Edge Of Pupil Research Articles

Curvature sensors: noise and its propagation

The signal measured with a curvature sensor is analyzed. At the outset, we derive the required minimum number of sensing elements at the pupil edges, depending on the total number of sensing elements. The distribution of the sensor signal is further characterized in terms of its mean, variance, kurtosis, and skewness. It is established that while the approximation in terms of a Gaussian distribution is correct down to fairly low photon numbers, much higher numbers are required to obtain meaningful sensor measurements for small wavefront distortions. Finally, we indicate a closed expression for the error propagation factor and for the photon-noise-induced Strehl loss.

Adaptive regulation of CCD camera for real time eye tracking

In this paper, an eye tracking method and an automatic focusing technique, which combine the regulation of the aperture with the adjustment of the focus of the camera lens, are proposed to acquire clear eye images in the eye-gaze tracking system. Firstly, the aperture of the CCD lens is controlled to adapt the system to external lighting circumstances with the average brightness value of the processed images as the basic value. Secondly, a sum-modulus-difference (SMD) operator is used for rough and quick focusing in a large scale to obtain the eye glints, and for the control of a pan-tilt unit to track and aim at the eye, and for regulation of the lens focus. Finally, a frequency selective weighted median (FSWM) operator is applied in the determined window to focus automatically and acquire clear eye images. If the pupil contour can be extracted from the eye image, then the average gradient value of the pupil's edge points can be used for real-time focusing. Experimental results show that this system can adapt to external lighting changes and to the user's head movements. It can track the eye and acquire clear eye images in real-time.

Threatened fishes of the world: Nannatherina balstoni Regan 1906 (Nannopercidae)

Common names: Balston’s Pygmy Perch, King River Perchlet. Conservation status: Data deficient under the IUCN Red List; Vulnerable (Australia) under the Environmental Protection and Biodiversity Conservation Act 1999. Identification: Dorsal rays VII-VIII, 9–11; anal rays III, 8–10; pectoral rays 12–13; greatest body depth 3.4–4.0 in SL; deep notch between 1st and 2nd dorsal fins; horizontal scales 34–40; gill rakers rudimentary; mouth large, jaws reaching below posterior edge of pupil; eye large; maximum size 90 mm TL (Illustration by Lindsay Marshall). Distribution: Endemic to south-western Australia; distribution disjunct, with an outlying population in the Moore River (although believed extinct from this system). Found in Margaret, Blackwood, Donnelly, Gardner, Shannon, Deep, Kent, Denmark, Hay, King, Goodga and Angove Rivers. Abundance: Low abundance, restricted to specific habitats, or in some cases a single wetland, lake or spring of the system. Habitat and ecology: Occurs in floodplain pools, springs, lakes or areas with groundwater input. Dietary shift occurs at about 25 mm TL from aquatic invertebrates to almost exclusively terrestrial input (Morgan et al. 1995, 1998; Gill and Morgan 1998). Reproduction: Matures at age one, at ~60 mm TL. Breeds during mid-winter when water levels are high and temperatures are near their minima (Morgan et al. 1995). Breeds amongst flooded vegetation. Mean fecundity is 1243. Longevity <2 years. Threats: Habitat loss from secondary salinisation, water extraction, river regulation and eutrophication; competition and predation from introduced fishes (Morgan et al. 1998; Beatty et al. 2007). Conservation actions: Genetic studies of the various populations and monitoring of a number of precarious populations continues (see Beatty et al. 2007). Salinity and temperature tolerances required in light of changing climate. Conservation recommendations: Determine link between groundwater intrusion and life history and genetically characterise populations. Fish Habitat Protection Areas required outside of Environ Biol Fish (2009) 84:409–410 DOI 10.1007/s10641-008-9437-4

Aberrations and Pupil Location under Corneal Topography and Hartmann-Shack Illumination Conditions

