bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Waterloo Vision and Mobility Study: postural control strategies in subjects with ARM
Authors: Elliot David B. , Patla Aftab E. , Flanagan John G. , Spaulding Sandi , Rietdyk Shirley , Strong Graham , Brown Steve 
Published: July 2002

SummaryBinocular visual function and standing balance control was assessed in 16 subjects with age‐related maculopathy (ARM) (mean age 73.9 ± 7.4 years) and 19 controls (mean age 69.1 ± 5.5 years). Balance control was assessed using the center of pressure signal from force plate data. It was quantified using the root mean square (RMS) error of the amplitude, sampled over a 1 min period. This was evaluated during normal standing, and while the input from the kinesthetic and/or visual systems were disrupted. The two subject groups showed significantly different RMS values across conditions (P < 0.005). The differences in RMS between ARM and control groups were only significant when the input to the kinesthetic sensory system was disrupted. Our results suggest that in the normal standing condition, the kinesthetic and vestibular systems compensated for the lack of useful information from the visual system in ARM subjects. When kinesthetic system input was disrupted, balance control of the ARM group was significantly poorer than the control. There was a weak correlation between postural control and contrast sensitivity. Various strategies for preventing falls in elderly patients with low vision are suggested.
Amblyopia: a tale of two approaches
Authors: Hess Robert F. 
Published: July 2002

SummaryOur understanding of the physiological basis for amblyopia in humans has undergone dramatic changes over the past two decades. The first such change occurred when we were first able to record from single neurones in different parts of the visual pathway and develop neural models of the anomaly. The second came from psychophysical investigations and evaluations of these animal models. Our understanding has progressed from one focused on the properties of single cortical cells to an appreciation of the anomalous behaviour of cellular networks.
Outcome of referrals for suspected glaucoma
Authors: Harper Robert , Reeves Barnaby , Hill Adrian 
Published: July 2002

SummaryThe source, content and accuracy of 178 referrals to Oxford Eye Hospital for suspected glaucoma were examined.The majority (82.6%) of referrals for suspected glaucoma were initiated by optometrists, other referrals being initiated by general practitioners (10.1%) and ophthalmic medical practitioners (7.3%). Most referrals (86.5%) reported the intraocular pressure (IOP) level. Comments on the optic disc were recorded in 53.9% of referrals. Only 21.3% of referrals mentioned the status of the visual field. The findings of all three ‘standard’ glaucome measures (i.e. IOP and the status of the optic disc and visual field) were reported in only 15.2% of referrals.A visual field defect consistent with glaucoma was found in 38.2% of referrals and a further 9.6% of referrals were prescribed treatment for glaucoma/ocular hypertension but had no manifest visual field defect. Approximately one‐third of referrals (34.2%) were considered ‘normal’ and were discharged. The remainder of referrals were either followed up as glaucoma suspects (9.6%) or were considered ‘abnormal’ but non‐glaucomatous (8.4%).There was evidence to suggest that (1) optometric referrals were more accurate than referrals from GPs and OMPs; and (2) referrals combining information from all three standard screening measures were more accurate than those based on IOP alone.These findings support previous surveys by the International Glaucoma Association. At least one‐third of referrals for suspected glaucoma are false positives. Visual field screening appears to be used very infrequently by primary vision carers suggesting that the false negative rate may also be high.
The source of disparity vergence innervation determines prism adaptation
Authors: McCormack G. , Fisher S. K. 
Published: July 2002

SummaryA physiological model of prism adaptation argues that adaptation magnitude and rate are functions of the magnitude of reflex vergence innervation. It has also been shown that there is reduced prism adaptation magnitude for a given disparity stimulus where only peripheral sensory fusion is present (the ‘eccentricity effect’). This study attempted to determine whether the eccentricity effect is attributable to reduced reflex vergence innervation in peripheral fusion. Experiments were run in a Maxwellian view haploscope. Convergence and divergence adaptation to 6 Δ disparity stimuli were quantified for seven binocularly normal subjects using subjective heterophoria measurements. Vergence response during central or peripheral fusion was quantified objectively by infrared oculography. Six of seven subjects revealed an eccentricity effect. However, in three of seven subjects the eccentricity effect was not predictable from the manifest vergence response. The results suggest that the source of reflex vergence innervation affects prism adaptation. A model is proposed whereby different sources of reflex disparity vergence innervation stimulate prism adaptation by way of separate neurological pathways of differing responsiveness.
Spatial interference with vertical pistol sight alignment
Authors: Carkeet Andrew , Brown Brian , Chan Peter 
Published: July 2002

