bluuebunny/crossref_metadata_2025 huggingface dataset:
VARIATION OF ASTIGMATISM WITH ACCOMMODATION AND ITS RELATIONSHIP WITH DARK FOCUS
Authors: Millodot M. , Thibault C.
Published: December 2007

Abstract— The refraction of 122 eyes was measured for five distances of fixation with an objective Canon Auto Refractor. The cylindrical component was found to vary, but by a small amount. We found no evidence of a deliberate reduction in astigmatism with accommodation, in accord with other studies. The axis was also found to vary by at least 5° in about half of the subjects tested, which is also in good accord with other investigations. The dark focus of 31 eyes was not found to correlate with a minimum astigmatic distance, since this only occurred in II out of the 31 eyes. For these 11 eyes, the correlation of dark focus and the dioptric distance where astigmatism was minimum was equal to + 0.54. It implied that for those eyes (about one‐third of all types) there was a tendency to yield the best optical quality at the dark focus.
ANOMALOUS RETINAL CORRESPONDENCE — A REVIEW
Authors: Jennings J. A. M.
Published: December 2007

Abstract— The theories and characteristics of anomalous retinal correspondence (ARC) are critically reviewed and a classification of ARC is proposed which attempts to reconcile various aspects of the different theories. It is suggested that ARC in microtropia, and perhaps some small‐angle squints, is a cortical adaptive mechanism, whereas squints with a larger and more variable angle have ARC with different characteristics, which are better explained by the motor theory.
PRISM‐INDUCED HOROPTER DISTORTIONS
Authors: Reading R. W.
Published: December 2007

Abstract— The effects that lateral prisms have on the horopter were evaluated in 11 subjects, including 6 subjects classified as binocularly abnormal. For normal subjects with good stereopsis the equidistance (stereoscopic distance matching) horopter shape was altered with the application of lateral prism. For other subjects this was not the case. Equidirection (nonius) horopters were unchanged by the application of lateral prism in all of the subjects tested. In addition to localized irregularities in the horopter locus, shifts in fixation disparity produced regional distortions of the horopter.
SUBJECTIVE VERGENCE ERROR AT NEAR DURING ACTIVE HEAD ROTATION
Authors: Ciuffreda Kenneth J. , Hokoda Steven C.
Published: December 2007

Abstract— There exists some controversy regarding the effects of active horizontal head rotation on vergence error. We used a conventional, Ogle‐type, subjective fixation disparity apparatus to measure vergence error at near over a full range of horizontal head‐rotation frequencies. Change in vergence error rarely exceeded 10 min arc. This finding demonstrates the adequacy of the vergence system to maintain relatively accurate bifixation at near and to allow for continuous maintenance of binocular sensorymotor integrative ability, even in the presence of system perturbations.
THE HUMPHREY AUTO KERATOMETER
Authors: Rabbetts R. B.
Published: December 2007

Abstract— A full description is given of the optical and analytical principles of the Humphrey Auto Keratometer.
OBJECTIVE AND SUBJECTIVE MEASUREMENT OF TONIC ACCOMMODATION
Authors: Bullimore Mark A. , Gilmartin Bernard , Hogan Robert E.
Published: December 2007

Measurements of tonic accommodation (TA) were made on 25 subjects using He‐Ne laser optometry (HNL), infra‐red optometry (IR) and near retinoscopy (NR) under darkroom conditions. All three techniques were shown to produce comparable mean estimates of TA (HNL: 1.10 D; IR: 1.15 D; NR: 1.07 D). Significant correlations were found between HNL and IR (r= 0.88, p < 0.001) and between HNL and NR (r= 0.81. p < 0.001). Control studies under cycloplegia indicate that the estimates are not seriously affected by fluctuations in accommodative state. These findings indicate that ophthalmic practitioners can gain access to refractive data that aids the clinical management of the “anomalous myopias” and asthenopia associated with VDU work.
AUTOMATED REFRACTION IN APHAKIA—II. ITS REPEATABILITY AND ACCURACY COMPARED TO CONVENTIONAL TECHNIQUES
Authors: Gullon Michel
Published: December 2007

The repeatability and accuracy of an i.r. electronic optometer (the Ophthalmetron) and of retinoscopy performed by experienced practitioners were studied in aphakia by testing a group of 17 patients three times with each method and by subjective techniques. The results show that the Ophthalmetron gives better repeatability than retinoscopy and that accuracy is marginally better for the sphere with the Ophthalmetron and for the cylinder power by retinoscopy when the mean of the three subjective results is taken as the true refractive value.
ANTERIOR CHAMBER PACHYMETRY DURING ACCOMMODATION IN EMMETROPIC AND MYOPIC EYES
Authors: Rabie E. P. , Steele C. , Davies E. G.
Published: December 2007

Optical pachymetry was performed on 15 nearly emmetropic and 15 myopic subjects with accommodation fully relaxed and with 3.00 and 6.00 dioptres of stimulus to accommodation. No significant difference was found between the change in anterior chamber depth per dioptre of stimulus between the two groups. This is in agreement with theoretical considerations, which suggest that a change in the length of the vitreous does not much affect the optical efficiency of the crystalline lens.
A COMPARISON OF THE EFFECTS OF CYCLOPLEGICS ON ACCOMMODATION ABILITY FOR DISTANCE VISION AND ON THE APPARENT NEAR POINT
Authors: Rosenfield M. , Linfield P. B.
Published: December 2007

Abstract— The relationship between distance accommodation ability and the near point of accommodation (NPA) was investigated following the instillation of a cycloplegic. A high correlation between the two parameters was found (p <0.001). It is suggested that the effect of a cycloplegic may be more directly assessed using distance accommodation measurement and, in the case of young children, with more ease. A limit of 0.75 D of distance accommodation ability is suggested as a threshold for satisfactory cycloplegia.
THE EFFECT OF REFRACTIVE ERROR ON THE ACCOMMODATIVE RESPONSE GRADIENT*
Authors: McBrien Neville A. , Millodot Michel
Published: December 2007

Abstracts—The accommodative responses of early‐onset myopes, late‐onset myopes, emmetropes and hyperopes were measured over a range of 5 dioptres using an objective infra‐red autorefractor. Differences were found between the four refractive groups, with hyperopes accommodating more for near targets than emmetropes, followed by early‐onset myopes then late‐onset myopes. Moreover a strong correlation between the accommodative response gradient and refractive error was found, suggesting that hyperopes accommodate more to a particular target than do emmetropes or myopes. The results are interpreted in the context of a dual innervation to the ciliary muscle.
VISUAL REPRESENTATION AT THE CEREBRAL CORTEX: QUALITATIVE AND QUANTITATIVE ASPECTS
Authors: Pointer Jonathan S.
Published: December 2007

Abstracts— The cerebral representation of peripheral sensory surfaces is strictly ordered. In the case of the visual system, the scale of the cortical representation of visual space is non‐linear: the area devoted to the fovea is greatly enlarged. Attempts have been made to quantify this retino‐cortical relationship in animals and man: the result is the cortical magnification factor (M) which indicates the linear distance in mm along the striate cortex concerned with each degree of the visual field. The cortical magnification factor has indicated an alternative approach both to the theoretical interpretation of visual processing and to the clinical aspects of visual field examination. By M‐scaling vision test stimuli, visual sensitivity, while quantitatively different at foveal and peripheral projections, remains qualitatively similar across the entire field.
EFFECT OF FRESNEL PRISM DISPERSION ON CONTRAST SENSITIVITY FUNCTION*
Authors: Woo George C. , Campbell Fergus W. , Ing Brian
Published: December 2007

Abstract— Fresnel prisms are often used in orthoptics for binocular anomalies and in low vision for visual field defects. These prisms are made of optical polyvinyl chloride (PVC) and this material increases chromatic dispersion and produces a loss of contrast. In this study, the effect of chromatic dispersion on contrast sensitivity is determined. Contrast thresholds over a wide range of spatial frequencies are obtained on a number of subjects with the use of Fresnel prisms ranging from 5 to 30 prism dioptres. As predicted there is a decrease in visual acuity and cut‐off spatial frequency threshold as prism power increases. Similarly, a decrease in contrast sensitivity at high and medium spatial frequencies is recorded.
TWO SIMPLE CALCULATING SCHEMES FOR USE IN OPHTHALMIC OPTICS‐II. TRACING AXIAL PENCILS THROUGH SYSTEMS INCLUDING ASTIGMATIC SURFACES AT RANDOM AXES
Authors: Bennett A. G.
Published: December 2007

Abstract— A paraxial computing scheme is described for tracing an axial pencil of rays through any system containing astigmatic surfaces with their axes at random. In conjunction with a scheme for tracing oblique rays (Bennett, 1986) it is applied to a problem in visual optics posed by Keating (1982). This involves determining the spectacle magnification for a schematic eye with three strongly astigmatic surfaces, corrected by a spectacle lens of bi‐toroidal form, the axes of all five surfaces being mutually oblique. It is shown that the suggested computing schemes yield very similar results to those found by the matrix methods of Keating. Although only two rays are needed to determine the principal dimensions of the basic retinal image of a circle, further insight into its true shape is obtained from a multiple trace, using a computerized version of the ray tracing scheme.
SPECTACLE LENSES AND THIRD‐ORDER DISTORTION
Authors: Atchison David A. , Smith George
Published: December 2007

Abstract— Third‐order formulae are developed for calculation of distortion in thin spectacle lenses, when one or both surfaces are conicoid aspherics. Solutions which allow correction of rotatory or peripheral distortion, when one lens surface is a conicoid aspheric, are illustrated. A study of these solutions shows that one of the off‐axis power crrors (e.g. oblique astigmatism) and one of the distortions can be simultaneously eliminated, but the lens forms required are too curved to be cosmetically feasible.
THE EFFECT ON FIXATION DISPARITY AND ASSOCIATED HETEROPHORIA OF READING AT AN ABNORMALLY CLOSE DISTANCE*
Authors: Pickwell D. , Jenkins T. , Yekta A. A.
Published: December 2007

Abstract— It is well established that prism stress on binocular vision produces fixation disparity. It is therefore suggested that fixation disparity is a sign of stress on binocular vision. The authors have previously looked at the stress caused by reading in reduced levels of illumination, and found that the average fixation disparity and associated heterophoria become more exophoric. In this paper the effect on fixation disparity and associated heterophoria of reading at an abnormally close distance is reported. It was found that in 50 young adults fixation disparity and associated heterophoria increased to a greater degree of exo‐disparity. An analysis of the visual symptoms indicated that there was also an increase in the visual discomfort and other symptoms.
PUPIL RESPONSE AS AN OBJECTIVE MEASURE OF VISUAL ACUITY*
Authors: Barbur John L. , Thomson W. David
Published: December 2007

Abstract— Pupillary responses to brief presentations of sinusoidal grating patterns were measured. The results show that the amplitude of the pupillary responses varies systematically with grating spatial frequency. Gratings of spatial frequencies in the range 1–5 c deg‐1 elicited the maximum percentage change in pupil area, with higher and lower spatial frequency gratings producing smaller responses. The bandpass nature of the pupil response function was compared to contrast sensitivity functions obtained under the same viewing conditions. The effects of defocus and eccentric fixation on both contrast sensitivity and pupil response functions were qualitatively similar. Grating acuities calculated from contrast sensitivity data correlated well with similar data extracted from pupil response functions. The results suggest that automated pupillometry can provide an attractive means for objective measurement of visual acuity.
THE EFFECT OF STIMULUS CONTRAST ON THE ACCOMMODATION RESPONSE
Authors: Ward P. A.
Published: December 2007

Abstract—Accommodation responses to stimuli of various contrasts at a vergence of—5.0 dioptres were measured with an objective infra‐red optometer. Both an edge and sinusoidal gratings were employed. The sinusoidal gratings were 1.67, 5.0 and 15.0 c deg‐1. The accommodation responses changed little as object contrast was reduced, until an accommodation response contrast threshold (ARCT) was reached; below this ARCT considerable accommodative error occurred. Intersubject variation in the ARCT was also noted. The ARCT for the 15.0 c deg‐1 grating was significantly higher than for the other two gratings. On two subjects accommodation responses to the 5.0 c deg‐1 grating were measured over a stimulus range of +0.5 to‐0.5 dioptres with three grating modulations of 2.7, 8.0 and 25%. The results indicated that no contrast dependence occurs in the near range but that contrast may be important as the system approaches the far‐point. The data further indicate the importance of intermediate spatial frequencies as accommodative stimuli.
EFFECT OF TARGET CONTENT AT HIGHER SPATIAL FREQUENCIES ON THE ACCURACY OF THE ACCOMMODATION RESPONSE
Authors: Tucker J. , Charman W. N.
Published: December 2007

Abstract The accommodation responses to sinusoidal and square‐wave gratings at the same vergence (‐5.0 dioptres) are compared as a function of the modulation of the fundamental of both waveforms. At low spatial frequencies (< 2 c deg‐1), responses to square‐wave gratings are found to be more accurate than those to sine‐waves. At higher frequencies the responses become very similar. An explanation is offered in terms of the contribution of higher harmonics to the square‐wave response.
VARIATION OF DARK FOCUS OF ACCOMMODATION WITH LASER SPECKLE EXPOSURE DURATION
Authors: Kothe A. C. , Lovasik J. V. , Campbell M. C. W.
Published: December 2007

Abstract Dark focus of accommodation (DFA) was measured in 10 subjects using a computer‐aided He‐Ne Badal laser optometer having high temporal and amplitude resolution. Accommodative responses were tracked during 5 min sessions for 10 speckle exposure durations ranging from 100 to 1000 ms. DFA‐speckle exposure functions fell into four distinct groups. This identifies the laser speckle exposure time as a possible contaminant in measures of DFA made by laser optometers if individual variability across exposure times is ignored. Group averaging of accommodative responses for laser exposure times obfuscates the reported individual variability.
A METHOD FOR RAYTRACING THROUGH SCHEMATIC EYES WITH OFF‐AXIS COMPONENTS
Authors: Clement R. A. , Dunne M. C. M. , Barnes D. A.
Published: December 2007

Abstract A linear algebraic method for tracing skew rays through aspheric surfaces is described. The advantage of this method is that the refracting surfaces can be translated and rotated with respect to each other. The method is used to investigate the optical factors affecting the location of Purkinje images.
VISION AND DRIVING*
Authors: Taylor J. F.
Published: December 2007

Abstract The major studies on the inter‐relationship between visual performance and road accident records are briefly reviewed. Statutory standards of vision for vehicle drivers are discussed, together with the responsibilities of the driver, Licensing Authority and those offering advice to drivers on their standards of vision.
Effect of magnification and field of view on reading speed using a CCTV*
Authors: Lovie‐Kitchin J.E. , Woo George C.
Published: December 2007

Reading speeds were measured in 18 subjects with normal vision and 10 with low vision for each of 20 experimental conditions with different magnifications and field sizes on the Closed Circuit Television System (CCTV). There was a significant difference between the results for the two groups of subjects. These results suggested that in low‐vision patients with faster reading speeds, minimum magnification for maximum field size on the CCTV would be valid advice. For low‐vision patients who read more slowly, reading speed may improve at higher magnifications despite reduced field size.
Accommodative accuracy to harmonically related complex grating patterns and their components
Authors: Dul Mitchell , Ciuffreda Kenneth J. , Fisher S. Kay
Published: December 2007

Monocular steady‐state accommodation was measured to harmonically related complex grating patterns and their components to determine the contribution of the various spatial waveforms to accommodative accuracy. Accommodative accuracy was greater for those waveforms containing summed odd‐harmonic spatial components than for those waveforms with specific spatial components either removed or isolated. The results suggest that the contrast gradient produced by the summed waveforms, rather than the presence of any particular subset of spatial frequency components per se, was a critical factor for accurate accmmodation.
The influence of contact lens wear on the corneal response to ultraviolet radiation
Authors: Ahmedbhai N. , Cullen A.P.
Published: December 2007

One eye of each of 15 male pigmented rabbits was fitted with a gas‐permeable rigid contact lens. Lenses were worn on a daily basis for an initial period of 7 days with the other eye serving as a control. After this initial period the lenses were removed and both eyes were irradiated with UV‐B (305 nm ± 9 full width half maximum) using either 0.03 J cm‐2 or 0.12 J cm‐2 which were approximately the epithelial and endothelial damage thresholds for this waveband respectively. The responses of the cornea were followed by microscopy and pachometry. Biomicroscopically there was a dramatic difference in response between contact lens wearing and non‐wearing eyes for the higher radiant exposure, whereas little difference was observed at the lower level. For both levels of radiant exposure there was a significantly less corneal thickness increase in contact lens wearing eyes after UV‐B irradiation. Recovery patterns were similar.
Effect of pupil size on dark focus accommodation
Authors: Miller R. J.
Published: December 2007

A potential concern in some studies of dark focus accommodation is the role of pupil size (and related spherical aberration) in laser optometer measurements. Dark focus measurements were obtained for 25 young adult subjects while they viewed the laser speckle pattern through artificial pupils of 3, 4, 5, 6, 7 and 8 mm diameter. Analysis showed no significant effect of pupil size on dark focus. It would appear that pupil size variations should not be a source of concern in laser optometer dark focus assessment.
Responses of myopes to volitional control training of accommodation
Authors: Randle Robert J.
Published: December 2007

Twelve young, low myopes were trained to control volitionally their accommodation responses and to achieve clear focus on visual targets moved progressively outward in optical distance. The trainees participated in from 15 to 40 daily training sessions (mean= 28 sessions). All demonstrated volitional control with varying degrees of control authority. Though three of the trainees were unsuccessful, the group achieved a statistically reliable extension of their far points. Post‐training optometric examinations were reliably improved over pre‐training examinations, but did not appear to be commensurate with the large gains in far‐point extension. It was hypothesized that the learned skill may have been ‘instrument‐specific’, i.e. it might not fully generalize to significantly improved post‐training binocular performance unless it were accompanied by clinical assistance to transfer the training.
Changes in the axis of astigmatism: A longitudinal study
Authors: Saunders H.
Published: December 2007

Changes in the axis of astigmatism have been followed up in the same individuals over several decades. Only a proportion of subjects with direct astigmastism in their youth change to inverse astigmatism by way of oblique astigmatism.
Visual reaction‐time versus action‐time
Authors: Campbell F.W. , Artigas J.M. , Felipe A.
Published: December 2007

The reaction‐time for movement was found to be around 150 ms and was compared with the time required to take action while two moving lines are on a collision course. Subjects were trained to either avoid or maximize collision. They did so accurately. The action‐time was about one‐third the reaction‐time.
Validity and reliability of visual acuity measurements
Authors: Lovie‐Kitchin J. E.
Published: December 2007

A more scientific method than the Snellen chart for determining visual acuity is imperative for research studies and is desirable in many clinical situations. The psychometric method using the constant contour interaction S‐chart of Flom has been regarded as an accurate and reliable visual acuity measure and has been used widely for research purposes. This paper compares visual acuity measured by the S‐chart with that measured by the Snellen and Bailey‐Lovie charts. The results indicate that the Baily‐Lovie chart is a valid, reliable and rapid method of measuring threshold visual acuity for research purposes.
Time‐of‐day variations in oculomotor function: II. Steady‐state accommodation to square‐wave gratings
Authors: Amerson Thomas L.
Published: December 2007

Time‐of‐day variations in both tonic accommodation and steady‐state accommodation to a grating were assessed for 16 observers who were tested once in the morning and again 12 hours later. The mean night‐time tonic accommodation was +0.5 D greater than the morning value. Square‐wave gratings of 4.2 and 8.4c/deg were presented to the observers at distances of 0,1.07, 2.13, 3.2 D. Over‐accommodation to far targets and under‐accommodation to near targets occurred for both gratings. All values of steady‐state accommodation were somewhat greater in the evening. Large individual differences were noted.
Long‐term endurance of adaptive shifts in tonic accommodation
Authors: Ebenholtz Sheldon M.
Published: December 2007

After an 8 min inducing period of sustained focusing on a target at the near point (NP) of accommodation, tonic accommodation was monitored at 8 min intervals over a 48 min period in darkness. A laser optometer provided evidence for asymptotically increasing tonic levels. Accordingly, eyes closed in darkness (EC) was not a condition for the relaxation or dissipation of enhanced tonic levels. Furthermore, refixating the NP target for 6 min, 24 min, after the initial focusing period, provided no significant enhancement of tonic accommodation over EC. On the other hand, focusing at far point (FP) or walking within a lighted hallway (WH) significantly reduced the tonic after‐effect to pre‐adaptative levels, but only transiently. Tonic after‐effect induced by NP focusing thus appear to be remarkably resistant either to long‐term attenuation or enhancement. A model based on the decay of accumulated sympathetic and parasympathetic neurotransmitters was developed to account for the contrasting fact that focusing at near targets for periods up to about 2–3 min as well as sustained focusing at far targets tends to yield complete decay to tonic after‐effects.
Crystalline lens accommodation and anterior chamber depth
Authors: Obstfeld Henri
Published: December 2007

Using paraxial equations, the change in dioptric power of the crystalline lens required to image objects at given distances from the eye, on the retina, is calculated. This shows that the depth of the anterior chamber affects crystalline lens accommodation more than other variables. The relationship between anterior chamber depth and presbyopia, and a possible geographical aspect, are discussed.
Optical matrices of lenticular polyindicial schematic eyes*
Authors: Raasch Thomas , Lakshminarayanant Vasudevan
Published: December 2007

The optical matrices for modified schematic eyes are derived. The primary modification is to replace the usual isoindicial or bi‐indicial crystalline lens with a polyindicial lens so as to more closely approximate the living human lens. Further modifications are made to simulate the accommodated state. The use of optical matrices to solve an optometric problem is demonstrated.
An evaluation of Bennett's method for determining the equivalent powers of the eye and its crystalline lens without resort to phakometry
Authors: Dunne M.C.M. , Barnes D.A. , Royston J.M.
Published: December 2007

Refraction and optical components have been measured in 36 eyes using objective optometry, keratometry, ophthalmophakometry and A‐scan ultrasonography. A computing scheme was used to confirm that the accumulated experimental errors for a phakometric technique tend to exceed the inherent errors of a new method which calculates the equivalent powers of the eye and its crystalline lens without resort to phakometry. Bennett's method was shown to be a valuable technique in biometric studies which obviates the need for lengthy experimental investigations.
Binocular vision, age and symptoms
Authors: Yekta A.A. , Pickwell L.D. , Jenkins T.C.A.
Published: December 2007

Changes with age in heterophoria, associated heterophoria, fixation disparity and stereopsis for near vision were investigated in a sample of 187 subjects (age range from 10 to 65 years) divided into six age groups. With increasing age, heterophoria, associated heterophoria and fixation disparity increased in the exo‐direction. No change in stereopsis was found.

A comparison with visual symptoms for near vision indicated a relationship between symptoms and the magnitude of fixation disparity and associated heterophoria for all age groups, but no relationship was found between the presence of symptoms and heterophoria measurement. No relationship between the presence of symptoms and the central slope of the forced vergence fixation disparity curve was found.

These findings suggested that neither the measurement of heterophoria nor the forced vergence disparity curve are appropriate tests in the assessment of binocular vision anomalies. However, fixation disparity and associated heterophoria are related to binocular problems for near vision in all age groups.
Analysis of a progressive addition lens population
Authors: Sullivan Colin M. , Fowler Colin W.
Published: December 2007

Analysis of 98 progressive addition lens (PAL) wearers was undertaken using both mailed questionnaires and by assessing patient records. Statistical analysis was undertaken to investigate the nature and dependant variables of a PAL population. The PAL patients were from the Aston University undergraduate optometric clinic. Social survey techniques, such as the use of personalized mail, first‐class stamps, and follow‐up letters, were employed to produce a high return rate for the questionnaire. The number of returned questionnaires reached 89.9 % of those originally sent which may be considered to be highly representative. The clinical survey showed the success rate for the undergraduate clinic to be either 85.7% or 80.6% depending upon the criterion for successful wear.
Theoretical principles of optical pachometry
Authors: Brennan Noel A. , Smith George , Macdonald John A. , Bruce Adrian S.
Published: December 2007

Various configurations have been suggested for the optical measurement of corneal thickness by slit beam doubling, and corresponding ray traces have been provided to relate actual thickness to apparent thickness. In this report, a set of equations is provided which apply to the general situation in which neither the angle of illumination nor the angle of observation are aligned with or symmetrical about the normal to the cornea. An explicit solution to these equations giving true corneal thickness in terms of apparent thickness cannot be established, and an iterative procedure is used to develop a relationship for a number of different pachometer configurations. The near linearity of these relationships suggests the existence of a simple equation to relate these entities. By making appropriate assumptions, a linear approximation relating the inverse of the true thickness to the inverse of the apparent thickness is developed. An equation for determining the location of measurements of peripheral corneal thickness is also derived. The equations presented here may be generally applied to all optical pachometer configurations, can be used to estimate the relative contributions of various sources of error in pachometry and provide a basis for obtaining uniform absolute derivations of corneal thickness.
Ectopic pupil associated with cerebral cortical injuries: a sentinel observation
Authors: Moress Ralph
Published: December 2007

Ectopic pupil (corectopia) not associated with primary eye disease, heredity, or midbrain injury is observed to be an incidental finding associated with most cerebral cortical injuries.
Hydrogel lens wettability during overnight wear
Authors: Guillon Michel , Guillon Jean‐Pierre
Published: December 2007

The in vivo wettability of soft contact lenses worn by a group of 10 subjects was monitored over a 24‐hour period including 8 hours closed eye. Two types of lenses were tested: Igel 67 (Prima) and Bausch & Lomb 70. They were each worn once in both eyes by all the subjects. The in vivo wettability of the lenses tested was evaluated by measuring the pre‐lens non‐invasive break‐up‐time (NIBUT) and assessing the nature of the pre‐lens tear film structure. The results obtained showed good wettability throughout the study and no difference between the two materials tested, but a significant difference between open and closed eye wear. The tear film was far more stable (p<0.01) immediately upon waking (mean NIBUT 21.2 s) than during open eye wear (mean NIBUT 11.2 s). Also at waking the pre‐lens lipid layer was thicker than during open eye wear and the lens surface had a greater mucous coating. The presence of a more stable pre‐lens tear film at waking was associated with a different tear film structure. We believe these differences in pre‐lens tear film structure are responsible for the greater stability recorded.
The effect of defocus on the contrast and phase of the retinal image of a sinusoidal grating
Authors: Walsh G. , Charman W. N.
Published: December 2007

The variation with defocus in the contrast and phase of the retinal image of a grating stimulus is computed from a knowledge of the meaured wavefront aberration of individual eyes. Contrast or modulation transfer is generally lower than in the aberration‐free, diffraction‐limited case, even at a pupil size of 3 mm, and marked spatial phase shifts, which can be seen as sideways shifts in the retinal image, frequently occur. A simple demonstration of these effects is given. The possible significance of the focus‐dependent spatial phase shifts for the phase discrimination of the visual system and accommodation is discussed.
Reduced vergence response velocities in dyslexics: a preliminary report
Authors: Hung George K.
Published: December 2007

Dyslexia is a developmental disorder characterized by a reduced ability to recognize or comprehend written or printed words. Two clinically diagnosed dyslexics and two normals served as subjects. Both dyslexic subjects showed reduced static accommodative and vergence ranges compared with normals and numerous regressions and fixation pauses during reading and target tracking tasks. The subjects were then presented with convergent and divergent ramp disparity stimuli ranging in speed from 1.33 to 32.0 deg/s and steps of either 2 or 4 degrees amplitude. The dyslexic subjects showed reduced vergence velocities and fewer step‐ramp and multiple‐step responses than normals. These preliminary findings suggest that certain vergence control functions may be diminished or absent in dyslexics. However, the vergence deficit may parallel dyslexia and may not be a causative factor. Thus vergence eye movement measurements may be used to provide additional insight into the components of the central deficits associated with dyslexia.
Comparison of accommodative adaptation using laser and infra‐red optometers
Authors: Rosenfield Mark
Published: December 2007

Previous investigations have reported differences in the rate of decay of accommodative adaptation depending on the form of optometer used to assess dark‐focus (DF). This study has used both laser and infra‐red optometers to measure pre‐and post‐task values of DF in 10 subjects. DF was assessed before and immediately after an 8 min near‐vision task performed at the subjective near‐point of accommodation. Examination of the data from the two optometers revealed significant differences in both magnitude and distribution of pre‐task DF. Additionally variations in the post‐to pre‐task shift in DF were observed between the two methods of assessment. Using the laser optometer, six subjects exhibited positive adaptation following the near‐task which was not apparent with the infra‐red optometer. The data suggest that both instruments may not be sampling open‐loop accommodation; the laser optometer is particularly vulnerable to extraneous influences.
Statistical inference on mean dioptric power: hypothesis testing and confidence regions
Authors: Harris W. F.
Published: December 2007

It has not hitherto been possible to apply formal methods of statistical analysis to data on dioptric powers. The solution to the basic statistical problem is now provided in this paper. Recognition of the matric‐variate nature of dioptric power allows calculation of sample means and variance‐covariances. These in turn can be used to calculate a statistic for testing hypotheses on population means and for obtaining confidence regions for those means. In a graphical representation of dioptric power the confidence region turns out to be an ellipsoid centred on the mean of the sample of dioptric powers. The theory is illustrated by means of numerical examples. Singularity of the variance‐covariance matrix may occur especially when the sample is small. When it does occur it is the cause of some difficulty in applying the statistics. Nevertheless singularity is rare in practical situations and can usually be avoided simply by increasing the size of the sample. Singularity, therefore, is not treated fully in this paper. Dioptric power is essentially four‐dimensional in character but in practice a three‐dimensional subspace is almost always sufficient. To avoid the difficulty of having to represent four‐dimensional shapes and to avoid the complication of singularity (which is the rule rather than the exception in practice in four‐space) only the common three‐dimensional problem is considered in detail.
Success rates in testing monocular acuity and stereopsis in infants and young children
Authors: Shute Rosalyn , Candy Rowan , Westall Carol , Woodhouse J. Margaret
Published: December 2007

This study demonstrated how success in stereopsis and monocular acuity testing in the under‐fives changes with age. Monocular testing was least successful with 1–2‐year olds, while success with stereopsis testing increased linearly to 100% by 3 years. The differing patterns mean that a reasonable degree of success with one test or the other is likely whatever a child's age. Since the demonstration of either stereopsis or normal monocular acuities rules out the presence of any gross visual anomaly, the age‐appropriate use of the two types of testing will facilitate the early detection of any abnormality.
Thickness and weight of lenses for myopia
Authors: Tang Churk‐yan
Published: December 2007

High index lens materials have been introduced to minimize lens weight and thickness. By studying the best form lenses for different refractive indices and the effects of changing lens forms on thickness and weight, a method is proposed for comparing minus lenses in weight and thickness for different refractive indices and lens diameters.
Topology of the near response triad
Authors: Myers Glenn A. , Stark Lawrence
Published: December 2007

The near response complex comprises three elements: accommodation, convergence, and pupillary constriction. The synkinesis between vergence and accommodation is well understood functionally, if not neuroanatomically. The latencies of near response components were measured in four healthy, experienced subjects to determine how the pupillary component is mediated. Addition of disparity stimulus to blur, yielding a near stimulus, reduces the latency of vergence eye movements and of accommodation by an amount that is significantly greater than the corresponding reduction in pupil latency. None of the existing hypotheses: vergence‐pupil, accommodation‐pupil or symmetric dual interaction, can account for this difference. Therefore, we present a new hypothesis: asymmetric dual interaction between accommodation and vergence.
Liquid crystal lens review
Authors: Fowler C. W. , Pateras E. S.
Published: December 2007

Liquid crystal lenses are possibly the spectacle lenses of the future for presbyopic corrections. They present a variable refractive index which can be used to produce the necessary addition needed for presbyopia. The variability of the refractive index is due to the fact that these materials are optically anisotropic. This effect is obtained by the application of an electric or magnetic field through the liquid crystal layer. A review of the literature relating to the evolution, the preparation and the operation of these lenses is given. A discussion is also included of the practical problems and drawbacks, which at present limit their use, and possible solutions.
Comparison of dioptric power
Authors: Harris W. F.
Published: December 2007

The important formal process of inferring properties of populations from statistics of samples requires a method by which variables can be compared or ranked. A suitable method of comparing dioptric powers is described. The method recognizes the essentially four‐dimensional nature of dioptric power and is sufficiently general to allow for comparison of powers (for example, equivalent powers of general thick bitorics) that cannot be represented in the usual manner, sphere/cylinder × axis.
Intracranial meningioma: an exercise in differential diagnosis
Authors: Flanagan John G. , Kothe Angela C.
Published: December 2007

A 48‐year‐old man presented with a unilateral visual disturbance including reduced visual acuity and decreased sensitivity of the temporal visual field. He was initially diagnosed as having optic neuritis. Four months later the condition not only remained unresolved, but showed signs of progression. This presentation was atypical for optic neuritis and further detailed investigation was warranted. The patient's symptoms, along with multi‐channel topographic visual evoked potentials and quantitative visual field analysis, were more indicative of a diagnosis of a space occupying lesion. A CT scan confirmed the presence of an intracranial tumour which was surgically excised. Pre‐and post‐operative visual function are described. The case report highlights the difficulty of differential diagnosis of optic neuritis and the clinical value of the appropriate and judicious use of multi‐channel evoked potentials.
Characteristics of the pre‐lens tear film during hydrogel contact lens wear
Authors: Young Graeme , Efron Nathan
Published: December 2007

The integrity of the pre‐lens tear film I PLTF) is an important determinant of the clinical performance of contact lenses. The PLTF of eight hydrogel lenses, ranging from 36.5% to 85% water content, was assessed on six asymptomatic lens wearers in a randomized, double‐masked experiment. Using a specular reflection technique, the thicknesses of the lipid and aqueous phases were found to be greater on lenses of higher water content. Water content was measured before and after 90 min wear using a hand‐held refractometer. Non‐invasive tear break‐up lime was also found to be greater for higher water content lenses. No association was found between lens dehydration and PLTF characteristics. The differences in PLTF noted in this study may help to explain the differences noted between some lenses in their rates of surface deposition.
The influence of age on the pattern and flash visual evoked magnetic response (VEMR)
Authors: Armstrong R. A. , Slaven A. , Harding G. F. A.
Published: December 2007

The visual evoked magnetic response (VEMR) was measured over the occipital cortex to pattern and flash stimuli in 86 normal subjects aged 15‐S6 years. The latency of the major positive component (outgoing magnetic field I to the pattern reversal stimulus (P100M) increased with age. particularly after 55 years, while the amplitude of the P100M decreased more gradually over the lifespan. By contrast, the latency of the major positive component to the flash stimulus (P2M) increased more slowly with age after about 50 years, while its amplitude may have decreased in only a proportion of the elderly subjects. The changes in the P100M with age may reflect senile changes in the eye and optic nerve, e.g. senile miosis, degenerative changes in the retina or geniculostriate deficits. The P2M may be more susceptible to senile changes in the visual cortex. The data suggest that the contrast channels of visual information processing deteriorate more rapidly with age than the luminance channel.
Spatial summation determines the contrast response of displacement threshold hyperacuity
Authors: MacVeigh David , Whitaker David , Elliott David B.
Published: December 2007

