Cataract surgery has been the most frequent surgical procedure for the last decades. Its primary goal was to restore the patient’s vision. Currently, the patient’s satisfaction and the restoration of the target refraction are of heightened interest. This leads to extensive research on more sophisticated lens surfaces which can eliminate even higher-order aberrations of the patient’s optical system. With the aim of maximal improvement of the patient’s visual performance, the latest developments focus on IOLs with customized freeform surface geometries which compensate corneal aberrations [
To our knowledge, there is no system available for scanning individual IOL surfaces. Currently, the quality inspection of conventional IOLs is done directly in the production chain by interferometry, deflectometry, or wavefront sensors. Interferometry devices compare signals from the sample’s surface and focus mainly on spherical surfaces. They are considered the golden standard for optical lens surface inspection. Their limited dynamic range, however, limits their application to basic lens geometries, such as rotationally symmetric or aspheric IOL surfaces. More complex surfaces require sophisticated measures to stay within their limited dynamic range [
In order to measure individual surfaces under sterile conditions, we introduce a new device for measuring individual IOL surface topographies: The WaveMaster Reflex UV (Trioptics, Wedel, Germany). Like its predecessors, the WaveMaster IOL and the WaveMaster Pro Reflex, it operates by a Shack-Hartmann sensor (SHS) setup [
The aim of this paper is to demonstrate the applicability of the new WaveMaster Reflex UV in the field of measuring individual IOL surface topographies.
The measurements were performed in a lab environment at a temperature of 22°C.
All measured IOLs are made from Contamac blanks [
The second group consists of six samples with surface geometries representing a superposition of higher-order aberrations: Zernike coefficients of coma, astigmatism, trefoil, and tetrafoil are added to a spherical surface with a base ROC of 11,5 mm to model higher-order aberrations [ Sample 1: Sample 2: Sample 3: Sample 4: Sample 5: Sample 6:
They are referred to as “higher-order samples.”
The third group holds two customized lenses derived from biometric patient data [
Alternatively, the surface can be described in matrix nomenclature by
The coefficients of the two surfaces under investigation are
Sample 1
Sample 2
This group is labelled “freeform samples.”
The WaveMaster Reflex UV is an SHS-based IOL topography scanner in reflection mode and measures the wavefront aberrations caused by the IOL front surface (Figure
Scheme of the beam path of the WaveMaster Reflex UV. The light is coupled into the left. It hits the beam splitter and is then imaged to the sample. The reflected part passes back through the beam splitter. It is imaged onto the SHS which detects the deviation from a purely spherical wavefront.
Figure
Scheme of the WaveMaster Reflex UV’s measurement positions. (a) Shows the CE position of the sample, (b) sketches the MP. The path difference along the optical axis corresponds to the sample’s best-fit ROC.
Screenshot of a measured residual of a toric sample. The residual shows a saddle-shaped pattern. An area of roughly 2.6 mm diameter was imaged. The device automatically calculates the RMS and P2V values on the top bar.
The device features the fitting of the measured residual to a Zernike composition, displaying the values of the respective Zernike coefficients [
The defocus term is used by the device as the criterion for acquiring the CE and MP positions along the optical axis. In those positions, it is required to be below lambda/10, that is, 37 nm.
The coefficients for tilt in the
Zernike coefficient decomposition: The software fits a Zernike function to the measured topography. It enables a coefficient analysis of the resulting Zernike fit. The values for each coefficient are listed as numbers or, in case of the above image, displayed by a bar graph. The coefficients for tilt in
The measured residual can be compared against a set of surface geometries such as spherical and aspherical, toric and user-defined freeform surfaces. The design topography is limited to the measured part of the surface to ensure comparability. The analysis screen consists of four panels (Figure
Residual comparison of the freeform surfaces. The upper half lists the results for the first surface, the lower half shows the comparison of the second freeform surface.
In the evaluation process, we record the following parameters: the sample’s best-fit ROC and its residual. The ROC serves as representation of its lower-order aberrations [
The residual evaluation consists of two parameters: the RMS and P2V values [
Let
The RMS and P2V values of spherical lenses are supposed to be zero. In case of nonspherical lenses, the measurement values have to match the corresponding values of the design data. As the RMS and P2V values represent averaged values of a measured residual, they serve to discern any major deviations between design and actual measurements. They do not reveal any information about the location of defects. This point is addressed by comparing the measured residual map against the design residual (see Figure
Table
ROC measurement of spherical surfaces.
Sample | Measured ROC/mm | Design ROC/mm | ROC Difference/µm |
---|---|---|---|
Sph 6 | 6.013 | 6.000 | 13 |
Sph 10 | 10.020 | 10.000 | 20 |
Sph 12 | 12.012 | 12.000 | 12 |
Sph 12.5 | 12.534 | 12.500 | 34 |
Sph 13 | 13.029 | 13.000 | 29 |
Sph 13.5 | 13.511 | 13.500 | 11 |
Sph 14.5 | 14.522 | 14.500 | 22 |
Sph 15 | 15.006 | 15.000 | 6 |
Sph 15.5 | 15.502 | 15.500 | 2 |
Sph 16 | 16.022 | 16.000 | 22 |
Sph 18 | 18.000 | 18.000 | 0 |
Sph 20 | 20.041 | 20.000 | 41 |
| |||
Average | 18 | ||
SDV | 12 |
The ROC measurements for the higher-order surface geometries are listed in Table
ROC measurements for higher-order samples.
