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  Zeiss IOLMaster®
Online Users Instruction Manual V.4
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Axial Length (ALM) Cataract Surgery Arizona
Best Technique
Summary of Results
Interpretation of Signals
Signal Curves
Pseudophakic Eyes
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Dense Cataract
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IOLMaster — Axial Length Measurement.

IOLMaster axial length measurement

Activate Axial Length Measurement (ALM) Measurement Mode:

  • Click on the ALM icon, or
  • Press key A, or
  • Press the button on the joystick in Overview (OVW) mode.
IOLMaster axial length measurement   Switching to ALM mode will automatically change the magnification ratio: a smaller section of the eye becomes visible with the reflection of the alignment light and a vertical line (1, Fig. 27).
  • The patient should look at the red fixation point in the center. A cross-hair (3, Fig. 27) with a circle in the middle will appear on the display.
  • Fine-align the IOLMaster so that the reflection of the alignment light (2, Fig. 27) appears within the circle.


IOL Master warning

WARNING: Ask the patient if he or she sees the fixation point. If the patient fails to fixate properly, the visual axis will not be correctly detected, which may result in measuring errors.

In the case of poor visual acuity/high ametropia ( + 6 D) it is advisable to measure through the spectacles. If the procedure is followed correctly, no measuring errors will be produced. Measurements should not be taken while a patient is wearing contact lenses, as it will result in measuring errors.

  • Take the measurement by pressing the button on the joystick.

The corresponding display field next to the video image will show the measured axial length. The video image will be overlaid with a graph similar to those in ultrasonic measuring instruments. Simultaneously, the axial length and signal-to-noise ratio (SNR) of the measuring signal will be displayed. The SNR is a gauge of the quality of measurement. Measurements with an SNR between 1.6 and 1.9 appear with an exclamation mark (!) after the measured value and the message "Borderline value!" will appear. For evaluation of the SNR see Post-run editing of axial length measurements.

IOLMaster Arizona   Note
Borderline value! does not necessarily mean that the reading is incorrect and must be rejected. It rather means that all axial length measurements for the eye should be checked for plausibility and consistency, e.g. according to the usual ultrasonic biometry criteria. If the Uncertain values are determined to concur with the other readings, the readings marked Borderline value! should also be accepted as valid axial lengths.


IOLMaster Arizona   Note
The IOLMaster requires FIVE measurements to be taken. The message Measure again will thus appear. Only then will a mean value be passed on to the IOL calculation and an evaluation enabled. Only the number of measurements is crucial here. To obtain consistent results we recommend checking the individual axial length measurements and carrying out further measurements if necessary.

With stronger lens opacities, it may be advisable to defocus the IOLMaster. You may choose a reflection (2, Fig. 27) as large as the circle on the display. If measurements are even now impossible, the IOLMaster can be refocused and the reflection shifted to the bottom and/or top margin of the circle on the display by varying the vertical adjustment (turning joystick).

IOLMaster Arizona   Note
Defocusing and shifting the reflection within the circle will have no effect on the result, because interferometric axial length measurement is completely independent of distance.
  • For the next measurement of this eye, press the button in the joystick.
IOL Master warning

WARNING: Up to 20 such measurements per eye may be taken on a single day. Avoid measurements of eyes with retinal detachment. In such cases, measuring errors cannot be precluded.

As a rule, the axial length should be viewed together with the values for corneal refraction and overall refraction, and checked for plausibility. It is likewise helpful to compare the right and left eyes.

After the second measurement, the mean of the axial length measurements will also appear. This value will be recalculated and updated with each additional measurement. If the result of one measurement differs by more than 0.1 mm from the other(s), an Evaluation! message will be displayed. This indicates that the measurement results must be edited later. See Post-run editing of axial length measurements.

As long as Evaluation! is displayed in place of the mean value, the potential measuring errors must be deleted or adjusted, as the readings will otherwise not be adopted in the IOL calculation and the database for optimization of the constants. The last reading is always displayed with a blue background. The blue marking can be moved through the table of readings with the help of the cursor buttons ↑ ↓.

Error in the display field denotes readings with an SNR smaller than 1.6. Such individual readings are excluded from the generation of a mean value and do not need to be deleted.

The number of measurements of the respective eye taken on this particular day is displayed in the Mode field of the status bar next to ALM. If the count reaches 20, no further measurements of this eye can be taken on this day. The counter cannot be reset. Deleted readings (see above) do not affect the measurement counter.

IOLMaster axial length measurement

ALM Measurement of Non-Aphakic Eyes

To measure non-aphakic eyes, select the corresponding mode from the AL Settings menu. This special AL mode is displayed in the video image field and will be active until you reset it via the menu. The IOL Master will also be reset to Phakic mode if you change to the patient's other eye or a new patient.

If the axis length of eyes with phakic implants not listed in the additional AL functions is to be measured, the following compensation values according to Dr Wolfgang Haigis of Wurzburg University Clinic, Germany, should be used.

IOLMaster axial length measurement

IOLMaster axial length measurement  

Every implant, e.g. a phakic IOL, influences the measurement of axial length in PCI biometry.

If a phakic lens implant is measured in a normal phakic mode, the result will be slightly elevated.

The reading must be corrected, depending on the material used and the center. thickness.


IOL Master warning WARNING: Two peaks may appear when measuring pseudophakic eyes and with certain intraocular lenses. The first peak is a side maximum of the IOL, while the second peak is produced by the retina. In this case, manual correction is necessary (see Measuring errors with pseudophakic eyes). It is expedient to measure at a number of different points.

IOLMaster Arizona Note:
Only in ALM mode is the fixation light RED Cataract Surgery Arizona; otherwise it is always YELLOW Cataract Surgery Arizona

 

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East Valley Ophthalmology, Arizona's premier eye specialists, provides this on-line information for educational and communication purposes only and it should not be construed as personal medical advice. Information published on this website is not intended to replace, supplant, or augment a consultation with an eye care professional regarding the viewer/user's own medical care. East Valley Ophthalmology's disclaims any and all liability for injury or other damages that could result from use of the information obtained from this site. Please read our full Disclaimer