The 3rd European Meeting in Physiological Optics took place at the Department of Optometry and Visual Science, School of Allied Health Sciences of City University in London from 7 to 9 September 2006. This international biennial meeting built upon its very successful predecessors in Wroclaw, Poland and most recently Granada, Spain. The meeting was attended by close to 100 delegates from 18 countries around the world. The meeting papers and posters covered many aspects of Physiological Optics (this term originally introduced by Hermann von Helmholtz has now been renamed as Vision Science), including clinical studies, basic research and instrumentation. The next edition of this meeting will take place in the city of Heraklion, in Crete, Greece from 31 August to 2 September 2008. It is organized by the Institute of Vision and Optics in the University of Crete.
This special issue of the Journal of Modern Optics represents the archival versions of many of the papers/posters presented at this meeting. In addition, included in this issue are other contributed papers and like the meeting, are quite interdisciplinary in nature.
We start off this special issue with the anterior portion of the eye, and more specifically with oculomotor studies. The first paper in this area by Li, Munn and Pelz (p. 503) deals with video-based eye tracking, a popular means of measuring eye movements. The authors provide a model of how the pupil and first surface corneal reflection of an illumination source are affected by different relative movements of the eye. The second paper by Gareze et al. (p. 533), introduces a novel computational concept (based on hydrodynamics and turbulence) to characterize the pattern of eye movements when a visual scene is viewed. This new concept is called the crossing number, a single parameter that can describe the complexity of the eye scan. The next two papers deal with accommodation and eye movements. Torii et al. (p. 557) study the effect of changes in convergence stimuli with unchanged accommodative stimuli (which would result in conflicting stereo images) and conclude with the hypothesis that transient responses to step stimuli is initiated by a convergence driven accommodation and followed by a slower fine control of accommodation modified by the amount of retinal blur. Thiagarajan, Lakshminarayanan and Bobier (p. 569) report on the relative contribution of proximal accommodation to the open loop accommodative response under open and closed loop conditions of vergence using difference of Gaussian stimuli. Analysis of binocular vision leads directly to studies of the horopter. The original formalism of the horopter given by Ogle in the 1950s is reanalyzed by Lakshminarayanan and Varadharajan (p. 583). This is followed by the evaluation of the nonius horopter as a function of wavelength (Seshadri and Lakshminarayanan; p. 589). They conclude that changes seen in the horopter for different wavelengths is purely optical, due to chromatic aberration of the eye.
The next section deals with studies of the cornea and are represented by three papers. Yasoubi, Edgar and Chisholm (p. 599) report on the effect of hydrogel contact lens wear on low contrast acuity. This is followed by a report on the refractive errors found in chicks due to prolonged wear of defocusing lenses (Kisilak et al., p. 611). In the third paper, Misson, Timmerman and Bryanston-Cross (p. 625) report on a novel polarized light method to study the macroscopic distribution of collagen lamellae of the cornea in vivo.
The next set of papers deal with the crystalline lens and pseudophakia. Siedlecki, Kasprzak and Pierscionek (p. 639) provide a model for a GRIN intra-ocular lens (IOL), and provide an algorithm for the optimal adjustment of GRIN distribution for individual parameters of the pseudophake eye. Veeramany and Lakshminarayanan (p. 649) provide a simple but computationally elegant method to solve the ray equation in GRIN media and show as an application, ray tracing through the human crystalline lens. In the third paper in this set, retinal images in a model pseudophake eye fitted with normal (refractive type) and hybrid (refractive-diffractive) IOLs are evaluated and the chromatic aberration of such lenses are analyzed by Siedlecki, Zając and Nowak (p. 653).
