Let's continue introducing our followers with the UL SPIE Students chapter members and their everyday lab researches. Dr.phys. Varis Karitans is working at the Institute of Solid State Physics, Department of Ferroelectrics, Laboratory of Visual Perception and Department of Optometry and Vision Science, University of Latvia. He is one of our UL SPIE Student chapter's honorary members who had been an UL SPIE member more than 10 years already. Now, he is working on a project of a model eye incorporating a manually tunable polymer lens.
|UL SPIE member and researcher Varis Karitans|
Many mathematical model eyes (Gullstrand, Helmholtz-Laurance, Emsley, Schwiegerling, Liou and Brennan model eyes and others)) have been proposed. However, there are very few real model eyes which can be mounted in an optical setup for practical applications.
A cross-section of the model eye is shown schematically in Figure 1. The cornea was simulated by a +45 D lens. The front surface was convex while the back surface was plane. Thickness of the cornea was 2 mm. The cornea was followed by the anterior chamber of depth 3 mm.
|Fig.1. The cross-section of the model eye|
Instead of being filled by the aqueous humour the anterior chamber was simply an air gap. Behind the anterior chamber the intraocular lens was located. The intraocular lens was simulated by a manually tunable lens ML-20-35-NIR-HR. The tuning range of the optical power of the manually tunable lens (from -25 D to +30 D)) overlap with that of the ocular lens in a living eye The vitreous humour consisted of both an air gap and water slab with boundaries made of glass plates. The air gap was about 5.5 mm wide while the total length of the vitreous humour was 12 mm. The sensor of CCD camera OpticStar DS-335C ICE simulated the retina.
The primary principal plane H1 was located about 0.9 mm behind the cornea while the secondary principal plane H2 was located about 3 mm in front of the cornea. The distance between the principal planes and the corresponding nodal planes HN was about 9 mm. The primary focal length f1=-18.6 mm, the secondary focal length f2=27.5 mm. Figure 2 shows Zernike aberrations of the model eye.
|Fig.2. Zernike aberrations of the model eye|
The amount of aberrations is consistent with that measured in a large population. Increased levels of both coma-x and coma-y can be observed. This may be due to the liquid polymer lens the shape of which has distorted slightly resulting in coma aberrations. As expected, the spherical aberration has the largest magnitude from all types of higher-order aberrations.
It can be concluded that the optical properties of the designed model eye are close to those of a real eye and thus this model eye can be used to simulate human vision in physiological optics and vision science.