bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment of contrast sensitivity of patients with macular disease using reduced contrast near visual acuity charts
Authors: Greeves A. L. , Cole B. L. , Jacobs R. J.
Published: December 2007

A set of near Bailey‐Lovie logMAR letter charts that varied in contrast from 0.40 dB (C = 0.95) to 58.0 dB (C=0.001) were used to measure the middle and high spatial frequency range of the contrast sensitivity function (CSF) of 15 subjects with age‐related maculopathy (ARM) and 15 age‐matched normal subjects. The letter charts were shown to have good test‐retest reliability. Compared with measures made using CRT generated square wave gratings of variable contrast and spatial frequency they were also shown to provide a valid measure of CSF in the mid to high spatial frequency range. The 20.0 dB letter chart alone was shown to be a good screening device for macular disease. The letter charts do not provide a measure of the peak of the CSF and a supplementary test of contrast sensitivity is needed to quantify contrast sensitivity at a low spatial frequency. Three measures are proposed as necessary to document foveal visual capability of patients with macular disease: distance logMAR visual acuity to measure high spatial frequency resolution, visual acuity with letter charts of 20 dB contrast to assess mid spatial frequency resolution; and contrast sensitivity for the detection of an edge to estimate contrast sensitivity for larger objects.
Detection of low spatial frequencies: A single filter or multiple filters?
Authors: Hess R.F. , Howell E.R.
Published: December 2007

Ever since it was first reported that the contrast sensitivity for low spatial frequency sinusoidal gratings falls off with a slope approximating unity it has been suggested that this may represent gradient detection by a single spatial filter tuned to higher spatial frequencies. We have further investigated this possibility using aperiodic as well as periodic stimuli. Experiments are presented that involve manipulations of luminance, field size and spatial adaptation, and the results are consistent with a multiple filter model accounting for the detection of low spatial frequency (0.2‐2 c/deg) periodic and aperiodic stimuli.
Stereoacuity levles and vision problems in children from 7 to 11 years
Authors: Williams Sheila , Simpson Anne , Silva Phil A.
Published: December 2007

A longitudinal study of stereoacuity levels of 859 children at 7 years, 811 children at 9 years and 796 children at 11 years was conducted using the TNO random dot stereotest. The prevalence of defective stereoscopic vision was found to be between 2.1 and 3.2 per cent. A further 10–16 per cent of children had only moderate stereoacuity levels when compared with their peers. The stereoacuity levels achieved by most of the children improved with age, but the rand order correlations for the stereoacuity levels between ages 7 and 9, and ages 9 and 11, were small. Defective stereopsis and poor stereoacuity levels were clearly associated with manifest strabismus and problems of visual acuity, and if failure to pass the quantitative plates was a cut‐off point for screening purposes most of the children with visual problems would have been identifies.
Vision and visual acuity in an elderly population
Authors: Lavery J.R. , Gibson J.M. , Shaw D.E. , Rosenthal A.R.
Published: December 2007

The data for this paper were collected during a two‐year study of the elderly in the market town of Melton Mowbray. The data show that typically, persons aged 75 years and older have poor uncorrected vision (6/36 Snellen acuity), but good corrected acuity, 73.8 per cent gaining 6/12 binocular Snellen acuity or better. Over 88 per cent were able to read N8 typesize or better, under test conditions. Those with low uncorrected vision were the most likely to possess spectacles.
Refraction and refractive errors in an elderly population
Authors: Lavery J.R. , Gibson J.M. , Shaw D.E. , Rosenthal A.R.
Published: December 2007

The data for this paper were collected during a two‐year study of the elderly in the market town of Melton Mowbray. The randomly selected subjects, aged 76 years of age and older, were found to be on average + 1.33 D hypermetropic and the average cylinder power was 0.82 D. The mean refractive error was found to be + 1.5 D with 0.5 negative cylinder at between 85 and 90 degrees. Of all the subjects, 30 per cent had significant anisometropia.
Progressive addition and veriables focus lenses: A review
Authors: Sullivan Colin M. , Fowler Colin W.
Published: December 2007

This paper reviews recent developments in the field of progressive addition spectacle lenses and variable focus lens systems design. The study is a sequel to the previous analytical work of von Rohr (1916), Graham (1942), and Bennett (1970). A brief history of the work documented by the aforementioned authors is presented. Comparative assessment is undertaken of the most recent patents of progressive addition and variables focus spectacle lenses. A largely verbal description is employed because patent literature is often devoid of mathematical models.
Time‐of‐day variations in oculomotor function: 1. Tonic accommodation and tonic vergence
Authors: Amerson Thomas L. , Mershon Donald H.
Published: December 2007

Time‐of‐day variations were studied both in tonic accomodation and in tonic vergence. Thirty‐six male volunteers were measured once in the morning and at one other time on the same day. The mean baseline value of tonic accomodation was 2.02 D. Time‐of‐day variations were found, with a late evening measure being + 0.6 D greater than the morning value. No independent time‐of‐day fluctuations were found in tonic vergence. Post‐hoc analysis, however, showed that tonic vergence tended to shift in the same direction as an individual's tonic accommodation during the afternoon. During the evening, tonic vergences tended to shift oppositely to tonic accommodation.
The effect of monocular versus binocular fixation on accommodative hysteresis
Authors: Fisher S. K. , Ciuffreda K. J. , Bird J. E.
Published: December 2007