Since the first publication by Liang and Bille in 1993, there has been an explosion in the amount of research coming out of laboratories from around the world. This is truly a ‘hot’ area in vision science currently and this area is well represented in this issue. The first papers in this area deal with techniques and instrumentation. Dubinin et al. (p. 671) report on different methods to widen the high resolution retinal imaging area. Alvarez Diaz, Shao and Bille (p. 683), report on using a three-sided pyramidal prism as a wavefront sensor with an artificial neural network control unit in an adaptive optical setup. An alternative to the Hartmann–Shack wavefront sensor is the curvature wavefront sensor. Torti, Gruppetta and Diaz-Santana (p. 691) report a novel layout using a wavefront curvature sensor and present initial results. This method appears promising and future results are expected. Hampson, Chin and Mallen (p. 703) have developed a binocular open view Hartmann–Shack sensor and present results to demonstrate the feasibility of the instrument. They also present an overview of coherence functional analysis as a tool to determine correlations between aberrations in the frequency domain. This is followed by a method to determine the wavefront aberration function eyes using a propagation analysis and phase reconstruction using SAR (synethtic aperture radar) techniques (Rouarch et al., p. 717). In imaging, aberration compensation is a major area of research and Zhang et al. (p. 727) present a means of doing this by utilizing the rotational properties of Zernike polynomials (which are conventionally used to represent wavefront aberrations). They use rotating Zernike phase plates as precompensation units to correct higher order aberrations. Jain and Schwiegerling (p. 737) propose a new colour Hartmann–Shack wavefront sensor. Here, in contrast to the traditional sensor that measures wavefront aberration at a single wavelength, they describe a modified sensor that measures simultaneously at three wavelengths. Lastly, Bille et al. (p. 749) present their progress in the implementation of a new compact hybrid adaptive optics system, which will be integrated into a multiphoton scanning laser ophthalmoscope. Aberration correction in a sample of 60 eyes is demonstrated.
Wavefront aberrations have a deleterious effect on the retinal image and visual performance. The next set of papers deal with this topic. In the first paper in this section, Plainis and Pallikaris (p. 759) have studied the statistics of high order aberration and report data from 393 nearly emmetropic eyes. They note that aberration levels for a fixed pupil size increase with age, but speculate that their effect on retinal image quality is possibly cancelled out by senile miosis. This is followed by a study of aberrations in older eyes (Sharma, Mikashi and Howland, p. 773). They note that even though some aberrations are compensated for by the internal optics of the eye in younger eyes, these compensations decrease with age and generally fail to compensate monochromatic aberrations of the cornea after 50 years of age. Jiménez et al. (p. 783) obtained data using an aberrometer as well as a double pass method on selected visual performance tests, namely, contrast sensitivity and discrimination under low light illumination conditions. Dalimier, Dainty and Barbur (p. 791) measured the effect of high order aberrations on contrast acuity as a function of light level. They conclude that at low light levels, the drop in neural sensitivity limits the impact that increased optical aberrations have on vision. Tian et al. (p. 805) report data on retinal image degradation due to higher order aberrations and light scatter in chick eyes after photorefractive keratectomy. In particular, they present a method to derive a light scatter map. The last paper in this set by Rauscher, Brandl and Baumbach (p. 819) present results of a study on the effects of large G-forces (such as those experienced by pilots) on the aberrations of the eye. They report that under the experimental conditions used, there is a small but significant change. This is followed by the article by Tahir et al. (p. 839) reporting that contrary to prior literature, there might be an optical component to orientation selectivity (the oblique effect) induced by high order aberrations of the eye.
The final paper in this special issue by Bueno and Artal (p. 849) reports the average amount of ocular diattenuation using a double pass polarimeter and the resulting Mueller matrix.
As can be seen by the above synopsis, this special issue contains papers on a wide variety of topics in Vision. May the reader enjoy and benefit!
Lastly, we, the editors, would like to thank the sponsors of the 3rd European Meeting on Physiological Optics, namely, Image Eyes, Inc., and EPSRC (the Engineering and Physical Sciences Research Council, UK) for financial support as well as the City University, London, the meeting venue. At the Journal of Modern Optics, special thanks go to the former editor, Sir Peter Knight, FRS and his successor Professor Jon Marangos, for their enthusiastic support of this special issue. Finally, we would like to thank all the contributors and especially the reviewers who ensured that we had first rate peer review, and thus a quality product.
Vasudevan Lakshminarayanan
Waterloo, Ontario
Luis Diaz-Santana
London, UK