Ultra small incision bimanual cataract surgery

October 1, 2007

I am sure many surgeons are familiar with these complaints and for those wishing to switch to bimanual cataract surgery, there are certainly a number of initial difficulties that must first be overcome.

"...I can't keep the anterior chamber stable. Please lift up the bottle! Better. Now slow down the pump...oops, it's flattening again..."

I am sure many surgeons are familiar with these complaints and for those wishing to switch to bimanual cataract surgery, there are certainly a number of initial difficulties that must first be overcome. However, I would argue that surgeons should not give up if they do experience these teething problems because bimanual phaco can offer numerous advantages over conventional phaco:

1. Separate irrigation and aspiration: biaxial surgery

2. Ultra-small incision

Despite recent progress in conventional phaco tips, I believe that only a sleeveless needle can actually provide a very small incision surgery of 1.4 mm or less.

Size & shape: myths and realities

Until now, irrigating choppers and phaco needles have been round in shape, hence during phaco, a circular instrument is introduced through a linear incision. When a surgeon introduces a round needle or chopper through an incision, he is not introducing a single diameter (for example a blade) but an infinity of diameters - the instrument's perimeter.

In fact we must understand that we are dealing with the perimeter of the system instrument/incision, and not with the diameter of the instrument.

If we take the formula perimeter = 2πr and apply it to a diameter of 1 mm, the perimeter is 3.1416 mm. Because the size of an incision opening is equal along its length (bearing in mind the vertical elasticity of the limbus), we can assume that the size of the incision should equal half of the perimeter. Hence, using this assumption for a 19-gauge round instrument (1 mm in diameter), the incision size needs to be 1.57 mm. The same theory would be true for a 20-gauge, 0.9 mm incision: the incision would need to be 1.41 mm. These are the true incision sizes; very far from 1 mm.

When people talk about 1 mm incisions, what they are really talking about is 1 mm instruments. The smallest and most functional incision I have been able to work with is a 1.2 mm incision for a 21-gauge, 0.8 mm diameter OVAL instrument. When I used round instruments (0.8 mm diameter), I only ever felt comfortable working with incisions over 1.7 mm, when this should be 1.41 mm, as told.

Addressing the issue of excessive leakage

After we use a blade to produce a linear incision, and when we start introducing an instrument, the elasticity of the limbus or cornea precludes us from transforming this into a circular incision, even if we force the incision (by forcing an incision, you transform a surgical wound into a traumatic wound; this is never acceptable). The most we can get, if we are gentle and precise, is an oval opening - never a circle.