The angle of approach of the keratome will determine the tunnel length of our phaco incision. If the angle is very flat and the blade is right against the ocular surface, the tunnel length will be long. If the angle is greater and the blade is now more parallel to the iris plane, the tunnel length will be shorter. We can vary this angle as we make the incision to tailor the technique to the anatomy so that every eye has a great incision.
This angle tends to be about 30 degrees but it can vary based on the patient’s anatomy. The corneal curvature plays a role as does the corneal thickness. There are variations in human anatomy so the surgeon must be able to make adjustments to provide the ideal result for each individual eye.
If your incisions tend to be too short, then using a smaller angle with the tip of the keratome angled more toward the corneal apex is appropriate. If your incisions tend to be too long, then using a larger angle will allow the tip of the keratome to enter the anterior chamber sooner, resulting in a shorter tunnel length.
Click below for this video showing external and microscope views as well as OCT: