bluuebunny/crossref_metadata_2025 huggingface dataset:
On proximal effects in objective and subjective testing of dark accommodation
Authors: Jaschinski‐Kruza Wolfgang
Published: December 2007

This study investigated to what extent objective and subjective measurements of accommodation in darkness are affected by instrumentation or by flashed light stimuli that are arranged close to the subject's eye, and by the instructions given to the subjects. Subjects differed markedly in their susceptibility to these factors. Dark accommodation measured with an infra‐red autorefractometer tended to be more distant by 0.2 D on the average if the autorefractometer allowed a free view into a large, but dark, room compared with a closed apparatus. When subjects were instructed to look into far or near distances during objective measurements, mean dark accommodation was more distant by 0.15 D and closer by 1.4 D, respectively, relative to the condition of ‘relaxed eyes’. To find a simple screening test of dark accommodation, a ‘number test’ was investigated: subjects had to report which was the most sharply visible among a series of numbers that were simultaneously flashed at different optical distances in a Badal optometer. Objective measurements revealed that this test induced near shifts of 0.37 D on the average, relative to accommodation in a dark surround. Therefore, the results of the number test were only moderately correlated to objective measurements.
What radius does the conventional keratometer measure?
Authors: Bennett A. G. , Rabbetts R. B.
Published: December 2007

The reflected mire images used in conventional keratometry suffer from oblique astigmatism, resulting in separated sagittal and tangential image planes. Futher complications aries if the cornea is assumed to be aspherieal. To investigate the consequential effects on the readings–hitherto largely neglected ray tracing methods were applied lo two hypothetical models. One was representative of modern variable‐doubling constructions and the other of the Javal Schiötz design. Both are seen to require the tangential image plane to be focused. Given a spherical cornea, the measured tangential image height can be converted into an accurate radius reading by means of a linear calibration formula. In the Javal‐Schiötz design, a non‐linear correction is needed for this. Appropriately calibrated in these ways, each model is shown to give readings extremely close to the sagittal radius of curvature at the point of incidence when applied to corneae of conicoidal form. Extensive numerical results are tabulated and the detailed calculating schemes illustrated by worked examples.
Tolerance to spherical aberration induced by rigid contact lenses*
Authors: Collins M. J. , Brown B. , Atchison D. A. , Newman S. D.
Published: December 2007

We have investigated the effects of spherical aberration (SA) on visual performance by fitting subjects with rigid lenses of varying front surface asphericity. Three pairs of lenses were worn by each subject with front surface asphericities of Q = 0 (conventional spherical surface), Q =−0.26 (similar to the average corneal asphericity and Q =−0.51. The calculated average change in spherical aberration induced by each pair of contact lenses in photopic conditions was +0.02D (Q = 0), −0.49 D (Q =−0.26) and −0.94 D (Q =−0.51). In mesopic conditions these same lenses induced an average change in spherical aberration of +0.01 D (Q = 0), −1.18 D (Q =−0.26) and −2.16 D (Q =−0.51). In this double‐blind study, 12 adapted, low to moderate myopic rigid lens wearers wore each pair of lenses for one week and noted visual performance. With each pair of lenses we also measured the subject's visual acuity with high and low contrast logMAR charts. All measurements were conducted using the right eye at distance in photopic and mesopic conditions. When forced to select the lenses they would accept as compensation for participation in the study, most subjects (9 out of 12) chose the Q = 0 lenses, 3 subjects those the Q =−0.26 lenses and none of the subjects chose the Q =−0.51 lenses. Visual performance measures showed little difference between the Q = 0 and Q =−0.26 lenses. However, the Q =−0.51 lenses significantly reduced visual acuity in mesopic conditions with the low contrast acuity chart.
Retinal information capacity and the function of the pupil
Authors: Laughlin Simon B.
Published: December 2007

When the pupil is opened to increase sensitivity there is a loss of image sharpness due to aberrations. This trade‐off between sensitivity and sharpness is analysed theoretically by calculating the information capacity of the retinal image. The analysis uses optical measurements of image sharpness made al different pupil diameters. At each luminance there is a pupil diameter that maximizes information capacity. This optimum is close to the diameter adopted under normal viewing conditions, The optimum is broad, consequently the system tolerates inaccurate adjustment. The benefits of correctly adjusting the pupil are evaluated. At low light levels the advantage is 68%, at intermediate levels it falls to around 20% but under daylight conditions it increases to 52%, These advantages suggest that the primary function of the pupillary light reflex is to maximize acuity over a wide range of luminances.
Preliminary observations concerning treatment of visual discomfort and associated perceptual distortion
Authors: Wilkins Arnold , Milroy Robert , Nimmo‐Smith Ian , Wright Anne , Tyrrell Ruth , Holland Keith , Martin Judith , Bald John , Yale Sheila , Miles Tim , Noakes Tim
Published: December 2007