Sample | Measured ROC/mm | Design ROC/mm | ROC Difference/µm |
---|---|---|---|
Ho 1 | 11.475 | 11.500 | 25 |
Ho 2 | 11.461 | 11.500 | 39 |
Ho 3 | 11.464 | 11.500 | 36 |
Ho 4 | 11.461 | 11.500 | 39 |
Ho 5 | 11.462 | 11.500 | 38 |
Ho 6 | 11.461 | 11.500 | 39 |
| |||
Average | 36 | ||
SDV | 5 |
Table
ROC measurements for freeform surface geometries.
Sample | Measured ROC/mm | Design ROC/mm | ROC Difference/µm |
---|---|---|---|
Freeform 1 | 6.551 | 6.210 | 341 |
Freeform 2 | 10.541 | 10.210 | 331 |
The values for the measured residual of the spherical surfaces are listed in Table
Residual analysis for spherical surfaces.
Sample | Measured RMS/µm | Measured P2V/µm |
---|---|---|
Sph 6 | 0.060 | 0.319 |
Sph 10 | 0.051 | 0.308 |
Sph 12 | 0.066 | 0.369 |
Sph 12.5 | 0.061 | 0.400 |
Sph 13 | 0.068 | 0.435 |
Sph 13.5 | 0.044 | 0.305 |
Sph 14.5 | 0.060 | 0.344 |
Sph 15 | 0.233 | 0.844 |
Sph 15.5 | 0.066 | 0.505 |
Sph 16 | 0.046 | 0.325 |
Sph 18 | 0.098 | 0.564 |
Sph 20 | 0.100 | 0.346 |
| ||
Average | 0.079 | 0.422 |
SDV | 0.049 | 0.149 |
Table
Residual analysis for higher-order surfaces.
Sample | Measurement | Design | Difference | |||
---|---|---|---|---|---|---|
RMS/µm | P2V/µm | RMS/µm | P2V/µm | RMS/nm | P2V/nm | |
Ho 1 | 0.114 | 0.533 | 0.034 | 0.263 | 80 | 270 |
Ho 2 | 0.251 | 1.353 | 0.143 | 1.125 | 108 | 228 |
Ho 3 | 0.333 | 2.279 | 0.255 | 1.938 | 78 | 341 |
Ho 4 | 0.166 | 0.883 | 0.046 | 0.306 | 120 | 577 |
Ho 5 | 0.151 | 0.943 | 0.096 | 0.641 | 55 | 302 |
Ho 6 | 0.263 | 1.617 | 0.124 | 0.845 | 139 | 772 |
| ||||||
Average | 0.097 | 0.415 | ||||
SDV | 0.099 | 0.439 |
The results for the residual analysis are found in Table
Residual analysis for freeform surface geometries.
Sample | Measurement | Design | Difference | |||
---|---|---|---|---|---|---|
RMS/µm | P2V/µm | RMS/µm | P2V/µm | RMS/nm | P2V/nm | |
Freeform 1 | 3.002 | 14.582 | 3.023 | 14.805 | 21 | 223 |
Freeform 2 | 1.750 | 9.880 | 1.681 | 9.603 | 69 | 277 |
The results for freeform surface 1 are shown in Figure
The graphical residual analysis for the second freeform surface is listed in Figure
The measurement of individual IOL surfaces by the wavefront analyser in the near-UV range is straightforward and accurate. Measurements on clinically available topographers revealed that there can be only a limited range of ROCs measureable by the device [
Measuring the RMS and P2V values of spherical surfaces shows the precision of the device. The values are well below 1
The measurements of individual freeform surfaces result in smaller values for the RMS and P2V differences than in the case for higher-order sample geometries.
Looking at the graphical analysis of the first freeform surface, the patterns for measurement and its design data closely match. The most critical deviations are located in the lower left part of the measurement area. We conclude that there is a slight decentration of the sample which results in the pattern seen in Figure
Although convex and concave lens surfaces can be measured by the WaveMaster Reflex UV, we limit this study to the measurement of biconvex IOL designs.
The WaveMaster Reflex UV represents a major advancement in the application of measuring individual IOL surfaces, which was impossible if the inspected IOL was required sterile for implantation. The operation in the near-UV range ensures the suppression of reflexes from the IOL back side without desterilizing the IOL. The device operates on a wide range of ROCs with smooth and nonpolished surfaces. The software’s capability of measuring and analysing in real time makes it applicable for quality testing in the field of freeform IOL production and manufacturing. Future measurements will show the limits of the device’s range in applicability.