bluuebunny/crossref_metadata_2025_split huggingface dataset:
Use of visual evoked potentials (VEPs) to investigate mechanisms involved in the reading process
Authors: Greatrex J. C. , Drasdo N. 
Published: July 2002

Aim: In this study we have attempted to use VEPs directly to investigate visual mechanisms in the initial stages of the reading process.Method: The pattern onset mode of stimulation (using a 330 ms presentation time) approximately stimulates the intake of information during reading and accordingly we have adopted this technique to investigate possible responses at several cortical loci which are known to be involved in the reading process. To obtain the best results from localized areas of the cortex, a technique using a 3 cm radius triangular Laplacian derivation was adapted. Right and left hemifoveal responses were recorded with a Medelec Sapphire system, using pattern and letter stimuli. Signals arising from two putative generators, one in the striate cortex (5% up from inion, on the midline) and another possibly from the human homologue of primate area V4 (12.5% up from inion, 17% right), were studied using the 1–3° stimuli to determine contrast responses and spatial selectivity. Four averaged responses from 32 sweeps, filtered (1‐50 Hz), were recorded for contrasts of 80% and 20% and spatial frequencies between 1–22.32 cpd.Results: The tuning function for checkerboard patterns at 80% contrast for the lateral generator peaked at 2.75 cpd and showed a rapid fall off. The midline response at 80% contrast peaked at 5 cpd and showed a much slower fall off. Responses to letter stimuli were attenuated to approximately 1 μV over V4 and 300 nanovolts from the angular/supramarginal gyri. No significant result was obtained from Wernicke's and Broca's areas.Conclusions: VEPs may be used to directly investigate the reading process. Further refinement of techniques is necessary to record responses from more specialized areas such as Wernicke's and Broca's areas.
Dual mechanisms of curvature detection
Authors: Davies J. A. , McGraw P. V. , Whitaker D. 
Published: July 2002

Purpose: The detection of object curvature is an essential feature of human spatial vision. We investigate the combined effects of contrast and blur on thresholds for curvature detection.Methods: Horizontally‐oriented line stimuli were displayed on a Macintosh monitor. The lines were windowed in both x‐ and y‐dimensions with a Gaussian profile. We examined a range of x‐ and y‐blur levels by varying the space constant of the relevant Gaussian window, such that stimuli varied in appearance from long, thin lines, to short fat ones. The maximum contrast of the lines varied between 12.5–100%. Subjects were required to indicate whether the line (presented for a duration of 250 msec) was curved upwards or downwards. A method of constant stimuli was used to determine curvature thresholds.Results: At each level of blur (y‐space constant), threshold remained constant up to a certain line length (x‐space constant) after which they increased. Thresholds also increased with increasing levels of blur. However, performance in all conditions became identical once thresholds were expressed in Weber terms (as a multiple of line length) and stimulus size was specified using a scale‐invariant metric (ratio of line length to blur). When line length is small relative to blur (short, fat lines), thresholds are proportional to blur and are contrast dependent. When line length is large relative to blur (long, thin lines), thresholds become proportional to line length and demonstrate reduced contrast‐dependence.Conclusion: Combined manipulation of blur and contrast reveals two distinct processes involved in curvature in human vision.Acknowledgements: Supported by the Visual Research Trust and a Wellcome Trust Vacation Scholarship to JAD.
Age‐related changes in central and peripheral contrast sensitivity
Authors: Latham Keziah , Ferguson Ian , Pacey Ian 
Published: July 2002