Changes in tonic accommodation were compared under monocular (6 or 10 D) and binocular (6 D/6 MA or 10 D/10 MA) inducing conditions in 26 visually normal young adults. Tonic accommodation was measured immediately before and after an 8 min fixation period. Statistically equivalent increases in tonic accommodation were produced under the two modes and levels of fixation. Even those individuals who showed large (+ 0.70 D) monocularly induced changes were equally responsive under binocular fixation conditions. The results suggest that monocularly and binocularly induced accommodative hysteresis effects are similar in magnitude, regardless of the potential presence of vergence‐driven accommodation under binocular but not under monocular viewing conditions.
The subjective assessment of cataract
Authors: Elliott D.B. , Gilchrist J. , Hurst M. , Pickwell L.D. , Sheridan M. , Weatherill J. , Whitaker D.
Published: December 2007

The medical treatment of cataract now appears to be a distinct possibility. A number of anti‐cataract formulations are being clinically tested, and more clinical trials are being planned. To obtain a true assessment of a drug's efficacy, a battery of tests are needed which can accurately assess cataract progress. A clinical trial of the proposed anti‐cataract drug Bendalina is being conducted. The six subjective methods used to assess cataract progression in the trial are presented. These are refractive error, LogMAR visual acuity, contrast sensitivity, glare sensitivity, retinal visual acuity and displacement threshold hyperacuity. The reasons for using each technique and their method of measurement is explained.
The effect of spatial frequency on binocular contrast inhibition
Authors: Pardhan Shahina , Gilchrist Jim , Douthwaite William
Published: December 2007

Previous work has shown that binocular contrast summation, obtained with equal monocular sensitivities, remains constant over a range of spatial frequencies. We measured binocular contrast detection with a log 1.00 ND filter placed in front of one eye. For all eight subjects, the binocular contrast detection decreased to a level below that of the monocular detection, demonstrating a contrast analogy to Fechner's paradox. The degree of binocular inhibition, like summation, remained constant across the range of spatial frequencies.
The measurement of adaptation of tonic accommodation under two open‐loop conditions
Authors: Bullimore Mark A. , Gilmartin Bernard
Published: December 2007

Pre‐and post‐task tonic accommodation (TA) was measured using an objective infra‐red optometer under two open‐loop conditions: a darkroom and a bright empty‐field (60 cd m‐2). The task was of 10 minutes' duration and was located at —1, —3 and —5 D. Post‐task TA was measured immediately after the task and over a period of 90 s. Mean data for the group of 10 young men subjects showed that the open‐loop condition adopted had no significant influence on the post‐task regression patterns of TA towards pre‐task values. Three subjects did, however, show significantly more sustained increases in post‐task TA for the bright‐field condition; one markedly so. Conversely, two subjects showed more pronounced post‐task shifts for the darkroom condition.
Accommodative fluctuations in Adie's syndrome
Authors: Ukai Kazuhiko , Ishikawa Satoshi
Published: December 2007

Recent reports suggest that the higher frequency components (around 2 Hz) of accommodative fluctuations may arise from the accommodative ‘plant’ and may have no role in the control of the accommodation system. The dynamic responses of accommodation in two cases with Adie's syndrome were recorded. The results showed that the velocity of accommodative responses was reduced, and the accommodative fluctuations in the higher frequency components were completely diminished. It can be concluded that the origin of fast fluctuations is not located at a more peripheral site than the lesion of tonic accommodation. Since the possible lesion exists at the ciliary ganglion, the origin of the fast oscillation may not be the accommodative ‘plant’, but the neural one.
Assessment of toroidal surfaces by the measurement of curvature in three fixed meridians
Authors: Fowler C.W.
Published: December 2007

A method is described where the surface curvatures and axis orientation of a toroidal surface can be determined by measuring the lens in three fixed orientations. This method also has possible applications in the measurement of progressive addition lenses.
Spherical lens decentration errors by Prentice's rule
Authors: Tang Churk‐yan
Published: December 2007

Sources and magnitude of errors in applying Prentice's rule in calculating decentration for spherical lenses were investigated. It was found that spherical aberration can be the only source of error in applying the rule. The overall magnitude of errors in effective prismatic effect is, however, clinically insignificant.
Criteria for decompensation in binocular vision
Authors: Jenkins T. C. A. , Pickwell L. D. , Yekta A. A.
Published: December 2007

Two groups of patients, one under 40 years of age and the other 40 years and over, were divided into subgroups according to whether they had symptoms associated with near vision. A method developed in ‘signal detection theory’ was used to determine whether a value could be found for heterophoria, or associated heterophoria, which would predict which patients had symptoms due to decompensated heterophoria in normal routine investigation. Receiver operator characteristic curves (ROC curves) were constructed to look for these cut‐off values between patients with, and without, symptoms.