SummaryWhen competition pistol shooters aim, they perform four basic visual alignment tasks. With optimal stimuli such tasks can be performed with exquisite sensitivity. However, pistol sights and the target may not constitute the optimal stimuli, and this may impose limits on how well shooters perform. By simulating pistol sights and targets on a computer monitor, we investigated how the vernier task of aligning the top edges of the front and rear pistol sights was affected by the proximity of the target aiming mark. Alignment random error in this task, an analogous measure to vernier acuity, was unaffected by the proximity of the aiming mark; however, alignment systematic error did change significantly as the proximity of the aiming mark changed. This effect was unlikely to significantly change pistol shooting performance as shooters can adjust their sights to compensate for systematic errors. Likewise, compared to the vertical spread of shots on the pistol target, alignment random error was extremely small (only 10s arc), which implies that other sources of variation limit pistol shooting performance.
Thickness extrema at the edge of astigmatic lenses including those with straight, circular and elliptical edges
Authors: Harris W. F. 
Published: July 2002

SummaryThe problem of locating the points of maximum and minimum thickness at the edge of a lens, and of calculating the thickness at those points, is examined for lens powers and for edge shapes in general. The edge extremal problem, as the problem is called, is solved explicitly for general powers along straight cut edges. The extremal problem is also analysed for lenses with circular and elliptical edges but explicit solutions are obtained only for centrally cut lenses, that is, lenses with coincident optical and geometrical centres. For edges that are neither straight nor centrally cut ellipses (including circles), it appears that explicit solutions cannot be obtained for the edge extrema: one has to resort to numerical solution of implicit equations or to the calculation of thickness at sufficiently many points around the edge. For the centrally cut ellipse the edge extremal problem turns out to be the eigenvalue problem of linear algebra. In general the thickness extrema at the edge do not lie on the principal meridians of the lens, nor do they lie on meridians that are mutually perpendicular. With minor modification the results apply equally well to the edge extrema for sagitta of a surface.
Effect of the menstrual cycle on corneal curvature
Authors: Oliver Katherine M. , Walsh Glyn , Tomlinson Alan , McFadyen Angus , Hemenger Richard P. 
Published: July 2002

SummaryThe purpose of this research was to determine if a clinically significant variation in corneal curvature occurs with the menstrual cycle. The EyeSys™ Corneal Analysis System™ (CAS) was used to measure corneal curvature of a test group of three normally menstruating female subjects over three cycles and compared with a control group of three males, for three pseudocycles of 28 days. Measurements were taken on days 1, 4, 8, 15 and 22 of each of three menstrual cycles, with four CAS images taken on each day. Four points (along 45, 135, 225 and 315 degrees) were selected for each of rings 1, 3, 6 and 8, and the average curvature for each of these rings was calculated. The results showed that no detectable temporal effect occurred with the menstrual cycle, thus demonstrating that either cyclic variation in corneal topography was too small to be identified by this system or it did not take place.
Spatial frequency dependent observer bias in the measurement of contrast sensitivity
Authors: Woods Russell L. 
Published: July 2002

SummaryA previously reported spatial frequency dependent change in contrast sensitivity, apparently produced by the psychometric method used, was investigated in two experiments. A relative reduction in the measured contrast sensitivity function at higher spatial frequencies was found when using a simple single staircase procedure, even when all external characteristics of the presentation procedure were the same as a more sophisticated and more reliable psychometric method (adaptive probit estimation). The estimated false‐negative response rate was found to be greater for the single staircase procedure and was greater at a higher spatial frequency, while the false‐positive response rate to interleaved blank presentations did not vary between spatial frequencies and between the two psychometric methods. This supports the suggestion that some subjects, given a knowledge of the psychometric method controlling grating contrast, may adopt different decision criteria at different spatial frequencies.
Calculating relative retinal image sizes of eyes
Authors: Atchison David A. 
Published: July 2002

SummaryI derive simple formulas which accurately give the relative retinal image sizes of corrected eyes. These are useful in calculations involving anisometropia and/or refractive surgery. Using the formulas, I derive simple equations for particular situations and provide two examples. I compare the formulas with the approach adopted by Applegate and Howland (1993) and Applegate and Chundra (1995) to determine relative retinal image sizes before and after refractive surgery.
The development of the chromatic visual evoked potential
Authors: Rudduck G. A. 
Published: July 2002