This study was conducted to determine the magnitude of pupil center shift between the illumination conditions provided by corneal topography measurement (photopic illuminance) and by Hartmann-Shack aberrometry (mesopic illuminance) and to investigate the importance of this shift when calculating corneal aberrations and for the success of wavefront-guided surgical procedures. Sixty-two subjects with emmetropia underwent corneal topography and Hartmann-Shack aberrometry. Corneal limbus and pupil edges were detected, and the differences between their respective centers were determined for both procedures. Corneal aberrations were calculated using the pupil centers for corneal topography and for Hartmann-Shack aberrometry. Bland-Altmann plots and paired t-tests were used to analyze the differences between corneal aberrations referenced to the two pupil centers. The mean magnitude (modulus) of the displacement of the pupil with the change of the illumination conditions was 0.21+/-0.11 mm. The effect of this pupillary shift was manifest for coma corneal aberrations for 5-mm pupils, but the two sets of aberrations calculated with the two pupil positions were not significantly different. Sixty-eight percent of the population had differences in coma smaller than 0.05 microm, and only 4% had differences larger than 0.1 microm. Pupil displacement was not large enough to significantly affect other higher-order Zernike modes. Estimated corneal aberrations changed slightly between photopic and mesopic illumination conditions given by corneal topography and Hartmann-Shack aberrometry. However, this systematic pupil shift, according to the published tolerances ranges, is enough to deteriorate the optical quality below the theoretically predicted diffraction limit of wavefront-guided corneal surgery.

Correction of ocular and atmospheric wavefronts: a comparison of the performance of various deformable mirrors

The main applications of adaptive optics are the correction of the effects of atmospheric turbulence on ground-based telescopes and the correction of ocular aberrations in retinal imaging and visual simulation. The requirements for the wavefront corrector, usually a deformable mirror, will depend on the statistics of the aberrations to be corrected; here we compare the spatial statistics of wavefront aberrations expected in these two applications. We also use measured influence functions and numerical simulations to compare the performance of eight commercially available deformable mirrors for these tasks. The performance is studied as a function of the size of the optical pupil relative to the actuated area of the mirrors and as a function of the number of modes corrected. In the ocular case it is found that, with the exception of segmented mirrors, the performance is greatly enhanced by having a ring of actuators outside the optical pupil, as this improves the correction of the pupil edge. The effect is much smaller in the case of Kolmogorov wavefronts. It is also found that a high Strehl ratio can be obtained in the ocular case with a relatively low number of actuators if the stroke is sufficient. Increasing the number of actuators has more importance in the Kolmogorov case, even for the relatively weak turbulence considered here.

Binocular Lens Tilt and Decentration Measurements in Healthy Subjects with Phakic Eyes

Tilt and decentration of the natural crystalline lens affect optical quality of the foveal image. However, little is known about the distributions of these variables in healthy subjects with phakic eyes and about their correlations in both eyes. A simple, portable, easy-to-use, and partially automated device was developed to study lens tilt and decentration in both eyes of 11 healthy subjects with phakic eyes. The first, third, and fourth Purkinje images (P1, P3, P4) were visualized using a single infrared (IR) light-emitting diode (LED), a planar lens (F = 85 mm; f/number of 1.4), and an infrared sensitive analog video camera. Software was developed to mark pupil edges and positions of P1, P4, and P3 with the cursor of the computer mouse, for three different gaze positions, and an automated regression analysis determined the gaze position that superimposed the third and fourth Purkinje images, the gaze direction for which the lens was oriented perpendicularly to the axis of the IR LED. In this position, lens decentration was determined as the linear distance of the superimposed P3/P4 positions from the pupil center. Contrary to previous approaches, a short initial fixation of a green LED with known angular position calibrated the device as a gaze tracker, and no further positional information was necessary on fixation targets. Horizontal and vertical kappa, horizontal and vertical lens tilt, and vertical lens decentration were highly correlated in both eyes of the subjects, whereas horizontal decentration of the lens was not. There was a large variability of kappa (average horizontal kappa -1.63 degrees +/- 1.77 degrees [left eyes] and +2.07 degrees +/- 2.68 degrees [right eyes]; average vertical kappa +2.52 degrees +/- 1.30 degrees [left eyes] and +2.77 degrees +/- 1.65 degrees [right eyes]). Standard deviation from three repeated measurements ranged from 0.28 degrees to 0.51 degrees for kappa, 0.36 degrees to 0.91 degrees for horizontal lens tilt, and 0.36 degrees to 0.48 degrees for vertical lens tilt. Decentration was measured with standard deviations ranging from 0.02 mm to 0.05 mm. All lenses were found tilted to the temporal side with respect to the fixation axis (on average by 4.6 degrees ). They were also decentered downward with respect to the pupil center by approximately 0.3 mm. Lens tilts and positions could be conveniently measured with the described portable device, a video camera with a large lens. That the lenses were tilted to the temporal side in both eyes, even if corrected for kappa, was unexpected. That they were displaced downward with respect to the pupil center could be related to gravity.