No value for dissociated heterophoria was found that would discriminate between the symptomatic and asymptomatic patients. It is concluded that heterophoria measurement is not useful as a routine procedure. In the case of associated heterophoria, for the under 40 years age group, patients with a value of 1 prism dioptre or more are more likely to have symptoms than not, and one‐third of patients with close work problems have a value of 2 prism dioptres or more. It was rare to find any asymptomatic patient with a value as high as this. In the 40 years and over age group those with an associated heterophoria of 2 prism dioptres or more are more likely to have symptoms than not. One‐third of patients in the latter age group, with symptoms, have a value of 3 prism dioptres or more whilst it is rare to find an asymptomatic patient with a value as large as this.
Contrast sensitivity with contact lens corrections for presbyopia
Authors: Collins Michael J. , Brown Brian , Bowman Kenneth J.
Published: December 2007

We measured contrast sensitivity at three distances (330 mm, 660 mm and 4 m) with six contact lens and two multifocal spectacle corrections for presbyopia. The two spectacle corrections were D‐segment bifocals and trifocals and the contact lens corrections were distance contact lenses with lookover spectacles, soft progressive bifocals, soft concentric bifocals, monovision, modified monovision, and hard crescent segment bifocals. The spectacle corrections in general gave better results for the contrast sensitivity function (CSF), than did the contact lens corrections. Distance contact lenses with lookover spectacles performed best of the contact lens corrections used. However, the differences in CSF between the various contact lens corrections were small and not statistically significant.
Use of the Farnsworth—Munsell 100‐Hue test in the examination of congenital colour vision defects
Authors: Birch Jennifer
Published: December 2007

Results for the Farnsworth‐Munsell 100‐Hue test are reported for 238 male subjects with congenital colour vision defects (47 protanopes, 17 protanomalous trichromats, 57 deuteranopes and 117 deuteranomalous trichromats). The results are analysed in terms of the error score and the presence of an axis of confusion. A wide range of results is obtained in each diagnostic group and the error score cannot be used to distinguish between dichromats and anomalous trichromats. Approximately 50% of subjects with anomalous trichromatism obtain error scores less than 100 without an axis of confusion. These subjects could be mistakenly identified as having normal colour vision if pseudoisochromatic and colour matching tests are not employed. The prime use of the F‐M 100 Hue test is in vocational guidance.
Ageing parameters of the ocular lens by scanning fluorophotometry*
Authors: Hemenger Richard P. , Occhipinti Joseph R. , Mosier Marjorie A.
Published: December 2007

A Beer‐Lambert analysis of fluorophotometric scans of ocular lenses has been carried out. It is shown that an assumption of a single flourophor allows us to calculate the distribution of this fluorophor along the central lens axis.

For the great majority of lenses in our study, covering a wide range of ages, our results are in essential agreement with published results on excised lenses. For a small subset of lenses in the study the assumption of a single fluorophor is found to be unsatisfactory. In these cases a reasonable symmetry assumption allows us to estimate the distribution of an additional agent which removes light from the entering or exiting beams without contributing to the fluorescence. The fact that this agent is restricted to the lens nucleus and that it occurs in lenses in which nuclear changes are clinically evident suggests that it is an expression of nuclear cataract.
Use of reflecto‐modulometry to study the optical quality of the inner retina
Authors: Gorrand J.‐M. , Bacin F.
Published: December 2007

The modulation of interference fringes reflected by the peripheral fundus is always lowered by passage through the outer segments of the photoreceptors. In addition, it also may be degraded by passage through a diseased inner retina or through the choroid (in cases where there is only light pigmentation of the fundus). The contributions of the inner retina and choroid can be differentiated by varying the spatial frequency of fringes, or by studying the directionality of the fundus reflection. Reflecto‐modulometry seems to be an appropriate method for analysing pathological changes in the optical quality of the inner retina.
Third‐order aberrations of pseudophakic eyes
Authors: Atchison David A.
Published: December 2007

The aberrations of pseudophakic eyes were analysed by third‐order theory assuming thin intraocular lenses. Third‐order aberrations with spherical surfaced lenses are quadratic functions of lens shape. Spherical aberration and coma are generally the most rapidly changing aberrations, at small field positions, with change in lens shape. Optimum designs probably lie within the shape factor range at which these attain minimum absolute values (+1.1, spherical aberration; ‐0.9 to ‐3.4, coma). The importance of spherical aberration declines relative to that of off‐axis aberrations as pupil size decreases. The introduction of a level of corneal asphericity alters each aberration by a constant amount for any lens shape.
The measurement of the corneal ellipse for the contact lens practitioner
Authors: Douthwaite William Arthur , Sheridan Michael
Published: December 2007

A keratometric instrument is described which can be used to measure the p‐value of the corneal ellipse. The performance of the instrument is compared with that of the Guillbert Routit topographical keratometer and the Wesley Jessen P. E. K. The application of the p‐value to contact lens fitting is discussed.
Adaptive disorders of accommodation and vergence in binocular dysfunction
Authors: Schor Clifton , Horner Douglas
Published: December 2007

Disturbances of binocular vision are described clinically by the Duane‐White classification in terms of the magnitude of the accommodative‐convergence ratio (AC/A). Convergence excess and convergence insufficiency are assumed to result from high and low AC/A ratios respectively. It is assumed that the abnormal AC/A ratio is an independent variable that underlies abnormal phorias. However, recent studies have demonstrated that the AC/A ratio is inversely related to the adaptability of tonic accommodation (lens adaptation) and directly related to adaptability of tonic vergence (prism adaptation). We have tested whether clinical categories of convergence excess and convergence insufficiency are associated with insufficient and excessive adaptation of tonic accommodation and tonic vergence. Results demonstrate greater amplitude and duration of accommodative after‐effects (lens adaptation) in the convergence insufficiency than the convergence excess group. Vergence after‐effects (prism adaptation) had the reverse trend for the two groups. These results indicate that adaptive disorders of accommodation and vergence may underlie binocular disorders in symptomatic patients categorized as convergence excess and convergence insufficiency.
A model for the determination of VECP latencies
Authors: Mierdel P.
Published: December 2007

The time between stimulus event and onset of the visually evoked cortical potential (VECP) reflects the dynamic transmission characteristics of the precortical part of the visual system. A simple mathematical model describing this sub‐system with regard to the triggering of luminance VECP is presented. The four functional parameters of the model can be calculated from the measured latency versus stimulus intensity curve of luminance VECP and can provide a quantitative evaluation of the functional state of the precortical visual system for clinical use. Some experiments and first clinical results show the applicability of the model.
The onset of prolonged glare recovery with age
Authors: Collins Michael
Published: December 2007

The effects of ageing upon the recovery of contrast discrimination following exposure to a bright source of light (glare recovery) were investigated. A total of 65 subjects were tested, with a distribution of ages ranging from 16 to 79 years. Total glare recovery times were relatively constant up to about 56 years of age, after which they became significantly prolonged. Contrast thresholds to a small spot target gradually increased with age.
Frequency analysis of accommodation: single sinusoids
Authors: Sun Fuchuan , Brandt Stephan , Nguyen An , Wong Margaret , Stark Lawrence
Published: December 2007

We present an experimental frequency analysis of a neurological control system, the accommodation system, using single sinusoids. Also, by means of continual experimental calibration and full coverage of one subject's dynamic range, we demonstrate an AC nonlinearity saturation, which probably lies in the motor‐response portion of the system; in contrast to the switching‐mode nonlinearity, which probably lies in the sensory‐processing portion. We offer our findings as a basis for further models. In addition, our results can be compared with studies using multiple sinusoids and transients to document how the different aspects of the accommodation system are realized given their different input conditions.
The second fundamental form of a surface and its relation to the dioptric power matrix, sagitta and lens thickness
Authors: Harris W. F.
Published: December 2007

The dioptric power matrix of a single refracting surface is shown to be directly related to the differential form known in differential geometry as the second fundamental form. Consequently it is a complete description of the local refractive character of the surface. Generalized equations are derived for sagitta and lens thickness for surfaces of any form. The equations hold approximately for points close to the optical axis except in the case of paraboloidal surfaces; for paraboloidal surfaces they hold exactly. Lens thickness approximately obeys what is termed the principle of form independence. The value of the second fundamental form is approximately double the sagitta. Formal support is provided for Keating's concept of a generalized matric vergence of astigmatic wave‐fronts.
The effect of high frequency flicker on accommodation
Authors: Neary Catherine
Published: December 2007

Monocular accommodation was measured by a laser optometer while two subjects viewed a letter matrix target illuminated by steady or intermittent (300, 100, 50 and 25 Hz) light and presented at a number of optical distances (0.5, 1.5, 2.5, 3.5 and 4.5 D). At certain rates of intermittent illumination, both above (50 Hz) and below (25 Hz) flicker fusion, an increased accommodation response was found. This increase occurred at all optical distances, except for the distance closest to each subject's dark focus, and resulted in a more accurate accommodation response for one subject, and a less accurate one for the other. Furthermore, for both subjects, evidence of an increase in the amplitude of the fluctuations in accommodation at 50 and 25 Hz was found for the higher stimulus levels. The implications of these findings for the control of accommodation and for practical problems of visual performance in the environment, such as visual discomfort associated with fluorescent lighting and intermittently illuminated visual display units, are discussed.
A procedural guide to the modification of a Canon Auto Ref R‐1 for use as a continuously recording optometer
Authors: Pugh J. R. , Winn B.
Published: December 2007

We have recently reported on the modification of the Canon AutoRef R‐1 for use as a continuously recording optometer, while retaining its capacity to measure in ‘single‐shot’ mode. Although the principles of the modification and performance of the dual mode of operation have been described in previous publications, this technical note aims to provide sufficient detail for research laboratories wishing to implement the modification.
Accommodation and the nerve pathway to the ciliary muscle: a review
Authors: Ruskell G. L.
Published: December 2007

