bluuebunny/crossref_metadata_2025 huggingface dataset:
Patterns and contrasts in ophthalmic investigation*
Authors: Drasdo N.
Published: December 2007

The Snellen test has been the most popular clinical measurement of spatial vision for over a century, but it does not fully express the visual ability of an individual. For more analytical purposes the information capacity of the visual system may be assessed by tests of contrast sensitivity and peripheral vision. The visual system selectively reduces the spatial information content of the visual field to avoid overloading the limited capacity for perception and decision making in the brain. The ways in which this reduction occurs and the processing of spatial information is of interest in many disciplines, and theoretical knowledge has been accelerated by the study of artifical intelligence. These processes may be investigated in human subjects by psychophysical and electrophysiological techniques. This provides additional information for diagnostic purposes and will form the basis of new systems of clinical investigation.
Comparison of associated heterophoria measurements using the Mallett test for near vision and the Sheedy Disparometer
Authors: Pickwell L.D. , Gilchrist J.M. , Hesler J.
Published: December 2007

The Mallett test for near vision and the Sheedy Disparometer are compared in terms of their ability to measure associated heterophoria. Twenty‐two asymptopmatic subjects were used. With the Disparometer, ten of these subjects, familiar with making prism vergence measurements, exhibited stable forced vergence fixation disparity curves, and the associated heterophoria values using both instruments were not significantly different. However, the twelve subjects not familiar with making such measurements generated fluctuating, unstable fixation disparity curves, and the associated heterophoria values were significantly different. Repeated trials with the randomly selected naäve subjects led to flatter, more stable fixation disparity curves and lower values for the x‐and y‐intercepts when using the Disparometer. The Mallett test, however, produced identical values for associated heterophoria in each successive trial. Therefore, the validity of measurements using the Disparometer in a clinical setting is questioned.
Prediction of visual function behind cataract using displacement threshold hyperacuity
Authors: Whitaker David , Deady James
Published: December 2007

Visual acuity and displacement threshold hyperacuity were measured in a group of patients awaiting cataract extraction, and this was repeated several weeks subsequent to surgery. In addition, measurements were made on a group of patients with various ocular pathologies but without the presence of cataract. Displacement thresholds in the cataract group increased only slightly with the severity of the opacity. On the other hand, displacement thresholds for the pathology group showed a marked dependence upon visual acuity‐the worse the acuity, the higher the threshold. This results in a clear distinction between vision loss due to optical factors (cataract) and retinal/neural factors. There was a good correlation between pre‐and post‐operative displacement thresholds in the cataract group, with post‐operative thresholds being slightly better than pre‐operative thresholds. The results suggest that this technique may offer patients a good indication of the likely quality of vision achieved following cataract extraction.
A brief review of magnetic fields from the human visual system
Authors: Armstrong R. A. , Janday B.
Published: December 2007

Both the eye and berain generate magnetic fields when stimulated with a variety of visual cues. These magnetic fields can be measured with a magnetometer; a device which uses superconducting technology. The application of this technique to measuring the magnetooculogram, magnetoretinogram and visually evoked fields from the brain is described. So far the main use of this technique has been in pure research. Its potential for diagnosing ocular and neurological diseases is discussed.
The spectral transmittance of hydrogel contact lens filters
Authors: Abadi Richard V. , Davies Ian P. , Papas Eric
Published: December 2007

The spectral transmittance characteristics of each of thirty‐two solid tint hydrogel contact lenses available in the United Kingdom were investigated using a dual beam spectrophotometer. Good agreement was found with the small number of spectral functions that had previously been published. Lenses with similar colour appearances were seen to differ markedly in terms of their transmittance factors. The importance of visual performance and radiation protection is discussed in the light of the spectral transmittances of the lenses.
Meridional differences in temporal response characteristics
Authors: Styles Tim , Flanagan John G.
Published: December 2007

It is well established that a large variety of psychophysical factors influence the critical flicker fusion frequency (CFF). Several recent studies have examined the relationship between CFF and retinal location with confounding and contradictory results. The aim of this study was to determine the CFF for a number of stimulus sizes and luminances in an attempt to evaluate the interactive effects of these parameters and the quadrantic variation in temporal sensitivity.

Retinal sensitivity gradients were measured along the two major oblique meridians out to an eccentricity of 50 degrees. CFF profiles for the 1.724 and 0.431 degree targets were shown to decrease with increasing eccentricity more rapidly in the inferior nasal quadrant (superior temporal retina). No significant difference between superior and inferior visual field temporal processing was evident.
Calculation of crystalline lens radii without resort to phakometry
Authors: Royston J. M. , Dunne M. C. M. , Barnes D. A.
Published: December 2007

A computing scheme was developed in 1988 to determine the equivalent powers of the eye and its crystalline lens without resort to phakometry. An adaptation to this scheme is described which allows calculation of the crystalline lens radii using an assumed average value for Q. The values obtained for lens radii using this method compare well with phakometric measurements made on 36 eyes (ocular refraction range‐9.37 D to +3.14 D) which suggests that the variations in Q for a large proportion of the population are small.
An extension of Helmholtz's explanation of Listing's law
Authors: Clement R. A.
Published: December 2007

Helmholtz argued that the eye moves in accordance with Listing's law to ensure that objects have the same apparent direction despite changes in the point of fixation. Listing's law ensures that the same pattern of image displacements is associated with a given eye movement, independent of the initial point of fixation. His explanation has been extended to the problem of ensuring that objects remain at the same apparent depth, with both direct and indirect fixation. This problem is simplified if disparity is analysed in the region of the frontal plane.
Geometrical ray‐tracing: a ‘ray free’ method
Authors: Ho Arthur
Published: December 2007

A new geometrical method of determining the location of the image of an optical component is described. This method does not require rays to be drawn. It can be applied to refractive and reflective components as well as multi‐component systems.
Light scatter in cataractous lenses
Authors: Hemenger Richard P.
Published: December 2007

A hypothesis is presented concerning the source of narrow‐angle light scatter in lenses with nuclear or cortical senile cataracts.
The influence of age on the pattern‐reversal electroretinogram
Authors: Hull B. M. , Drasdo N.
Published: December 2007

Pattern reversal electroretinograms (PERGs) in response to 30′ checks and 6 degree checks were recorded from 60 eyes of 30 normal healthy individuals aged between 20 and 78 years. Results were assessed to show age changes in the amplitudes and latencies of the PERGs, the ratio of 30′ to 6 degree PERG amplitude, the ‘N95/P50’ ratio and the inter‐eye ratio of the 30′ PERG. The positive component of the PERG decreases in amplitude and increases in latency with increasing age. In addition, it was found that the 30'PERG/6 degree PERG ratio decreases, the N95/P50 ratio increases and the inter‐eye ratio shows a greater difference between the two eyes in the older subjects.
Measurement of eye rotations in three dimensions and the retinal stimulus projection using scanning laser ophthalmoscopy
Authors: Ott Dietmar , Lades Martin
Published: December 2007

A transformation algorithm is introduced to specify eye rotations in three dimensions from two‐dimensional translations of ocular fundus landmarks dynamically monitored by means of the novel Scanning Laser Ophthalmoscope (SLO). The rotation parameters are expressed as Y‐X‐Z Euler angles and in terms of the rotation axis and one rotation angle. Additionally, the angular distance of the retinal stimulus projection can be evaluated relative to the fovea. By simultaneously operating as eye movement measurement device, fundus camera, and visual target projector, the SLO opens a variety of new applications for the combined analysis of eye movements and the underlying ‘retinal events' in viion’ and oculomotor research.
Direct, vec and other squares, and sample variance—covariance of dioptric power
Authors: Harris W. F.
Published: December 2007

Matrices can be multiplied in several ways. As a result one can define a number of distinct squares of the dioptric power matrix. Additional squares can be defined for matrices vectorized by means of the vec and vech operators. These various squares can form the basis for the definition of variance and covariance of samples of dioptric powers. The complete form of the variance of dioptric powers is a 4 × 4‐matrix (a variance covariance matrix) with 10 distinct elements; four of them represent the variances of the four elements of the dioptric power matrix and the other six are the covariances between those four elements. For thin systems there are only six distinct elements of the variance‐covariance matrix, three of which are variances and three covariances. Examples are included that show the calculation of the different types of squares and the variance‐covariance matrix for a sample of equivalent powers of thick bitoric lenses and for a sample of powers of thin systems, including conventional refractive errors. Variances calculated in the past, including those of nearest equivalent spheres and Gartner's and Churms's variances turn out to be components (or combinations of components) of the generalized variance defined here. They are valid as far as they go but they do not completely represent the dispersion of a sample of dioptric powers. The complete variance‐covariance matrix does represent the dispersion fully and thus opens the way for the formal statistical analysis of measurements of dioptric power.
Accommodation and flicker: evidence of a role for temporal cues in accommodation control?
Authors: Flitcroft D. I.
Published: December 2007

Static accommodation responses to sinusoidal grating stimuli that displayed temporal modulations in luminance contrast (i.e. contrast flicker) were measured with a laser speckle optometer. The effects of a variety of temporal waveforms were investigated including square‐wave modulations, sinusoidal modulations, and band‐pass filtered noise. The effects of altering both the amplitude and the temporal frequency (0.4–30 Hz) of the contrast flicker and the spatial frequency of the stimulus (0.77–9.2 c/deg) were also examined. All the flicker waveforms investigated (square wave, sinusoidal and band‐pass noise) reduced accommodative accuracy, the effect being most apparent at tower spatial frequencies (0.77–1.15 c/deg). With band‐pass filtered noise the effects of flicker were most apparent wilh frequencies in the range 1–4 Hz, at both lower (0.4 Hz) and higher flicker frequencies (8–32 Hz) accommodation was less affected. It was found that flicker impaired accommodation under conditions where the contrast was at all times suprathreshold. This is incompatible with the proposal that flicker reduces accommodation responses because for part of each flicker cycle the stimulus was below threshold. However, these results are compatible with the alternative hypothesis that flicker impairs the ability of the accommodation system to utilize temporal cues such as those derived from the higher frequency component (1–2 Hz) of accommodative oscillations.
Reading addition analysis of progressive addition lenses
Authors: Sullivan Colin M. , Fowler Colin W.
Published: December 2007

The optico‐physicakl characteristics of four different designs of progressive addition lenses (PALs) were assessed using a computer‐controlled automated focimeter. For each design and for the four designs taken together, reading addition power was shown to correlate positively with PAL progression corridor length and negatively with PAL progression corridor width. Empirical measurements from the four PALs measured showed each design to have more favourable characteristics when compared with a theoretical single power law model.
Errors in distance appreciation and binocular night vision
Authors: Bourdy C. , Cottin F. , Monot A.
Published: December 2007

Studying binocular vergence in relation to luminance levels, we isolated two types of behaviour which may explain differences in distance appreciation:

Underestimation of distances in subjects with overconvergence in darkness.

Overestimation of distances in subjects with underconvergence in darkness.

Progression towards the limiting value of convergence varies from one individual to another for each mesopic and scotopic luminance level and for different experimental conditions: variable discrepancy between the observation distance and the tonic vergence distance: accommodative or fusional stimuli at varying degrees of eccentricity; mobile stimuli in the observer's peripheral field. The study of bipartition in depth of a given interval for different observation distances confirms the existence of two major categories of individuals, Over‐ or underestimation of the nearer subjective half correlates to the binocular dark convergence capacity of each individual. These findings may explain errors in distance appreciation for road users in night vision.
Ocular chromatic aberration and age
Authors: Morrell A. , Whitefoot H. D. , Charman W. N.
Published: December 2007

The amount of longitudinal chromatic aberration in group of younger and older subjects is compared in three separate studies, using a laser speckle optometer. Badal optometers with monochromatic illumination. and monochromatic retinoscopy. No evidence is Found for any systematic change in chromatic aberration with age.
Weight of edged spectacle lenses
Authors: Obstfeld Henri
Published: December 2007

Uncut spectacle lenses of various powers and materials were edged lo three different eye shapes and three box eye sizes. Their weights were measured. This demonstrated that the eye shape has very little effect on the weight of edged lenses and that there is very little difference in weight for neighbouring eye sizes. The density of the lens material is of major importance, but other characteristics also influence the edged lens weight.
Dynamic retinoscopy and accommodation
Authors: Whitefoot Helen , Charman W. N.
Published: December 2007

The added positive lens power required for low and high neutrals at a distance of 1/3 m is determined as a function of age for a sample of 221 clinically normal subjects, aged between 10 and 80 years. These dynamic retinoscopy results are compared with corresponding laser optometer measurements of the levels of accommodation under each condition. Dark focus (tonic accommodation) measurements are carried out on a further sample of 58 subjects. Although the mean results of dynamic retinoscopy agree with those found by earlier authors, on the basis of our sample it is concluded that the considerable scatter in neutral values found in normal subjects at any age limits the usefulness of the technique as an indication of abnormality in near responses. Much of this scatter in pre‐presbyopic subjects appears to be related to individual variation in the level of tonic accommodation, although near phoria may also play some role.
The influence of stimulus luminance and contrast on hyperacuity thresholds for oscillatory movement*
Authors: Watkins Russell , Buckingham Terry
Published: December 2007

Hyperacuity thresholds for oscillatory movement were determined under conditions of decreased contrast and decreased luminance. Responses were found to be resistant to contrast reduction down to 15%; below this level thresholds increased, The contrast response function is thus similar to that of the magnocellular channel of the visual system. Systematic reduction in luminance caused a corresponding rise in thresholds. It is suggested that this effect is due to undersampling of the retinal image as a result of a towered quantal absorption and an increase in critical duration of temporal integration al lower levels of luminance.
Focimeter measurement of the astigmatism arising from oblique central refraction
Authors: Illueca Carlos , Hernández Consuelo , Domenech Begona
Published: December 2007

In this article, a method for measuring the astigmatism produced by an oblique central refraction is proposed. Measurements were taken using two different values of the pantoscopic angle that can be produced by lenses mourned in frames. We show that in sped lie cases, and as a function of the angle and power of the lens, the resulting astigmatism can surpass the tolerance level of the eye.
Inter‐observer variability in a computer‐assisted optic nerve head assessment system
Authors: Cox Michael J. , Wood Ivan C. J.
Published: December 2007

A computer‐assisted optic nerve head analysis system was used to measure parameters of the optic nerve head from one eye from each of 15 subjects. The subjects comprised three groups of live, being glaucomalous, ocular hypertensive, and normal. The 15 images produced were analysed in a randomized marked fashion by ten observers of varying levels of experience to test the inter‐observer variability of the measurements. An analysis of variance demonstrated significant differences in the measurements made by the different observers. Fisher's K‐test showed that all the parameters assessing the pallor area of the optic nerve head had significantly lower inter‐image variance (reported previously) compared with inter‐observer variance (at the 5% level). Variability in taking measurements of the pallor area of the optic nerve head is mainly due to observer variations rather than the image variations.
Mutual rod–cone suppression within the central visual field
Authors: Hess Robert F. , Mullen Kathy T. , Nordby Knut
Published: December 2007

Under mesopic conditions the contrast sensitivity of the central visual field is reduced as the result of a non‐linear interaction between rod‐ and cone‐mediated signals, each of which is capable of higher sensitivity in isolation. The interaction is produced only when the rod‐mediated system is driven at flicker rates above 6 Hz. This finding bears upon how rod and cone signals are combined and therefore affects our interpretation of the significance of the relationship between retinal illuminance and both contrast sensitivity and temporal resolution.
Image enhancement filters significantly improve reading performance for low vision observers
Authors: Lawton Teri B.
Published: December 2007

As people age, so do their photoreceptors: many photoreceptors in central vision stop functioning when a person reaches their late sixties or early seventies. Low vision observers with losses in central vision, those with age‐related maculopathies, were studied. Low vision observers no longer see high spatial frequencies, being unable to resolve line edge detail. We developed image enhancement filters to compensate for the low vision observer's losses in contrast sensitivity to intermediate and high spatial frequencies. The fillers work by boosting the amplitude of the less visible intermediate spatial frequencies more than the lower spatial frequencies. These image enhancement fillers not only reduce the magnification needed for reading by up to 70%. but they also increase the observer's reading speed by 2–4 times. A summary of this research is presented.
Colour, contrast and the visual evoked potential
Authors: Thompson Dorothy A. , Drasdo Neville
Published: December 2007

Visual evoked potentials exhibit interesting morphological changes when they are elicited by checkerboards of different spatial and chromatic contrast, counterphasing in the Coveal and lower macula Held. The characteristic, positive wave of the phase‐reversal visual evoked potential, for example, is preceded by an increasingly prominent negative peak as luminance contrast progressively increases above 10% and, at isoluminance, the response to red and green checkerboards becomes a predominantly monophasic negative wave. To study the nature of the morphological change we synthesized these waveforms with a computer simulation consisting of Gaussian components. The amplitudes of positive and negative components were altered until the synthesized response was closely similar to the recorded data. These Gaussian components have response characteristics which are identified with those of magnocellular and parvocellular neurones.
Effect of attention on the VEP in binocular and monocular conditions
Authors: Heravian‐Shandiz J. , Douthwaite W. A. , Jenkins T. C. A.
Published: December 2007

To study the effect of voluntary concentration on the visual evokedotential (VEP) with monocular and binocular rivalry stimulation, attern reversal VEPs were recorded using 5.5 min arc and 50 min arc check sizes. Subjects viewed the VEP stimulus with the left eye and a light emitting diode (LED) with the right eye. They were asked to concentrate on either the VEP stimulus or the LED. The two targets were arranged so that the left eye remained accurately focused on, and directed to. the centre of the VEP stimulus throughout the recordings. The binocular VEP wave became attenuated when the subject concentrated on the LED. The wave was reduced lo around two–thirds of the amplituderesent when concentrating on the VEP stimulus. This reduction in the VEP amplitude is considered lo be due to a binocular interaction because there was a lack of amplitude attenuation when the experiment was repealed with monocular conditions. The results also suggest that the wave is smaller when the non–dominant eye receives the VEP stimulus compared with that when the dominant eye is stimulated by the VEP target.
Construction of a model eye and its applications
Authors: Rudnicka Alicja R. , Edgar David F. , Bennett Arthur G.
Published: December 2007

Construction details are given of a model eye, based on the Bennett and Rabbetts schematic eye. It incorporates a cornea, lens, and spherical fund us. Distilled water filled the anterior and vitreous chambers. By means of a micrometer screw, the vitreous chamber depth can be precisely varied to produce axial ametropia from +11 to −17D. Readings taken over the greater part of this range with a Topcon Auto refractor RM‐A6500 were found to be repeatable and reproducible within ±0.25 D. The model eye was used to investigate the relationship between the actual size of a fundus feature and its photographic image in two different fundus cameras. With a Zeiss Oberkochen camera of lelecentric design the magnification was found lo remain constant whatever the degree of axial ametropia, whereas with a Carl Zeiss Jena camera the magnification varied linearly with amelropia. A technique developed by Littmann for determining the actual size of a retinal feature when using a fundus camera of telecentric design is discussed briefly.
Use of scrolled text in a scanning laser ophthalmoscope to assess reading performance at different retinal locations*
Authors: Culham L E. , Fitzke F. W. , Timberlake G. T. , Marshall J.
Published: December 2007

A new technique is described for assessing reading performance using a scanning laser Ophthalmoscope. Letters of different sizes and contrasts were projected onto specific retinal locations of normal and low vision observers. Successive letters were scrolled in a horizontal direction at different speeds through a ‘window’. Throughout the experiments the subjects' fundus and the retinal location of the stimuli could be visualized. With this scanning laser ophthalmoscope text‐scrolling computer program the subject does not search for adjacent letters, and because the eye is held relatively stationary the tedious eye movement analysis incurred in other studies is reduced. Five retinal areas were investigated in two normal observers. The percentage of letters correctly identified decreased with eccentricity, increased velocity of the text and reduced text contrast. The reading performance of two patients, one with age‐related macular degeneration and the other with juvenile macular disease, was investigated. Decrements in performance were related to morphology of the lesions.
Intraocular pressure measurement in children using the Keeler Pulsair tonometer
Authors: Evans K. , Wishart P. K.
Published: December 2007

A study to determine whether Keeler Pulsair tonometry is a feasible alternative to tonometry under general anaesthesia in children was undertaken. We recruited 53 children aged from 6 months to 9 years old. Readings were obtainable from 78% and a complete set of four readings from each eye was obtained from 45% of the group in an out‐patient setting. Averaged Pulsair measurements agreed well with Perkins applanation tonometry values under general anaesthesia. Techniques to improve compliance are discussed. In conclusion, the Pulsair tonometer is a viable method for obtaining estimates of intraocular pressure in children in this age‐group.
Compensatory eye movements during near fixation after fast adaptation to lenses
Authors: Hine Trevor
Published: December 2007

When the eyes are converged on a near target, the gain of the vestibulo‐ocular reflex (VOR) during a subsequent head rotation is dependent upon both the amount of vergence and the degree to which it is asymmetrical. In conditions without visual feedback, we measured the gain of the VOR in the right eye of observers as they rotated their heads to the right or left while viewing a target placed 22, 32.5 or 200 cm from the centre of head rotation. We then adapted the VOR to the magnifying effects of + 5 D lenses, and retested the VOR under the former convergence conditions. We found an inverse relationship such that the greater the VOR gain due to convergence, the less the effect of the rapid adaptation to lenses.
QROC curves and kappa functions: new methods for evaluating the quality of clinical decisions
Authors: Gilchrist Jim
Published: December 2007

The application of statistical methods for measuring the ability of clinical judgements and tests to discriminate between normal and diseased patients is increasing in optometry and ophthalmology. This paper presents two new methods for assessing the quality of such diagnostic decisions. Both are based on measurement of the kappa coefficient of association and offer theoretical and practical advantages over traditional methods. The paper first introduces the family of kappa coefficients with examples of their calculation and application. The use of weighted kappa values for measuring test sensitivity and specificity is explained, and it is shown how the results may be plotted in the form of the QROC curve which enables different aspects of test discriminability to be represented graphically. Kappa functions are then proposed as an alternative method for representing and predicting test performance, having the advantage of identifying optimal test criteria in addition to providing measures of discriminabilty. The clinical application of the new methods is illustrated using data for the detection of glaucoma from measurements of intraocular pressure.
Keratoreformation by contact lenses after radial keratotomy: a re‐analysis
Authors: Harris W. F. , Malan D. J. , Astin C. L. K.
Published: December 2007

A recent paper analysed change in refraction and corneal curvature associated with contact lens wear in patients who had had radial keratotomy at least a year beforehand. Conventional methods of analysis were used. This paper applies methods that have only recently become available. The results are clearer and less ambiguous. Formally, the analysis shows that there are significant mean changes in refraction (estimated to be + 1.69/−0.50 × 105) and corneal power (−0.66/−0.25 × 155). In spite of the difference between these two mean changes, the analysis shows that the change in refraction may be associated with change in the corneal power alone. There is no reason 10 believe that any other change is occurring in the eye. Care needs to be executed in assigning a causative role to contact lenses in changing refraction and corneal curvature. Almost certainly the lenses do have such a role but the analysis does not formally allow an unequivocal conclusion concerning that role.
Influence of proximal, accommodative and disparity stimuli upon the vergence system*
Authors: North R. V. , Henson D. B. , Smith T. J.
Published: December 2007

The most important cues to the normal vergence response are retinal disparity, accommodative effort and perceived distance (proximal cue). In the past, proximal cues have been thought to contribute little to the total vergence response but more recent studies have suggested that they play an important role. The relative contributions of the proximal, accommodative and disparity cues to the vergence response were assessed by measuring the effect upon the vergence system when each of these cues were altered. The effect upon the vergence system was measured by the change in ‘phoria, the change of fixation disparity and the amount of prism adaptation after 210 s of binocular viewing. The results indicate that the greatest effect of cue disharmony occurred when the proximal and disparity cues were altered. A finding which signifies the importance of the proximal cue to the overall vergence response.
Tonic accommodation: a review I. Basic aspects
Authors: Rosenfield Mark , Ciuffreda Kenneth J. , Hung George K. , Gilmartin Bernard
Published: December 2007

