# CAS_Calc — Castrop IOL power calculation > Castrop IOL power calculation (iPhone/iPad app by Peter Hoffmann.) - Source: https://appshunter.io/ios/app/cas-calc/id6798420368 (this page in markdown: same URL + `.md`) - Developer: [Peter Hoffmann](https://appshunter.io/developer/6797644932) - Category: Education - Price: Free - Age rating: 4+ - Requires: iOS 16.6 · 15 MB - Languages: American English - Released: 2026-08-23 - Data updated: 2026-10-01 - User reviews in markdown: https://appshunter.io/ios/app/cas-calc/id6798420368/reviews.md ## What is CAS_Calc? CAS IOL Calc calculates the power of an intraocular lens. It is written for ophthalmic surgeons performing cataract surgery, and for anyone working with ocular biometry. FOUR ENGINES, SIDE BY SIDE • CAS Rx — the engine for routine work. Gaussian optics with a thick corneal model; the machine-learned part is the effective lens position and nothing else. Toric, suitable for all eyes. • CAS classic — the original Castrop formula with the C/H/R constant triplet. It calculates what the web version at iolcon.org calculates. • CAS AI — pure machine learning without any optical calculation, a feasibility study and a cross-check. Spherical only, with hard limits. • SRK/T — the 1990 formula, included as a yardstick because the comparison has been asked for repeatedly. We do not recommend it for clinical use. Where the four diverge, that divergence is information in itself. TWO MODES • Simple — one eye, the short form, the result directly below it. The corneal refinements sit behind a switch. • Full — both eyes in turn, with side comparison, a note field, QR import and a printable calculation sheet: one A4 page, both eyes side by side, with the inputs, the constant footing, the power table, the axis sketch, every note and the scope and limitations of the engine. FOUR MODULES The menu "Module" under the title switches between four calculation paths; the case in the main calculation stays as it is. • IOL calculation — the routine case, the lens in the capsular bag. • Add-on IOL — the supplementary lens in front of a lens already implanted, from the refraction and the pseudophakic anterior chamber depth. • IOL exchange — the replacement lens for a pseudophakic eye; the cylinder comes from the refraction, the radii run alongside as a cross-check. • Secondary implantation — the eye without capsular support, with the lens position set by hand. Each module has its own inputs, its own note field and its own printable sheet. WHAT THE APP DOES • Toric calculation with axis rose, misalignment and residual refraction • Result table with spherical equivalent and the whole lens (sph/cyl) • Refined cornea: posterior surface, thickness, tomographic cylinder • Corneal spherical aberration, derived from the radii and the asphericity (Q or e) and calibrated to the CASIA2 • Post-refractive corneas via funny cornea and the posterior radius • Read biometry from the QR code on the device printout, through the camera or from an image or PDF; the code format is documented at https://iolcon.org/download/LPCM_QR-Import.pdf • Warnings instead of silent extrapolation: percentile limits on every field, eye rarity score, side comparison of the pair, a note when keratometric and tomographic cylinder diverge • Lens catalogue with optimised constants; unknown lenses via the A constant • Full manual inside the app, in three languages • German, English, Italian PRIVACY Everything is calculated on the device. No account, no sign-in, no network connection, no data collection. There are no fields for a name or a date of birth. The report carries no patient identifier, and nothing entered survives closing the app. IMPORTANT CAS IOL Calc is not a medical device. It is for investigational use. Every clinical decision remains with the treating physician. The models were trained on IOLMaster 700 measurements; for other biometers a slight loss of accuracy cannot be excluded. The limitations of each engine are shown permanently in the result panel, on the printout and in detail in the manual. The basis is the Castrop formula: Langenbucher A, Szentmáry N, Cayless A, Weisensee J, Wendelstein J, Hoffmann P. Considerations on the Castrop formula for calculation of intraocular lens power. PLoS One 2021;16(6):e0252102. ## Version history (last 4 releases) ### 2.31 — 2026-09-22 Version 2.31 adds three further calculation paths — modules of their own, beside the familiar calculation for the capsular bag. NEW: THE MODULE MENU Under the title there is now a menu, "Module". It opens on the usual IOL calculation, and the case there stays as it is while you switch. • Add-on IOL — the supplementary lens in front of a lens already implanted, from the refraction and the pseudophakic