Traumatic pupillary capture of the haptic of an angle-supported phakic intraocular lens

A 27-year-old woman had implantation of an angle-supported phakic intraocular lens (pIOL) for myopia in the left eye in 2003. Moderate iris atrophy and pupil ovalization were noted in 2005. In 2006, the eye was hit by a plastic bullet shot from a toy gun. The pupil became distorted as the inferior haptic engaged the pupil edge. Visual acuity was not affected. Surgical repositioning was uneventful, yielding a round pupil with no damage to the iris sphincter or the lens. The endothelium was not affected by the trauma or surgery. Previous iris atrophy may have facilitated pupillary capture because of reduced iris elasticity and pupil ovalization by the haptic. Blunt trauma can dislocate angle-supported pIOLs. Implantation of these IOLs should be discouraged in patients who perform activities that put them at risk for eye trauma.

Dynamic Measurement of Accommodation and Pupil Size Using the Portable Grand Seiko FR-5000 Autorefractor

The purpose of this study was to evaluate the potential of the portable Grand Seiko FR-5000 autorefractor to allow objective, continuous, open-field measurement of accommodation and pupil size for the investigation of the visual response to real-world environments and changes in the optical components of the eye. The FR-5000 projects a pair of infrared horizontal and vertical lines on either side of fixation, analyzing the separation of the bars in the reflected image. The measurement bars were turned on permanently and the video output of the FR-5000 fed into a PC for real-time analysis. The calibration between infrared bar separation and the refractive error was assessed over a range of 10.0 D with a model eye. Tolerance to longitudinal instrument head shift was investigated over a +/-15 mm range and to eye alignment away from the visual axis over eccentricities up to 25.0 degrees . The minimum pupil size for measurement was determined with a model eye. The separation of the measurement bars changed linearly (r2 = 0.99), allowing continuous online analysis of the refractive state at 60 Hz temporal and approximately 0.01 D system resolution with pupils >2 mm. The pupil edge could be analyzed on the diagonal axes at the same rate with a system resolution of approximately 0.05 mm. The measurement of accommodation and pupil size were affected by eccentricity of viewing and instrument focusing inaccuracies. The small size of the instrument together with its resolution and temporal properties and ability to measure through a 2 mm pupil make it useful for the measurement of dynamic accommodation and pupil responses in confined environments, although good eye alignment is important.

Diffraction Analysis of Two‐dimensional Pupil Mapping for High‐Contrast Imaging

Pupil mapping is a technique whereby a uniformly illuminated input pupil, such as from starlight, can be mapped into a nonuniformly illuminated exit pupil, such that the image formed from this pupil will have suppressed sidelobes, many orders of magnitude weaker than classical Airy ring intensities. Pupil mapping is therefore a candidate technique for coronagraphic imaging of extrasolar planets around nearby stars. Unlike most other high-contrast imaging techniques, pupil mapping is lossless and preserves the full angular resolution of the collecting telescope. So it could possibly give the highest signal-to-noise ratio of any proposed single-telescope system for detecting extrasolar planets. Prior analyses based on pupil-to-pupil ray-tracing indicate that a planet fainter than 10-10 times its parent star, and as close as about 2λ/D, should be detectable. In this paper we describe the results of careful diffraction analysis of pupil-mapping systems. These results reveal a serious unresolved issue. Namely, high-contrast pupil mappings distribute light from very near the edge of the first pupil to a broad area of the second pupil, and this dramatically amplifies diffraction-based edge effects, resulting in a limiting attainable contrast of about 10-5. We hope that by identifying this problem, others will provide a solution.