Evidence has accumulated recently which challenges the conventional description of the parasympathetic division of the oculomotor nerve pathway to intraocular smooth muscles. It is claimed that the pathway from the midbrain to the ciliary muscle is direct and uninterrupted by a synapse in the ciliary ganglion. A similar, separate claim has been made regarding the innervation of the sphincter muscle of the iris. The weaknesses in the arguments supporting the revised versions are discussed in this review and they are rejected in favour of the conventional pathway.
Effects of stimulus distance on measurements of dark convergence
Authors: Jaschinski‐Kruza Wolfgang
Published: December 2007

Dark convergence is often measured psychophysically by aligning two dichoptic stimuli, which are briefly flashed in a dark surround. In the present study, the effect of different stimulus parameters on dark convergence measurements was investigated. Chief among these was the effect of viewing distance (50, 100 and 500 cm) of the stimulus. Measured dark convergence was biased towards the actual viewing distance of the stimuli; this effect was stronger with bar stimuli than with point‐and‐line stimuli. Measured dark convergence depended on the viewing distance to a lesser extent if bar stimuli were observed through pin‐holes (open accommodative feedback loop). The subject's knowledge of the viewing distance had a small but significant effect; the size of the nonius bars had none. To reduce artefacts due to the stimulus distance on psychophysical measurement of dark convergence, point‐and‐line stimuli should be used at a viewing distance of about 1 m. In this case, the effect of stimulus distance can be about 0.25 meter angle (ma), averaged over subjects, but it may be as large as 0.5 ma in some individuals.
Proximal and cognitively‐induced accommodation
Authors: Rosenfield Mark , Ciuffreda Kenneth J.
Published: December 2007

The aim of this study was to investigate proximally‐induced accommodation (PIA) at two levels of cognitive demand. PIA was assessed by comparing the open‐loop accommodative responses to stimuli located at viewing distances of 6 m (0.17 D) and 0.33 m (3 D), respectively. The vergence and accommodation loops were opened by subjects monocularly viewing the targets through a 0.5 mm pin‐hole. PIA was measured while subjects either were encouraged to relax and listened to popular music, or performed a relatively demanding mental arithmetic task (counting backwards in sevens). The results indicated that for 4 of the 12 subjects examined, increased cognitive demand produced a marked (> ± 1.00 D) change in the magnitude of PIA. This finding suggests the presence of an interaction between the output of proximally‐and cognitively‐induced accommodation in these subjects. Such an interaction may hinder attempts to examine individual, non‐optical components of accommodation.
Tri‐meridional analysis using arbitrary meridians
Authors: Burek Henry
Published: December 2007

The evaluation of the sphero‐cylindrical components of curvature or refraction from measurements taken along three distinct meridians has been solved for various sets of three fixed meridians. A constraint of those solutions has been that the meridians of measurement are necessarily predetermined, which introduces an unwelcome restriction in experimental or clinical applications of tri‐meridional analysis. A new solution is presented (in three formats: analogue computer, graphical and algebraic), which enables any set of three meridians to be used for tri‐meridional analysis. A computer program listing (in BASIC) is included.
A general numerical method evaluating three‐dimensional eye rotations by scanning laser ophthalmoscopy
Authors: Ott Dietmar , Lades Martin , Holthoff Knut , Eckmiller Rolf
Published: December 2007

A general computational method is described to specify completely the rotational state of the eye in three dimensions by scanning laser ophthalmoscopy (SLO). The method uses the simplex algorithm to fit the eye's rotational parameters to data given by n individually selected ocular fundus landmarks before and after the eye rotation.

The rotational parameters are expressed as the rotation vector and three spherical Euler angles. The method, which was implemented in the C programming language, can be applied for various eye movement measurements in clinical and laboratory environments, including SLO.
Ocular hazards arising from depletion of the natural atmospheric ozone layer: a review*
Authors: Charman W. N.
Published: December 2007

The processes contributing to the maintenance of the natural, atmospheric, ozone layer, which screens the earth's surface from solar ultraviolet radiation at wavelengths below 300 nm, are described. The possible adverse effects of man‐made chemicals such as chlorofluorocarbons (CFCs) on this layer are outlined. Consideration of the flux of ultraviolet light reaching the earth's surface as a function of the ozone concentration and other factors allows the effect of ozone changes on ocular health to be evaluated. It is concluded that the changes of the order of a few per cent that are predicted by current models of the atmosphere, and which are comparable with natural fluctuations in ozone, would have relatively little effect on the incidence of solar keratitis at the cornea. Larger changes, in the order of 50%, would be expected to have a significant effect. There might also be an increase in the incidence of brunescent cataract. Ozone changes would have a negligible effect on the amounts of solar radiation reaching the retina.
Corneal desiccation staining with hydrogel lenses: Tear film and contact lens factors
Authors: Guillon Jean‐Pierre , Guillon Michel , Malgouyres Sylvain
Published: December 2007