A system for therapeutic precision tinting is described. Some individuals who are subject to perceptual distortion of text no longer perceive the distortion when the text has a particular colour. A simple colorimeter enables an observer to illuminate text with light of a particular chromaticity. varying first CIE 1976 hue angle (huv). then saturation (suv), and then luminance, to obtain a setting that maximizes visual comfort and reduces any perceptual distortion. The colorimeter setting is then matched by a combination of tinted trial lenses. The combination uses only two dyes at a time from a selection of seven, unless a dark lens is required, when a third neutral (grey) dye is added. The subject observes both text and a normal scene when wearing tinted trial lenses. A variety of trial lenses are compared including those that match the colorimeter setting and others with similar hue angle. Spectacle lenses are then limed so as lo have a spectral transmission identical to that of the chosen combination of trial lenses. Certain patients with reading disorders, eye‐strain, headaches or photosensitivy epilepsy report benefit when wearing spectacles limed according to the above techniques. The physiological basis for the therapeutic effects is uncertain, but may involve a selective impairment of luminance or colour‐difference channels.
Effect of restriction of the binocular visual field on driving performance
Authors: Wood Joanne M. , Troutbeck Rod
Published: December 2007

The importance of the visual field on driving performance was investigated. This was undertaken by simulating binocular visual field defects for a group of young normal subjects and assessing the impact of these defects on performance on a driving course. Constriction of the binocular visual field to 40° or less, significantly increased time taken to complete the course, reduced the ability to detect and correctly identify road signs, avoid obstacles and lo manoeuvre through limited spaces. Accuracy of road positioning and reversing were also impaired. Constriction of the binocular visual field did not significantly affect speed estimation, stopping distance, or the time taken for the reversing and manoeuvring tasks. The monocular condition did not significantly affect performance for any of the driving tasks assessed.
Negative feedback control model of proximal convergence and accommodation
Authors: Schor Clifton M. , Alexander Jack , Cormack Lawrence , Stevenson Scott
Published: December 2007

A comprehensive model has been developed to illustrate the interactions between the observer and the surrounding environment in the control of oculomotor responses to distance or 3‐D space. Accommodation and vergence respond to both spatiotopic (body referenced) proximal percepts and retinotopic (eye referenced) physical stimuli of blur and disparity. Both spatiotopic and retinotopic stimuli are derived respectively from perceptual and physical correlates of negative feedback for eye position. The spatiotopic and retinotopic stimulus errors are combined in the feed forward path and drive a common occulomotor controller which has a phasic‐tonic organization. Spatiotopic and retinotopic stimuli are shown to be effective over complementary operating ranges. Perceptual spatiotopic errors of gaze provide optimal stimuli for near responses to large depth intervals whereas physical‐retinotopic cues of blur and disparity provide quantitative information about small binocular fixation errors. Small dynamic variations of target distance are sensed both spatiotopically and retinotopically. Coarse and fine spatiotopic errors of gaze are processed differently. Large spatiotopic errors are sampled intermittently al the beginning of the near response, whereas small retinotopic position errors and spatiotopic velocity errors are sampled continuously throughout the near response. Former reports of empirically observed higher velocity of vergence responses to very large depth intervals is explained in terms of stimulus sampling modes rather than in terms of separate oculomotor control mechanisms. The model demonstrates a complementary function of top‐down spatiotopic cues, which are used to initiate the near response, and bottom‐up retinotopic cues, which are used to refine and complete the near response. Cross‐couplings by vergence‐accommodation and accommodative‐vergence serve to coordinate the components of the near response when feedback from the sensed response of one motor system (i.e. vergence) is more accurate than that of the other motor system (i.e. accommodation). The model presented here is concerned primarily with the near response mediated by accommodation and disjunctive eye movements and not by the independent vergence mediated by non‐conjugate or yoked saccades of unequal amplitude.
Reliability of high‐ and low‐contrast letter charts
Authors: Reeves B. C. , Wood I. M. , Hill A. R.
Published: December 2007

The aim of this study was to measure the reliability, in test score units, of several clinical tests which use high‐ and low‐contrast letters, and to provide an estimate of what constitutes a significant change in performance over time. Patients with normal vision and with early or subtle eye disease were recruited so that the results would be representative of the population likely to present for primary vision screening. Patients were tested on the Bailey‐Lovie logMAR chart, the Regan low‐contrast letter charts and the Pelli Robson low‐contrast letter chart on two occasions: the two test sessions were separated by at least four weeks to give an estimate of reliability appropriate for the conditions under which the tests are likely to be used. A ‘significant change’, i.e. one which would be observed in only about 5% of patients with stable visual performance, was about ±2 ‘steps’ of the measurement scale, i.e. ±2 lines for the Bailey‐1.m it‐and Regan charts and ±2 letter groups for the Pelli‐Robson chart.
Initial control component in disparity vergence eye movements
Authors: Semmlow John L , Hung George K. , Horng Jia‐Long , Ciuffreda Kenneth
Published: December 2007

