Operation

Wavemaster^® IOL is based on a Shack-Hartmann wavefront sensor measurement system in infinite conjugate set up. Wavefront sensors measure aberrations which are introduced to a wavefront while passing through any kind of optical material, lens or objective.

In the infinite conjugate set up a point light source is placed in the focal plane of the sample under test. A telescope images the exit pupil of the sample under test onto the wavefront sensor. At the same time the image is magnified in order to use the full area of the wavefront sensor to guaranty highest spatial resolution.

System components

Wavefront sensor

The standard design of a Shack-Hartmann sensor mainly consists of a CCD camera which is placed in the focal plane of a microlens array. An incoming wavefront is sampled by the lenses of the microlens array and the foci form a spot pattern on the camera which would be evenly spaced in case of a plane wavefront. Any aberration introduced by the sample lens leads to a curvature of the wavefront thus resulting in small local wavefront tilts. These induce a measurable shift of each focus spot position. An integration of the obtained slope information allows for reconstruction of the wavefront profile with high accuracy.

Using state of the art computers this wavefront reconstruction can be done within the CCD camera frame rate i.e. within fractions of a second even if microlens arrays with a large number of lenses are used to obtain high spatial resolution.

Sample holder
The sample holder can be adapted to the requirements of the individual IOL measurement
task.

In-air measurement
Single IOL sample jigs which allow for a measurement of the lenses in air can be used with WaveMaster® IOL. The lenses are placed in the jig which is then inserted into the holder base of the instrument. Because of the high precision holder base no extended sample alignment is necessary. Due to the easy handling, lenses can be exchanged very quickly resulting in a high throughput

In-situ measurement
When in-situ measurements are required a model eye can be used. It fits into the high precision holder base of the instrument and is easily exchangeable with the single lens jigs.
The Model Eye has been designed to simulate the effect of the real human eye during measurements of IOL and is defined in the ISO 11979 standard.
It is composed of two parallel plates delimitating an area filled with saline solution. The IOL is placed at a specific position between these two plates on a sample holder including the aperture stop. An achromatic doublet simulates the eye cornea. The complete Model Eye is held at a constant temperature of 35°C.
The aperture size can be changed due to measurement requirements. By default it is Ø = 3mm.
The model cornea can be removed easily to allow for measurement of optical power of the IOL.

The WaveMaster^®IOL with sample holder for in-air measurements

The WaveMaster^®IOL with sample holder for in-situ measurements

High volume production testing

In case of testing in a high volume production environment the system can be factory configured with a tray system which allows for fully automatic measurement of a multitude of IOL. This tray system which contains a fully motorized high precision XY linear stage can be proposed for in-air as well as in-situ measurements including the Model Eye.

During the measurement an automatic classification of all IOL in different quality classes is done according to user defined pass fail criteria. A classification map is displayed at the end of each tray measurement allowing for an easy sorting of the lenses.

Light source

The point light source consists of a stabilized monochromatic laser light source with an absolute wavefront error < λ/15.
It is available with different wavelengths, numerical apertures and working distances. A kinematic mount allows for easy change.
The point light source is placed on an automatic high precision linear focusing stage.

Operating Principle

Optimized for simplicity in use and high accuracy WaveMaster^® IOL provides a fast and accurate tool for testing intraocular lenses in a research and development as well as in a production environment.

The wavefront is measured and analyzed with frame rates of up to 16 Hz and provides real time power map, -PSF and -MTF as well as analysis of the lower and higher order lens aberrations. In addition WaveMaster^® IOL also determines EFL and average Diopter power. Already during the measurement a real time comparison with design or reference data can
be performed.
Since simultaneous measurements of different
aperture diameters are possible the IOL can be analyzed at e.g. Ø = 3mm and Ø= 6mm at the same time without changing the instrument setup.

All measurements on IOL can be done in-air or in-situ. Hardware as well as software support
an easy and fast change between the different measurement conditions.
On the software side this is enabled by the possibility to save and load individual measurement settings files, on the hardware side by using the high precision sample holder. In addition alignment error compensation and automatic focusing allow for an easy and fast sample setup.
When measuring large numbers of the same type of IOL, statistic functions in the software are available.

Diopter and power map

The Diopter power of an IOL is defined as the reciprocal of the reduced paraxial focal length in aqueous humor. From the measured effective focal length of the IOL, the power can be determined directly when the measurement is made in situ.

When measuring in air the WaveMaster^® IOL software converts the Diopter power of the IOL for in situ conditions taking the design conversion factor of the lens into account. Measuring in air leads to easier handling of the lenses and fast throughput in production conditions for example when using a tray with several tens of IOL.
In the power map the local effective focal length for each point of the aperture of the IOL is displayed. It is directly deduced from the measured wavefront.

PSF und MTF

The Modulation Transfer Function (MTF) is a parameter describing objectively the performance of optical imaging systems by testing the ability of an optical system to transfer the details of an object to the image in terms of contrast. It has the value 1 for a perfect contrast reproduction and the value 0 for a system being unable to produce any image contrast.

PSF as well as MTF can be calculated directly from the measured wavefront and are displayed in real time.

Lens aberrations

The measured wavefront can be decomposed into a linear combination of polynomials of the Zernike- or the Seidel series which describe typical optical properties and errors of a lens as e.g. coma and astigmatism or spherical aberrations. This allows for real time measurement and comparison of lower and higher order lens aberrations of the IOL.

Software module for measuring MTF and PSF