Rule of the 9s
There are several formulas for guessing the best lens power. Some of them have to be previously calculated, some of them can be done on the spot.
One of the most popular rules is the “rule of the 9s”2: decrease 0.5dp from the intended power for each 9dp away from 0. Check the table below these lines:
However, you still to need to account for the lens constant and consider if you are going to capture the optic body or not. Recent studies show that lenses with captured body should use traditional formulas for lens-in-the-bag.
Though the rule of the nines is a huge improvement over the “decrease by 1dp” to power of the lens for sulcus placement1. However, it does have a flaw: it’s an approximation. If we could have a proper sulculs lens power calculator, using the emmetropia value and apply the proper correction (not the 9s rule) we would get better results. That’s is exactly what the Sulcus calculator in our app, Cataractools, does.
Suto C, Hori S, Fukuyama E, Akura J. Adjusting intraocular lens power for sulcus fixation. J Cataract Refract Surg. 2003 Oct;29(10):1913-7. doi: 10.1016/s0886-3350(03)00250-5. PMID: 14604710.
The Rule of Nines for Sulcus IOL Power. Professor Uday Devgan MD