Recent experimental evidence indicates that a portion of the oculomotor response to disparity stimulation is functionally open‐loop; that is, the response occurs without the aid of visual feedback. To investigate the stimulus features that elicit or influence this dynamic movement, convergence responses to a step, a step followed by target disappearance, and a pulse followed by target disappearance were obtained from four subjects using infrared oculography. The target was a thin vertical line (0.25) either 2 or 10 in height. Stimuli having different amplitudes (1. 2, 4 and 8) and disappearance times (50. 100 and 200ms) were selected randomly along with occasional divergent stimuli to minimize prediction and voluntary vergence. Experiments showed that the dynamic characteristics of the initial portion of the response were essentially the same, even when the target disappeared before the movement took place. The magnitude of the initial response depended on the stimulus amplitude, but was not influenced by either stimulus duration or target height. For example, stimulus durations as short as 50 ms elicited responses similar to those caused by standard steps. The initial response was shown to be active over a well‐defined time period of about 200 ms. after which the response appears to be mediated by a visually‐guided control component. These results support the recently developed dual‐mode theory of vergence control in which an initial preprogrammed (open‐loop) control component is followed by a feedback (closed‐loop) controlled component which reduces any remaining disparity.
Simplified closed circuit television magnifier for the partially sighted
Authors: Fowler Colin
Published: December 2007

Although the use of closed circuit television (CCTV) magnifiers is now well established, the instruments tend to be bulky, complex and expensive. A magnifier is described which consists of a miniature TV camera used as a hand‐held scanner, which can be plugged into a wide variety of monitors and television sets.
Rigid lens fitting made easier using a modified keratometer
Authors: Lam Andrew K. C.
Published: December 2007

After simple modification, a keratometer can measure both the central and peripheral regions of the cornea. The apical radius and p‐value of the cornea can be determined with this information using a computer program. This computer program suggests lens parameters similar lo those chosen by conventional methods in rigid lens fitting. The computerized fitting method is also applicable to Chinese subjects.
Measurement of glare sensitivity in cataract patients using low‐contrast letter charts*
Authors: Regan D. , Giaschi D. E. , Fresco B. B.
Published: December 2007

The Committee on Ophthalmic Procedures Assessment of the American Academy of Ophthalmology suggested using low‐contrast visual acuity measured before and after adding a glare source as a test for assessing overall visual disability from immature cataracts. We have developed a test that follows the Committee's three principles of design, and we report that the effect of glare on visual acuity is considerably greater for recognizing low‐contrast letters than for recognizing high‐contrast letters. The effect of glare on visual acuity increases progressively as letter contrast is reduced in the stages 96%, 50%, 25%, 11% and 4%, The 25% chart (and possibly the 11% chart) gives the most suitable sensitivity for eyes with immature cataracts. Age‐related brunescence and aging itself do not necessarily produce high sensitivity to glare. Sensitivity to glare was markedly different in eyes with different kinds of cataract.
Decrease in stereoacuity in the seventh decade of life
Authors: Brown Brian , Yap Maurice K. H. , Fan Wallace C. S.
Published: December 2007

We measured stereoacuity in 41 subjects with normal Snellen acuity in each eye, and normal ocular health. Patients were measured in each of the age ranges 21–28, 41–49, 51–59 and 60–70 years. Stercoacuity was reduced from about 16 sec are for the three younger groups to about 27 sec arc for the older subjects. Since stereopsis has a cortical neural substrate, these data suggest that there may be cortical changes affecting the interaction of information from the two eyes with advancing age, but whether these changes result from loss of contrast sensitivity, instability of ocular alignment or binocular stress, all of which have been reported in elderly subjects, is not known.
Effect of induced fixation disparity by negative lenses on the visually evoked potential wave
Authors: Heravian‐Shandiz J. , Douthwaite W. A. , Jenkins T. C. A.
Published: December 2007

The effect of induced fixation disparity produced by negative lenses and base‐in prisms on the pattern visually evoked potential (VEP) was investigated. Monocular and binocular pattern reversal VEP were recorded through the negative lenses and base‐in prisms using a 9.5 min arc check size. The results suggest that the mean binocular amplitude was 27% larger than the mean monocular amplitude which indicates partial summation in the absence of negative lenses or base‐in prisms. A reduction of the binocular VHP amplitude appears to arise in the presence of fixation disparity induced by both the negative lenses and base‐in prisms. Both the prisms and the negative lenses had no appreciable effect on the monocular VEP amplitude.
Investigation of parameters influencing intraocular pressure increases during sleep
Authors: Wildsoet Christine , Eyeson‐Annan Margo , Brown Brian , Swann Peter G. , Fletcher Terry
Published: December 2007

In previous studies, we have observed that young normal subjects show an increase in intraocular pressure (IOP) after sleep. Here we describe three experiments which investigated: (i) the effects of sleep in five groups of subjects: glaucoma, suspect glaucoma, young high‐normal IOP, old high‐normal IOP groups and an elderly control group, (ii) the effect of exposure to bright light (2500 lux) during sleep on associated IOP changes, and (iii) the relationship between changes in IOP and plasma melatonin during sleep, For all experiments IOP was measured before and after sleep. We found that IOP increased significantly after sleep. There was also a significant difference between the five groups with the old high‐normal group showing the greatest increase, and the young high‐normal group showing the lowest increase in IOP. The increase in IOP after sleep was reduced when the same subjects slept in bright light compared to that recorded when subjects slept in the dark. Plasma melatonin levels, as well as IOP, increased after sleep in the dark although there was no correlation between these changes for individual subjects.
Measurement of corneal topography in keratoconus
Authors: de Cunha D. A. , Woodward E. G.
Published: December 2007