This investigation monitored the response of established contact lens wearers using contact lenses made from Filcon 4a 77% water‐content material in three different thicknesses (0.08, 0.10 and 0.12 mm) over a 6‐hour period of wear under adverse environmental conditions. The results obtained showed the following. (1) In accordance with previous studies carried out with lenses of similar water content, the present lenses produced corneal desiccation staining under the challenging conditions of use. However, the staining produced was similar for all three lens thicknesses tested. (2) Corneal desiccation staining was present despite the good and stable fitting characteristics observed during the study, confirming that mechanical trauma is not a necessary cause for soft‐lens‐induced desiccation staining. (3) Corneal desiccation staining was associated with a rapidly destabilizing pre‐lens tear film (PLTF) and a thinning lipid layer. The initial break‐up of the PLTF and corneal staining were recorded with a higher incidence in the vertical quadrants than in the horizontal quadrants. The PLTF is thinnest and most unstable at the tear prism margin border, hence least efficacious at preventing evaporation. Corneal desiccation staining may be due, at least partly, to excessive evaporation at the contact lens front surface.
The role of small‐field tritanopia in two measures of colour vision
Authors: Tuck J. Porter , Long Gerald M.
Published: December 2007

The present work extends the findings of previous efforts examining the comparability of current colour‐screening tests. Several popular tests are shown to differ greatly in the performance exhibited by colour‐normal observers as well as in their differential sensitivity to experimental manipulations of viewing duration and viewing distance. Those tests designed to identify yellow‐blue dichromacy are especially sensitive to the manipulation of viewing distance, which is interpreted as reflecting ‘small‐field tritanopia’ and the asymmetry in retinal density of the three cone types. These findings are discussed in terms of factors that influence the comparability of current colour‐screening devices and the particular need for close adherence to standardized conditions with such instruments.
Investigation of Progressive Addition Lens patient tolerance to dispensing anomalies
Authors: Sullivan Colin M. , Fowlert Colin W.
Published: December 2007

Numerous reasons have been cited for patient non‐tolerance to Progressive Addition Lenses (PALs). This paper considers two presbyopic subject populations‐those who successfully wore PALs (n = 20), and those who were non‐tolerant to them (n = 18). The dispensing accuracy of the PALs worn by subjects was assessed and the surface quality of those lenses worn by unsuccessful patients studied. These factors do not account for any significant differences between the two groups, suggesting that other causes must separate the subject populations.
Horizontal fusional amplitudes after adaptation to prism
Authors: Stephens Gregory L. , Jones Ronald
Published: December 2007

Horizontal fusional limits and lateral phorias were measured subjectively on five normal subjects after adaptation to increments of base‐in and base‐out prism. Both the phoria and the fusional limits were found to change by approximately the amount of the adapting prism. The fusional amplitudes (the difference between the phoria and the fusional limits) were relatively unaffected by vergence adaptation except at the largest values of adapting prism. These results are in agreement with current models of disparity vergence eye movement control which suggest that there are independent fast and slow fusional vergence mechanisms, each with its own saturation limit.
Heterophoria and monocular occlusion
Authors: Dowley D.
Published: December 2007

Prism adaptation responses in orthophoric, exophoric and esophoric subjects are compared and found to be significantly different. Following a prolonged period of monocular occlusion the prism adaptation responses were compared, after occlusion the differences are no longer significant. This supports the theory that vergence (prism) adaptation is responsible for the existence of heterophoria. This paper shows that changes in heterophoria with monocular occlusion are caused by desaturation of prism adaptation.
Modelling oblique astigmatism in eyes with known peripheral refraction and optical dimensions
Authors: Dunne M. C. M. , Barnes D. A.
Published: December 2007

The optical dimensions of 34 young adult eyes were measured by optical and A‐scan ultrasound methods. Peripheral refraction was recorded up to field angles of 40 degrees to produce results for oblique astigmatism. These findings were modelled in schematic eyes with a monoindicial crystalline lens but with varying levels of asphericity of the optimal surfaces.
Automatic measurement of varifocal spectacle lenses
Authors: Fowler C. W. , Sullivan C. M.
Published: December 2007

An instrument is described for the automatic measurement of lens power across the whole aperture of a varifocal lens. The apparatus is based on an electronic focimeter controlled by an external computer, which also positions the lens by two stepper motors. Methods of display of the data are discussed, and the repeatability of measurement is illustrated.
Toroidal surface assessment by curvature measurements in three fixed meridians
Authors: Burek H.
Published: December 2007

A method is described to evaluate the sphero‐cylindrical components of a toroidal surface by curvature measurement along three fixed meridians which are orientated at 60 degrees to each other.
Possible allergic reactions to cyclopentolate hydrochloride: case reports with literature review of uses and adverse reactions
Authors: Jones Lyndon W. J. , Modes Deborah T.
Published: December 2007

Cyclopentolate has been widely used as a cycloplegic and mydriatic agent for over 30 years. It has gained widespread use as the cycloplegic drug of first choice for most children over the age of I year and allows many optometrists and ophthalmologists lo carry out quick, successful cycloplegic refractions with few complications. During this time very few side‐effects have been reported with the most commonly used 1 % solution. This paper outlines two cases in which a possible allergic‐type reaction occurred shortly after the instillation of 1% cyclopentolate hydrochloride in ‘Minims’ form (Smith and Nephew). This article also reviews the uses and side‐effects of cyclopentolate and aims to warn practitioners about the possibility of such reactions, ways of avoiding their occurrence and suitable measures to take should they occur.
Computer‐assisted optic nerve head assessment
Authors: Cox Michael J. , Wood Ivan C. J.
Published: December 2007

