When an intraocular lens cannot go in the capsular bag, it is placed in the ciliary sulcus, where it sits more anteriorly than planned. Implant the power you calculated for the bag and the patient ends up myopic. This free calculator gives you the corrected sulcus IOL power in seconds — at the slit lamp, in theatre, or planning a secondary lens — and works fully offline once installed on your phone or tablet.
Sulcus fixation is rarely the plan and almost always a decision made under pressure. You will reach for it when:
In every one of these scenarios the lens ends up closer to the cornea than the bag position your biometry assumed — and that single shift is enough to change the refractive result
The ciliary sulcus sits roughly half a millimetre to one millimetre anterior to the capsular bag. A more anterior effective lens position increases the lens’s effective plus power, so an IOL calculated for the bag becomes too strong in the sulcus. The result is a myopic surprise. The correction is to reduce the implanted power — but by how much depends on the lens and the power involved, which is exactly where simple rules fall short
The most widely taught shortcut is Dr. Devgan’s rule of 9s: take the in-the-bag power and reduce it by roughly 0.5 D for every 9 D of lens power when placing the IOL in the sulcus. It’s elegant, fast, and exactly what you want at the operating microscope — a reliable mental calculation when you need an answer in seconds.
What a calculator adds is precision for the moments when you can be exact. Two refinements are easy to lose in head math: the residual decimals that rounding leaves behind, and the influence of each lens’s own constant, which a single rule necessarily treats as uniform.
Rather than a stepwise rule, the tool starts from the emmetropic power and applies a lens-specific in-the-bag-to-sulcus conversion — the method described by Dr. Hill (see references) — accounting for the IOL’s optimised constant and the optic-capture scenario. The result appears as a large, copyable figure, with the constants used shown beneath it, so the calculation is fully transparent.
You planned a Tecnis ZCB00 (single-piece, SRK/T 119.3) for the bag at +17.5 D. The posterior capsule ruptures, so you place a Tecnis ZA9003 — a 3-piece lens — in the ciliary sulcus.
| Step | Rule of 9s | This calculator |
|---|---|---|
| Planned in-the-bag power (ZCB00) | +17.5 D | +17.5 D |
| Bag → sulcus correction | −0.5 D (flat 9–18 D step) | −0.77 D (optimised table @ 17.5 D) |
| Constant conversion ZCB00 → ZA9003 | — (ignored) | −0.20 D |
| Corrected sulcus power | +17.0 D | +16.5 D |
Difference: 0.5 D. The rule of 9s misses it twice over — its flat step undershoots the real −0.77 D correction, and it has no way to account for the different constant of the 3-piece lens you actually implanted. Half a dioptre at the IOL plane is enough to turn a planned emmetrope into a noticeably myopic one.
Tap the button above. On a phone or tablet, add it to your home screen and it opens full-screen, like a native app, online or offline.
Select the planned lens and its in-the-bag power, then set the optic-capture status for this eye.
Copy the corrected sulcus power. The delta and the constants used are shown so you can audit the number before you implant.
It depends on the planned power and the specific lens. The rule of 9s gives 0.5 to 1.5 D in steps, but a constant-aware calculation is more accurate, especially at the extremes of the power range.
It is strongly discouraged. Single-piece acrylic haptics can irritate the iris and cause UGH syndrome. A three-piece lens is the appropriate choice for sulcus fixation.
Yes. If the optic is captured in the bag or behind the rhexis, the lens sits near the planned position and needs little or no reduction. Full sulcus placement needs the full correction.
Implanting the power calculated for the capsular bag into the more anterior sulcus position, without reducing it, is the classic cause.