Purpose: Loss of foveal contrast sensitivity at mid‐high spatial frequencies with increasing age is well documented. The effects of increasing age on peripheral vision are less clear. This study examines the relative effects of age on contrast sensitivity at the fovea and in the periphery, using scaled 2D Gabor patches.Methods: Five young (age 23.4 ± 2.4 yrs) and five elderly (age 71.9 ± 3.4 yrs) visually normal subjects participated. Stimuli were a series of size‐scaled Gabor patches, each consisting of a constant 0.8 grating cycles per envelope standard deviation. To achieve this, Gaussian envelope size varied inversely with the spatial frequency of the carrier grating. Stimuli were presented at 0° and 10° eccentricity in nasal visual field. Contrast sensitivity was measured using a staircase procedure which converged to a performance level of 79% correct. The subject's task was to correctly identify grating orientation as vertical or horizontal.Results: For both the young and elderly subjects, contrast sensitivity functions at the two eccentricities are displaced from one another simply by a change in size scale. E2 values, describing the rate of scale change with eccentricity, are 5.8° for young and 8.1° for elderly observers. At the fovea, the elderly show a 0.29 log unit sensitivity loss relative to the young, independent of spatial frequency. At 10° eccentricity, the age‐related loss is 0.19 log units. Inclusion of a 0.5 log unit neutral density filter reduces the sensitivity of young observers by 0.09 log units at the fovea and 0.07 log units at 10°.Conclusion: Age‐related contrast sensitivity loss occurs predominantly at the fovea. Only part of the loss observed can be attributed to optical factors. Contrast sensitivity is qualitatively the same in the fovea and periphery of young and elderly observers. The only variables affecting the quantitative variations are a scale change dependent on both eccentricity and age, and an age‐related sensitivity loss.
Low vision: a regional evaluation of service provision
Authors: Jackson A. J. 
Published: July 2002

As we move rapidly towards the 21st century epidemiologists predict that within the western world, the number of individuals living into their 7th, 8th, and 9th decades will increase dramatically. The implications for those responsible for the provision of ophthalmic care will be a colossal increase in the incidents of age related degenerative pathology. Those specialising in low vision care will find that as the pool of persons requiring services expands, the financial resources available to provide materials will diminish. Targeting those most likely to benefit from low vision services can only be done when the population profile is fully understood and factors affecting success and failure are evaluated.In this study records for three groups of 50 new low vision patients referred to a regional low vision clinic over a ten year period are evaluated (1 year, 5 years, 10 years). A total of 50 of those supplied with low vision aids were contacted by telephone and a questionnaire was used to determine whether low vision aids had been useful. Information was also gathered on patients' attitudes to the services provided at the clinic and the manor in which they were provided. A total of 52% of patients assessed were female (female 79/male 71). The average age of the population was 65 +/−22 (SD) years (range 15–98).Thirty three percent of patients were registered as blind or partially sighted (blind 21%, partially sighted 11%). The proportion of clinic attendees who were registered increased by almost 12% over the ten year period. Of those attending, 48% had age related macular degeneration, 7% had diabetic retinopathy, 6% had myopic degeneration, 5% had glaucoma and 5% cataracts. A total of 39% of patients attending the clinic were seen within two years of having become visually impaired. The majority of these patients had been on a waiting list for between 4 and 9 months before having attended for a low vision assessment. This figure reflects the demands placed on an under funded regional service.The most popular low vision aids supplied were stand magnifiers (52%) and (of which 77% were internally illuminated), 22% hand magnifiers, 12% were spectacle magnifiers and 4% were spectacle mounted telescopic devices. Only 6% of low vision aids were supplied for distant visual tasks. The majority of those supplied with low vision aids (92%) claimed to have benefited from attending the low vision clinic.
The quantitative evaluation of total internal reflection in keratoconus
Authors: Hood A. , Veen C. , Vaughan S. , Edwards M. P. , Simmons I. , Misson G. 
Published: July 2002