In the absence of an adequate visual stimulus, accommodation adopts an intermediate position of ∼ I D. Since this position was believed to reflect the level of tonic innervation to the ciliary muscle, this response has been termed tonic accommodation (TA). Part 1 of this review will consider various aspects of this parameter, including its reference to closed‐loop accommodative function and autonomic physiology. In addition, both the methods of measurement and appropriate terminology for this function will be discussed. It is concluded that the response, which becomes apparent under so‐called ‘stimulus‐free’ conditions, in fact probably represents an aggregate response resulting from multiple, non‐optical stimuli. Thus the designation tonic accommodation may not be appropriate, since it fails to describe accurately the heterogeneous composition of the stimulus‐free accommodative response. An associated paper (to be published as part II of this review) will examine accommodative adaptation and both clinical aspects of TA and adaptation of TA.
Peripheral astigmatic asymmetry and angle alpha
Authors: Dunne M. C. M. , Misson G. P. , White E. K. , Barnes D. A.
Published: December 2007

The association between peripheral astigmatic asymmetry and angle alpha was tested in the present study. Measurements were made in 34 eyes. Peripheral astigmatism was measured over the horizontal meridian using a Zeiss (Jena) Hartinger coincidence optometer and a Canon R‐1 autorefractometer. Curves were fitted to the measured data of each eye and the minima determined by differentiation. Angle alpha was estimated by alignment of Purkinje images 1 (anterior cornea) and IV (posterior crystalline lens). Peripheral astigmatism was found to be symmetrical about a point on the nasal retina. This point departed from the visual axis by 8.8 ± 7.0° (Hartinger) and 9.4 ± 9.8° (Canon). Both values were found to he significantly higher than angle alpha 5.0 ± 1.2°. The results indicate that either peripheral astigmatic asymmetry is due to additional factors such as lack of symmetry in the peripheral curvature of individual optical surfaces, or that there is further misalignment of optical surfaces away from an optical axis.
Rabbit corneal endothelial cell membrane potential
Authors: Wigham Chris C. , Green Keith , Hodson Stuart
Published: December 2007

Membrane potential of rabbit corneal endothelial cells measured using microelectrodes was − 29.3 ± 0.8 mV, n= 45. (mean ± SEV1). Histological location of Lucifer Yellow dye iontophoresed out of the microelectrode confirmed that the microelectrode was located intracellularly, The Lucifer Yellow diffused five to six cell diameters away from the impaled cell indicating endothelial cell coupling. Depolarization by ouabain (10−4 M) and high extracellular potassium (potassium for sodium substitution) showed the cells to be responsive to changes in the bathing solution whilst impaled, that the cell membrane is more permeable to potassium than sodium and that membrane bound Na+‐K+ ‐ATPase activity generates the transmembrane electrolyte gradients.
TNO stereopsis test as an aid to the prevention of amblyopia*
Authors: Walraven Jan , Janzen Piet
Published: December 2007

In this investigation, carried out under a Youth Health Care postgraduate course in Nijmegen, the stereopsis of a school population of 730 children, aged 4–18 years, was recorded and clinically evaluated. Stereopsis was measured using the TNO test, a random‐dot stereo test especially designed for the early detection of amblyopia. The main aims of this study were to establish the validity of the TNO test as a screening test for amblyopia, obtain information about the variability and age dependence of stereopsis, and to evaluate the efficacy of amblyopia prevention. The most important findings can be summarized as follows:

1. All amblyopes are detected by the TNO test's recommended referral criterion of 240 sec arc (binocular threshold parallax in sec arc).

2. The red‐green anaglyphs used in the test do not pose problems for individuals with a colour vision deficiency.

3. The ability to discriminate depth improves by a factor of two over the age interval 4–12 years.

4. A stereoacuity of ≤ 120 sec arc is a good predictor of normal or correctable normal vision, and may therefore help in evaluating the often incomplete results of eye tests of young children.

5. Where there is an increased perinatal risk, there is a greater chance of disturbed binocular vision.

6. It is estimated that 75% of amblyopes remain amblyopic. possibly because of delayed detection; 60% of the amblyopes in the population examined were not identified before the age of 5 years.
Accommodative adaptation and age of onset of myopia
Authors: Woung Lin‐Chung , Ukai Kazuhiko , Tsuchiya Kunihiko , Ishikawa Satoshi
Published: December 2007

Tonic accommodation in an empty field and accommodative adaptation, defined as accommodation shift after 2 min viewing of a 4 D near task, were measured using an infrared optometer. Subjects were classified into three types: emmetropes (n= 18). early onset myopes (n= 18) and late onset myopes (n= 15). The relationship between accommodative adaptation and the onset age of myopia were compared. There was no statistical difference in the pre‐task ionic accommodation among the three subject groups. However, the accommodative adaptation differed in the three groups during the 5 min post‐task period. The average accommodative adaptation of emmetropia. early onset myopia and late onset myopia were 0.66. 0.27 and 1.19 D. respectively. Accommodative adaptation in the late onset myopia group was significantly higher than in the emmetropia group. Furthermore, the accommodative adaptation in the early onset myopia group was significantly lower than in the emmetropia group. Two possible aetiologies of myopia are discussed: one for the group which shows low accommodative adaptation that has no relationship with the age of onset and another for the group which shows high accommodative adaptation that has a relationship to an onset age of 15 years or later. The aetiology is also considered with regard to a potentiating chemical effect on the synapses of the ciliary muscle.
Tonic accommodation, tonic vergence and surround propinquity
Authors: Chiu Nancy N. , Rosenfield Mark
Published: December 2007

