Research Seminars 2009/10
Vision Science and its Clinical Applications
| Date | Speaker | Title | Venue |
|---|---|---|---|
| Wednesday 17 March | Stephen Dain | "Energy efficient" lighting, is it all good news? Abstract | C350 |
| Friday 5 March | Ron Douglas | Fish that see with mirrors and frogs that see with their belly | C244 |
| Friday 4 December | Manfred Fahle | Visual deficits in patients with normal results in ophthalmological tests | C244 |
| Wednesday 28 October | Navaz Davoudian | The Impact of Background Lighting Complexity on the Visual Saliency of Urban Objects Abstract | C244 |
| Tuesday 3 November | Sabine Raphael | Luminance in the twilight range Abstract | 12.30pm in C244 |
| Wednesday 2 December | Catherine Suttle | Interocular Interactions in Normal and Amblyopic Visual Systems Abstract | C244 |
| Friday 4 December | Manfred Fahle | Visual deficits in patients with normal results in ophthalmological tests | C244 |
| Wednesday 27 January | Jos Rozema | Introduction to Ocular Straylight Abstract | C244 |
| Friday 5 March | Ron Douglas | Fish that see with mirrors and frogs that see with their belly | C244 |
Talks will commence at 1.15pm. All rooms with the C prefix are in the Tait Building, City University, Northampton Square.
For enquiries please contact Monica Nelson-Iye on (020) 7040 8797
External Seminars
| Date | Speaker | Title | Venue |
|---|---|---|---|
| Tuesday 16 March | John Barbur | Trotter Paterson Lecture: Mesopic Vision. Sponsored by CIBSE Abstract |
Abstracts
"Energy efficient" lighting, is it all good news?
Speaker: Stephen Dain, School of Optometry and Vision Science, University of New South Wales.
Many countries in the world are phasing out the incandescent lamp in favour of compact fluorescent lamps(CFLs), LEDs and quartz halide filament lamps (only slightly more efficient). There seems to be universal disappointment with compact fluorescent lamps. A survey of the performance of CFLs, claimed as equivalent to a 75W filament lamp, showed that 2/3 of them failed to meet the intenational standard for this claim. Investigations of some LED spotlights showed high amplitude 100Hz flicker. These two are two principal reasons why the modern light sources may be a disappointment.
The Impact of Background Lighting Complexity on the Visual Saliency of Urban Objects
Speaker: Navaz Davoudian, University of Sheffield, School of Architecture.
One of the main objectives of urban lighting masterplans has been to highlight important urban objects and landmarks at night. This process of lighting design, as with other types of visual design, needs to consider the relationship between the object and its context and how the background lighting could influence the design of the lighting applied on the urban objects. Most studies of the factors which influence the saliency of urban objects consider only their luminance contrast against a simple background; real objects are observed against a complex background but this tends to be ignored.
This study investigates the impact of background lighting on the visual saliency and conspicuity of urban objects. Previous studies have shown that salience is strongly influenced by visual context, which means that the saliency of a target depends on how it is embedded in the scene. Two variables have been investigated; the density of background patterns of light and their proximity to the target, and these have been measured in comparison with object/background luminance contrast. The aim is to examine whether these background factors have significant affect on the visual saliency of urban objects. The results will improve understanding of the conspicuity in urban areas and ultimately improve the guidelines in urban lighting to have more efficient lighting plans for cities.
The results suggest that luminance contrast alone is not sufficient to describe the visual saliency of an urban object: the density and proximity of background patterns of light also have a significant effect. This result implies that applying the lighting guidelines based solely on object-background luminance contrast, without considering the lighting context of the objects, are not sufficient.
Luminance in the twilight range
Speaker: Sabine Raphael, Psychology Department, UCSD.
Since by definition the term luminance is restricted to the photopic and scotopic domains only, there are considerable discrepancies between the current daylight-based photometry and the visual perception under dim light conditions. Establishing a reliable photometric system for the mesopic range would, among others, allow to evaluate light distributions for safety related applications such as automotive, street, and emergency lighting. Consequently, the goal of this work is to define and characterize a measure for achromatic (sensation) luminance for the mesopic brightness range.
In order to characterize the change in the relative contribution of rods and cones for foveal and peripheral vision under various adaptation levels, we performed different psychophysical experiments.
The techniques of “Minimum motion” and “Minimally distinct borders” were performed to determine isoluminance ratios. In addition contrast threshold contours were measured with counterphasing moving stimuli to detect and identify motion.
Results exhibit both a strong influence of the adaptation state, as well as a dependence on the eccentricity. At all intensities foveal vision can be described by the cone response only, whereas far peripheral vision at high mesopic as well as low photopic adaptation conditions is rod dominated. The point of equal rod and cone contribution to luminance undergoes a pronounced shift from 0.02 cd/m² for near foveal vision to 0.7 cd/m² for 18° off-axis vision. Moreover, at mesopic light levels an increase in S/P ratio of the adaptation background and an increase of the spatial frequency of the stimulus are associated with a decreased effectiveness of rods relative to cone stimulation.
At last, the transition from photopic to scotopic vision can be very well described by a sigmoid function with only two parameters that change with eccentricity and spatial frequency.
Interocular Interactions in Normal and Amblyopic Visual Systems
Speaker: Catherine Suttle, School of Optometry and Vision Science, University of New South Wales, Sydney.
For many years, amblyopia has been treated by occlusion of the non-amblyopic eye. More recently, amblyopia treatment methods have been introduced that allow the amblyopic eye to view central and peripheral stimuli, while the non-amblyopic eye’s view is restricted to the peripheral stimuli. However, it is not yet clear whether binocular viewing is advantageous in amblyopia treatment. The present study investigates the way in which stimulation of one eye affects function of the fellow eye, with the ultimate aim of determining whether a binocular view is likely to offer an advantage over occlusion treatment for amblyopia. Shutter goggles were used to present dichoptic stimuli to groups of adults and children with normal vision and to adults with anisometropic amblyopia. Resolution acuity, contrast sensitivity and alignment sensitivity were measured using a range of viewing conditions and comparisons were made across subject groups and between dichoptic, monocular (occluded), half-binocular and binocular conditions. In children (<14 years) with normal vision, interocular interactions of the kind investigated here are not mature. In amblyopic adults, these interocular interactions vary widely across individuals. Implications of these findings for amblyopia treatment methods will be discussed.
Introduction to Ocular Straylight
Speaker: Jos J. Rozema, Dept of Ophthalmology, Antwerp University Hospital, Antwerp, Belgium.
Ocular straylight is a parameter that is relatively new in clinical practice after being studied for many years in experimental settings. It concerns the part of the incident light that is scattered by the ocular media and does not participate in the normal image formation on the retina. Instead, this light creates a more or less homogeneous haze over the retinal image. Several pathologies are known to increase retinal straylight considerably, which may lead to symptoms such as loss of contrast sensitivity, disability glare, and halos. This will reduce a patient´s quality of vision in everyday life, for example while driving at night and recognizing a person against a light source, but has only a very limited effect on visual acuity as measured during an ophthalmic examination.
This talk discusses the different sources of straylight in the eye and how to measure straylight using Van den Berg´s compensation comparison method. It also gives an overview of the latest clinical research in the field to determine parameters that influence straylight. These include age, iris and skin pigmentation, contact lens wear, type of contact lens being worn, and axial length, which have all conclusively shown to significantly increase straylight, but also laser refractive surgery, which has been surprisingly shown to decrease straylight measurements in many eyes. Finally, a new theory based on contact lens wear is presented to model these observations.
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