Lyot Coronagraphy on Giant Segmented-Mirror Telescopes

We present a study of Lyot style (i.e., classical, band-limited, and Gaussian occulter) coronagraphy on extremely large, highly-segmented telescopes. We show that while increased telescope diameter is always an advantage for high dynamic range science (assuming wavefront errors have been corrected sufficiently well), segmentation itself sets a limit on the performance of Lyot coronagraphs. Diffraction from inter-segment gaps sets a floor to the achievable extinction of on-axis starlight with Lyot coronagraphy. We derive an analytical expression for the manner in which coronagraphic suppression of an on-axis source decreases with increasing gap size when the segments are placed in a spatially periodic array over the telescope aperture, regardless of the details of the arrangement. A simple Lyot stop masking out pupil edges produces good extinction of the central peak in the point-spread function (PSF), but leaves satellite images caused by inter-segment gaps essentially unaffected. Masking out the bright segment gaps in the Lyot plane with a reticulated mask reduces the satellite images'intensity to a contrast of 5x10^{-9} on a 30 m telescope with 10 mm gaps, at the expense of an increase in the brightness of the central peak. The morphology of interesting targets will dictate which Lyot stop geometry is preferable: the reticulated Lyot stop produces a conveniently uni-modal PSF, whereas a simple Lyot stop produces an extended array of satellite spots. A cryogenic reticulate Lyot stop will also benefit both direct and coronagraphic mid-IR imaging.

Requirements for segmented correctors for diffraction-limited performance in the human eye

Wavefront correctors have yet to provide diffraction-limited imaging through the human eye's ocular media for large pupils (>/= 6 mm).To guide future improvements in corrector designs that might enable such imaging, we have modeled the performance of segmented piston correctors in conjunction with measured wave aberration data of normal human eyes (mean=34.2 yr; stdev= 10.6 yr). The model included the effects of pupil size and wavelength in addition to dispersion, phase wrapping, and number and arrangement of facets in the corrector. Results indicate that </= 100x100 facets are needed to reach diffraction-limited performance for pupils up to 8 mm (extrapolated) at 0.6 microm wavelength. Required facet density for the eye was found to be substantially higher at the pupil's edge than at its center, which is in stark contrast to the requirements for correcting atmospheric turbulence. Substantially more facets are required at shorter wavelengths with performance highly sensitive to facet fill. In polychromatic light, the performance of segmented correctors based on liquid crystal technology was limited by the naturally occurring longitudinal chromatic aberration of the eye rather than phase wrapping and dispersion of the liquid crystal. Required facets to correct defocus alone was found highly sensitive to pupil size and decentration.

Parametric characterization of the form of the human pupil from blurred noisy images

The fluctuation of the human pupil is an important parameter in order to make non-invasive diagnosis of many different diseases and in several clinical applications. The relevant measurement device, the pupillometer, consists in a CCD camera, which shoots the pupil. We suppose that the measured image is blurred by a Gaussian kernel and corrupted by an additive white noise; moreover an elliptic shape for the pupil is assumed. We here present the extension of a multiscale approach for edge detection to identify some parameters of the pupil: the location of its centre, the length of the semi-axes and the orientation of the corresponding ellipse. The chosen method requires knowledge about the degradation parameters of the assumed model; so we first present a simple but efficient method to determine such quantities for the measured image. Then we apply the edge detection procedure to identify points close to the pupil edge, within a chosen probability. Finally we find the optimal ellipse fitting a suitable subset of the previously detected edge points. Results are presented, with comparisons to other approaches for edge finding.

Simultaneous continuous recording of accommodation and pupil size using the modified Shin-Nippon SRW-5000 autorefractor.

