CCC.2 Intraocular Lens Calculations Introduction
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## CCC.2 Intraocular Lens Calculations Introduction

Axial measurements devices and software on other systems perform intraocular lens power calculations for cataract surgery patients. The power selection of intraocular lens to place in a patient's eye determines the refractive correction (e.g., glasses, contact lenses, etc.) the patient will require after cataract surgery.

The data input for these calculations consists of ophthalmic axial length measurements (one dimensional ultrasound scans that are called "A-scans" in the eye care domain) and keratometry (corneal curvature) measurements in addition to constants and sometimes others kinds of measurements. The data may come from measurements performed by the device, on which the intraocular lens calculation software resides, or from manual data entry, or from an external source. There are a number of different formulas and constants available for doing these calculations. The selection of formula to use is based on clinician preference and on patient factors such as the axial length of the eye. The most commonly used constants, encoded by Concept Name Code Sequence (0040,A043) using CID 4237 “Lens Constant Type”, are a function of the model of intraocular lens to be used.

The most commonly used formulas, encoded by IOL Formula Code Sequence (0022,1029) using CID 4236 “IOL Calculation Formula”, for intraocular lens calculation are inaccurate in a patient who has had refractive surgery, and numerous other formulas are available for these patients. Since most of them have not been validated to date, they were not included in this document.

Intraocular lens calculation software typically provides tabular displays of intraocular lens power in association with each lens's predicted refractive error (e.g., glasses, contact lenses, etc).

Figure CCC.2-1. Sagittal Diagram of Eye Anatomy (when the lens turns opaque it is called a cataract)

Courtesy; National Eye Institute, National Institutes of Health; ftp://ftp.nei.nih.gov/eyean/eye_72.tif

Figure CCC.2-2. Eye with a cataract

Courtesy; National Eye Institute, National Institutes of Health; ftp://ftp.nei.nih.gov/eyedis/EDA13_72.tif

Figure CCC.2-3. Eye with Synthetic Intraocular Lens Placed After Removal of Cataract

This file is licensed under the Creative Commons Attribution Share Alike 2.5 License, Author is Rakesh Ahuja, MD (http://en.wikipedia.org/wiki/Image:Posterior_capsular_opacification_on_retroillumination.jpg)

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