bluuebunny/crossref_metadata_2025_split huggingface dataset:
Clinical uses of the scanning laser ophthalmoscope
Authors: Culham Louise , Fitzke Fred , Marshall John G. 
Published: July 2002

SummaryThe scanning laser ophthalmoscope (SLO), designed in the early 1980s, has many advantages over conventional imaging techniques. Continuous, real‐time images are displayed on a TV monitor and usually recorded on video‐tape. Images can be obtained without pupil dilation and it is often possible to image through cataract and other media opacities. The lasers used for retinal imaging, helium‐neon, argon and infra‐red diode, are low powered and the light levels used in the SLO are about 1000 times less than in conventional fundus photography. Fluorescein and indocyanine green angiography can be performed and the dynamic sequences recorded on video‐tape.Several systems are available, for example Rodenstock, Zeiss and Heidelberg, and each have specific features. Typically the field of view is 20 or 40 degrees. Instruments can work in a non‐confocal, confocal or indirect mode. While the non‐confocal mode is used for general retinal imaging, in the confocal mode, thin slices of a structure can be imaged, e.g. the optic nerve head, and by means of a computer three‐dimensional reconstruction is possible. In the indirect mode, the image is formed from structures that scatter light, e.g. the choroidal vessels.The SLO also has the ability to perform psychophysical measurement. Any graphics which can be displayed on a TV monitor can be encoded into the scanning laser beam. The stimuli can be altered in character, size, contrast and velocity. The tests that allow assessment of visual function include visual acuity, retinal perimetry and measurements of fixation stability. Scrolled text can be used to allow precise evaluation of reading ability at different retinal locations.Using these tests we have investigated residual vision in patients with macular disease. Microperimetry was able to define accurately the size and location of retinal lesions and in some patients residual visual function was detected in areas that appeared to be non‐functioning. Some patients had fixation stability which was exceptionally poor whilst in others it was normal. The ability to recognize scrolling text declined with increasing retinal eccentricity and decreasing text contrast. The imaging and psychophysical abilities of SLOs are providing valuable information on patients with retinal diseases.
Blue‐on‐yellow perimetry
Authors: Hudson Chris , Wild John 
Published: July 2002

SummaryLaboratory based studies which employ foveal stimuli have demonstrated a selective short‐wavelength sensitive (SWS) pathway deficit prior to visual field loss in glaucomatous patients. Early glaucomatous visual field loss as revealed by conventional perimetry, however, is generally accepted to occur outside the fovea. Consequently, blue‐on‐yellow perimetry was developed which permits the assessment of SWS function across the central visual field. This new clinical technique employs a blue stimulus to preferentially stimulate the SWS pathway and a high luminance yellow background to saturate the other receptor types. Clinical studies suggest that blue‐on‐yellow perimetry reveals early glaucomatous field loss before conventional perimetry which follows a pattern dictated by the anatomy of the retinal nerve fibre bundles.Blue‐on‐yellow perimetry is particularly prone to attenuation by the ocular media and macular pigment because of the use of a short‐wavelength stimulus. Ocular media absorption (OMA) increases with increase in age (approx. a 10 dB increase in mean OMA between 20 and 70 years relative to 410 nm), exhibits a large variation between individuals of the same age (approx. 9 dB) and is exaggerated in diabetics. Both OMA and forward light scatter (LS) result in a diffuse reduction of blue‐on‐yellow sensitivity. Macular pigment absorption (MPA) does not vary systematically with age (P > 0.05) but exhibits a large variation between individuals (approx. 10 dB relative to 460 nm). MPA results in a symmetrical reduction of blue‐on‐yellow sensitivity centred on the fovea (mean foveal MPA 4 dB, P < 0.001) with 5° eccentricity.The psychophysical techniques employed to quantify OMA, forward LS and MPA are time‐consuming and not suitable as routine clinical procedures. Methods of analysis which avoid the use of absolute sensitivity values need to be employed to identify abnormality in the blue‐on‐yellow visual field. Such an approach may rely on the identification of change in shape (i.e. pattern standard deviation) or symmetry (i.e. glaucoma hemifield test) of the visual field. Alternatively, the clustering of stimulus locations with markedly reduced sensitivity and the conformity of clusters to recognized patterns of glaucomatous nerve fibre loss should provide sensitive measures of abnormality.
Research opportunities in the Hospital Eye Service
Authors: Woodward E. G. 
Published: July 2002

