It can be helpful to place our phaco incisions on the steep axis of cornea astigmatism in order to provide a mild flattening effect. The degree of corneal flattening depends on a few factors: the width of the incision, the tunnel length, and the placement. The ability to place the incision on the steep axis can vary with OD versus OS and also whether the surgeon is right or left handed.
Incision width is typically in the 2.2 to 2.8 mm range with the larger incision having a little more astigmatic effect. We find that the surgically-induced astigmatism from a typical temporal incision is about 0.25 to 0.50 diopters, depending on the factors mentioned above. For a superior incision, this is often a bit more, perhaps in the 0.50 to 0.75 diopter range primarily because the superior limbus is closer to the visual axis.
Surgeons should be able to sit temporally as well as superiorly for most routine cataract surgeries. There are exceptions such as when a very deep-set eye, a prominent brow, or a narrow palpebral fissure limit access to the superior limbus.
We can also pair these phaco incisions to increase the astigmatic effect, with paired temporal & nasal incisions having about 0.75 D of flattening and paired superior & inferior incisions have about 1.00 D of flattening.
Ideally, a surgeon would be able to operate reasonably well with both hands because this allows the greatest flexibility. If you are in the earlier stages of learning surgery (the first few years), I encourage you to develop dexterity in both hands and also learn to operate with both temporal and superior phaco incisions.
Click below to see a video of many different incisions and their placement: