bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison of clinical acuity and contrast sensitivity charts: effect of uncorrected myopia
Authors: Bradley Arthur , Hook John , Haeseker John
Published: December 2007

We have exmained the effect of corrected and uncorrected myopia on visual acuity and contrast sensitivity using a standard acuity chart and two commercially avilable printed contrast sensitivity charts (Vistech and Pelli–Robson). We tested 140 eyes of 70 young adults. Most subjects were myopic and were tested with and without their optimum spectacle or contact lens correction. We found no effect of myopia, if well corrected, on acuity or contrast sensitivity. All three test scores were sensitive to uncorrected myopia. The Pelli–Robson contrast sensitivity chart, which was designed to be insensitive to defocus, required more than three diopters of refractive error to elicit a two line change in performance, and it was generally very insensitive to uncorrected myopia. Although the Vistech chart was sensitive to uncorrected myopia, the large step sizes used in the chart, and the higher inter‐ and intra‐subject variability in scores reduces its potential value for refraction. The snellen letter chart gave the most sensitive and reliable changes in performance with uncorrected myopia.
Autosomal recessive inheritance of myopia in Hong Kong Chinese infants
Authors: Edwards† Marion , Lewis W. H. P.
Published: December 2007

Hong Kong Chinese infants were refracted by retinoscopy at regular intervals between (he age of approximately 10 and 40 weeks. Cyclopentolate 1 % was used to obtain cycloplegia. The spherical equivalent of the refractive error was calculated for each child and analysis of variance carried out according to the refractive status of the parents. From approximately 20 weeks of age a significant difference was found between the mean spherical equivalent of the refractive error of infants of parents both of whom were myopic and that of infants of parents neither of whom was myopic. At 40 weeks of age a good fit with an autosomal recessive probability model was obtained.
Statistical inference on mean dioptric power: asymmetric powers and singular covariance
Authors: Harris W. F.
Published: December 2007

Methods have been developed recently for testing hypotheses on mean dioptric power and for constructing confidence regions in situations that are most likely to be encountered. In this paper the methods are extended to make the analysis complete. A new situation covered specifically is that of dioptric power not of the form sphere/cylinder × axis. Such powers, termed asymmetric powers because the dioptric power matrices are asymmetric, include the equivalent power of a thick obliquely crossed bitoric lens. A second situation is that in which the covariance matrix of the sample of powers is singular. Symmetric dioptric power (the more familiar form of power) can be represented by a point in three‐dimensional space. In general, however, dioptric power is four dimensional in character. Singularity of covariance arises when variation in (he sample is limited to a subspace of dimension less than the full three or four. The space spanned by the sample is called the range space of the sample. The dimension of the range space may be four, three, two, one or zero. Each case is considered in turn. Numerical examples of hypothesis testing arc presented m range spaces of dimension four to one. The lest statistic devised for each case also gives the equation of the confidence region about the mean of a sample of dioptric powers. Singularity can sometimes he avoided merely by taking larger samples and by taking more accurate readings. The problem of near singularity is briefly discussed. The paper allows basic hypothesis testing on mean dioptric power and the construction of confidence regions in all possible circumstances.
Linear model of accommodation and vergence can account for discrepancies between AC/A measures using the fixation disparity and phoria methods
Authors: Hung George K.
Published: December 2007

The AC/A ratios obtained previously by the fixation disparity method were in most cases greater than those by the phoria method. An earlier study analysed a simplified linear model of the accommodation and vergence system. It was determined that equations corresponding to the two methods were equal, indicating that such a model could not account for the discrepancy found experimentally. However, two important components – tonic accommodation and tonic vergence – were omitted from this simplified model. In the present study, an analysis of the complete linear model showed that the equations corresponding to the two methods are different. In addition, calculation of the error between the cross‐link gain and the overall accommodative input – convergence output values indicated that the AC/A should be higher using the fixation disparity than the phoria method, Therefore, the predictions of the complete linear model are consistent with the data obtained experimentally.
Regional variations in binocular summation across the visual field
Authors: Wood J. M. , Collins M. J. , Carkeet A.
Published: December 2007

Binocular summation for a contrast detection task was measured as a function of eccentricity and target size along the horizontal and vertical meridians fur ten young normal subjects. Binocular summation at the fovea was of the order of 1.4 for all target sixes, although there was some inter subject variation. Binocular summation was highest along the vertical meridian. With increasing eccentricity from the fovea, binocular summation for target size I (0.108° projected diameter) decreased, remained relatively constant for target size III (0.431° projected diameter] and increased with increasing eccentricity from the fovea for target size V (1.724 projected diameter). For target sizes I and III, binocular summation was present only when inter ocular differences in sensitivity were under 5 dB, for target size V this relationship did not hold. Influences such as stimulation of corresponding retinal points and cortical representation are considered.
Constrained least‐squares estimation of surface curvature and dioptric power from meridional measurements
Authors: Harris W. F.
Published: December 2007

A dioptric power or surface curvature may be presumed or known to be of some particular type, for example spherical, or astigmatic and with a particular nearest equivalent sphere. Such knowledge or presumption represents a constraint on the power or curvature. This paper shows how meridional measurements can be used to obtain least‐squares estimates of surface curvature or dioptric power under the constraint.
Scanning laser measure of optical quality of the cultured crystalline lens
Authors: Weerheim J. A. , Sivak J. G.
Published: December 2007

An apparatus has been designed to automate the laser measuring technique and make it possible to monitor lens refractive function (spherical aberration) as well as change in lens transmittance during lens culture. A scanning laser beam (helium–neon) is used so that a number of beams puss through different spots on the lens to determine lens spherical aberration compared over time. Each refracted beam, received by two video cameras (X and Y directions), is digitized. The system first locates the optical centre of the lens by determining the beam position providing the least deflection for both the X and Y directions. The beam is then moved in predetermined steps on either side of the centre, and focal lengths are determined relative to the optic axis for each position. A measure of beam scatter is noted from post‐refraction pixel excitation for each beam position. Improvements to the scanning laser system have led to greater accuracy and speed as well as to improved culture cells. Accuracy was increased by using high resolution (1 μm) stepping motors to move the scanning helium neon laser. A new alignment process involving the superposition of the incident beam reflected on it self ensures that the incident beam is perpendicular to the lens equatorial axis. Scanning speed has been improved through a variety of hardware and software changes. Scanning time for a lens, including locating the optical centre and measuring focal length for 20 lens positions along the X and Y directions, takes about 60 seconds. Long‐term studies on the degradation of lens optical performance frequency yield diffuse beams of very low intensity. An option now exists to build an image using repeated frame grabs until a pre‐set level of intensity is reached. New lens cells consist of a flexible silicon rubber base enclosing a flat face plate, a lens carrier and a four‐sided, upper glass chamber.
Immediate colour constancy
Authors: Foster David H. , Craven B. J. , Sale Elizabeth R. H.
Published: December 2007

Colour constancy is traditionally interpreted as the stable appearance of the colour of a surface despite changes in the spectral composition of the illumination. When colour constancy has been assessed quantitatively, however, by observers making matches between surfaces illuminated by different sources, its completeness has been found to be poor. An alternative operational approach to colour constancy may he taken which concentrates instead on detecting the underlying chromatic relationship between the parts of a surface under changes in the illuminant. Experimentally the observer's task was to determine whether a change in the appearance of a surface was due to a change in its reflecting properties or to a change in the incident light. Observers viewed computer simulations of a row of three Mondrian patterns of Munsell chips. The centre pattern was a reference pattern illuminated by a simulated, spatially uniform daylight; one of the outer patterns was identical but illuminated by a different daylight; and the other outer pattern was equivalent but not obtainable from the centre pattern by such a change in illuminant. Different patterns and different shifts in daylight were generated in each experimental trial. The task of the observer was to identify which of the outer patterns was the result of an illuminant change. Observers made reliable discriminations of the patterns with displays of durations from several seconds to less than 200 ms, and for one observer, with displays of 1 ms. By these measures, human observers appear capable of colour constancy that is extremely rapid, and probably preattentive in origin.
Springer's lines and Hermann's grid
Authors: Laming Donald
Published: December 2007

Hermann's grid is a complete matrix of black squares; Springer's figure has alternate squares whited out. Both figures generate illusory elements, bright and dark lines in the white spaces, with different elements seen from different distances, The visibility of these different elements is shown to be related to the detectability of sinusoidal gratings of wavenumbers corresponding to certain critical components of the Fourier decomposition of the figure, Evidence from the detection of gratings shows that near‐and sub‐(but not supra‐) threshold contrasts are subject to a fourth power compression which shows, in the present figures, as a defect in the percept, equivalent to the deletion of (a part of) the corresponding Fourier components. There are some residual problems in understanding the perception of Hermann's grid.
Using distinctive Fourier components to discriminate between complex patterns
Authors: Thomas James P. , Olzak Lynn A. , Shimozaki Steven S.
Published: December 2007

Observers discriminated between a plaid pattern formed by summing vertical and horizontal cosine gratings, and a plaid formed by multiplying the gratings. Such patterns are alike with respect to many non‐Fourier primitives, but differ in the Fourier domain by diagonal components which are present in the plaid formed by multiplication, but not in the one formed by summing. When discrimination performance is related to the contrast of the diagonal components, it Ls found that the contrast threshold for discrimination is approximately the same as the threshold for detection of the isolated components. However, the psychometric function for discrimination is shallower than that for detection, suggesting the presence of masking. Despite the masking, the results support the proposition that discrimination processes may operate directly on the representations of local Fourier components.
Orientation anisotropy: some caveats in interpreting group differences and developmental changes
Authors: Ross Helen E.
Published: December 2007

We tested 220 children aged 7–12 yr and 20 university students for visual contrast sensitivity at spatial frequencies of 1.2 21.9c'deg for vertical, horizontal and oblique sinusoidal gratings. Males had higher menu sensitivity then females and adults had higher mean sensitivity than children‐ Sensitivity was greater for cardinal than oblique orientations, and this oblique effect increased with spatial frequency and mean sensitivity, and with age in children. Developmental growth of oblique anisotropy can be explained by growth in com nisi sensitivity. Different sizes of oblique effect were found between groups living in different locations, hut variations were mainly linked to differences in age and contrast sensitivity. Genetic or environmental interpretations of group differences should be t KM led with caution. Other anisotropies occurred (horizontal was better than vertical and right than left obliquest, but these differences were small and irregular and may represent response biases rather than neurological effects.
Amplitude spectra of natural images
Authors: Tolhurst D. J. , Tadmor Y. , Chao Tang
Published: December 2007

Several studies have suggested that the amplitude spectra of photographs of natural scenes are remarkably similar and have the form:
image
This is, of course, a straight line with slope of −1.0 when plotted on double logarithmic coordinates. We have examined the amplitude spectra of 135 digitized photographs of natural scenes and have Found that relatively few images conform exactly to the suggestion. About 25% of the images in our sample have spectra which show significant curvature when plotted on log log coordinates. The best‐fitting regression lines have slopes that range from −0.8 to −1.5: the average slope is −1.2, rather sleeper than previously suggested.
Effect of myelination on the conduction velocity of optic nerve fibres
Authors: Tolhurst D. J. , Lewis P. R.
Published: December 2007

It was proposed by Rushton in 1951. from theoretical considerations, that myelinaled fibres less than 1 μm in diameter would conduct more slowly than unmyelinnted fibres of the same size and that myelinaled fibres below about 0.7 μm would not conduct at all. The experimental data on which he based his theory are all from the peripheral nervous system where small myelinated fibres are rare, and no experimental verification of Rushton's hypothesis has been attempted. In mammalian optic nerve, nearly all the fibres are myelinaled; yet half have diameters below 1 μm, with many below 0.7 μm. The many studies of conduction velocities in the visual system enable a test of Rushton's hypothesis to he made. We have examined the correlations between conduction velocity and fibre diameter from a wide range of published studies of the mammalian visual system. The results of our analysis suggest that the small myelinated fibres of the optic nerve and optic tract conduct action potentials more rapidly than is predicted by Rushlon's hypothesis, while the unmyelinated along within the retina actually conduct more slowly than predicted. There is no reason to believe in this case, that myelination of a small axon will reduce its conduction velocity.
Screening for glaucoma: age and sex of referrals and confirmed cases in England and Wales
Authors: Tuck Maurice W. , Crick Ronald P.
Published: December 2007

This paper is based on a prospective survey covering 275600 sight tests by optometrists in England and Wales. It analyses the age and sex distribution of 1402 referrals for suspected glaucoma and 456 confirmed cases of the disease. The proportion of sight tests which led to a confirmed case increased with age, for both sexes, to a maximum at ≈70 years, and then tended to decline. Cases of glaucoma in people aged 36–51 years accounted for about LI tenth of the total, which is more than is generally recognized. Wider adoption of routine tonometry for middle aged people would help to ensure that these cases are detected at an early stage. Continued cases of glaucoma in which raised intraocular pressure had not been given as a reason for referral, i.e. probable low tension glaucomas, increased from 5% of patients <51 years old to 13% of patients >75 years old. Glaucoma was found to be much more common in men.
Evaluation of two infrared autorefractors in pseudophakia
Authors: Reeves B. C. , Hill A. R. , Carter S. C. , Sparrow J.
Published: December 2007

We investigated the viability of using an objective infrared autorefractor to identify high corneal astigmatism (>3.00D) in a pseudophakic population. The eyes of 91 patients, who had recently undergone cataract extraction and intraocular lens implanation, were refracted manually and using two infrared autorefractors, a Canon RK‐1 and a Nikon NR‐2000. Autorefractor measurements were repeated to provide estimates of reliability for each instrument. LogMAR visual acuities were also recorded with both the manual and autorefractor corrections. Approximately 75% of repeal autorefractor measurements were within 0.50 D of the initial readings, and about 75% of measurements were within 1.00 D of the manual refractions. Visual acuities with manual corrections were, on average, one line better than with autorefractor corrections. By validating the auto refractors against manual refraction, the efficiency of the autorefractors for detecting astigmatism > 3.00 D was calculated. Setting the cut‐off criterion to ensure high sensitivity (95%), so that almost all patients with >100D were detected, resulted in both instruments having a poor specificity of about 40%.
Refractive plasticity of the developing chick eye
Authors: Irving E. L. , Sivak J. G. , Callender M. G.
Published: December 2007

We have developed a lightweight plastic goggle with rigid contact lens inserts that can be applied to the eyes of newly hatched chicks to explore the range and accuracy of the developmental mechanism that responds to retinal defocus. Convex and concave lenses of 5, 10, 15, 20 and +30D were applied to one eye on the day of hatching. The chick eye responds accurately to defocus between ‐10 and + 15D. although hyperopia develops more rapidly than myopia. Beyond this range there is first a levelling off of the response and then a decrease. The resulting refractive errors are caused mainly by increases and decreases in axial length, although high levels of hyperopia are associated with corneal flattening. If ±10 D defocusing lenses are applied nine days after hatching the resulting myopia and hyperopia are equal to about 80% of the inducing power. After one week of inducing myopia and hyperopia with ±10 D lenses, the inducing lenses were reversed. In this case, the refractive error did not reach the power of the second lens after another week of wear. Instead, astigmatism in varying amounts (0–12 D) was produced, being greater when reversal was from plus to minus. Finally, astigmatism can also be produced by applying 9 D toric inducing lenses on the day of hatching. The astigmatism produced varies from 2 to 6 D. and the most myopic meridian coincides with the power meridian of the inducing lens. This astigmatism appears to be primarily due to corneal toricity. Furthermore, the greatest magnitude of astigmatism was produced when the piano meridian of the inducing lens was placed 45° from the line of the palpebral fissure.
Meridional profiles of variance—covariance of dioptric power, Part 2. Profiles representing variation in one or more of sphere, cylinder and axis
Authors: Harris W. F. , Malan D. J.
Published: December 2007

Meridional profiles of variation of dioptric power are constructed. Using the basic theory developed in an accompanying paper, samples are selected in a systematic way to illustrate variation only in sphere, only in cylinder and only in axis, and in all possible combinations of sphere, cylinder and axis. For each of the seven samples, scatter plots are constructed together with ellipsoids that represent the estimated distribution of powers in the population from which the sample was taken. The surfaces of the ellipsoids are surfaces of constant probability density within which 95% of the population is calculated to lie. The scatter plots and distribution ellipsoids are plotted in a three‐dimensional space called h‐space. Meridional profiles of variation are constructed for each of the samples. Properties of the profiles are discussed. Meridional profiles are also presented for eyes before and after radial keratotomy. Among other things, the profiles show meridians of greatest and least variation and are intuitively satisfying. They are potentially useful for the researcher and clinician including the surgeon. They may help to improve surgical and therapeutic‐techniques. Certain patterns may prove to be characteristic of physiological or pathological conditions, in which case meridional profiles may have use as a diagnostic tool.
Strategy for the design of multifocal surfaces
Authors: Hemenger Richard P.
Published: December 2007

A method is proposed which may prove useful as an aid in the design of non‐spherical surfaces with desired multifocal properties. More specifically, if an axially symmetrical surface is described by a polynomial then the coefficients of this polynomial can be found such that optical path lengths between given object and image points are nearly constant over desired portions of the surface. Three examples are given. One of the examples, a ‘trifocal’ surface, is compared to an aberration‐free two‐segment concentric bifocal contact lens.
Adaptation model of accommodation and vergence
Authors: Hung George K.
Published: December 2007

Both accommodation and vergence have been shown to exhibit adaptation after extended near viewing. Normally, when the stimulus to accommodation is removed, the accommodation system returns rapidly towards its ionic position. However, if the stimulus is removed after an extended focusing effort, the decay is much slower. A similar effect can be observed in the vergence system. After prolonged wearing of horizontal prisms, blockage of one eye results in a much slower decay of the vergence output towards its tonic value. No previous models have been shown to simulate quantitatively these effects. An interactive dual‐feedback model of accommodation and vergence was developed to simulate the adaptive behaviour found experimentally. The unique feature of the model is that the output of each controller drives a dynamic adaptive component whose output governs the time constant of the controller. The model was able to simulate the rapid and slow decays following short and long viewing intervals m each of the accommodative and vergence systems. It also simulated adaptation during alternate binocular and monocular viewing under the accommodation closed‐loop condition. Thus, this model can serve as the basis for detailed quantitative evaluation of adaptive behaviour in the accommodation and vergence systems.
Variation in ocular modulation and phase transfer functions with grating orientation
Authors: Walsh G. , Charman W. N.
Published: December 2007

For circular pupils of diameters 2 mm the optical performance of the eye in monochromatic light is effectively diffraction‐limited, so that its modulation transfer function (MTF) is essentially independent of grating orientation and its phase transfer function (PTF) is close to zero. For larger pupils, however, the wave aberration of the eye usually exceeds the Rayleigh quarter‐wavelength limit. It is shown that the monochromatic MTF may then display marked variation with orientation and the associated PTFs can be non‐zero. The exact effects vary markedly with the individual subject. In white light additional asymmetries may occur due to transverse chromatic aberration.
Scheme for the calculation of ocular components in a four‐surfaced eye without need for measurement of the anterior crystalline lens surface Purkinje images
Authors: Dunne Mark C. M.
Published: December 2007

The computing scheme described in this paper allows calculation of the internal radii of the human eye on the assumption that it possesses four (two corneal and two lenticular) axially aligned spherical surfaces separated by homogeneous optical media. It involves measurement of Purkinje images I, II and IV. This approach is novel in that it accounts for the contribution of the posterior corneal surface and does not require measurement of the Purkinje images arising from the anterior crystalline lens surface which are notoriously poor in quality.
Colorimeter for the intuitive manipulation of hue and saturation and its role in the study of perceptual distortion
Authors: Wilkins Arnold J. , Nimmo‐Smith Ian , Jansons Judy E.
Published: December 2007

A simple optical method for mixing coloured light is described. The observer has intuitive and approximately independent control over hue and saturation at constant brightness. The method facilitates colour matching by unpracticed observers. It allows children with reading difficulties to select a colour that reduces perceptual distortion of text. The chromoticity coordinates of this colour vary from one observer to another but can be very specific. Complementary colours can exacerbate the distortions and induce pain. For the majority of children reporting beneficial perceptual effects, the ú coordinate is less than 0.25.
Fixation disparity at different viewing distances of a visual display unit
Authors: Jaschinski‐Kruza Wolfgang
Published: December 2007

Fixation disparity was measured while subjects observed a realistic alphanumeric pattern on the cathode ray tube (CRT) of a visual display unit at viewing distances of 25–85 cm. The psychometric function of fixation disparity was determined by analysing the observers' responses to a series of short (100 ms) flashes of nonius targets that were superimposed on the CRT‐image by means of a half‐silvered mirror. Test‐retest correlation of fixation disparity was high (r= 0.8) at viewing distances of 40 and 82 cm and lower (r= 0.55) at the shorter distance of 26.5 cm. Mean fixation disparity increased to a more exophoric condition as the display approached the eyes. However, this effect was observed only in some of the subjects. so the susceptibility of fixation disparity to viewing distance appears to be an individual characteristic. When subjects observed the VDU screen continuously for 30min at viewing distances of 85, 47. 31 and 25cm in different sessions, fixation disparity and accommodation remained unchanged over time.
Structural model for emmetropic and myopic eyes
Authors: Scott Rolene , Grosvenor Theodore
Published: December 2007

A structural model for the eye was tested using refractive component data for 42 emmetropic eyes (−0.50 to +1.50 D) and 42 eves having front 5.00 to 7.00 D of myopia. Parameter estimates derived by applying the structural model to emmetropic eyes and to myopic eyes demonstrated that; I common model described the two types of eyes, but that emmetropic eyes and myopic eyes could be considered to belong to statistically discrete populations. Cornea] radius and vitreous chamber depth were the most important components determining refractive state.
Mathematical models of the general corneal surface
Authors: Burek Henry , Douthwaite W. A.
Published: December 2007

Although the curvature of the general cornea's two principal meridians can be acceptably modelled (within limits) by ellipses, this is insufficient to delineate the overall corneal surface. Applying different assumptions in either case, two corneal models arc advanced which interpolate x, y, z points over the whole corneal surface, dependent only on the specifications of the plane curves of the principal meridians.
Effect of light filters on contrast sensitivity function in normal and retinal degeneration subjects
Authors: Leguire L. E. , Suh S.
Published: December 2007

Contrast sensitivity functions were measured with live light tillers and without a filter, in the presence of a glare source, in 12 retinal degeneration subjects and 9 normal subjects. The light filters included yellow‐tinted, CPF 527, NoIR 111, 0.6 neutral density and sunglasses with a 95% UV filter. Retinal degeneration subjects showed a mild improvement in contrast sensitivity at the higher spatial frequencies and maintained mean log contrast sensitivity with light filters which reduced photopic light transmission up to 75%. Normal subjects exhibited a systematic decrease of contrast sensitivity at higher spatial frequencies with all light fillers and overall mean log contrast sensitivity was significantly correlated (r= 0.86, P < 0.025) with photopic light transmission of the fillers. It is concluded that, when in the presence of a glare source, the benefits of certain light filters to retinal degeneration subjects is related to the reduction of overall photopic luminance.
Modelling sensitivity losses in ocular disorders: colour vision anomalies following intense blue‐light exposure in monkeys
Authors: Kalloniatis Michael , Harwerth Ronald S.
Published: December 2007

The effects of prolonged exposure to intense, short‐wavelength light were studied in monkeys through the measurement of increment‐threshold spectral sensitivity (ITSS) and threshold‐versus‐intensity (TVI) functions using a behavioural method. The long‐term effect of intense blue‐light exposure was to induce a short‐wavelength (SW) sensitivity loss which did not depend on the intensity or chromatic composition of the adapting field. The TVI curves for short wavelength stimuli revealed an increase in test threshold without changes in field sensitivity. Since this SW sensitivity loss may generalize to characteristic colour vision defects found in many outer retinal diseases, models of acquired alterations of colour vision mechanisms are considered. These models describe probable changes in ITSS functions and TVI curves in diseases affecting the inner or outer retina as well as changes in dark adaptation.
Weight of edged spherical lenses in simulated eyewire shapes
Authors: Tang Churk‐Yan
Published: December 2007

Eyewire shapes of some currently available spectacle frames were constructed mathematically and weights of spherical lenses cut to these shapes were computed for different decentrations in three commonly used lens materials. The results confirm a previous observation that the edged shape of a negative lens has only a minor effect on its weight, although this is often not the case for positive lenses. The appropriate diameters of circular centred lenses to be used in comparing lens weight for different materials were also examined Relative to those adopted in previous studies, it was found that the weight of a larger lens, 58 mm diameter for negative lenses and 65 mm diameter for positive lenses, would more adequately represent the average weight of edged lenses in modern spectacle frames.
Red–green flicker resolution as a function of heterochromatic luminous modulation
Authors: Capilla P. , Aguilar M.
Published: December 2007

Critical fusion frequencies have been evaluated in heterochromatic red–green flicker as a function of red green luminous modulation defined by mL= (R ‐ G)/(R+G)%, at live different mean luminance levels, two test sizes (2° and 5°) and square wave stimuli. The extreme values mL=±100 correspond to ordinary light–dark flicker (red or green); mL= 0 corresponds to pure chromatic flicker, and any other values correspond to simultaneous luminous and chromatic flicker. To implement the stimuli we have developed a new stimuli generator (AVICO, colour vision analyser) using bicolour LEDs as (he light source and electronic control of the luminances and frequencies. The results for any luminance level and both test sizes show a minimum critical fusion frequency in the case of pure chromatic flicker (photometric match condition) and a critical fusion frequency which is slightly higher in the green extreme (mL= ‐100) than in the red (mL=+100). The shape of the variation between the minimum and the extremes is consistent with the results recently reported by Swanson and the theoretical models for the luminance channel response to heterochromalic flicker.
Relative effectiveness of different modes of glaucoma screening in optometric practice
Authors: Tuck Maurice W. , Crick Ronald P.
Published: December 2007

This study analyses records from 189 optometric practices in England and Wales on the glaucoma screening of 123415 patients aged >40 years during a prospective 6 month period Its purpose is to compare the effectiveness of the various modes of screening which were used. All optometrists tested every patient by ophthalmoscopy. The 146 who, in addition, conducted tonometry on n routine basis delected a confirmed glaucoma in 0.35% of their patients, whilst the 43 who used tonometry ‘on suspicion’ detected a case in 0.25%, (p < 0.02). The 47 optometrists who conducted perimetry frequently (i.e. in 15% of sight tests) detected a case in 0, 46% of patients, whilst the other 142, who did little or no perimetry, detected a case in 0.29%, (P < 0.001), Eleven optometrists who relied mainly on ophthalmoscopy had a detection rate of only 0.12%. Optometrists with the most comprehensive modes of screening had the greatest referral accuracy. It was concluded that more widespread adoption of routine tonometry for people aged ≥40 years is necessary to reduce the present substantial number of false negatives: and that the frequent use of visual field analysis is additionally required to achieve the best results.
Mechanical manipulation of the lids and tear break‐up time measurements in Hong Kong Chinese
Authors: Brown Brian , Cho Pauline , Yap Maurice K. H.
Published: December 2007

We measured tear break‐up time (TBUT) after lid‐rubbing in a single masked experiment, and found that TBUT was unaltered. A further single masked experiment in which non‐invasive tear break‐up Lime (NITBUT) was measured after the lids were raised as if to apply fluorescent also showed no effect of this interference with the lids. An experiment in which fluorescent was applied either with the lid raised or not raised during fluorescein application, again with the experimenter masked with respect to treatment, also produced no significant difference in TBUT. When we measured TBUT with the lid raised so that it was not in contact with the cornea, there was no difference in TBUT for the group between the “lifted” and ‘non‐lifted’ eye; some subjects showed substantially shorter TBUT values, while others showed substantially longer TBUT values. These findings are surprising in view of the concerns expressed in the literature regarding the sensitivity of the tear film to mechanical interference, and suggest that the tear film is more resistant to disruption than has previously been thought.
Accommodative and pupillary responses to sinusoidal target depth movement
Authors: Takagi Mineo , Abe Haruki , Toda Haruo , Usui Tomoaki
Published: December 2007

We evaluated the accommodative and pupillary responses to sinusoidal target depth movement in 10 normal subjects and one patient by analysing frequency responses and associated Bode plots. The phase of the pupillary response significantly lagged behind that of accommodative response, which suggests that they are controlled by separate central nervous systems. We measured the baseline shift of each response trace using a regression line and found that they were larger at higher stimulation frequencies. A patient with severe asthenopia showed a considerable baseline shift in accommodative response.
Effects of a visual task with cognitive demand on dynamic and steady‐state accommodation
Authors: Iwasaki Tsuneto
Published: December 2007

Dynamic accommodative response before and after, and steady‐state accommodation during, a visual task were measured using an infrared optometer to investigate the effects of psychological stress on accommodative facility. Increase in the post‐task dynamic accommodation response time (for a near‐to‐far condition) was greater for a group of subjects given a mental task at a higher presentation speed. In addition the steady‐state accommodation showed an inward shift under a closed‐loop condition which was enhanced when computation time was decreased. However, an inward shift was not evident when the performance level of subjects increased following training. The relationship between psychological stress. cognitive demand and accommodative function is discussed.
Ocular rotation factor and orientational demand with astigmatic lenses*
Authors: Harris W. F.
Published: December 2007

Ocular movements required in most visual functions are affected by lenses in front of the eye. Fundamental to an understanding of these movements are concepts such as the ocular rotation factor and the ocular orientational demand. In this paper the ocular rotation factor for thin spherical lenses is generalized for astigmatic lenses. A compact matrix equation is obtained for the orientational demand in the case of such lenses. The equations are satisfactory in ordinary situations but they break down under certain circumstances. Equations arc derived for these special circumstances in particular and also for all circumstances in general.
Colour vision screening in children: an evaluation of three pseudoisochromatic tests
Authors: Birch J. , Platts C. E.
Published: December 2007

We examined 513 children (258 boys and 255 girls), between 3 and It years of age, with three pseudoisochromatic tests which involve different visual tasks. These were a selection of numeral designs from the Ishihara test, the Ishihara test for Unlettered Persons and the Velhagen Pflügertrident test. Eighteen children were found to be colour deficient. The symbol designs of the Unlettered Persons test were found lo be the quickest and most effective method for examining children under 7 years of age. After 7 years of age the symbol designs of the Unlettered lest and the numeral designs of Ishihara lest were equally effective. The preferred numeral designs for screening children with the Ishihara plates are listed. Verbal identification always produced the most accurate results, Drawing over the figures or selecting replicas increased the viewing lime and assisted children with normal colour vision lo see both figures in transformation designs, especially pathway designs. The Velhagen Pflügertrident test was found to be unreliable for colour vision screening and younger children had difficulty performing the figure matching task.
Effect of filters on disability glare
Authors: Steen Richard , Whitaker David , Elliott David B. , Wild John M.
Published: December 2007

Disability glare is the reduction in visual performance caused by a peripheral glare source. We examined the effect of a long wavelength pass (red) and a short wavelength pass (blue) filler on disability glare in the presence of varying amounts of induced wavelength dependent stray light. Measurements were made in the absence of any filter and then repeated in the presence of the red and blue fillers whose luminous transmission factors were equal relative to both the stimulus and the glare source. Neither of the filters had any effect on disability glare. Filters not only reduce the amount of veiling luminance from the glare source, but also reduce the ability to detect the stimulus. Disability glare was not significantly different with the red and blue filters, even in the presence of wavelength dependent scatter. Calculation of the veiling luminance transmitted by each filter revealed that the difference in veiling luminance in the two filter conditions was insufficient to result in a measurable difference in disability glare.
Optic disc interpretation in glaucoma: is confidence misplaced?
Authors: Montgomery Donald M. I. , Craig Jennifer P.
Published: December 2007

A photographic questionnaire has been used to investigate whether or not clinicians have realistic expectations of their ability lo distinguish optic discs associated with glaucomatous visual field loss from discs of healthy eyes. The questionnaire consisting of 30 non‐stereoscopic fundus photographs from 15 patients was administered to 40 ophthalmologists of varying experience and 10 optometrists. Each group displayed large discrepancies between their expected and achieved scores suggesting that clinicians may overestimate their ability lo recognize the glaucomatous optic disc. This could lead to diagnostic errors especially in cases where tonometric and visual field parameters are considered equivocal. An over‐reliance on the cup/disc ratio appeared to be the most likely cause of error.
Glasgow Acuity Cards: a new test for the measurement of letter acuity in children
Authors: McGraw Paul V. , Winn Barry
Published: December 2007