SummaryAn analysis was undertaken of higher degrees by research awarded to optometrists based in the Hospital Eye Service since 1968. When these were considered in conjunction with current registration for higher degrees, it was possible to analyse research areas.The most popular topics were glaucoma, detection and measurement of progression (5); cornea (4); ocular biometry (3); infant vision and development (3); keratoconus (3); and contact lenses (3).In recent years, the scope of research has increased considerably and now embraces epidemiology, health economics and interdisciplinary decision making with other healthcare professionals.Successful completion rates for British College of Optometrist's Scholars for higher degrees for the hospital and university sectors were analysed. The total completion rate was 16/26 (65.4%), university based: 11/20 (55%), and hospital based: 6/6 (100%).
Differences in apparent contrast in yellow and white light
Authors: Rabin LTC Jeff , Wiley Roger 
Published: July 2002

SummaryThe purpose of this study was to investigate suprathreshold contrast perception in white and yellow light. The contrast of black‐on‐white letters was adjusted to match the perceived contrast of yellow‐on‐yellow letters presented simultaneously on a video display. At lower contrasts (7–15%), the apparent contrast of yellow letters was slightly enhanced compared to black‐on‐white letters (mean enhancement = 23%), but this effect diminished with increasing contrast. The slight enhancement in yellow light was independent of letter size, and could not be explained by luminance differences between yellow and white displays. This effect may relate to the subjective improvement often reported when wearing yellow (blue‐blocking) lenses.
Dyslexia: the link with visual deficits
Authors: Evans Bruce J. W. , Drasdo Neville , Richards Ian L. 
Published: July 2002

SummarySome research reports suggest that visual anomalies may have a causative role in dyslexia, and on this basis certain forms of therapy have been proposed. Recently, we have published the initial results of a matched group study which found dyslexia to be associated with binocular instability, reduced amplitude of accommodation, and reduced contrast sensitivity for both low spatial frequencies and uniform field flicker. The binocular instability was best identified by measuring the vergence amplitude: a modified Dunlop test failed to differentiate reliably between the two groups. Here, we report a significant correlation between flicker threshold and binocular instability, thus linking sensory and motor visual correlates of dyslexia. We also present further new analyses on the interaction between optometric variables and the psychometric measurement of coding skills. The results of these analyses disagree with a recent claim that binocular vision anomalies might cause poor performance at coding tasks. Our studies indicate that visual characteristics are not the major aetiological factors in specific reading difficulty.
Visual evoked potentials in children with developmental coordination disorder
Authors: Mon‐Williams M. A. , Mackie R. T. , McCulloch D. L. , Pascal E. 
Published: July 2002

SummaryChildren who demonstrate problems with skilled movement in the absence of physical handicap are formally designated as suffering from developmental coordination disorder (DCD). Diagnosis of DCD was confirmed by the ‘movement assessment battery for children’. Visually evoked potentials (VEPs) were recorded to evaluate the integrity of the visual pathway and to rule out the presence of any neurological lesions affecting visual input. Binocular, pattern onset VEPs were recorded in 14 children with DCD aged between five and seven years, and an age‐matched control group using pattern onset, high contrast, grating stimuli. Implicit times to the first and second peaks and troughs were measured, and results between the two groups were compared. Inattention and movement artefact meant that VEPs were more difficult to record within the DCD group, resulting in smaller amplitudes of the waveform, but no significant differences in the implicit times were observed between the DCD group and controls. Further research is required to determine the specific source of the neurological deficits in DCD but a problem with the integrity of the afferent visual pathway does not appear to be a causal factor.
The exact solution for the centre thickness of spectacle and contact lenses
Authors: De Faria e Sousa Sidney J. , Ventura Liliane 
Published: July 2002