The effect of line length on displacement threshold hyperacuity at various levels of contrast was investigated. At high contrasts there was no significant effect of line length, but as contrast was reduced thresholds for shorter line lengths increased rapidly. Thresholds at longer tine lengths demonstrated a form of contrast saturation which differed from vernier acuity whose thresholds increased consistently with a reduction in contrast. As line length in the displacement threshold task was reduced, the amount of contrast saturation became less and displacement thresholds therefore resembled the contrast response of vernier acuity. Results are explained in terms of spatial summation along the length of the lines, the effects of which depend upon the spatial configuration of the hyperacuity stimulus under consideration.
A simple parametric model of the human ocular modulation transfer function
Authors: Deeley Robin J. , Drasdo Neville , Charman W. Neil
Published: December 2007

The ocular modulation transfer function (MTF) has an important role in many investigations into human Vision. It can be approximated by the equation MT= exp[‐ (SF/SFc)n]. where MT, SF, SFc and n are the modulation transfer, spatial frequency, frequency constant and MTF index respectively, in a theoretical study, the parameters n and SFc were determined by a mathematical method from previously published data. A general equation was deduced expressing the MTF as a function of pupil size for diameters of 1.5–7.5 mm. For pupil diameters below 1,5 mm different equations providing MTFs as a function of pupil diameter have been produced. These are based on the assumption that for these pupil diameters diffraction and retinal scatter determine the optical degradation. The use of these models is described in studies on spatial vision, where they have widespread applications and the effects of optical degradation are frequently neglected.
Representation of dioptric power in Euclidean 3‐space
Authors: Harris W. F.
Published: December 2007

Every dioptric power of the usual form sphere/cylinder x axis may be represented by means of a point in three‐dimensional space. Graphical representation of data in this manner is important for statistical analysis. In particular, graphical representation may be used to display confidence regions about a mean power, far example, A disadvantage of these representations, however, is that simply changing the reference meridian for cylinder axes changes distances in the space and therefore, changes the shapes of the confidence regions. Because the shapes define the nature of the variation and give, in particular, the principal components of variation, a researcher who happens to measure the orientation of cylinder axes from the 20 degree meridian. for example, instead of the conventional horizontal meridian, could be led to different statistical conclusions The implication is that such conclusions are unlikely to have much physical meaning. A representation is described here in which distances and shapes do not depend on the meridian that happens to be chosen as reference. Each dioptric power is represented by a point in Euclidean. 3‐spaec. Several examples of graphical representation are given. The spherical powers occupy a particular line in the space, the Jackson crossed cylinders occupy a plane, The cylindrical powers occupy a cone, and so on. for all types of conventional dioptric power. These lines and surfaces are illustrated. The statistical implications are discussed briefly. The representation satisfies the requirements at the statistics and is proposed as the standard one for future use.
Design of aspheric intraocular lenses
Authors: Atchison David A.
Published: December 2007

The value of aspherizing intraocular lens surfaces for the purpose of improving retinal image quality of pseudophakic eyes was investigated. Surfaces were made as coincoids. Changes in primary wave aberrations and refractive errors were found to be proportional to changes in surface asphericity, The optimum asphericity depends markedly on ocular parameters, lens fitting position and how well lenses are centred within the eye. If lenses are not well centred, the asphericity that eliminates spherical aberration may result in poorer performance than that occurring with spherical surfaces. It is suggested that there is no general benefit in aspherizing surfaces of intraocular lenses.
The amelioration of myopia using biofeedback of accommodation: a review
Authors: Gilmartin Bernard , Gray Lyle S. , Winni† Barry
Published: December 2007

The purpose of this review is to give an account of the issues raised by reports that myopia can be treated by operant conditioning or biological feedback. Devices are available that provide auditory feedback of accommodative state such that variation in tone frequency provides a means by which the patient can monitor his or her ability to induce changes in accommodation response, the task thus being to change the pitch of the tone in a direction corresponding lo a more distant far point. The aim of a training programme is to reinforce and establish control over the accommodative response by a process akin lo operant conditioning and subsequently to transfer the skill to normal visual environments such that a manifest reduction in myopia becomes apparent. Although there are reports that the technique can induce a reduction in myopia by up to 3 D the findings are of limited value owing to the tack of objective data, for example pre‐ and post‐training cycloplegic refraction. The pre‐ and post‐training measures of subjective letter acuity used by many studies are, with repeated trials, particularly vulnerable to individual differences in the ability to learn how to discriminate and interpret blurred images. The review concludes that more comprehensive clinical trials arc needed before accommodation biofeedback can qualify as an established method of clinical treatment of myopia. The trials should be designed to encompass the following issues: the characteristics of a feasible physiological model linking accommodation and myopia development; the rationale with regard to patient selection: the technical performance of the optometer employed; the characteristics of the control group used; the criteria for assessment of myopic change: the transfer of training to performance in normal visual environments; the economic viability of the programme of training and equipment: and the skill, training and knowledge of the clinician implementing the training programme.