An IBM‐compatible microcomputer‐based system has been developed for the assessment of pallor area size, shape and degree of pallor in the optic nerve head. The system allows the instantaneous capture of optic nerve head images, and software analysis of these images produces measurements of the pallor area in about 2 mm. The various methods of image analysis arc presented. These are enhancement, thresholding, and digital Filtering for edge detection. The results of their application to the images of the optic nerve head are shown. The results of the system's analysis on a particular optic nerve head are also shown. The potential uses and difficulties of such a system are discussed.
Inter‐ and intra‐image variability in computer‐assisted optic nerve head assessment
Authors: Cox Michael J. , Wood Ivan C. J.
Published: December 2007

A computer‐assisted system for optic nerve head analysis was used to measure one eye from each of 15 subjects. These comprised three groups of five, being glaucomatous, ocular hypertensive, and normal subjects. Each eye was imaged with the system 10 times. The 150 images produced were analysed in a randomized masked fashion to test the inter‐image variability of the measurements. Linear pallor: disc ratios had mean coefficients of variation of 6.6% (normal), 4.8%. (ocular hypertensive) and 2.6% (glaucomatous). This trend of reducing coefficient of variation from normal to ocular hypertensive to glaucomatous was reflected in other parameters also. Intra‐image variability was assessed by analysing one image from each subject 10 times, in a randomized masked fashion. The mean coefficients of variation of the linear pallor: disc ratios were 6.3%. (normal), 3.6% (ocular hypertensive) and 3.2% (glaucomatous). Fisher's F test showed that no parameters had significantly lower intra‐image rather than inter‐image variance (at the 5% level). Variability is apparently due to operator variations rather than the image variations.
Age‐related maculopathy. II: The nature of the central visual field loss
Authors: Swann P. G. , Lovie‐Kitchin J. E.
Published: December 2007

This is the second of three papers dealing with age‐related maculopathy (ARM) and its effects on visual function (Swann, P. G. and Lovie‐Kitchin. J. E. Age‐related maculopathy. I: A review of its morphology and effects on visual function. Ophthal. Physiol. Opt.10, 149–158 (1990)). We investigated the nature or character of the central visual field loss in ARM and pre‐age related maculopathy (FARM) and compared them with age‐mulched normal subjects. Central visual fields were examined using the Friedmann Visual Field Analyser. Mark II, the Bausch and Lomb Autoplot Tangent Screen and Amsler charts. The central visual field defects in ARM were predominantly paracentral with a relative sparing of foveal sensitivity. PARM subjects did not show significant visual field defects. However, three FARM subjects did show slight distortions with the Amsler charts. The third paper in this series will compare the efficacy of the three methods of visual field investigation in the detection of these defects.
Determination of the nodal point position in the pseudophakic eye
Authors: Snead M P. , Lea S. Hardman , Rubinstein M. P. , Reynolds K. , Haworth S. M.
Published: December 2007

The optics of the schematic eye have been described by Gullstrand and Listing (System of Ophthalmology (ed. H. Kimpton), Vol. 5, C. V, Mosby, London (1970)). data being averaged from a series of adult eyes with a crystalline lens. A ray of light from the height of any given object passing, undeviated. through The nodal point will determine the height of its image cm the retina. The nodal point positions, therefore, are fundamental in determining image size, and any eye‐to‐eye variation in a patient will control the amount of aniseikonia. The optics of the pseudophakic eye are described together with a scientific method for determining the nodal point positions, and the implications are discussed.
Atropine occlusion in the treatment of strabismic amblyopia and its effect upon the non‐amblyopic eye
Authors: North R. V. , Kelly M. E.
Published: December 2007

A total of 1S9 cases with amblyopia, where atropine sulphate 1 % had been used as a method of unilateral occlusion, were reviewed. The results show that after atropine had been appropriately applied, permanent reversal of amblyopia is rare, and unwanted side‐effects are few and of minor nature. Pupil size, light reflex and accommodation of the atropinized eye appear to be unaffected. The angle of squint was unaffected and fixation of the amblyopic eye either remained unchanged or shifted to a more central point.
Thickness extrema at the edge of shaped lenses: the general problem and the solution for a straight edge obtained by means of direct elimination and of Lagrange multipliers
Authors: Harris W. F.
Published: December 2007

