In a recent study published in Optics Communications, scientists from Bar-Ilan University in Israel have presented a new technique that significantly reduces the halo effect that is generated when using multifocal (contact and intra-ocular) lenses and looking at bright point sources in dark conditions.
Presbyopia is a result of natural aging and stems from a gradual thickening and decrease in elasticity of the lens inside the eye. Corrective lenses used to address presbyopia often lead to a halo effect. This is basically a glow or color light pattern observed when looking at a bright source of light in front of a dark background. It is mostly experienced at night when people see halos around street lamps and car headlights, and it can make driving at night unsafe or even impossible in extreme cases.
Co-author of the paper, Prof. Zeev Zalevsky, head of the Electro-Optics study program of the Faculty of Engineering at Bar-Ilan, explains, “Our solution involves smoothening the surface structure of a contact lens or an intra-ocular lens that has extended depth of focus or multifocal capabilities. The smoothening does not complicate the fabrication complexity of the lens and yet yields the same optical performance in treating presbyopia and assisting people after cataract surgery, but with about one order of magnitude smaller. This allows people that use such lenses to be able to use them also at night.”
More and more commercial ophthalmic products incorporate EDOF (extended depth of focus) and multifocal technologies in contact and intra-ocular lenses to solve presbyopia. Until now, such lenses were very problematic when used in dark illumination conditions. The researchers say their proposed concept can resolve the above difficulties and make the existing products even more applicable and useful.
Ophthalmic halo reduced lenses design
The halo effect is a very problematic visual artifact occurring in extended depth of focus or multi-focal ophthalmic lenses such as e.g. intra-ocular (after cataract surgery) or contact lenses when used in dark illumination conditions. This artifact is generated due to surface structures added on top of those lenses in order to increase their depth of focus or to realize multiple focal lengths. In this paper we present novel solution that can resolve this major problem of ophthalmic lenses. The proposed solution involves modification to the surface structure that realizes the extended depth of focus. Our solution is fabricated and numerically and experimentally validated also in preliminary in-vivo trials.
Halo effects are known as a glow or color light pattern that can be best observed when looking at a bright source in front of a dark background, for example a broad spot of light seen around a street light in the dark. This optical phenomenon is mainly caused by interaction of light with matter, and is enhanced due to diffraction of light when interacting with the eye, e.g. passing through the eye pupil, eye tissue, or any other diffraction of light caused by sharp edges or artificial diffraction structures, such as those added to intraocular lens.
Techniques aimed at reducing the halo effects in lenses have been developed. For example, Ref. discloses ophthalmic lenses, e.g. intraocular, contact and corneal implant lenses having multifocal characteristics which provide beneficial reductions in at least the perception of one or more night time visual symptoms such as “halos”, and “glare or flare”.
In this paper we propose an improved and novel approach based upon smoothening of the structures generated on the surface of the ophthalmic lens (e.g. in the case of extended depth of focus imaging in a very specific way that significantly reduces the residual halo artifacts.
“Ophthalmic halo reduced lenses design” by Ofer Limon and Zeev Zalevsky (doi:10.1016/j.optcom.2014.12.049). The article appears in Optics Communications, Volume 342, 1 May 2015, Pages 253-258 published by Elsevier.
The article is freely available until 31 Dec 2015 and is available at: http://www.sciencedirect.com/science/article/pii/S0030401814012139
About Optics Communications
Optics Communications invites original and timely contributions containing new results in various fields of optics and photonics. The journal considers theoretical and experimental research in areas ranging from the fundamental properties of light to technological applications. Topics covered include classical and quantum optics, optical physics and light-matter interactions, lasers, imaging, guided-wave optics and optical information processing. http://www.journals.elsevier.com/optics-communications/
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