Zeiss IOLMaster

Optical Coherence BiometryThe Zeiss IOLMaster is a breakthrough in measurement technology and patient care.It is the first single instrument solution to precisely and quickly determine axial length, corneal curvature, and anterior chamber depth (ACD) without ever touching the cornea.

Optical Coherence BiometryThe increased measurement precision and postoperative refractive accuracy achieved with the IOLMaster translates into enhanced patient quality of vision and life.

Problems with Acoustical Biometry (ultrasound)InaccuracyHigh Technician VarianceMany error sources (subjective)Anesthetic requiredTime consumingTransmission of Infectious Agents

The New Standard The performance of the IOLMaster far exceeds that of Conventional Biometry in the following most important criteria:Accuracy and ObjectivitySpeed and Ease of UsePatient ConvenienceDoctor or Practice Convenience

AccuracyThe Axial Length Measurement error is smaller than ultrasound biometry because the IOLMaster always measures along the visual axis with proper patient fixation.The ultrasound biometry measurement may be off the visual axis from -3 to +8.When a staphyloma(elongated globe) is not coincident with the visual axis ultrasound biometry is measuring the off axis axial length erroneously. Staphylomas do not affect Axial Length results with the IOLMaster.Features / Benefits

Features / BenefitsAccuracy of the Axial length measurement with the IOLMaster is better than 0.05 mm and more around 0.03 mm. Ultrasound has at best an accuracy of 0.1mm and typically it is 0.12 to 0.20 mm. We are at least a factor of 2 upwards to about a factor of 5 times more accurate than typical ultrasound. The IOLMaster does not produce a corneal applanation error as seen in contact ultrasound biometry. This ultrasound corneal applanation error is a result of the subjective nature of ultrasound measurement. Technician error may produces shorter axial lengths of about 0.2mm which corresponds to an error in the postoperative refractive result by approximately -0.50D. The IOLMaster delivers reliable & repeatable readings independent of technician technique.

IOLMaster Repeatability AnalysisConducted at University of Mainz in Germany.Determined the reproducibility of measurements.Intra- and Inter-Observer Variability.

Intra-Observer Variability1 investigator measured on each of 10 eyes20 times Axial Length20 times ACD20 times Corneal CurvatureVariability found:AL .0256 mm (this corresponds to < 0.10D post-operatively)ACD .0334 mmKs .0129mmSignificance- negligible effects on the target refraction.

Inter-Observer Variability20 eyes measured by 5 investigatorsVariability found:AL .0215 mm (also < 0.10D)ACD .0298 mmKs .0159 mm

Optical Biometry is a highly precise and reliable measurement method that delivers results that are essentially independent of the investigator (technician).Conclusion

Ease of useNo corneal applanation/No pupil dilation. Operational under all lighting conditions.Measurement procedure learned very quicklyAutomatic R/L eye detection.Intuitive and familiar Windows interface.Option of data transfer or printout.Features / Benefits

Practice Efficiency and Patient Flow Three measurements on a single instrument reduces prep and exam time.Minimal operator training.Measure Axial Length, Corneal Curvature, and ACD on one eye in about 1 minute.Features / Benefits

Features / BenefitsPatient Safety and ComplianceNo anesthetic required.A quick and easy procedure.Non-contact technique precludes corneal lesions and transmission of infectious agents.

Mulitple user operationStorage of user related constants and defaults. Each doctor (at least ten) can input his or her own personalized lens constants for multiple lenses (about 20) in his or her own database.Features / Benefits

Data for IOL power calculationMeasurement data for determination of IOL power to implant:Axial Length - requiredCorneal Curvature - requiredAnterior Chamber Depth (ACD) - optional (formula specific)

Sources of Errors in IOL power calculationMeasurement inaccuracy of these parameters has been shown to contribute to deviations from target refractions by the following percentages:50% of the deviations are due to an Inaccurate Axial Length measurement30% of the deviations are due to an Inaccurate Corneal Curvature measurement20% of the deviations are due to an Inaccurate Anterior Chamber Depth measurement

SolutionThe Accuracy of the IOL Master combined with surgeon personalization of lens constants for use with this new measuring device minimizes these deviations from target refractions. This leads to less patient dependence on spectacles postoperatively and hence an increased quality of life (better visual outcome). Evaluation and Personalization of lens constants is critical for any device from which surgical technique is determined!