SummaryThe available methods for the exact calculation of centre thickness presuppose that one knows simultaneously both surfaces of the lens and that the lens' power is determined afterwards. However, this approach is of secondary importance in practical situations. The issue in daily practice is the determination of the centre thickness of lenses that already have explicit vertex powers. In such cases one can set only one surface. The other has to be calculated following the prescription, the known surface and the optical effect of the centre thickness. Exact solution for this problem leads to four expressions, reflecting the number of ways one can treat it. Two of them are complete second‐order algebraic equations and the other two, complete third‐order algebraic equations. The practical value of the latter is limited by the fact that one cannot always obtain their three roots by pure algebraic procedures.
A new non‐contact corneal aesthesiometer (NCCA)
Authors: Murphy Paul J. , Patel Sudi , Marshall John 
Published: July 2002

SummaryA novel method for testing the corneal nerve function, through non‐invasive measurement of corneal sensitivity, is presented. The method of using a controlled pulse of air to stimulate the corneal surface is described. Technical information of the aesthesiometer's construction is given. Examples of the ability of the instrument to accurately locate the corneal sensitivity threshold using either a method of constant stimuli, or a method of limits, is described for 14 normal, non‐lens wearing eyes. Measurements are made in millibars of air pressure required. Mean normal values found were 0.342 ± 0.068 millibars. Discussion is made of the instrument's mode of action, its advantages over other invasive instruments, and potential clinical application.
A new computer assisted objective method for quantifying vascular changes of the bulbar conjunctivae
Authors: Owen Christopher G. , Fitzke Fred W. , Woodward E. Geoffrey 
Published: July 2002

SummaryA novel computer software method was used to quantify the conjunctival plexus on the scleral background for measurement of the vascular surface area from photographs. A previously described method was used (Palmer, J. R., Owen, C. G., Ford, A. M., Jacobson, R. E. and Woodward, E. G. (1996). Optimal photographic imaging of the bulbar conjunctival vasculature. Ophthal. Physiol. Opt.16, 144–149) to optimise photographic imaging of the bulbar conjunctival vasculature by increasing the information content in the image. Repeatability of this technique was evaluated. Twenty subjects (20 eyes) free from ophthalmological and systemic abnormality were examined on two separate occasions. The maximum 95% confidence limits for repeatability are +8.58/−3.95%. For 10 consecutive estimates of vascularity the maximum 95% confidence interval lie between ±6.54%. To evaluate the technique the lateral‐bulbar conjunctivaein 10 soft (SCL) and 10 rigid gas permeable contact lens (RGPCL) wearers during the first 10 months of contact lens wear, were assessed and compared with subjective grading of hyperaemia. The new method showed sufficient sensitivity in detecting increased hyperaemia in the RGPCL wearing group and demonstrated statistically significant change. Subjective graded assessment of vascularity (using established classifications) detected increased hyperaemia, however, this was not statistically significant. Conjunctival vasculature is a dynamic structure and a source of valuable quantitative information where the ocular environment is varied, or where the ocular surface is affected by disease. Hence it is worthy of further investigation. A simple inexpensive method of computer assisted determination of vascularity is described.
Intracellular chloride activity in corneal endothelial cells
Authors: Turner Helen C. , Wigham Chris G. , Hodson Stuart A. 
Published: July 2002