A new method is described for calculating the topography and curvature of an irregularly shaped cornea, Vertical planes of light are projected onto the cornea and points in x, y, z space are calculated from the light images on the corneal surface. A matrix of points is produced on the cornea and a mathematical surface is filled to them. Using differential geometry theory, curvature values are calculated to find the corneal apex position, apex curvature and curvature change away from the apex. Typical results, in the form of a contour map, are shown for normal corneas and corneas with mild to severe keratoconus. The method gives an accurate quantitative measurement of keratoconuc and other irregular corneas.
Prescribing for presbyopes who use VDUs
Authors: Burns David , Obstfeld Henri , Saunders John
Published: December 2007

It has been widely assumed that VDU users position their paperwork closer than the screen to their eyes by an amount which may exceed their depth of field. The design and prescription of spectacles for the presbyopic VDU user must take these working distances into account. From theoretical considerations, the focal characteristics of occupational spectacles are matched to combinations of working distances. Measurement of these distances was carried out on a sample of 243 VDU users, 101 of whom were presbyopic and 53 nearing presbyopia. The results were analysed in terms of type of work and accommodative reserve, and compared with previous studies. Contrary to the views of several previous workers, it was found that paperwork did not tend to be positioned closer than the screen to the eyes. This finding was little affected by the type of VDU use or the accommodative reserve of the subject. Special occupational spectacle lens forms are thus not generally indicated for presbyopes at the VDU workstation.
Use of visual field tests in glaucoma detection by optometrists in England and Wales
Authors: Tuck Maurice W. , Crick Ronald P.
Published: December 2007

This paper is based on a survey of 241 optometrists (5% of the national total) in England and Wales, which covered many aspects of glaucoma detection. There were 45 optometrists (19%) who did not use a field screener. Of the 196 who did. 173 reported their criteria for deciding which patients to test: 17 (estimated at 8% of the original sample) used a field screener routinely in patients over age 40 years; 40 (19%) selectively tested all patients with intraocular pressure >20 mmHg, together with most others in whom any glaucoma risk factor was present, (this required a visual field test in only one in rive patients aged over 40 years and may he relatively cost‐effective); the remaining 116 (55%) on average tested less than one in ten of their patients with a field screener. practice which is shown to contribute little to the number of glaucomas detected. Routine field testers had the highest glaucoma detection rates, and those of the selective testers were not significantly lower.
Reliability of the Cambridge Low Contrast Gratings
Authors: Jones Helen S. , Moseley Merrick J. , Thompson John R.
Published: December 2007

We examined the reliability of the Cambridge Low Contrast Gratings over four sessions at intervals of 1 hour, 1 day and 1 week. The 95% ranges of difference scores were found to be ± 10.3 and ± 10.5 test units, for left and right eyes respectively. These reliability estimates span almost one‐quarter of the test's dynamic range and one‐third of the subjects' performance range. Practice effects were not found to be significant. Though previous reports have emphasized the usefulness, of the Cambridge Gratings in screening for eye disease, caution is advised when interpreting changes that occur over time.
Variation of the visual acuity‐luminance function with background colour
Authors: Domenech B. , Segui M. M. , Capilla P. , Illueca C.
Published: December 2007

The relationship between visual acuity (VA) and background colour is a question that still creates a certain amount of confusion even today, although most authors agree that colour background does not basically affect VA, or at best, values that are only slightly better are obtained with monochromatic yellow light. The object (if this paper is to try to clarify if, when the axial chromatic aberration (ACA) has been compensated for, certain differences due exclusively to colour persist or not. In order for this, the VA‐luminance functions with red, green, blue and white backgrounds have been measured for two emmetropic observers, before and after compensating for the ACA. The results show that after the compensation, the curve corresponding to red is above the one corresponding 10 blue, with the one corresponding to green in between. The achromatic function (white background) practically overlaps with the green one. This behaviour is consistent with that shown recently for contrast sensitivity functions (CSFs). However, the asymptotic values are identical for the three colours, and so, it is understandable that no significant differences are normally found when only u standard measurement of VA is taken using the typical illumination from an optotype projector.
Precise placement of nonius lines on a personal computer screen for measuring fixation disparity
Authors: Bonacker Matthias , Schubert‐Alshuth Ewald , Jaschinski Wolfgang
Published: December 2007

A method is described for measuring fixation disparity psychophysically using the conventional monitor of a personal computer. Both the nonius test stimuli and the fusion stimulus were presented on the same screen. To be able to adjust the offset of the nonius lines in very small steps, special electronic circuitry was developed that allows up to 16 steps within the pixel separation of the monitor. The method is flexible in that various geometrical dimensions of the visual stimuli and different psychometric procedures can be used.
Effect of fixation disparity on distance binocular visual acuity
Authors: Jenkins T. C. A. , Abd‐Manan F. , Pardhan S. , Murgatroyd R. N.
Published: December 2007

