A practical spreadsheet tool designed to help cataract surgeons calculate and monitor surgically induced astigmatism (SIA), record IOL selections, and track postoperative visual outcomes — all in one place.
SIA Calculator & Biometry
Track your surgically induced astigmatism and build your personal lens outcomes database
- Separate or combined analysis of right and left eyes, with filtering by incision location.
- Record IOL model, type and power alongside postoperative visual acuity for each case.
- No macros or scripts — hosted on Google Sheets, free to use for non-commercial purposes.
About the SIA Calculator
Most legacy SIA calculators rely on outdated Excel features no longer compatible with current software. The ASCRS calculator remains functional but is limited to corneal data only.
This spreadsheet was developed to address those gaps: it supports broader surgical and refractive outcome analysis, allows exclusion of cases with relevant ocular pathology or complications, and is continuously updated with new features.
Modern Intraocular Lenses
Current lens selection with updated classification according to the ESCRS European guidelines.
| Firm | Model | Optic type | Filter | Toric model exists? | Aberration | Comment |
|---|---|---|---|---|---|---|
| Hoya | Vivinex | monofocal (Partial RoF Narrow) | Transparent | NO | -0.22 | |
| Zeiss | 621 | monofocal (Partial RoF Narrow) | Transparent | NO | Negative | Behaves like monofocal plus |
| Ophtec | Precizon | monofocal (Partial RoF Narrow) | Transparent | Yes | 0 | |
| Johnson & Johnson | PCB00 | monofocal (Partial RoF Narrow) | Transparent | Yes | -0.27 | |
| Johnson & Johnson | Eyhance | monofocal plus (Partial RoF Enhance) | Transparent | Yes | -0.27 | Only powers >24 and high corneal aberration |
| Ophtec | Precizon Go | monofocal plus (Partial RoF Enhance) | Transparent | Yes | 0 | Only powers >24 |
| BVI | Isopure Serenity | Monofocal plus (Partial RoF Enhance) | Yellow | Yes | ? | Any power but corneal aberration >0.30 |
| Johnson & Johnson | PureSee | EDOF (Partial RoF Extend) | Transparent | Yes | -0.27 | |
| BVI | Finevision PODF | Trifocal (Full RoF Smooth Transition) | Transparent | Yes | -0.11 | |
| ZEISS | ELANA | Trifocal (Full RoF Continuous Transition) | Transparent | NO | 0 | |
| Johnson & Johnson | Odyssey | Trifocal (Full RoF Continuous Transition) | Transparent | Yes | -0.27 |
Sulcus lens calculation
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.
Rule of the 9s
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:
| Original IOL Power | Adjustment for sulcus IOL Power |
| < 9 dp | None |
| 9 to 18 dp | -0.5 dp |
| 18 to 27 dp | -1 dp |
| > 27 dp | -1.5 dp |
| Optics captured in bag and haptics in sulcus | None |
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.
Sulcus calculator
The rule of nines is a clear improvement over the older habit of simply subtracting 1 D from the planned power when moving a lens to the sulcus.¹ It still carries the same fundamental limitation, though: it is only an approximation. The reduction a sulcus lens needs is not a fixed step — it scales with the base power of the IOL, because shifting the optic anteriorly raises its effective power in proportion to that power. A single blanket rule cannot capture that relationship.
A more accurate approach is to start from the exact power planned for the capsular bag and apply the precise, power-specific correction for the anterior shift into the ciliary sulcus, instead of a rule of thumb. This is exactly what the Sulcus calculator in our app, Cataractools, does: it takes the planned in-the-bag power and returns the corresponding sulcus power from an optimized bag-to-sulcus correction table² — derived from the change in effective lens position — so the adjustment is tailored to each individual lens power rather than averaged across all of them.
Bibliography
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
Calculating Bag vs. Sulcus IOL Power. Dr. Hill.
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