Purpose: Current models of hydration control by the corneal endothelium suggest that HCO−3 movement across the cell is driven by the energy contained in the re‐entry of NA+ into the cell down its electrochemical gradient. The nature of the coupling between HCO−3 and Na+ is not yet fully resolved. One suggestion is that the Na+/K+/2Cl− co‐transporter drives Cl− into the cell which then exits the same membrane via a HCO−3/Cl− exchanger. This would drive HCO−3 into the cell from where it could exit down its own electrochemical gradient into the aqueous. Such a system would also raise Cl− above its electrochemical equilibrium. The purpose of this study was to determine if Cl− is passively distributed across the plasma membrane or elevated above its electrochemical equilibrium.Method: To determine if this situation was present in rabbit corneal endothelial cells, we measured [Cl−]i directly using potential sensing and Cl− selective microelectrodes. To make the Cl− selective microelectrodes, filamented glass capillaries were silanized and back‐filled with Cl− ionophore (Corning or WPI) immediately before use. Electrode sensitivity was determined using the fixed interference method.Results: Endothelial membrane potential (PDm) in this series was similar to that in previous studies, 29 ± 0.9 mV (mean ± SEM, n = 22). Chloride potential (PDCl) was used to calculate [Cl−]i, which was 53 ± 2.0 mM (mean ± SEM, n = 22).Conclusions: The [Cl−]i measurement is significantly higher (P < 0.001) than that predicted from the measured PDm (39 ± 0.9 mM) and suggests that Cl− is not passively distributed in corneal endothelial cells.
Binocular summation in the peripheral visual field
Authors: Whitaker Angela , Pardhan Shahina 
Published: July 2002

Purpose: To investigate binocular summation for a light detection task in the central and peripheral retina along 4 meridians.Methods: 10 young subjects aged 22‐30 years (mean 26 years) with healthy eyes and normal visual fields participated in the study. A custom‐designed program on a Humphrey Visual Field Analyser measured thresholds at the fovea and at 5°, 10°, 15°, 25°, 40° and 55° along the horizontal meridian, and at 5°, 10°, 15°, 25°, 40° along the vertical, 45° oblique and 135° oblique meridians. Right and left monocular fields and binocular fields were measured on each subject using white spot stimuli (Goldmann sizes I and III). Binocular summation ratios were calculated for each eccentricity by dividing binocular sensitivity be the better monocular sensitivity.Results and conclusion: As expected, binocular and monocular sensitivities decreased with increasing eccentricity. The mean binocular summation ratio at the fovea was 1.38 for size I stimulus and 1.42 for size III. Binocular summation was demonstrated in the peripheral retina along all meridians and is of similar magnitude to foveal binocular summation. ANOVA showed that binocular summation was significantly higher in the vertical meridian than horizontal meridian for both size I and III stimuli. There was no significant variation in binocular summation ratios with eccentricity along any of the 4 meridians examined.
Analysis of refractive & visual development from an infant screening programme
Authors: Grounds Annette R. 
Published: July 2002

It has been shown by Aurell and Norrsell (1990), that infants who were 4.00D. hypermetropic or more in one meridian at six months showed a 50% tendency to go on to develop squints and/or amblyopia. The other 50% showed emmetropisation characteristic. Similar trends were found by Dobson and Sebris (1989).A prescribing criteria developed in this clinic for infants with higher refractive errors is presented and shows that the 50% trend towards squint and amblyopia can be dramatically reduced.Previous studies have shown that the most rapid decline in hypermetropia occurs between 6 months and 2 years in the normally developing infant eye and similar trends have been reported in infant monkey eyes, (Neuringer et al, 1984). Our results generally agree with this trend.Data will be presented showing the refractive changes of premature and term infants presented separately between 6 months of age and 3 years. Visual acuity and stereo‐acuity development will also be presented from the age of 6 months to 4 years. It is shown that VA development (with normal visual potential), falls in line with the level of prematurity, that is if 3 months early, then at 6 months of age VA level will be at the 3 months level. Visual acuity gradually improves to the expected level, and the time taken will depend on the amount of prematurity. Generally babies who are eight weeks or less premature catch up within their first year. While those greater than eight weeks but less than twelve weeks normalise by eighteen months to two years, with those greater than twelve weeks taking up to three years. This is in agreement with findings of general development delay changes, in prematurity.
A summary of recent developments in computer technology to aid the visually impaired in the workplace
Authors: Joseph Anna , Harper Robert 
Published: July 2002

