The A-scan and IOLMaster both can help you to calculate what dioptric strength is required for a cataract patient’s intraocular lens. Last month we explained how to code for A-scans and also described the underlying technology. This month, we review use of the IOLMaster.

Billing for the IOLMaster
When billing for the IOLMaster, use CPT code 92136 Ophthalmic biometry by partial coherence interferometry with intraocular lens power calculation. (This code is in the Special Ophthalmological Services section of the CPT book.)

The technical component of this code is bilateral and the professional component is unilateral. So if you initially performed this service on the left eye, you would code 92136–LT. Payment would be for the global technical component and the professional component of the operated (left) eye. If, some time later, you performed the service on the right eye, you would code 92136–26–RT. (For more on billing, see March’s Savvy Coder at www.eyenetmagazine.org/archives.)

Power Calculations 101
Before implanting an IOL, the surgeon determines what IOL power is needed. A knowledge of how this is done provides billing staff with a firmer foundation when they tackle reimbursement.

In order to calculate the IOL power preoperatively, the surgeon needs to know the eye’s axial length, corneal curvature and anterior chamber length. Of these three parameters, an error in measurement of axial length is thought to be the largest contributor to a postop refractive error. If this refractive error is 2 D or more, the patient may need a second operation to exchange the IOL.

The most commonly used technology for measuring axial length is ultrasound employing an applanation technique (i.e., the ultrasound transducer is in contact with the corneal surface). The accuracy of standard ultrasound biometry techniques is estimated at 0.1 to 0.12 millimeters. In addition, errors in measurement may result if the transducer even slightly indents the surface of the eye. Based on the formulas used to calculate intraocular power, a 0.1-mm error in axial length will result in a 0.28-D refractive error.

The IOLMaster uses a noncontact technique that is reported to measure axial length more accurately in some situations than ultrasound biometry does.1 Other advantages include increased comfort for the patient, and easier measurement of axial eye length in patients with retinal detachment, silicone-filled eyes (e.g., after vitrectomy) or abnormally shaped eyes. The device uses a Doppler technique to measure the echo delay and intensity of infrared light reflected back from tissue interfaces. These measurements are used to calculate axial length.

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1 Connors et al. J Cataract Refract Surg 2002; 28:235–238.