Evidence exists to suggest that visual function of very young infants is not cortically controlled and may in fact be mediated by a more primitive subcortical system. Visual evoked potentials (VEP) are used widely as a clinical and research tool and in this study the development of the chromatic VEP was investigated. Chromatic vision is a cortical function, hence the presence of a chromatic VEP may suggest the presence of a functioning cortical pathway.Using pattern reversal stimuli of red and green checks, the presence and morphology of the transient chromatic VEP were assessed. The checkerboards reversed in chromaticity and control of the relative brightness (luminance) of the checks allowed the production of a range of stimuli of different red/green luminance ratios. A black/white stimulus was included in all trails for comparison. VEPs to these stimuli were recorded from 36 infants aged between 1 and 14 weeks post‐term. Fourteen of these infants were then assessed on two further occasions to monitor the longitudinal development of the chromatic VEP. All infants tested demonstrated clear VEPs to achromatic stimuli and to those red/green stimuli that contained luminance information. As the luminance information within the stimuli decreased, the morphology of the wave changed with the major component (P1) becoming diminished and delayed. No VEP could be recorded from any infant less than 7 weeks post‐term at time of testing when using an isoluminant stimulus. In the longitudinal study, all of the infants, who initially demonstrated no response to isoluminant stimuli, did so on reaching their eighth post‐term week.These results would suggest that those channels responsible for the processing of chromatic information do not function until the eighth post‐term week. During the period prior to this, visual processing takes place via a colour‐insensitive pathway, probably subcortical.
100 years of scleral lenses: where are we now?
Authors: Pullum Kenneth W. 
Published: July 2002

The threat of long‐term hypoxic corneal changes together with the complex and unpredictable nature of fenestrated lens fitting have made scleral lens practice unattractive to practitioners. Gas permeability has allowed use of sealed lenses, simplifying the fitting procedures even with advanced pathology.The case notes for 322 patients seen wearing scleral lenses or assessed for scleral lens fitting were retrospectively analysed to determine the indication for contact lenses, the reasons for scleral lens fitting and the outcome: 47% were for keratoconus or other primary corneal distortions, 19% for postoperative corneal transplant, 12% aphakia, 10% myopia and 10% ocular surface disease. 68% continued to wear RGP sclerals or were fitted or refitted with RGP sclerals, with 19% remaining with PMMA sclerals and 13% discontinuing scleral lens wear or lost to follow‐up.Scleral lenses remain the lens of choice for a group of contact lens wearers which is relatively small in number but with a high clinical requirement for contact lens correction. The introduction of gas permeable materials has enabled their application for less advanced pathology compared to that possible with PMMA.
Ametropia in Down's syndrome
Authors: Doyle S. , Bullock J. , Gray K. , Spencer A. 
Published: July 2002

A matched cohort of 50 individuals (29 male and 21 female) with Down's syndrome in the Manchester area aged 16–18 years was studied by refraction, corneal topography, A‐scan biometry, slit‐lamp examination and orthoptic examination.1. A linear relationship was found between axial length and spherical equivalent refraction as in the normal population.2. Forty (80%) of the group had a hypermetropic refraction (mean ±2.46 D, range +0.5 to +7.5 D). Nine (18%) were myopic (mean −2.75 D, range −0.5 to −0.8 D). One (2%) was emmetropic (within ±0.5 D of zero). This indicates a failure of emmetropisation compared to a similar group of normal teenagers of the same age range.3. There was one (2%) overt keratoconus. Three (6%) had corneal topography with inferior steepening which may be a preclinical keratoconic process.4. Corneal topography was generally of a regular ‘bow‐tie’ pattern, but there was a high incidence of oblique cylinders with 38% of eyes having their axis outside 10° of the orthogonal axes. 22% had cylinders ‘with the rule’ (±10° to 90°) and 39% had cylinders ‘against the rul’ (±10° of 130°).5. 8% had amblyopia secondary to childhood squint. 14% had an A‐esophoria.These findings are discussed.
Paediatric examination spectacles in the assessment of ptosis
Authors: Wood C. M. , Jones C. A. , Loo A. 
Published: July 2002

Measuring ptosis in children can be fraught with difficulties as one tries to hold a ruler up to the eye with one hand whilst trying to get the child to look at a toy in the other hand. To overcome this problem, we have designed some decorative spectacles acceptable to the children. These spectacles are lightweight with a vertical measurement in millimetres grid on the lenses. They are colourful, attractive with different cartoon figures. They come in two sizes, which are suitable for children aged between 2 and 6 years. These sizes were chosen by our optician after studying the average sizes of frames worn by children of this age group.The clinical measurements which can be made are: palpebral fissure height, levator function, margin‐reflex distance and upper lid crease.By having the children wearing the customised examination spectacles, the examiner has the advantage of having both hands free and so not frightening the children by approaching them with a ruler. These are invaluable in more accurate assessment of ptosis. We have found in our clinic that the majority of children are happy to wear the glasses. We therefore recommend the use of these glasses in the assessment of congenital ptosis.
Objective assessment of spatial vision using the visual evoked potential
Authors: Hadjizenonos C. , Parry N. R. A. 
Published: July 2002