The internal optics of the recent models of the Shin-Nippon SRW-5000 autorefractor (also marketed as the Grand Seiko WV-500) have been modified by the manufacturer so that the infrared measurement ring has been replaced by pairs of horizontal and vertical infrared bars, on either side of fixation. The binocular, open field-of-view, allowing the accommodative state to be objectively monitored while a natural environment is viewed, has made the SRW-5000 a valuable tool in further understanding the nature of the oculomotor response. It is shown that the root-mean-square of model eye measures was least (0.017 +/- 0.002 D) when the separation of the horizontal measurement bars were averaged twice. The separation of the horizontal bars changes by 3.59 pixels/dioptre (r2 = 0.99), allowing continuous on-line analysis of the refractive state at up to 60 Hz temporal resolution to an accuracy of <0.001 D, with pupils >3 mm. The pupil edge is not obscured in the diagonal axis by the measurement bars, unlike the ring of the original optics, so in the newer model pupil size can be measured simultaneously at the same rate with a resolution of <0.001 mm. The measurements of accommodation and pupil size are relatively unaffected by eccentricity of viewing up to +/-10 degrees from the visual axis and instrument focusing inaccuracies over a range of 10 mm towards the eye and 5 mm away from the eye. The resolution and temporal properties of the analysis are therefore ideal for the simultaneous measurement of dynamic accommodation and pupil responses.

The Investigation of Eye Tracking Accuracy using Synthetic Images

Accuracy of videooculography was tested using synthetic eye images. The novel pupil center coordinates extraction method wasproposed. The method exploits averaging of pupil edge coordinates in the same scan line. The novel method accuracy is similar tone ofapproximation by circle method. The proposed method has better computational effectiveness, but is less robust to influence of artifacts.Errors for both methods increase versus noise standard deviation with the same velocity. However the influence of noise is small, ifregion between iris and pupil is sharp. The results of study confirmed that method of videooculography is suitable for recording eyemicromovements. Ill. 6, bibl. 3 (in English, summaries in Lithuanian, English, Russian).

Rotation Vector Analysis of Eye Movement in Three Dimensions with an Infrared CCD Camera

We have developed a new technique for analyzing the rotation vector of eye movement in three dimensions with an infrared CCD camera based on the following four assumptions: i) the eye rotates on a point; ii) the pupil edge is a circle; iii) the distance from the center of eye rotation to pupil circle remains unchanged despite the rotation; iv) the image of the eye by the CCD camera is projected onto a plane which is perpendicular to the camera axis. After taking digital images of voluntary circular eye movements, we first constructed a three-dimensional frame of reference fixed on the orbita of the subject wearing a goggle equipped with an infrared CCD camera, and determined the space coordinates of the center of eye rotation, the center of the pupil, and an iris freckle. We then took digital images of the eye movements during a saccade or vestibulo-ocular reflex (VOR) and analyzed the axis and angle of the eye movements by the trajectories of the center of the pupil and the iris freckle. Finally, Listing's plane of saccade and the gain and the phase of VOR were obtained. The suitability of this technique is examined.

Corneal geometry reconstruction with the Keratron videokeratographer.

Color-coded corneal maps produced by computer-assisted videokeratographers (CAVKs) have become an indispensable tool for clinical understanding of corneal shape. However, Placido-based CAVKs are criticized as theoretically incapable of producing accurate corneal height information. This paper describes how the Keratron (Optikon 2000, Rome, Italy) integrated design innovations to achieve accuracy and map use previously thought to be unobtainable. The Keratron implemented a spherically unbiased surface reconstruction method that yields height, axial power, and instantaneous curvature without derivation of one quantity from another. Processing innovations resulted in sub-micron height accuracy. The Keratron includes axial power, instantaneous curvature, refractive maps, a height map (spherical offset), pupil edge detection, a "move axis" feature, process editing, indices, a contact lens program, and photorefractive keratectomy (PRK) simulation. The algorithms for surface reconstruction and the design solutions implemented in the Keratron resulted in accurate height, axial power, and instantaneous curvature measurement and valid, clinically useful maps, as well as additional user options and features.