DescriptionThe IOL Master is a non-contact optical coherence biometry instrument which quickly and accurately measures the following parameters of the human eye:Axial Length(AL)Corneal Curvature(K)Anterior Chamber Depth(ACD)It is much, much more than a non-contact A-scan.

DescriptionThe Intraocular Lens (IOL) calculation window applies these measured parameters to one of five international IOL calculation formulas to offer the cataract surgeon with up to 4 IOL implant options with corresponding powers to reach the target refraction (desired postoperative refractive result).

Biometrical FormulasThe following empirical or geometric-optical formulas for IOL calculation are available in the IOL Master:Haigis (requires optical ACD measured value)Hoffer QHolladaySRK IISRK/T(Note: Holladay 2 is not available on the IOLMaster).

New Patient

New Patient Window TipsAlways enter date of birth as mm/dd/yyyy (the instrument will only recognize slashes / between the numbers).Double clicking on a patient name is the same as single clicking on it and then clicking on new. However, do not double click on a name unless you plan to take a measurement on that date because the instrument will create a file for that date as an exam date.To review a previous examination result: 1. type in a few letters of the patients last name in the search box. 2. Click on the small plus icon to the left of the patients name. 3. Double click on the desired exam date.

Screen Layout

Overview Mode

AL MeasurementPartial Coherence Interferometry(PCI)A semi diode laser emits light (780nm) of short coherence length that is split up into two beams in a Michelson Interferometer. Both beams illuminate the eye through a beam-splitting prism and reflect at both the cornea and retina. The light reflected from the cornea interferes with that reflected by the retina if the optical paths of both beams are equal.

AL Measurement PCI continuedThe interference is detected by a photodetector. The signals are amplified, filtered and recorded as a function of the position of the interferometer mirror(high accuracy). From this mirror the system determines the axial length as the path difference between the cornea and the retinal pigment epithelium (RPE).

Retinal Structures The axial length as measured with a ultrasound biometrical instrument is that distance from the cornea to the inner limiting membrane (ILM). Since the IOLMaster measures to the RPE it is important to know that the system internally takes into account the distance difference between the ILM and the RPE. Thus the displayed AL values with the IOLMaster are directly comparable to those measured acoustically using the immersion ultrasound technique.

AL Measurement Alignment

AL Measurement TipsInstruct the patient to look at the red fixation light.Note: in all other modes the fixation light is yellow. Take 5 measurements (maximum allowable is 20 / eye / day)If error measurements occur- keep trying! (20 chances)If unsuccessful: Vary the location of fixation light within green circular cross hair on display to find window of opportunity through the opacity.

AL Measurement TipsAfter each measurement a new average is usually displayed. When one or more measurements varies by >0.1mm from the mean no average will be displayed, but the word Evaluate! This alerts the operator to evaluate the AL measurement results(more later).

AL Measurement Tips

AL SetingsThe AL Settings may be selected for conversion to proper axial length for different eye types.May be selected before or any time after the measurement.The default setting after switching eyes is Phakic.

AL MeasurementTechnical DataMeasuring Range 14 - 39 mmAccuracy on Test Eye0.01mmDisplay Resolution0.01mmReproducibility on eye

K MeasurementAutokeratometer-The Corneal Curvature is determined by measuring the distance between 6 reflected IR light images. A CCD camera captures the image.Recommend blinking to replenish tear film to improve image quality.The displayed result is an average of 5 measurements taken within 0.5 seconds.

K MeasurementWith each new measurement the previous result is overwritten.For measurement errors as well as limitations (dry eye, corneal scarring) see Tips for keratometer measurement in users manual.

K MeasurementAlignment: Focus the 6 peripheral lights so that they are lying concentric between the two auxiliary circles on the display. The center point is used only for alignment and is usually dimmer and smaller than the peripheral lights.

K Measurement

K MeasurementIn the Options menu it is necessary under the Setup then Program Settings submenu to input the Refractive Index of the practice Keratometer(see owners manual). In the U.S. this value is typically 1.3375. This value is used to convert corneal radii into refractive powers(D).

