our surprise, the very first step of introducing 1% ultrasound power made all the difference.No further increments were required as all techniques of nuclear management and lens aspiration were conveniently possible at this setting.

The procedure of aspiration of fragments was smooth and continuous, it also caused a reduction in the surgical time in comparison to zero power phaco.The cases revealed less corneal endothelial trauma in comparison to conventional phacoemulsification using higher power settings. The most surprising observation was that we could dissemble the nucleus with any known technique of nucleus fragmentation(stop and chop, divide and conquer, phaco-chop) in almost all grades of cataracts .Possibly that high vaccum 300-350 is responsible for this nuclear fragmentation and not only the cavitational effects of ultrasound power.

Keeping all the other parameters uniform we wish to design an RCT to study the effect of eliminating phaco power. With this in view,this study compares the endothelial status in addition to various complications and visual outcome following standard coaxial microincision cataract surgery and coaxial microincision cataract surgery using 1% ultrasound.