By Lisa B. Arbisser, MD
This prospective study assessed the impact on incision size of motorized versus standard manual IOL injection. It found that the motorized injector was easy to use and caused significantly less incision enlargement.
I'm not sure we really need more automation but the finding that a smooth and quick (4.4 mm/sec) injection stretches the wound least is useful. We should all strive for this rate of injection manually.
Subjects were 256 patients divided into four groups according to preimplantation incision size: 1.9 mm, 2.0 mm, 2.1 mm, 2.2 mm, or 2.3 mm. Each subject received a hydrophobic acrylic aspheric IOL implanted using a D cartridge and an Autosert motorized injector at fast speed (4.4 mm/sec), an Autosert motorized injector at slow speed (1.5 mm/sec), or a manual Monarch III injector made by the same manufacturer.
All procedures were performed by one of two experienced surgeons in the same operating room. They analyzed a sample of 20 videos of the implantation to estimate the time taken for an average IOL to pass through the incision (transition time) for each technique.
The fast-speed motorized injector caused significantly less incision enlargement than the slow-speed injector or the manual injector for all preimplantation incision sizes. For four of the five preimplantation sizes, the slow-speed injector produced less incision stretch than the manual injector, although the difference did not reach statistical significance.
The mean transition time was 3.5 seconds with the manual injector, 2.5 seconds with the fast injector and 7.0 seconds with the slow injector. Injection with the manual device required five “turn and pause to re-grip the head of the screw mechanism before another turn” cycles, while the motorized injector allowed a two-handed technique with the eye stabilized by a second instrument in the side port.
The authors note that IOLs with a power higher than 22.0 D (the median value) caused statistically more enlargement than IOLs with a power of 22.0 D or less with the fast motorized injector and with the manual injector, but not with the slow motorized injector. This is interesting because although the total volume of the IOL optic is greater with higher diopter IOLs, the cartridge system ensures that the diameter of the folded, elongated IOL is always constant as it leaves the cartridge tip.
If higher diopter IOLs are associated with greater incision enlargement, it is presumably because their larger bulk causes them to re-expand quicker as they pass through the corneal stroma of the incision. This also suggests that the data for the slow Autosert injector should be treated with caution because this group had a statistically significantly lower mean IOL power.
The authors conclude that further studies are needed to confirm these findings and to examine incision integrity and linear enlargement.