Subjects with appreciable values (2 Δ and greater) of associated' phoria, as measured by a Mallett unit, had their distance monocular and binocular visual acuities measured. In the latter case measurements were taken both with the associated' phoria corrected by prisms and without such a correction. The improvement in binocular acuity compared to monocular acuity was less than would occur in normal subjects with minimal associated' phorias although the improvement differed accordingly as to whether the readings were eso‐ or exo‐in nature. When the associated' phorias were corrected with prisms the improvement in binocular over monocular visual acuity was similar to that found in normal subjects.
Pupillary function in human amblyopia
Authors: Barbur John L. , Hess Robert F. , Pinney Huw D.
Published: December 2007

Quantitative measurements of pupillary function (response amplitude and latency) were made for normal eyes and For normal and fellow amblyopic eyes of groups of strabismic and anisometropic amblyopes. Stimuli consisted of luminance modulation of a large, evenly lit area (pupil light reflex) as well as contrast modulation of sinusoidal gratings (pupil grating response) of fixed, space‐averaged luminance. Measurements were made of the direct and the consensual reflex under monocular stimulation. A comparison of the amplitude of the pupil light reflex as a function of luminance modulation showed no significant differences between normal and fellow amblyopic eyes for both the strabismic and anisometropic groups of amblyopes studied. A similar comparison of the associated response latencies showed significant difference between normal and fellow amblyopic eyes for both groups. In general, reductions in response amplitude and latency of (he pupil grating response were found in individuals from each group when comparing the good and the affected eyes, although the observed group differences were only significant in the strabismic group. Interestingly, statistically significant reductions in both amplitude and latency for both the pupil light reflex and the pupil grating response were found between the eyes of normal observers and the so‐called normal eyes of amblyopes in both groups studied. These results suggest that the type of pupillary deficit in amblyopia is a complicated one, depending not only on the type of amblyopia (strabismic or anisometropic) and the type of stimulus employed (light or pattern), but also on the parameter assessed (amplitude or latency) and whether the amblyopic result is referenced to its fellow normal eye or to the normal eye of a non‐amblyopic observer‐ Since the pupil response to light flux changes is not mediated exclusively via the retinal projection to the midbrain and may also involve the activity of central visual pathways, the results obtained in this study cannot be used to provide definitive evidence for the site of abnormality in amblyopia.
Resolving power of the human visual system to monochromatic stimuli
Authors: Koczorowski Pawel , Kędzia Bolesław , Niworowski Marek , Kucharski Sławomir
Published: December 2007

The resolving power in monocular, foveal vision was found to depend on the size of a white light source made of two white rectangles separated by vertical black bar. The question arises whether the wavelength of light influences this dependence. An experiment was done on three subjects using six monochromatic lights the range 450–625 nm. and while light for control measurements. The diagram of the dependence of the minimal angle of resolution on the source size takes the shape of a biphasic curve, i.e. decreasing and constant function. The wavelength was found to have no impact on the curve shape or values. The data points obtained for white light coincide with those for monochromatic lights. The results confirm a thesis that all three colour mechanisms in the human visual system are stimulated and are active in spatial summation processes, but to a degree conditioned by a spectral sensitivity of the particular colour apparatus. It was confirmed that all colour mechanisms have potentially the same acuity but the axial chromatic aberration causes observed reduction of acuity.
Effectiveness of unsupervised oculokinetic perimetry for detecting glaucomatous visual field defects
Authors: Harper Robert A. , Hill Adrian R. , Reeves Barnaby C.
Published: December 2007

Oculokinetic perimetry (OKP) is a simple, inexpensive technique which was introduced primarily to promote more widespread use of visual field screening for glaucoma. The effectiveness of unsupervised OKP screening was evaluated using 145 non‐glaucomatous patients and 64 patients with previously undiagnosed primary open angle glaucoma. Glaucoma cases were validated by the extended l32 point program on the Henson CFS2000 instrument. Both sample populations were representative of patients presenting for primary vision care. The effectiveness of the 26 point OKP test was compared with the 26 point Henson screening program. The results suggest that, in contrast to the Henson screening test (sensitivity = 85.1 %. specificity = 93.8%). unsupervised OKP screening (sensitivity = 25.0%, specificity = 93.6%) has limited effectiveness for detecting glaucomatous visual field defects.
Changes in refractive trends and optical components of Hong Kong Chinese aged 19–39 years
Authors: Goh Winnie S. H. , Lam Carly S. Y.
Published: December 2007

The distribution of refractive errors and its relationship to the optical components in 105 Hong Kong Chinese aged 19–39 years was studied. Myopia was most frequent (71%) in this population. The mean spherical equivalent was ‐3.00 DS. The trend of changes of the direction of refractive and corneal astigmatism from with‐the‐rule to against‐the‐rule with increasing age was shown. Significant correlations were found between age and anterior segment distance. Ultrasound examination showed that an increasing axial length was associated with higher myopia. Men had flatter corneal radii, but longer axial length. The prevalence of myopia in the Chinese population seems to be a new trend for the younger Hong Kong Chinese when compared with adults aged over 40 years. Thus the importance of genetics in determination of myopia is called into question by these findings.
Unilateral ocular vascular stress in man and retinal responsivity in the contralateral eye
Authors: Kergoat Hélène , Lovastk John V.
Published: December 2007