Problems with design and format of the traditional Snellen chart have led to the development of alternative charts for the measurement of visual acuity in adults. However, advances in chart design for the measurement of visual acuity in pre‐school children have not paralleled those used in adult test charts. Visual acuity can be measured in infants and very young children using behavioural and electro‐physiological techniques but clinical measurement of letter acuity tends to commence when the child is old enough to interact and co‐operate with the examiner. Charts which arc commercially available in the UK for measuring letter acuity in pre‐school children (3–5 years old) either use single optotypes or are derivatives of the Snellen format. There is a need for a test of letter acuity for use with this young age group which is accurate, reliable and based upon sound and established design principles. Glasgow Acuity‐Cards have been designed to include features that should allow change in letter acuity to be detected in pre‐school children, especially those undergoing vision therapy training. The test is performed at 3 m and incorporates several design features which have been used previously in adult charts but are new to childrens' test charts. These include: linear progression of letter sizes using a log scale; letters of approximately equal legibility; equal number of letters per line; control of contour interaction; screening cards to determine initial level of acuity. The test is quick and easy to perform and should provide a means of detecting change in letter acuity, with increased confidence.
Supernumerary eyes and man's search for hyper‐vision: a historical review of relevant representational arts
Authors: Diamandopoulou‐Drummond A. H. , Diamandopoulos A. A. , Marketos S. G.
Published: December 2007

In this paper we present examples or man's identification of superiority with visual hyper‐efficiency. From Babylonian, Egyptian. Minoan and Biblical times, the eye was the symbol of the master or the inspector. Similarly, a being or deity that was endowed with multiple eyes‐with or without multiple heads‐was considered to be extra powerful. An example is the crest of the British College of Optometrists, which is surmounted by a bird with three heads and hence supernumerary eyes, linking it to the College's motto 'aequis oculis videre' denoting equal vision. We present here photographic and textual data from several historical periods extending from the fourth millennium nr to the sixteenth century AD; and from different religious sources, both Christian and non‐Christian, to support this thesis. However, these are only a few examples, selected from a larger on‐going study of the subject.
Visual field analysis using artificial neural networks
Authors: Spenceley S. E. , Henson D. B. , Bull D. R.
Published: December 2007

There have been several reports on the application of artificial neural networks (ANNs) to visual field classification. While these have demonstrated that neural networks can be used with good results they have not explored the effects that the training set can have upon network performance nor emphasized the unique value of ANNs in visual field analysis. This paper considers the problem of differentiating normal and glaucomatous visual fields and explores different training set characteristics using field data collected from a Henson CFS2000 perimeter. Training set properties including size, balance between normals and glaucomas, extent of field loss and the spatial location of glaucomatous defects are explored. A multilayer network with 132 input nodes, 20 hidden layer nodes and 2 output nodes is trained using an error backpropagation algorithm. Both sensitivity and specificity are measured during testing. The results demonstrate that large random sets are better than small random sets since sensitivity improves with size and specificity is not adversely affected. The variability in performance also reduces as training set size increases. In addition, sets that are biased towards glaucoma examples are more sensitive and less specific, while sets biased with normal examples are more specific and less sensitive than balanced sets. Thus large training sets with class balance are generally desirable for good sensitivities and specificities. The actual glaucoma examples contained in the set are also important, A training set deficient in examples of early loss produce poor sensitivities and good specificities, while an absence of advanced loss training examples has no detrimental effect on sensitivity or specificity. The spatial distribution of detects is also crucial. Spatially biased sets are unable to recognize defects that occur in locations where no previous defect has been presented while more balanced sets lead to better performance. In conclusion the ‘ideal’ training set should contain many examples of early defects that represent the full range of locations where these defects may occur.
Vision evaluation in people with Down's syndrome
Authors: Pérez‐Carpinell J. , de Fez M. D. , Climent V.
Published: December 2007

We tested the colour vision of 72 people with Down's syndrome using the Ishihara test and an anomaloscope. We found that 13 of the subjects, 6 males and 7 females, had defective colour vision according to Pickford's classification. In monocular vision 10 eyes were protan (five simple, three extreme and two deviant), one eye was simple deuteranomalous and the remaining eyes were normal: in binocular vision four of the subjects were protan (two simple and two deviant), two subjects were deutan (one simple and one deviant) and the rest were normal. Many of our subjects had lens opacities, strabismus, nystagmus, hypermetropia, high myopia and astigmatism, confirming literature reports. The contrast sensitivity function measured with the VCTS test showed a considerable toss of low‐frequency sensitivity in our subjects compared to a normal population, which was more marked in the more severely impaired subjects.
The Health and Safety (Display Screen Equipment) Regulations 1992
Authors: Taylor S. P.
Published: December 2007

A European Community directive issued in 1990 set down minimum requirements for health and safety of visual display equipment users. These requirements have now become a legal reality in the UK with the Parliamentary approval of the Health and Safety (Display Screen Equipment) Regulations 1992. While only a relatively small section of the legislation is directly relevant to optometric and dispensing practice it is important that the overall content of the legislation is known by members of these professions to assist them in their work with display screen equipment users. This brief review identifies the elements that make up the new legislation.