In general thickness varies along the cut edge of a lens. There is some interest in being able to predict the locations of the thickest and thinnest points on the edge. One purpose of this paper was to formulate the general problem mathematically of finding the locations of thickness extrema on the edge of an arbitrary lens cut into an arbitrary shape. A second purpose was to illustrate how the problem can be solved.In particular, the problem is solved completely and explicitly for what is probably the simplest case, the straight cut edge. A component‐free matrix expression for the position of the extremum is derived by employing Lagrange multiplieers and concept of the generalized inverse of a matrix. The equation applies to spheres., cylinders and sphero‐cylinders and allows for the presence of prism as well. Along some edge the thickness is constant. Along other edges the thickness varies linearly; there are no extrema except for the practical extrema at the two ends of the edge: thickest at the one and thinnest at the other. The mathematical conditions for these two cases are presented. Equivalent to the matrix equation for the position vector of the thickness extremum is a pair of scalar equations expresed in terms of components of the matrices. The pair is useful when locating extrema using manual calculations. On the other hand, the component‐free matrix equations is useful in other circumstances such as for mathematical manipulations and hen using computere software that handles matrices. The former is used in a number of numerical examples: the latter was used to check the answers by computer. The mathematical techniques described here are likely to find application in other areas of opthalmic and visual optics.
Keratoreformation by contact lenses after radial keratotomy
Authors: Astin Christine L. K.
Published: December 2007

Since the number of patients undergoing radial keratotomy has increased, more have required contact tens fitting to correct residual ametropia. A number of practitioners suggest that the postoperative changes stabilize after 12 months, so contact lens lining on the unusual resultant conical topography can begin. This paper discusses corneal and refractive changes that are revealed even when correctly lining lenses are worn 1–5 years postoperatively. These changes indicate that lens wear may influence corneal topography and refraction even several years after radial keratotomy.
The Opticians Act 1989 and UK optometry
Authors: Taylor S. P.
Published: December 2007

The build‐up lo the original 1958 Opticians Act is used as an introduction to the more recent developments in UK optics that have culminated in the introduction of the Opticians Act 1989. The changes introduced as a result of the Health and Social Security Act 1984 and the Health and Medicines Act 19X8 are briefly described before discussing the sectional arrangement of the new Act. This new legislation pulls together much of the law relating to Optometry and dispensing optics in the UK und provides a single accessible source.
The provision of ophthalmic services for a rehabilitation day care centre population with multiple physical handicaps
Authors: Jackson A. J. , O'Donoghue E. , Wilson H. , Canavan Y. M. , Gibson M.
Published: December 2007

The provision of the wide variety of support services necessary for patients with multiple handicaps is often poorly coordinated. In this study of 108 adults, aged from 19 to 90 years, who suffered from multiple physical handicaps and attended a rehabilitation day care centre, had their visual functions and requirements assessed by a multidisciplinary team. The programme consisted of five stages. Each patient was initially screened and subsequently referred for more detailed optometric, ophthalmological, low vision or rehabilitation assessments, where appropriate. Results indicated that many of the patients had not been receiving regular ocular assessments and would benefit from the provision of an optical appliance of ophthalmological treatment. The survey provided staff at the rehabilitation centre with information on the visual status of individual patients and enhanced general eye‐care awareness.
The effect of mental effort on open‐ and closed‐loop accommodation
Authors: Winn B. , Gilmartin B. , Mortimer L. C. , Edwards N. R.
Published: December 2007

The accommodative response to stimuli in normal visual environments is determined by a complex and subtle integration of optical and non‐optical factors. Mental effort associated with the visual task can modify significantly the steady‐state accommodative level, but. owing to the diversity of experimental designs, there is no clear consensus on the mechanisms involved. Changes in the accommodation response of ten emmetropic subjects (mean (±SD) age = 20.4 ± 4.5 years) under open‐ and closed‐loop conditions were investigated for three levels of mental activity. (1) A passive task whereby subjects simply read letters, to themselves. (2) A stimulus‐ dependent task (SDT) whereby subjects are instructed to respond only when the letter ‘e’ appears in one of a series of presentations. (3) A stimulus‐independent task (SIT) whereby subjects count backwards in sevens to themselves while viewing the target. An objective infra‐red (IR) optometer was used in its static mode of operation to make monocular measurements of accommodation under monocular viewing conditions. Open‐loop conditions were achieved by placing a pinhole (0.5mm diameter), drilled into an IR filter. 12mm in front of the eye. Under closed‐loop conditions the mean accommodation response for passive viewing of the near target was +3.08D. A significant (F= 5.45 d.f. 9,18 P < 0.005) accommodative shift induced by mental effort in the mean response of +0.17 D occurred for the SDT, The SIT induced a mean shift of −0.05 D which was not significantly different to the passive viewing response. A significant negative correlation between the magnitude of the passive open‐loop response and the size of the shift induced by mental effort was found for both tasks (SIT: y = 1.314 − 0.815x R = 0.86. SDT: y = 2.169 − 0.821xR = 0.70). With respect to zero shift, the relationship was pivotal about 1.61 for SIT and 2.64 D for SDT. It is proposed that when the effect of optical feedback is minimized a significant interaction occurs between mental effort and perceived proximity.
Ocular adverse effects to the therapeutic administration of digoxin
Authors: Hobley Angela , Lawrenson John
Published: December 2007

Disturbances in colour vision are a well‐reported adverse ocular effect to toxic levels of digoxin. We present a case history of a patient with both colour vision changes and transient visual field defects to therapeutic serum levels of digoxin.