Modern lens surgery?cataract as well as lenticular refractive?is a process that can be described in just three words: control, control, and control. A significant component of improved surgical control is predictability of the refractive outcome; this has considerably improved since the introduction of partial optical coherence interferometry for axial length measurements, as developed by Adolf Friedrich Fercher, PhD, of the Vienna group.1
We were happy to acquire one of the first versions of the IOLMaster (Carl Zeiss Meditec AG, Jena, Germany), and we noticed a significant improvement in our refractive results as compared with ultrasound.2 It is beyond doubt that the potential accuracy of optical biometry is greater than that of ultrasound, considering the (1) much higher spatial resolution of light as compared with the ultrasound, (2) no-touch technique of optical measurement as compared with the possibility of compressing the eye during ultrasound, and (3) improved coaxial conditions offered by optical biometry, ensuring that the measurements are along the line of sight. This is especially important in myopic eyes with any degree of staphylomas or rotational nonsymmetry.
One drawback of optical biometry is that not every patient can be measured with this technique, as optical measurements depend on light transmission through the media of the eye. This is problematic in dense cataracts, and the first IOLMaster versions had difficulty measuring the subcapsular types of cataract. However, the latest IOLMaster software (version 5) uses an advanced technology that allows detection of signals in previously immeasurable patients, including those with more dense cataracts and subcapsular types. The technology uses a composite technique by which is it possible to automatically integrate several separate measurements, thereby increasing the signal-to-noise ratio (SNR) by several orders of magnitude.
CLINICAL RESULTS
Based on the first 620 measurements performed with the IOLMaster (version 5), the success rate (ie, percentage of patients in which a valid measurement can be obtained) has increased from approximately 80% to 92% (Figure 1), thereby significantly decreasing the necessity of ultrasound for the measurement of axial length. The higher success rate was seen in all grades of cataract, but it was especially apparent in patients with more dense cataracts (Figure 2). Of particular interest was the high percentage of patients with subcapsular cataracts who could be measured with the new technology (Figure 3).
The average SNR was increased 20-fold over that of the previous IOLMaster version. This improved signal quality was of particular importance in patients with dense cataracts and/or low visual acuity, as it increased the performance of the instrument in these groups (Figure 4).
CONCLUSIONS
The improved quality of the SNR with the latest IOLMaster software (version 5) has made it possible to measure even dense cataracts with optical biometry. With this tool, an accurate biometry can be performed in a higher percentage of patients, increasing the accuracy of their refractive outcomes. The improved clinical performance and ease of operation make the Zeiss IOLMaster the leading biometric device for refractive lenticular surgery.
Depending on the IOL power calculation formula a surgeon uses, the IOLMaster may minimize the need for ultrasound in a majority of patients. If the Holladay II or the Olsen formula are used,3 the lens thickness does play a role in predicting the postoperative position of the implant,4 and therefore, an ultrasound biometry is still needed for every patient. The lens thickness is on my wish list for the next version of the IOLMaster.
In addition to improved feasibility of axial length measurements, the newer versions of the Zeiss IOLMaster have improved the keratometry procedure with automated readings and traffic light indications for good/bad measurements. This feature has added to the safety of the keratometry measurements. We are in the process of evaluating this new keratometry option in a prospective series.
Thomas Olsen, MD, is Professor of Ophthalmology at the University Eye Clinic, Aarhus Hospital, in Denmark. Dr. Olsen states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +45 89 493 228; fax: +45 86 121 653; or tkolsen@dadlnet.dk.