Previous studies have typically assessed tonic accommodation (TA) and tonic vergence (TV) by placing subjects in total darkness. However, a recent investigation demonstrated that even under such apparently stimulus‐free conditions, subjects' awareness of the proximity of the adjacent surroundings and overall room topography (i.e. surround propinquity) may still influence the accommodative response. Accordingly, the aim of the present study was to measure TA and TV while subjects (n= 34) viewed an illuminated distant target (viewing distance = 6 m) to minimize this propinquity effect. TA was measured using an objective, opentield. infrared optometer under two conditions: first, while viewing the distant target monocularly through a 0.5 mm pinhole, and second in total darkness. Additionally, TV was assessed by determining the heterophoria subjectively while subjects viewed the distant target biocularly through 0.5 mm pinholes. The mean level of TA using the pinhole technique (mean = 0.28 D) was significantly lower than that observed in total darkness (mean = 0.60 D). Furthermore, a significant positive correlation (r= 0.86) was found when comparing the difference between the two TA measurements with the level obtained in total darkness. Those subjects having apparently high levels of TA in darkness exhibited the largest propinquity effect. Thus measurements of accommodation recorded in total darkness are likely to have overestimated both the magnitude and normal range of TA. The mean level of TV was 0.58 metre angle. No significant correlation was observed between TV and either of the two TA measurements. Therefore more accurate assessments of both TA and TV may be obtained by having subjects view distant targets while placing both the accommodation and vergence systems under open‐loop conditions.
Screening of infants for significant refractive error using videorefraction
Authors: Hodi Samara
Published: December 2007

Isotropic photorefraction has been suggested as a suitable method for screening infants for refractive error. Recently published data suggested that reasonable consistency with retinoscopy results might be achieved using cycloplegic videophotore fraction (VPR) for spherical refractive error but that results might be unreliable for astigmatic errors. Non‐cycloplegic VPR did not appear to produce results consistent with retinoscopy. A practical idea of how many children might he identified using this technique and how many missed was needed by personnel designing screening projects. Hence the VPR was tested by screening a population of 247 infants for significant refractive error, and comparing the results with cycloplegic retinoscopy, Sensitivity and specificity scores were calculated for a range of test levels of ametropia. Without cycloplegia, sensitivity of VPR was poor. With cycluplegia the situation was much improved, with sensitivity for hyperopia + 4.00 D or over of 83.3% and specificity of 90.6%. Sensitivity for astigmatism of 1 D or greater (84.6%) was high but specificity was poor (45.6%). Acceptable sensitivity was achieved for identifying children in this age group at risk of developing squint and amblyopia due to refractive error, providing cycloplegia was used.
Large sample study of the effects of phenylephrine 2.5% eyedrops on the amplitude of accommodation in man
Authors: Gimpel Gary , Doughty Michael J. , Lyle William M.
Published: December 2007

A single drop of phenylephrine 2.5% (MYDFRIN TM) was instilled into the eyes of 160 volunteers (aged 20 to 30 years) and their amplitude of accommodation assessed under standard illumination using a push‐up technique without an artificial pupil‐ The amplitude was assessed every 5 or 10 min over a period of 90 min. Within 30 min, nearly 75% of the subjects showed a measurable change in amplitude. Overall, the amplitude declined slowly with time to realize an average 11 % reduction from an average starting amplitude of 10.7 D. A large range of responses from a 30% increase to a 60% decrease in amplitude was. however, observed. Subjects with large amplitudes of accommodation were more likely to show significant decreases while some subjects with smaller amplitudes showed an apparent increase in accommodation (r2= 0.176). The phenomenon was observed in both blue‐ and brown‐eyed subjects and in non‐contact lens wearers and soft contact lens wearers (r2 values of 0.144 to 0.265).
Mean response and oscillations of accommodation with colour and contrast
Authors: Denieul P. , Corno‐Martin F.
Published: December 2007

The mean level and microfluctuations of accommodation were objectively recorded, in natural viewing conditions, by infrared optometry on steady presentation of various combinations of achromatic and coloured Snellen E on achromatic or coloured fields, with or without a luminance contrast. In addition to the absolute mean power spectrum of the microfluctuations, the HF/LF ratio of the high (HF. 0.5–6 Hz) and low (LF. 0–0.5 Hz) frequency activity of this phenomenon, which provides a sensitive objective description of the control, was analysed. In the case of maximum luminance contrast, for any monochrome situation, the HF/LF ratio decreases when changing from an achromatic‐only contrast to a saturated coloured situation. At the same time, the relative shifts of the mean level of accommodation, which compensate ocular chromatism under coloured conditions, increase with colour saturation. In the case of an isoluminant chromatic contrast, the decrease in the HF/LF ratio was significant. This result confirms the inefficiency of chromatic contrast to control accommodation. Furthermore, this study confirms that both LF and HF absolute activity of the microfluctuations of accommodation are usually related to the stimulus characteristics. Their antagonistic behaviour is an argument for considering the HF/LF ratio.
Screening for glaucoma: the time taken by primary examiners to conduct visual field tests in practice
Authors: Tuck Maurice W. , Crick Ronald P.
Published: December 2007