Optical Modulation Transfer and Contrast Sensitivity with Decentered Small Pupils in the Human Eye

Human observers experience a large decrement in visual acuity when a small artificial pupil is displaced from the center to the edge of the dilated natural pupil. This decrement in visual resolution, called the Campbell effect, has been attributed to the retina, the ocular optics, or a combination of the two. Given the uncertainty about the relative magnitudes of these two components over the range of spatial frequencies used in normal vision, we have obtained objective measurements of the retinal image quality and psychophysical measurements of visual performance, with decentered pupils. The contributions of monochromatic aberrations were determined by using double pass measurements of the modulus of the optical transfer function (MTF). For all of the observers, there was a substantial decrement in the MTF with decentering, showing that even when using a 1.5 mm pupil and appropriate spherical/cylindrical refractive corrections, there is a considerable contribution of monochromatic aberrations to the effect. We have compared these optical MTFs with the psychophysical contrast sensitivity functions (CSFs) measured under exactly the same conditions using green gratings generated on the screen of a color monitor. At the low and intermediate spatial frequencies considered (2–16 c/deg), we find the fall in the CSF is much greater than the fall in the monochromatic MTF, with the difference becoming greater as the spatial frequency increases. We show that this discrepancy can be mostly attributed to the effect of transverse chromatic aberration due to the bandwidth of the green stimulus used for the CSF measurements. In conclusion, the combination of the ocular transverse chromatic aberration and monochromatic aberrations accounts for the loss in visual sensitivity found with a decentered small pupil at low and intermediate spatial frequencies. Copyright © 1996 Elsevier Science Ltd.

Stability of the Stiles-Crawford Function in a Unilateral Amblyopic Subject over a 38-Year Period: A Case Study

The relative luminous efficiency curves for light entering different parts of the entrance pupil [Stiles-Crawford functions (SCFs)] of subject TG, whose right eye is amblyopic, were determined earlier for both the normal and the amblyopic eye. The left eye was found to have a normal SCF, varying from the center to the edge of the entrance pupil by an entire log unit. However, the SCF for the right eye was found to be abnormal, showing peak sensitivity far toward the temporal edge of the pupil and varying from center to edge by only one-third of a log unit. From these data it was inferred that the photoreceptors were in poor alignment. In October, 1993 the subject experienced a retinal detachment in the left (nonamblyopic) eye, requiring cryoretinopexy, drainage of subretinal fluid, and a scleral buckle. Postoperatively, visual acuity recovered to 6/9 to 6/7.5 (20/30 to 20/25), but vision was poor when illumination or contrast was low. In order to determine whether the decrement in visual performance was the result of misalignment of the photoreceptors, the subject's SCFs were determined 9 months postoperatively for both eyes, using a procedure similar to that used earlier. The relative luminous efficiency curves for both eyes were found to be surprisingly similar to the corresponding curves found 38 years earlier. It was concluded that any decrease in visual function resulting from the retinal detachment and repair was not caused by misalignment of the photoreceptors. We infer that the mechanisms resulting in the exceptionally high degree of photoreceptor alignment in the left eye and the disturbed alignment in the right eye are still present.

Intensity and resolution at the diffraction focus of optical systems with rotationally symmetric aberration functions: erratum

The intensities and resolutions at the diffraction focus of optical systems with rotationally symmetric minimum-variance aberration functions as well as functions with slight variations from this shape and a prescribed fixed maximum deviation value at the edge of the exit pupil are calculated for circular and annular exit pupils. The results for the intensity at the diffraction focus obtained either by numerical integration of the diffraction integral or by using the Marechal formula show that the maxima of these intensities are achieved for optical systems with wave aberration functions of minimum variance, thus verifying the Marechal criterion. The resolutions (first zeros of the intensities in the radial direction) at this diffraction focus are also presented.

Intensity and resolution at the diffraction focus of optical systems with rotationally symmetric aberration functions

The intensities and resolutions at the diffraction focus of optical systems with rotationally symmetric minimum-variance aberration functions as well as functions with slight variations from this shape and a prescribed fixed maximum deviation value at the edge of the exit pupil are calculated for circular and annular exit pupils. The results for the intensity at the diffraction focus obtained either by numerical integration of the diffraction integral or by using the Maréchal formula show that the maxima of these intensities are achieved for optical systems with wave aberration functions of minimum variance, thus verifying the Maréchal criterion. The resolutions (first zeros of the intensities in the radial direction) at this diffraction focus are also presented.