Autoregulation (AR), the capacity of retinal vessels to maintain a constant flow of blood during alterations in vascular perfusion pressure, has been studied by a variety of techniques. Psychophysical and electro‐physiological procedures have been used as indirect measurements of the effectiveness of AR for maintaining normal visual function during altered ocular perfusion pressure (OPP) in a single eye. However, there have been no studies in normal subjects which have investigated the responsivity of the contralateral eye while the fellow eye undergoes transient vascular stress. In the present study, the components of the bilaterally recorded scotopic flash electroretinogram (ERG) were used as objective indices of visual neural function during transiently altered OPP. The principal finding was that a decrease in the OPP for the test eye was associated with a reversible attenuation of the retinal responsivity in that eye, and a supranormal oscillatory' potential index in the contralateral eye. The existence of a central control mechanism, triggered at the eye level, may be responsible for this contralateral neural phenomenon.
Effects of colour adaptation and stimulus size on the detection of chromatic deviations from achromatic as a function of eccentricity in man
Authors: Iivanainen Antti , Rovamo Jyrki
Published: December 2007

By using constant size and M‐scaled stimuli (the stimulus size was magnified towards the visual field periphery in inverse proportion to the lowest local sampling density of the human retina) we measured the thresholds for perceiving the complementary colours of blue, green and red (i.e. yellow, purple or blue‐green) under chromatic adaptation at the eccentricities of 0–15° in the nasal visual field. The CIE 1931 (x, y) chromaticity coordinates corresponding to complementary hue perception were subtracted from the chromaticity coordinates of achromatic threshold. The difference was found to be constant irrespective of stimulus size and eccentricity. This means that the perception (if chromatic deviation from achromatic under chromatic adaptation is independent of stimulus size and eccentricity.
Reinvention of visual fatigue: accumulation of scientific knowledge or neglect of scientific history?
Authors: Watten Reidulf G.
Published: December 2007

The development of science is believed lo be a continuous accumulation of knowledge, giving rise to the somewhat false idea that the most recent knowledge is the most valid and most appropriate. Neglect of the history of a scientific discipline might therefore lead to reinvention of theories that have already been proposed and experimentally investigated. In the case of visual fatigue the pioneering works of Lucien Howe. Walter Lancaster and others at the beginning of this century are very similar to contemporary work in terms of conceptual definitions, methodological approach, assessment and results. The temporal and dynamic aspects of accommodation and vergence considered important today were intensely studied and discussed by Howe and others.
Comparison of the techniques of videorefraction and static retinoscopy in the measurement of refractive error in infants
Authors: Hodi Samara , Wood Ivan C. J.
Published: December 2007

Photorefraction has been suggested as a suitable tnethod of screening for refractive error in infants. The relative performance of cycloplegic and non‐cycloplegic videorefraction and cycloplegic retinoscopy was investigated on 150 Infants. Under cycioplegic conditions the correlation between findings for spherical error (R, = 0,70) was compatible with a previous study. However, where cycloplegia was not used for videorefraction. there was poor agreement between the two techniques in the case of astigmatic error, and all types of ametropia. Interobserver repeatability was very high both for cycloplegic retinoscopy Rxy ‐ 0,96 spherical error, and Rxy= 0.75 astigmatic error) and for videorefraction measurements (Rxy= 0.95 horizontal meridian of photograph and Rxy= 0.85 vertical meridian), Intraobserver repeatability was also good, both for cycloplegic retinoscopy (Rxy= 0.91 spherical error and 0.82 astigmatic error) and for videorefraction with regard to spherical errors (Rxy= 0.84), Throughout the experiments videorefraction measurements of astigmatic errors proved less consistent when compared with cycioplegic retinoscopy, and to its internal reliability.
Changes in ocular and visual variables during the menstrual cycle
Authors: Guttridge Nancy M.
Published: December 2007

For most women the menstrual cycle is an integral part of a major portion of their lives. There is widespread agreement about the hormonal changes that occur during the menstrual cycle, but studies of physical and psychological changes have been more controversial. The influence of the menstrual cycle on various ocular and visual variables has been investigated. These include the potential protective role of female sex hormones in some ocular conditions, reports of reduced tolerance to contact lens wear, and changes in visual performance during the cycle. This paper critically reviews the literature on visual and ocular changes across the normal human menstrual cycle. Stereotypical views of an impairment of performance premenstrually and during menstruation are challenged. The shortcomings of, and difficulties associated with, much of the research on this topic are highlighted.
Review of past and present techniques of measuring corneal topography
Authors: Fowler C. W. , Dave T. N.
Published: December 2007