Early assessment of the visual function is very important, as many congenital and acquired visual anomalies may lead to permanent visual loss, if not detected and effectively treated within the critical period of visual system development. Any tests employed to assess vision in infants should be objective and give a valid result quickly.The visual evoked potential (VEP) does not require active responses from the patient. It is recorded in relation to a time‐locked stimulus, typically a grating that reverses in phase (pattern reversal VEPs). Reversal VEPs have been used to estimate visual acuity. A more complete psychophysical description of the visual function is obtained with the contrast sensitivity function (CSF) which determines visibility not only of the finest detail, but also of a wide range of spatial frequencies. However, the VEP amplitude versus spatial frequency function does not accurately reflect the normal CSF when reversing gratings are employed. Reduced VEP responses are obtained in the middle spatial frequency range where stimulus visibility is highest.Here we show that 16 Hz on‐off modulation of a grating elicits a VEP versus spatial frequency plot which is similar to the CSF in a group of normal adults. When compared with reversal modulation, the test was more predictive of spatial vision defects in a group of amblyopes, thus demonstrating its clinical utility. We have shown that the same technique can be used to monitor age‐related changes in spatial vision in a group of infants whose ages ranged from 5 weeks to 14 months. The test promises to be a useful clinical tool in paediatric ophthalmology.Supported by a grant from the North Western Regional Health Authority.
An evaluation of vision screening and eye examinations performed on display screen equipment users
Authors: McClure M. , Barnett S. , Jackson A. J. 
Published: July 2002

The introduction of regulations governing ‘work with display screen equipment’ has placed a number of important obligations on employers. One of the most widely debated issues concerns an employee's entitlement to ‘an appropriate eye and eyesight test’. Opinions are divided on the relative merits of the new generation of vision screening tests and their relevance within the context of the regulations. In this study the results of 112 full optometric eye examinations performed on ‘regular’ display screen users, 98% of whom had previously failed the City University Computerised Vision Screening Program, are analysed. Comparisons are made between the results of eye examinations and the results of individual vision screening tests which contributed to overall test failure.Results confirm that those identified by the City University's illiterate E visual acuity screening test as having substandard acuities often required an update to their current spectacle correction. Sixty‐eight percent of those failing vision screening were spectacle wearers and of these 40% were identified as requiring an updated prescription to optimise visual potential. Results also confirm that those failing vision screening on the basis of substandard binocular vision had either a long‐standing history of oculomotor problems or an imbalance of the oculomotor system which may contribute to the presence of visual symptoms. The proportion of those complaining of ocular or visual symptoms, when assessed using the on‐screen questionnaire (69%), was similar to that revealed during the recording of history and symptoms by an optometrist (65%). Interestingly, only 3% of those examined by optometrists were identified as requiring spectacles solely for display screen use. Three percent of those tested were identified as requiring medical referral, using conventional general ophthalmic services referral criteria.The authors conclude that the City University screening system, when utilised in a coordinated manner within the context of a display screen equipment work‐station risk assessment programme, fulfils both staff and managerial expectations. The utilisation of (on‐site) vision screening identifies those most in need of a full examination and thus allows employers to concentrate financial resources on those most likely to obtain benefit from the provision of professional services.
Prevalence of significant pre‐clinical contrast sensitivity loss in diabetics
Authors: Gilchrist Jim , Pope Richard , Dhanesha Usha , Young Sally , Horsley Clare 
Published: July 2002

Aim: To estimate the prevalence of impaired contrast sensitivity (CS) in diabetic patients with normal visual acuity and no clinical detectable retinopathy.Methods: We measured CS in 75 diabetics with visual acuity of logMAR 0.0 or better, no evidence of retinopathy by direct ophthalmoscopy and fundus photography, and no evidence of cataract. The sample comprised 27 IDDM (15–44 years), and 48 NIDDM (35–71 years). The CS of each patient was measured with sinusoidal gratings at 2, 4 and 8 cdeg−1 using a two‐alternative forced‐choice staircase procedure, and the data were compared with CS values from age‐related non‐diabetic patients. A decision was made for each diabetic that CS was either normal or impaired, based on whether that individual's CS fell more than 2 standard deviations (Criterion A) or 3 standard deviations (Criterion B) below the age‐related non‐diabetic mean value.Results and conclusions: Estimated proportions, averaged across all spatial frequencies, of diabetic patients with impaired CS were: 28% by Criterion A and 15% by Criterion B. Population estimates (95% confidence intervals) for the prevalence of significant pre‐clinical CS loss in diabetics based on these results are: 18–38% using Criterion A and 7–23% using Criterion B.