Purpose: The phenomenon of apical total internal reflection in the cone of keratoconic patients has been described previously. This study was designed to assess the quantifiable nature of this sign and its ability to diagnose and monitor keratoconus.Method: A sample of 30 patients with varying severity of keratoconus was compared with a series of sex and age matched normal controls and selected cases of spherically equivalent myopia. Each patient had a comprehensive corneal assessment including pachymetry, corneal topography, and standardised oblique slit lamp photography. The slit lamp photographs were digitally analysed to assess the area of total internal reflections. The severity of keratoconus was graded with a six stage ranking system based on the clinical appearance.Results: The area of total internal reflection was compared to the ranking system of clinical grading. For moderate and marked cones, the area of total internal reflection correlates well with both the clinical appearance and corneal topography. For mild and borderline cases, the photographs show a less well defined area but this is nevertheless distinguishable from normals or spherically‐matched equivalents.Conclusions: The area of total internal reflection visible in a keratoconic cornea correlates with the established techniques of grading keratoconus. Imaging this phenomenon may form the basis of a quantitative clinical for this condition.
Attendance of contact lens wearers at an ophthalmic Accident and Emergency unit
Authors: Radford C. F. , Gastaldo‐Brac V. , Hill A. R. 
Published: July 2002

SummaryContact lens (CL) complications account for 2.2–10.0% of patients attending ophthalmic Accident and Emergency (A&E) units. A survey was conducted to evaluate disease severity among CL wearers attending the Oxford Eye Hospital A&E Unit. CL wearers without a medical indication for CL wear completed a short questionnaire eliciting CL type and wear schedule. Subsequently, A&E Senior House Officers indicated the diagnosis and whether, in their opinion, the patient could have been managed by their optometrist or contact lens practitioner. Approximately half of the CL wearers (321/653, 49%) presented with CL related disorders, but only 16% (53/321) of these had potentially sight‐threatening disease. More than a third of these patients were deemed to be inappropriately attending (125/321, 39%), presenting with minor problems such as corneal abrasions, CL handling difficulties and CL solution ‘accidents’. Better patient instruction, together with encouragement to consult their optometrist or contact lens practitioner first if problems occur, would greatly reduce the burden of A&E attendance by CL wearers with minor complaints.
Rigid gas permeable contact lenses surface roughness examined by interferential shifting phase and scanning electron microscopies
Authors: Merindano M. D. , Canals M. , Saona C. , Costa J. 
Published: July 2002

SummaryThe anterior surface roughness of seven factory new rigid gas permeable (RGP) contact lenses has been studied by interferential shifting phase microscopy (ISPM) and scanning electron microscopy (SEM). Five lenses were fluorsilicone acrylate and two lenses were silicone acrylate. Their material Dk ranged from 14 to 210.ISPM is shown to be a reliable and non‐destructive method to observe and measure the relief of the contact lens surface. Moreover, profile and contour data are easily stored for further quantitative studies.ISPM contour patterns of the studied lenses are qualitatively compared with those obtained by SEM for the same lenses. Results point out that ISPM gives similar accuracy but it is non‐destructive and cheaper than SEM.Moreover, the quantitative study of surface roughness suggests that there is a relationship between surface roughness and Dk of the lens material: surface roughness increases with Dk and allows to distinguish between lenses with low, medium and high Dk.
Fuchs' endothelial dystrophy: a fresh look at an aging disease
Authors: Bergmanson Jan P. G. , Sheldon Todd M. , Goosey John D. 
Published: July 2002

SummaryThe increasing number or corneal and intraocular surgeries performed together with longer life expectancy, elevates the risk for developing symptomatic Fuchs' endothelial dystrophy (FED). This article reviews the current understanding of FED, and, in addition, a case of early FED is presented clinically and histopathologically. Two FED corneas from one patient were examined histopathologically using an established histological protocol for light and electron microscopy. FED is an inherited autosomal dominant corneal endothelial disorder with incomplete penetrance that is up to 3 times less likely to develop in men. Treatment options are primarily palliative while surgical intervention routinely involves a penetrating keratoplasty. In this disease process the endothelium produces excessive amounts of basement membrane material of an abnormal composition resulting in the formation of a posterior collagenous layer. Extreme accumulations of this material created mushroom‐like formations, guttae, projecting into the anterior chamber. The endothelial cells were extremely thinned over the guttae, to the point where the cells may provide little more than barrier function. Despite a presumably compromised endothelial pump the corneas appeared relatively free of edema clinically and histopathologically. However, some edematous pockets deep in the basal epithelial layer were present suggesting that epithelial involvement occurs at an early stage in the disease. An early diagnosis of FED will help patients and surgeons to better elect optimal surgical timing and procedures. The current trend is to intervene surgically before the patient reaches the painful end‐stage. Interestingly, in the case examined, the endothelium presumably provided only a barrier function over large areas with an apparently reduced contribution from the endothelial fluid pump and yet the corneas remained relatively clear. Future research may confirm that decompensation occurs only when complete endothelial coverage is lost. If the endothelial barrier function is more important to corneal transparency than the endothelial pump function in FED, then the relative combination of these two functions in the normal cornea should also be reassessed.
The influence of interactions between accommodation and convergence on the lag of accommodation
Authors: Schor Clifton 
Published: July 2002

SummarySeveral models of myopia predict that growth of axial length is stimulated by blur. Accommodative lag has been suggested as an important source of blur in the development of myopia and this study has modeled how cross‐link interactions between accommodation and convergence might interact with uncorrected distance heterophoria and refractive error to influence accommodative lag.Accommodative lag was simulated with two models of interactions between accommodation and convergence (one with and one without adaptable tonic elements). Simulations of both models indicate that both uncorrected hyperopia and esophoria increase the lag of accommodative and uncorrected myopia and exophoria decrease the lag or introduce a lead of accommodation in response to the near (40  cm) stimulus. These effects were increased when gain of either cross‐link, accommodative convergence (AC/A) or convergence accommodation (CA/C), was increased within a moderate range of values while the other was fixed at a normal value (clamped condition). These effects were exaggerated when both the AC/A and CA/C ratios were increased (covaried condition) and affects of cross‐link gain were negated when an increase of one cross‐link (e.g. AC/A) was accompanied by a reduction of the other cross‐link (e.g. CA/C) (reciprocal condition). The inclusion of tonic adaptation in the model reduced steady state errors of accommodation for all conditions except when the AC/A ratio was very high (2 MA/D).Combinations of cross‐link interactions between accommodation and convergence that resemble either clamped or reciprocal patterns occur naturally in clinical populations. Simulations suggest that these two patterns of abnormal cross‐link interactions could affect the progression of myopia differently. Adaptable tonic accommodation and tonic vergence could potentially reduce the progression of myopia by reducing the lag of accommodation.
Developmental visual system anomalies and the limits of emmetropization
Authors: Smith Earl L. , Hung Li‐Fang , Harwerth Ronald S. 
Published: July 2002

SummaryOptical defocus can within certain limits predictably alter ocular growth and refractive development in infant monkeys. However defocus, particularly unilateral defocus associated with anisometropia, can also promote abnormal sensory and motor development. We investigated the relationship between the effective operating range for emmetropization in infant monkeys and the refractive errors that produced amblyopia. Specifically, we examined the refractive‐error histories of monkeys that did not demonstrate compensating ocular growth for imposed refractive errors and used operant psychophysical methods to measure contrast sensitivity functions for 17 infant monkeys that were reared with varying degrees of optically imposed anisometropia. Imposed anisometropias that were within the operating range of the monkey’s emmetropization process were eliminated by differential interocular growth and did not produce amblyopia. On the other hand imposed anisometropias that failed to initiate compensating growth consistently produced amblyopia; the depth of the amblyopia varied directly with the magnitude of the imposed anisometropia. These results indicate that amblyopia and anisometropia are frequently associated because persistent anisometropia causes amblyopia. However, the failure of emmetropization in infants with refractive conditions that are known to promote sensory and motor anomalies indicates that factors other than optical defocus, presumably factors associated with the development of amblyopia and/or strabismus, can also influence early refractive development and in some cases cause anisometropia.
Effects of defocus and pupil size on human contrast sensitivity
Authors: Strang Niall C. , Atchison David A. , Woods Russell L. 
Published: July 2002

SummaryDefocus lowers the contrast sensitivity function (CSF), producing a complex function with local dips and peaks. Previously, we were able to predict the shape of the CSF with large pupils from measured transverse aberrations with hypermetropic defocus but not with myopic defocus (Atchison et al., 1998c, J. Opt. Soc. Am. A.15, 2536). As there is no reason that myopic defocus should be more difficult to predict than hypermetropic defocus, we modified the procedure to try to improve CSF predictions with myopic defocus. Also, we extended the study to consider a range of pupil sizes. CSFs were measured for three subjects at three defocus levels (in‐focus, −2D and +2D) and three pupil sizes (2  mm, 4  mm and 6  mm). Using a diffraction optics model, transverse aberration measures and in‐focus CSF measures, we predicted the defocused CSFs. The predicted defocused CSFs were lower than the in‐focus CSF as expected, and had complex shapes that varied with defocus and pupil size and between subjects. While a few predictions were poor, generally, the overall magnitude and shape of the defocused CSFs were well predicted and similarly so for myopic and hypermetropic defocus. Some further improvements in technique are indicated.
Oral Care Reduces Pneumonia in Older Patients in Nursing Homes
Authors: Yoneyama Takeyoshi , Yoshida Mitsuyoshi , Ohrui Takashi , Mukaiyama Hideki , Okamoto Hiroshi , Hoshiba Kanji , Ihara Shinichi , Yanagisawa Shozo , Ariumi Shiro , Morita Tomonori , Mizuno Yasuro , Ohsawa Takayuki , Akagawa Yasumasa , Hashimoto Kenji , Sasaki Hidetada , Of The Oral Care Working Group Members 
Published: July 2002

OBJECTIVES:Aspiration of oral secretions and their bacteria is increasingly being recognized as an important factor in pneumonia. We investigated whether oral care lowers the frequency of pneumonia in institutionalized older people.DESIGN:Survey.SETTING:Eleven nursing homes in Japan.PARTICIPANTS:Four hundred seventeen patients randomly assigned to an oral care group or a no oral care group.INTERVENTION:Nurses or caregivers cleaned the patients' teeth by toothbrush after each meal. Swabbing with povidone iodine was additionally used in some cases. Dentists or dental hygienists provided professional care once a week.MEASUREMENTS:Pneumonia, febrile days, death from pneumonia, activities of daily living, and cognitive functions.RESULTS:During follow‐up, pneumonia, febrile days, and death from pneumonia decreased significantly in patients with oral care. Oral care was beneficial in edentate and dentate patients. Activities of daily living and cognitive functions showed a tendency to improve with oral care.CONCLUSION:We suggest that oral care may be useful in preventing pneumonia in older patients in nursing homes. J Am Geriatr Soc 50:430–433, 2002.
Excess Mortality or Institutionalization After Hip Fracture: Men Are at Greater Risk Than Women
Authors: Fransen Marlene , Woodward Mark , Norton Robyn , Robinson Elizabeth , Butler Meg , Campbell A. John 
Published: July 2002

OBJECTIVES:To assess 2‐year excess mortality or institutionalization risk associated with hip fracture in community‐dwelling people aged 60 and over.DESIGN:Cohort study.SETTING:Auckland, New Zealand, from July 1991 to February 1996.PARTICIPANTS:Five hundred sixty‐five community‐dwelling older people recently hospitalized with a hip fracture and 782 randomly selected controls, frequency matched for age and gender, living in the same catchment area as the cases.MEASUREMENTS:Two‐year mortality or institutionalization status.RESULTS:Over half (52.1%) of male hip fracture cases and 12.4% of male controls were dead or institutionalized, compared with 39.2% of female hip fracture cases and 19.7% of female controls. The odds ratio, adjusted for baseline demographic characteristics, medical status, and physical function, for death or institutionalization was 6.89 (95% confidence interval (CI) = 2.75–17.27) for men and 1.48 (95% CI = 1.02–2.19) for women.CONCLUSIONS:For both men and women who incur a hip fracture, the risks of dying or being institutionalized within 2 years are higher than for their peers. The independent effect of hip fracture on this outcome was significantly greater for men than women. The marked influences of prefracture health status, physical limitations, and gender on outcome have important implications for preventative strategies. J Am Geriatr Soc 50:685–690, 2002.