A panel of 101 primary examiners (optometrists or their ancillary staff) in England and Wales prospectively recorded the time taken to examine the central visual fields of each of 10 (or more) of their patients. The results indicate that the time depended not only on the test procedure but on how frequently the examiner conducted such a test. A basic test with semi‐automated field screening equipment, applied routinely by 30 examiners on 547 patients, took an average 3.7 min per patient; (lower quartile 2.8 min). For such examiners, a standard extended test took 4.9 min. Similar times applied whether tests were conducted by an optometrist or an assistant. It was concluded that visual Held screening in a normal population could reasonably be assumed to take an average 4 min per patient.
Analysis of method‐comparison data
Authors: Shaw David E. , Jones Helen S. , Moseley Merrick J.
Published: December 2007

Method‐comparison studies, in which new‘candidate’techniques are compared with an established‘gold standard', feature commonly in optometric research. Investigators often analyse their findings using least squares regression. Pearson's product‐moment correlation coefficient and the paired t‐test. We describe more appropriate methods which include: the‘limits of agreement', the intraclass correlation coefficient, and Deming's method for estimating a straight line fit. Comparisons between methods are made with the aid of a computer simulation. Computer program listings are provided to assist in implementing the analyses.
Tri‐meridional analysis using arbitrary meridians: a new solution
Authors: Burek Henry
Published: December 2007

A new solution is presented for the evaluation of the spherocylindrical components of curvature or refraction from measurements taken along three distinct, arbitrary, meridians. Unlike previous approaches, the axis direction is found first, thereby making sphere and cylinder evaluation relatively simple. The derivation of the solution is reasonably uncomplicated using straightforward trigonometrical operations.
The microbiology of the eye
Authors: Armstrong R. A.
Published: December 2007

Infection of the external structures of the eye is one of the commonest types of eye disease worldwide. In addition, although relatively impermeable to microorganisms, infection within the eye can result from trauma, surgery or systemic disease. This article reviews the general biology of viruses, bacteria, fungi and protozoa and the major ocular infections that they cause. In addition, the effectiveness of the various antimicrobial agents in controlling ocular disease is discussed. Because of changes in the normal ocular flora, continuous monitoring of the microbiology of the eye will continue to be important in predicting future types of eye infection. Basic research is also needed into the interactions of microbes at the ocular surface. There is increasing microbial resistance to the antimicrobial agents used to treat ocular infections and hence, new antimicrobial agents will continue to be needed together with new methods of drug delivery to increase the effectiveness of existing antimicrobial agents.
The inter‐relationship between magnification, field of view and contrast reserve: the effect on reading performance
Authors: Mohammed Zainora , Dickinson Christine M.
Published: December 2007

For the reading task, contrast reserve is defined as the ratio of the letter contrast of the printed letters, to the reader's contrast threshold. Acuity reserve is the ratio of the print size used for the reading task, to the reader's visual acuity. The effects of low contrast reserve on reading performance were investigated at various magnifications, ranging from 3 × to 7.5 ×, with the field of view systematically controlled. Eye movements were recorded whilst normally sighted subjects read using the magnifiers. It was shown that with adequate contrast reserve, increasing the field of view improved the reading rate because of the resulting increase in forward saccade length. Conversely, reducing the contrast reserve slowed the reading rate by decreasing the length of forward saccades and increasing the mean fixation duration, suggesting that the perceptual span is reduced at low contrast reserve. This study also shows that when the contrast reserve is low, providing magnification higher than that required for letter recognition (that is, increasing the acuity reserve) will not improve the reading performance. Furthermore, even when the contrast reserve was high, reading rates were lower for the magnifications of 5 × and higher, because increases in saccade length do not match those of the retinal image size at these magnifications.
Why Some Adult Canadians Do Not Have Blood Pressure Measured
Authors: Amankwah Ernest , Campbell Norman R. C. , Maxwell Colleen , Onysko Jay , Quan Hude
Published: December 2007

Regular blood pressure (BP) measurements are required to identify people with hypertension and to optimally manage their cardiovascular risk. Analyses of data from the 2000–2001 Canadian Community Health Survey showed that most adult Canadians have had a BP assessment in the previous 2 years and few have never had one. Large numbers of persons without BP recordings were observed, however, among persons who were younger, were male, who did not have either a regular doctor or physician contact in the previous year, who were recent immigrants or visible minorities (nonwhite and non‐Aboriginal), and who spoke neither French nor English. Common reasons reported for not having a BP assessment included believing it was not necessary and simply not getting around to it. Education programs targeting those at risk as well as more convenient BP screening may improve awareness and testing.

(J Clin Hypertens. 2007;9:944–951)