anterior chamber depth, toric with axis. • IOL exchange — the replacement lens for an eye that is already pseudophakic. The cylinder comes from the refraction, meridian by meridian; the radii run alongside as a cross-check and speak up from 0.50 D vector difference. • Secondary implantation — the eye without capsular support: the lens position is set by hand instead of predicted. Two anterior segment OCT images show how it is read off. SRK/T with the manufacturer's A constant stands beside it, expressly as a last resort only. Each module has its own inputs, its own "Remarks/surgeon" field and its own printable sheet. "Take from the case" fetches the corneal values from the eye currently open. ALSO • Lenses everywhere in ISO 11979 notation: spherical equivalent and cylinder without a sign • The power table now carries the sphere of the minus-cylinder notation beside the spherical equivalent • Toric calculation with a freely entered lens as well, through a field for the cylinder used • Axial length correction of CAS classic selectable: Hoffmann 2, Cooke or off • A new warning as soon as a measurement reaches the edge of the training range, with a prompt to recalculate the case without ML • CAS Rx: with the lens position set by hand, anterior chamber depth and lens thickness are no longer required fields • "Account for tilt" keeps chord µ and angle α when switched off; the direction now runs over the full 360° • Required fields outlined alike in every module • Manuals in all three languages extended by the chapter "The additional modules" ### 2.2 — 2026-09-08 Version 2.2 brings the report to the App Store — and takes the patient data out. NEW: FULL MODE • Both eyes in turn, with a side comparison of the differences between them • A printable calculation sheet, one A4 page, both eyes side by side • Read biometry from the QR code on the device printout — through the camera or from an image or PDF • A free-text field for the surgeon and any peculiarity of the case NO PATIENT DATA The fields for name and date of birth are gone for good. The app holds nothing that names a person; the sheet carries no patient identifier, and the PDF file name is made of date and time alone. Anyone who has to tie the printout to a person writes the name on it. ALSO • In simple mode the corneal refinements sit behind a switch; switching it off clears the fields, so nothing goes on calculating out of sight • Lens catalogue: the B&L MX60(E) also with a 0.90 D cylinder • Manuals revised in all three languages ### 2.0 — 2026-09-05 Version 2.0 doubles the number of engines and opens up the cornea. NEW: TWO MORE ENGINES • CAS classic — the original Castrop formula with the C/H/R triplet, separate anterior and posterior surfaces and surgically induced astigmatism. Calculates as the web version at iolcon.org does. • SRK/T — included as a yardstick, not as a recommendation. The note to that effect stays under the selector. NEW AT THE CORNEA • Asphericity, entered as either Q or e, behind its own switch because it is meant for advanced users • Corneal spherical aberration, calibrated to the CASIA2 • A warning when keratometric and tomographic cylinder diverge vectorially by more than 0.75 D • A note under the funny cornea switch stating what it assumes NEW IN THE WARNINGS • Soft percentile limits on the input fields, amber alongside the hard limits, against a reference set of 47,408 eyes • Eye rarity score: how unusual the measurements are taken together CHANGED • The result table shows the spherical equivalent, as the ISO standard reports it, and the whole lens as sph/cyl in the first column • The manuals have been revised and are bundled in all three languages ### 1.5 — 2026-08-23 No release notes. ## Apps similar to CAS_Calc | App | Rating | Price | Category | | --- | --- | --- | --- | | [DOC 2026](https://appshunter.io/ios/app/doc-2026/id6763319522) | — | Free | Education | | [DOG Kongress 2025](https://appshunter.io/ios/app/dog-kongress-2025/id6745271664) | — | Free | Education | | [IOLEvidence (Qvision Academy)](https://appshunter.io/ios/app/iolevidence-qvision-academy/id1661456887) | 4.7 (7) | Free | Education | | [I Courses Academy](https://appshunter.io/ios/app/i-courses-academy/id6474273380) | — | Free | Education | | [Pupil Wizard](https://appshunter.io/ios/app/pupil-wizard/id6742019257) | — | Free | Education | | [Masjide Noorul Islam Blackburn](https://appshunter.io/ios/app/masjide-noorul-islam-blackburn/id1513163078) | — | Free | Education | ## More apps by Peter Hoffmann - [ToricTrouble](https://appshunter.io/ios/app/torictrouble/id6800201189) All apps by Peter Hoffmann: https://appshunter.io/developer/6797644932 --- *Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-10-01.*