Cataract surgery patients today are increasingly interested in reducing their dependence on spectacles across a full range of vision. Created using optical principles and knowledge of ocular physiology, the Liberty trifocal (677MY / 677MTY) presbyopia-correcting trifocal IOL from Medicontur was engineered to meet the functional needs of the modern cataract surgery patient population and optimise the quality of vision.
Revolutionary Optical Design (EPS)
The Liberty trifocal IOL is distinguished from other commercially available trifocal IOLs by unique features in its optic which is equally utilised on the 1stQ AddOn® IOL designed for placement in the sulcus. Both lenses make use of Medicontur’s proprietary, patented Elevated Phase Shift (EPS) technology – a novel optical concept for trifocal performance and efficient light energy utilisation. A brief review of visual optics is helpful for understanding the performance and benefits of this optical design and how EPS compares with other trifocal technologies, said Alexandra Kontur MD, PhD, Scientific Director, Medicontur.
Light Propagation – Diffraction
The optics of multifocal IOLs (MIOLs) are based on a diffractive paradigm that takes advantage of the wave nature of light. A wavefront of the light consists of waves that have the same amplitude in their crest and trough. Diffraction describes the physical phenomenon that occurs when a wavefront meets an obstacle (surface). When a wavefront encounters an obstacle, it changes its waveform. As waves emanate through, the waves can overlap, causing their amplitude to change, becoming equal to the sum of the amplitudes of the individual waves. The overlapping waves can reinforce each other (Fig. 1a), which is known as constructive interference, or cancel each other out, which is known as destructive interference (Fig. 1b).
"Through EPS we are able to create a third focal point for an intermediate peak with only seven rings within the central 3mm of the optic, leaving 75% of the lens surface as refractive."
Tuning Light Interference
Diffractive optics modify the interference of light, but the level of light interference depends on the design of the diffractive structure. Every lens manufacturer has the same amount of light to play with. When developing a diffractive MIOL, it is the job of the optical physicist to tune the light interferences that are generated by the diffractive design in order to achieve the desired optical properties while also using the incoming light as efficiently and effectively as possible so as to optimise visual function and minimise compromises. “With those goals in mind and based on our knowledge of ocular physiology, at Medicontur we took a very conservative approach to design a trifocal IOL,” said László Kontur, MD, CEO, Medicontur. “By using the proprietary Elevated Phase Shift (EPS) technology that causes constructive interference at the wavefront arriving at the intermediate region, we can use only one diffractive array to create two additional diffractive focal points (Fig.2). In contrast, other trifocal IOLs generate an intermediate focus by combining two bifocal diffractive profiles on a single surface or by using a trifocal diffractive profile combined with a bifocal diffractive array.” Through EPS we are able to create a third focal point for an intermediate peak with only seven rings within the central 3mm of the optic, leaving 75% of the lens surface as refractive.
|A. Constructive interference||B. Destructive interference|