Various methods of measuring corneal topography are described. The advantages and disadvantages of the principles used in the measurement of corneal shape by the various techniques are discussed. The corneal surface may be described in a number of ways; some researchers have used conic sections while others have used more complex polynomial expressions. Computer algorithms have also been developed to calculate quantitative measures of corneal topography to augment the information obtained from topographical maps. These descriptors are discussed in this article.
Overlays for classroom and optometric use
Authors: Wilkins Arnold
Published: December 2007

Perceptual distortion of printed text can sometimes be reduced by placing upon the page a sheet of coloured plastic (overlay). The colour that best reduces the distortion differs from one individual to another and may need to be selected with precision. A set of overlays has been developed that samples the CIE UCS diagram systematically. The overlays are robust and have a matt finish. They can he combined in an intuitive way to provide a wide range of chromaticities.
Pathway of the primary afferent nerve fibres serving proprioception in monkey extraocular muscles
Authors: Gentle Alex , Ruskell Gordon
Published: December 2007

Following intracranial section of either the oculomotor or ophthalmic nerve, Wallerian degeneration studies revealed 1.38–3.7% of nerve fibres in the nerves to the inferior and superior rectus muscles were of ophthalmic nerve origin; more than half of them were unmyelinated. The results of the two experiments were complementary. The proportion of fibres identified as sensory is substantially smaller than the 10%, estimated in other studies, required to serve muscle receptors. These results indicate, contrary to some reports, that a substantial majority of proprioceptive fibres are conducted from extraocular muscles to the brainstem in the motor nerves and that their somata are not housed in the trigeminal ganglion.
Identifying Which Treated Hypertensive Patients Without Known Coronary Artery Disease Should Be Tested for the Presence of Myocardial Ischemia by Perfusion Imaging
Authors: Lacourcière Yves , Côté Christian , Lefebvre Jean , Poirier Luc , Dumont Marcel
Published: December 2007

Stress dipyridamole technetium‐99m sestamibi single photon emission computed tomographic imaging was used to study myocardial perfusion in 1116 hypertensive patients without known coronary artery disease (CAD). The test confirmed the presence of CAD in 28.9% of patients. As expected, patients with diabetes mellitus (DM) had a significantly higher prevalence of myocardial perfusion abnormalities (35.9% vs 23.9%; odds ratio, 1.79; 95% confidence interval [CI], 1.38–2.33; P<.0001) and high‐risk myocardial imaging (16.4% vs 10.6%; odds ratio, 1.67; 95% CI, 1.18–2.37; P=.004) than those without DM. Odd ratios further increased, again as expected, with dyslipidemia (2.19; 95% CI, 1.54–3.12; P<.0001), peripheral arterial disease (2.61; 95% CI, 1.77–3.85; P<.0001), microalbuminuria (3.03; 95% CI, 1.91–4.82; P<.0001), and abnormal electrocardiographic findings (3.06; 1.68; 95% CI, 2.08–4.48; P<.0001). This large cohort study showed that more than 1 of 4 treated hypertensive patients have subclinical CAD. These study data should be clinically helpful in selecting hypertensive patients who are the most suitable candidates to screen for the presence of CAD.
Understanding Uncontrolled Hypertension: Is It the Patient or the Provider?
Authors: Rose Adam J. , Berlowitz Dan R. , Orner Michelle B. , Kressin Nancy R.
Published: December 2007

The relative contributions of adherence and treatment intensity to blood pressure (BP) control are not well understood. The authors studied patients with uncontrolled hypertension (N=410) from 3 primary care clinics in the Veterans Affairs (VA) medical system. A questionnaire was used to assess patient adherence to therapy, and VA system pharmacy fills were used to assess the intensity of the antihypertensive regimen. At baseline, an inadequate antihypertensive regimen was implicated as the most probable reason for uncontrolled BP in a majority of patients (72%), while nonadherence could only be implicated in 13%. In multivariate longitudinal analyses, patients who had an increase in their medical treatment during the study had lower final diastolic BP levels compared with the patients who did not (−3.70 mm Hg; P<.05). While patient adherence to therapy plays a role, vigorous clinical management by the clinician is a more important contributor to BP control.
Fish Oil Supplementation Improves Left Ventricular Function in Children With Idiopathic Dilated Cardiomyopathy
Authors: Olgar Seref , Ertugrul Turkan , Nisli Kemal , Omeroglu Rukiye Eker , Dindar Aygun , Aydogan Umrah
Published: December 2007

Fish oil has a cardioprotective effect in adults with ischemic heart disease. The authors examined the effects of fish oil in children with idiopathic dilated cardiomyopathy (DCM). Eighteen DCM patients (group I) and 12 healthy children (group III) were given fish oil (10 mL/d). Their cardiac findings were compared with those of 11 patients with DCM who did not receive fish oil (group II). After 6.62±1.70 months, left ventricular ejection fraction had increased by 8.44%±3.80% (P<.05), in group I; 2.48%±3.85% (not statistically significant) in group II; and 0.84%±2.34% (not statistically significant) in group III. Left ventricular internal diastolic diameter (mm) was reduced by 4.36±4.86 (P=.001) in group I and 1.92±5.37 (P=.263) in group II, but increased by 0.22±2.54 (not statistically significant) in group III. The results suggest that fish oil leads to accelerated improvement of left ventricular function. The authors believe that if these results are confirmed in larger studies, fish oil should be added to the standard anticongestive therapy of children with DCM.
Dynamic Analysis of Exercise Oxygen Consumption Predicts Outcomes in Advanced Heart Failure
Authors: MacGowan Guy A. , Pohwani Amar , Murali Srinivas
Published: December 2007

