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Göteborgs universitets publikationer

Light scatter and wavefront aberrations in the human eye

Författare och institution:
Jörgen Thaung (Institutionen för neurovetenskap och fysiologi, sektionen för klinisk neurovetenskap och rehabilitering)
Publicerad i:
IMPROVE International Symposium - IMPROving the Visual Environment for all, 22-23 May 2014 Lund, Sweden, s. 20-21
Konferensbidrag, övrigt
Sammanfattning (abstract):
Like all other optical systems, the human eye is limited by diffraction, optical aberrations and light scattering. Diffraction can be described by diffraction theory and is the fundamental limitation of any optical system. At small pupil sizes the retinal image quality is mainly limited by diffraction. Optical aberrations are errors that concern the focusing capability of an optical system. When aberrations are present focus spots will be spread out and the image quality degraded. Optical aberrations can be both chromatic and monochromatic, and both are present in the human eye. Opposite to the effects from diffraction, aberrations usually increase with pupil size. Light scatter in an optical system causes a reduction of image contrast due to a superimposed veil of light. Depending on the size of the scattering particles, the angular distribution of the veil will be different. Small particles will scatter in large angles, and large particles in narrow angles. Angular distribution in the human eye is fairly constant (inverse square of angle) but the number of particles increases with age. ! 20! ! In young normal eyes less than 10% of the light entering the pupil is scattered by the cornea and the lens. The light scattering increases exponentially with age, and in individuals with diagnosed cataract the amount of light scattering can be very high. One problem with diagnosing cataract is that light scattering has small impact on visual acuity. It is instead image contrast that is reduced and consequently it is retinal contrast sensitivity that should be tested. Preferably, tested with and without a glare source in the visual field [1]. Scattering is also one of the most important causes of glare complaints. To demonstrate the problems with degraded vision due to ocular aberrations and scattering our research group is working on a simulation system (VISSLA) that can visualize retinal image quality. Individual ocular aberration data and estimates of light scattering are calculated and applied on pixel-based images from digital cameras or CAD models. Besides the visualization capabilities, the underlying image data can be further explored by using embedded tools to measure the reduction in image contrast, e.g. to demonstrate the effect of inappropriate lighting designs. Our system, with a simplified eye model, has been validated in a feasibility study [2] and we have recently adopted the CIE standard glare observer model for more accurate simulations. Today there are no tools to ensure that lighting meets the requirements for people with visual impairments. Lighting designers must instead rely on their own experience. We are working close with architects and lighting designers to explore if our tool can be successful in creating visual environments better suited for people with normal ageing and ocular diseases (c.f. Fig). [1] Paulsson L-E, Sjostrand J. (1980) Contrast sensitivity in the presence of a glare light. Invest Ophthalmol Vis Sci.. 19:401-406. [2] Thaung J, Billger M, Löfving B and Sperling K. (2012) ”Visualization tool for increased quality of vision”, Proceedings ARCH12, Perspectives on Nordic Healthcare environments, Gothenburg 2012.
Ämne (baseras på Högskoleverkets indelning av forskningsämnen):
Fysik ->
Atom- och molekylfysik och optik ->
Medicinska grundvetenskaper ->
Neurovetenskaper ->
light scattering, glare, wavefront aberrations, retinal imaging
Postens nummer:
Posten skapad:
2015-10-21 15:24
Posten ändrad:
2015-11-12 14:10

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