K MeasurementTechnical Data (Human Eye) Measuring Range of Cornea 33-67D (5-10mm)Astigmatism Rangeup to 10DRepeatability0.02mmDisplay Resolution0.01mmDiameter of measuring area< 3.0 mm

ACD MeasurementThe ACD is determined as the distance between the optical sections of the cornea and the crystalline lens produced by lateral slit illumination of approximately 30 to the optical axis. Facilitated via a CCD Camera.The lateral slit illumination flickers during measurement and it always originates from the temporal field of the eye being measured.

ACD MeasurementWith each measurement 5 readings are taken and displayed along with their average on the monitor. After each measurement there is a 15 second processing time( have patient sit back to avoid excess illumination). The K Measurement must be done prior to the ACD Measurement. If K Readings were not possible with this instrument they must be entered manually prior to the ACD Measurement.

ACD Measurement Alignment1. Focus the fixation point image in screen rectangle by making it small with sharp borders . It should be near the optical section of the lens but not in it.2. The corneal optical section should not be disturbed by reflections3. The anterior crystalline lens is optimally visible.Note: Due to system design the corneal section is unclear. See handout Tips.

ACD Measurement

ACD MeasurementTechnical Data (Human Eye)Measuring Range1.5 to 6.5 mmDisplay Resolution 0.01 mmRepeatability 0.1 mm

Evaluation of AL MeasurementsThe IOL Master is capable of resolving fine structures on the fundus of the eye. Depending on the anatomical conditions of the measured eye, it may also happen that the measuring beam produces interference not only at the RPE but at the inner limiting membrane of the retina and/or at the choroid. Verification is necessary when multiple peaks are present and/or significant variance between results exists such that Evaluate! is present instead of an average value.

Evaluation of AL MeasurementThe results of AL measurements are to be interpreted on the basis of signal-to-noise ratio(SNR) and the appearance of the graphs.The SNR value is an indicator of the quality of the measurement.A SNR value < 2.0 may be due to:Strong ocular opacities, poor fixating patients, high refractive error( > 6D), pathological retinal changes. (Note: In some case of high refractive error, measurement through the patients spectacle lenses may be needed).

SNR ValuesIf SNR is > 2.0 then the measured value is validIf SNR is in the range 1.6 to 2.0 then the measured value is not reliable or borderline (!). It still may be usuable!If SNR is < 1.6 then the measured value is unusable (Error)

Evaluation of AL Measurement

AL Graph AnalysisThe measuring cursor (circle) is automatically placed on the center of the signal peak with the highest amplitude. By variance among measurement values in a series such that no average is present and Evaluate! is present, the graphs must be analyzed to determine if the signal peak is the true axial length( RPE ) or if another fundus structure has produced the highest peak (and hence the wrong axial length). To achieve this, one must zoom in on the graph. If a structure other than the RPE has the circle above it that result may be 1) deleted or 2) corrected by shifting the circle above the RPE (manipulation). When the cursor has been shifted the result will always have an asterisk* next to it to denote its manipulation. See users manual to learn how to shift cursor.

For optimal AL graph analysis use the zooming feature:Move the arrow cursor on the length axis (x-axis) to the position that should be in the center of the zoomed image.Press the left mouse button up to 4 times for sequential zooming.Press the right mouse button to return to original view of graph.

Triple peak

Double peak with RPE > ILM (Correct Axial Length Value)Distance between peaks is .15 to .35 mm.

Double peak with ILM > RPE (Incorrect Axial Length Value)AL value would be .15 to .35 mm shorter than other values from that eye. Delete reading or move cursor to RPE (manipulate).

Triple peak ILM, RPE, Choroid (Incorrect Axial Length Value)

IOL Calculation

IOL Database

Clinical EvaluationThe following specialists have overwhelmingly endorsed the IOLMaster:Dr. Holladay (Houston, TX)Dr. Wallace (Alexandria, LA)Dr. Hoffer (Santa Monica, CA)Dr. Haigis (Germany)Dr. Fine (Eugene, OR)Dr. Gills (Tarpon Springs, FL)

LimitationsHaigis showed that between 5-10% of patients are not measurable with the IOL Master. tremor or poor fixating patientssignificant ocular opacities (scars, vitreous hemorrhages, dense nuclear or posterior subcapsular cataracts )Corneal ablationsVisual Acuity alone is not predictive of measurement capability. Better said: 90-95% of patients will have a more precise postoperative refractive result because of the accuracy and ease of use of the IOLMaster. Practice efficiency will be greatly improved using the IOLMaster.

Zeiss IOLMaster William P. Burnham, O.D.