In the UK, an estimated 75% of the visually disabled population of working age are unemployed. The EC is funding research into methods for assisting the visually impaired. One of the main areas of development involves the use of person computers (PCs).Enlarged characters on a VDU screen can be achieved either by using a large monitor, or by running a Screen Magnification System. Large monitors vary in size from 17″ to 28″; a 20″ screen will give roughly 1.5 times magnification. A screen magnification system is a software package which increases the size of the characters by between 1.2 and 12 times.A significant technological development is the amalgamation of CCTVs with PCs. Instead of displaying their information on an integral screen, new generation CCTVs can employ a VDU screen, magnifying by 2 to 60 times. A PC screen can be split between the computer display and input from an external CCTV camera. The proportion of the screen dedicated to the CCTV image can be varied, as can its position.In some situations, audible rather than visual information is preferable. Speech synthesizers enable the text from a PC display to be read to the user. A Stand Alone Optical Character Reader converts printed text into speech via an integral microprocessor and speech synthesizer.Despite the wide range of aids available, they are used by only a small proportion of employees with visual impairment. A responsibility of the Hospital Optometrist is clearly to promote awareness of the products available and to encourage liaison with Disability Employment Advisors. Full consideration of the individual's needs, together with an awareness of their entitlements through the Access to Work Scheme, will allow those with a visual disability to compete effectively in the workplace.
Training of patients with age‐related macular disease (AMD) using a scanner laser ophthalmoscope (SLO)
Authors: Culham L. E. , Fitzke F.W. , Marshall J. 
Published: July 2002

Purpose: AMD is the leading cause of blindness in developed countries. Rehabilitation is predominant in management since medical intervention is appropriate only in limited circumstances. Prescription of low vision devices is standard but additional low visual training using eccentric viewing techniques has been advocated. The SLO allows visualisation on a TV monitor of both the fundus image and presented visual stimuli and hence is ideally suited to undertake training. The aim was to test the concept that SLO training influenced patients' reading ability.Methods: Eleven patients were assessed by scotoma and acuity mapping, identification of the preferred retinal location (PRL) and evaluation of fixation stability and letter recognition. A novel SLO training programme totalling 6 hours over a period of 6 weeks emphasised optimal viewing strategies.Results: Of the ten patients who had a strong PRL an alternative retinal area that provided better performance could not be identified. With training, no significant change was observed in reading speed. However, improvements were recorded in visual acuity for distance (t = 2.765) and near (p < 0.0016), and in fixation stability (p > 0.0316) and letter recognition (p < 0.0009).Conclusions: SLO training improved patients' performance. This was not due to changing the retinal area used, but possibly was related to psychological benefits associated with training and the acquisition and perfection of new visual strategies.
Isolation of chromatic and achromatic mechanisms: A new approach
Authors: Sharanjeet‐Kaur  , Kulikowski J. J. , Carden D. 
Published: July 2002

SummaryThe purpose of this study was to optimise the testing paradigm for isolating the contributions of chromatic and achromatic mechanisms to the human spectral sensitivity function. Spectral sensitivity was determined for a test spot size of 1.2 deg presented with various spatial and temporal masks on a large, 10 deg background field of moderate intensity (1000 td) and colour temperature, CT = 2700 K. Sinusoidal temporal presentation (1 Hz) and a masking annulus of between 3 and 10 min of arc surrounding the test spot, was found to be most effective in separating chromatic from achromatic mechanisms. Square‐wave (1 Hz) temporal presentation combined with the annulus was slightly less selective. The presence of the annulus did not affect the shape of flicker detection at 25 Hz which is a measure of the luminosity (achromatic) spectral sensitivity function.
Control of the myopic shift in modified Badal optometer
Authors: Kȩdzia Bolesław , Twardowski Piotr 
Published: July 2002

SummaryRefractive error measurements made with the Badal optometer typically register more myopia than is actually present. In this paper we measured the influence of the image size on the end‐point of a Badal optometer's refractive error measurement. The optometer was modified with a camera's zoom lens in such a way that the retinal image size could be controlled. It was found that retinal image size is a major factor in controlling the subjective endpoint. When retinal image size is diminished rather than increased as the target approaches the subject, as is the case under normal circumstances, the perceived endpoint more closely agrees with the actual refractive error.