It is unclear whether cardiopulmonary stress testing provides prognostic information in patients with very advanced heart failure receiving contemporary medical therapy. Analysis of cardiopulmonary treadmill stress data in a group of patients with advanced heart failure and severe functional impairment was performed (N=102, peak exercise oxygen consumption [VO2] ≤14 mL/kg/min, 47% receiving β‐blockers). Dynamic variables (peak ‐ baseline values) better predicted outcomes than did single value peak measurements, especially ΔVO2. Multivariate analysis showed that usage of β‐blockers and ΔVO2 (both P<.05) independently and significantly predicted outcomes. Subgroup analysis showed that ΔVO2 was particularly useful in predicting outcomes in patients with ischemic cardiomyopathy or who were not receiving β‐blockers. Thus, in patients with very advanced heart failure, cardiopulmonary stress testing‐derived ΔVO2 provides important prognostic information useful to help predict clinical deterioration or death, particularly for patients with ischemic cardiomyopathy or who are not receiving β‐blockers.
The Frequency of Angiotensin‐Converting Enzyme Genotype and Left Ventricular Functions in the Obese Population
Authors: Bitigen Atila , Cevik Cihan , Demir Durmus , Tanalp Ali Cevat , Dundar Cihan , Tigen Kursat , Mutlu Bulent , Basaran Yelda
Published: December 2007

The authors investigated the relationship between angiotensin‐converting enzyme (ACE) genotype and left ventricular functions in an obese population and compared their findings with controls. Ninety‐six obese patients and 50 controls were enrolled. Obesity was subgrouped into mild (body mass index [BMI] 25–29.9 kg/m2), moderate (BMI 30–34.9 kg/m2), and significant (BMI ≥35 kg/m2). Body fat distribution was categorized according to waist‐to‐hip ratio and waist circumference. Left ventricular systolic and diastolic functions were evaluated by echocardiography. ACE gene polymorphism was investigated by standard polymerase chain reaction, and frequency distributions were calculated for the subgroups. Systolic functional indices were found to be increased in mild and moderate obesity subgroups. The obese population had increased left ventricular diameters. None of the patients had systolic dysfunction, while diastolic dysfunction was significantly more common in the obese group; the frequency of diastolic dysfunction was proportionally increased with body mass index. Diastolic dysfunction was more common in persons with abdominal obesity. ACE DD genotype frequency was increased in moderately and significantly obese subgroups and also in all obese patients with diastolic dysfunction.
PERMIAN AND TRIASSIC STRATIGRAPHY, ZAGROS BASIN, SOUTH‐WEST IRAN
Authors: Szabo Frank , Kheradpir Ahmad
Published: December 2007

The Permian and Triassic beds deposited in the Zagros Basin form a massive carbonate and evaporite sequence in excess of 2000m. These strata were divided into clearly recognizable and mappable lithostratigraphic units and major lithofacies types using surface exposures, subsurface log information and sample cuttings.

Formation and member designations are given to distinct and widespread lithostratigraphic units and where possible, the boundaries of these units are selected to coincide with sedimentary gaps or boundaries of sedimentary cycles.

A well type‐section and a surface reference section are established to illustrate the distribution of these units both vertically and horizontally.

Major unconformities were observed and documented at the base of the Permian and at the top of the Triassic, a smaller break was noted between the Triassic and Permian sediments.

Revision of the Jurassic‐Triassic boundary is made, based on this new stratigraphic evidence.
FUTURE HYDROCARBON EXPLORATION ON CONTINENTAL MARGINS AND PLATE TECTONICS
Authors: Pratsch Johann‐Christian
Published: December 2007

Continental margins, the border zones between continents and oceans, are preferred sites for hydrocarbon accumulations throughout geologic history. Passive Atlantic‐type margins are found worldwide. Active Pacific‐type margins exist together with passive margins where endogenous vertical crustal mobility took place. Vertical mobility is preferred over lateral mobility. Plate‐tectonic hypotheses are doubted. Exploration for gas and oil must be based on sound data.

Kontinentalränder, die Grenzen zwischen Kontinenten und Ozeanen, sind durch die geologische Geschichte hindurch bevorzugte Räume für Ansammlungen von Gas und Öl. Passive atlantische Kontinentalränder sind weltweit verbreitet. Aktive pazifische Kontinentalränder erscheinen zusammen mit passiven Kontinentalrändern, wo endogene vertikale Krustenmobilität auftritt. Vertikalmobilität wird einer Lateralmobilität vorgezogen Plattentektonische Hypothesen werden in Zweifel gestellt, sie werden ohnehin zunehmend abgeändert. Exploration auf Gas und Öl muss auf einer gesunden Datenbasis beruhen, nicht auf wissenschaftlicher Spekulation.