Reducing Photic Phenomena and Retinal Background Illumination by Using an Intraocular Lens
Background. After implantation of monofocal intraocular lenses (IOLs), the risk of developing light phenomena is 9%, and after implantation of multifocal IOLs the one is 41%. These effects not only cause discomfort, but also poor image quality. The existing IOLs have a number of deficiencies that cause different types of photic phenomena.
Objective. The aim of the work is optical calculation and simulation of the parameters that an IOL should have in order to reduce photic phenomena and retinal background illumination while increasing the transmission contrast. We also are aimed to design a new IOL on the basis of the results obtained.
Methods. To calculate the reflected rays, we used the Snell–Descartes law, according to which we obtained the value of the critical angle for a hydrophobic acrylic IOL with the refractive index of 1.55 at the wavelength of λ = 0.55 μm. This is consistent with aqueous humor, the refractive index of which is 1.33. The calculation of the transmitted light loss was determined by Fresnel reflection coefficient. We handled with optical system in which the aperture diaphragm fulfilled the role of a pupil. Using the Zemax 13 software environment, we simulated ray path for a human eye, the sagittal axis of which is 28 mm at different height of IOL placement. We applied the results obtained to design a new IOL in the SolidWorks environment.
Results. The calculations made it possible to identify the shortcomings of modern IOLs and methods for their elimination. It was found that in order to reduce the risk of photic phenomena and, as a result, of increasing luminous transmission, an IOL should be placed at a distance of at least 4 mm from the iris. It should contain two or more optical layers, the refractive index of which changes towards the center of the lens, and have the surface roughness of 35 nm. Based on the calculations, we carried out simulation in the Zemax 13 environment, which confirmed their veracity. When simulated with these parameters, the standard deviation of an image fell completely within the Airy disk, which has a size of 3.598 μm with an image size of 2.972 μm. Thus, the optical system is considered diffraction limited and no further optical optimizations are possible. Using the Solidworks software and the results obtained, we proposed the proprietary IOL model called "NVision OP". This IOL has an optical part thickness of 1 mm with a diameter of 5 mm. In general, the hollow, volume-replacing IOL with a coating has a diameter of 10 mm and a thickness of 5 mm, the thickness of the coating is 150 μm.Conclusions. The study revealed a number of factors that require improvement and elimination to prevent the occurrence of various types of photic effects. These include: lens surface roughness, IOL refractive power, shape, lens edge thickness, depth of IOL implantation into an eye, phacodonesis and lens displacement, aperture diaphragm diameter. After data optimization, according to the calculated results, we carried out the simulation in the Zemax 13 and Solidworks environments. On the basis of this simulation we proposed the model of an intraocular lens "NVision OP"; the photic effects namely arcs, flare, flashes, glare and halo are eliminated as much as possible. The hollow, volume-replacing IOL "NVision OP" has elements on its coat that allow to use the suture fixation, which prevents the dislocation of the IOL. For the implantation of the proposed IOL "NVision OP", it is recommended to use a viscoelastic and the Alcon injector with the cartridge B. Due to the fact that the shape of the IOL corresponds to the native human lens, the lens is located in the place of the phacoemulsified substance, and the implantation does not take much time.
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