bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multi‐meridional keratometry
Authors: Rosenfield Mark , Portello Joan K. 
Published: July 2002

SummaryDuring conventional keratometry, the two principal meridia are identified and measurements of the anterior corneal curvature determined along these orientations. However, in cases of corneal irregularity, the principal meridia may be difficult to identify. Accordingly, the present study sought to evaluate two alternative procedures which do not require identification of the principal meridia. Instead, measurements of anterior corneal curvature were determined along either three or four preselected meridia and subsequently converted into the standard format for measurements of anterior corneal curvature. The study was performed on 25 visually normal subjects and the results compared with conventional two meridian keratometry findings. No significant differences were observed between the mean findings for the three and four meridian techniques. Furthermore, both procedures gave comparable results to the conventional two meridian method. Accordingly, multi‐meridional keratometry may be valuable in cases of irregular astigmatism, for example produced by keratoconus or scarred corneas, since measurements can be obtained without the necessity for identification of the principal meridia.
Optical consequences of asymmetries in normal corneas
Authors: Hemenger Richard P. , Tomlinson Alan , Oliver Katherine 
Published: July 2002

SummaryA survey of videokeratographs of normal corneas shows many with substantial peripheral asymmetries. For sufficiently large pupils (5.5 mm in this study) these asymmetries lead to coma‐like axial aberrations large enough to produce measurable losses in vision in a number of cases. Starting from the output of a videokeratographic instrument, a method of estimating the optical effects of corneal asymmetries using Zernike circle polynomials is outlined. It is further shown that in a first approximation corneal asymmetries can be identified with the primary aberration coma and that this aberration is approximately due to a uniform gradient of refractive power across the cornea. Calculations for a representative case predict that a significant improvement in modulation transfer would follow from correction of this aberration.
Contrast and luminance as parameters defining the output of the VERIS topographical ERG
Authors: Brown Brian , Yap Maurice K. H. 
Published: July 2002

SummaryThe Visual Evoked Response Imaging System (VERIS I) topographical electroretinogram system (EDI Associates, San Francisco, CA) allows measurement of the response of large numbers of retinal areas simultaneously. This paper examines ERG responses derived with the VERIS system to changes in target contrast and to local reductions in luminance. There is a linear reduction of response with reductions of target contrast. Neutral density filters were placed over part of the display, to mimic the localised reductions in response which occur in glaucoma, age‐related maculopathy or diabetic retinopathy. There is a definite reduction in response seen with a 0.4 ND filter, indicating that the system should have similar sensitivity in detection of retinal lesions to the commonly used visual field analysis systems.
Reduced accommodation in children with cerebral palsy
Authors: Leat Susan J. 
Published: July 2002

SummaryAccommodation in 43 subjects with cerebral palsy was measured objectively using a dynamic retinoscopy technique, which has already been shown to be reliable and repeatable. The subject's ages ranged from 3 to 35 years. Of these, 42% were found to have an accommodative response pattern which was different from the normal control group for his/her age. Nearly 29% had an estimated amplitude of accommodation of 4 D or less. The presence of reduced accommodation was found to be associated with reduced visual acuity, but was not associated with cognitive or communication ability, refractive error or age. The prevalence of other ocular disorders in this group is also high. These findings have developmental and educational implications.
The dynamics of tear flow within a phenol red impregnated thread
Authors: Blades Kenneth J. , Patel Sudi 
Published: July 2002

SummaryA method for the laboratory production of a phenol red impregnated thread is described. Using the thread, tear flow was measured in the right eye of 2 groups of normal subjects: group I,n = 20, average age 26.2 years (± 5.6); and group II, n = 20, average age 56.4 years (± 13.8). Data were collected by placing a thread over the lower lid margin for a time period of 15 s. A further seven threads were inserted at 5 min intervals for periods increasing by 15 s up to 120 s. A significant difference in mean thread wetting between the two age groups was found for thread insertion times of 30, 60 and 90 s. For each eye, the rate of thread wetting was exponentially related to the period of thread insertion. Thread wetting and the constant of the exponential were not found to be gender dependent. Simulating the tears in the lower fornix, using a bath of saline, it was concluded that the exponential constant was a property of thread material and not tear fluid. For practical purposes, the rate of thread wetting reached equilibrium by 120 s where mean total thread wetting was 19.5 mm (± 6.5). The typical flow of tears (y) in mm/s, along the phenol red thread can be described by: y = 0.16 + 0.47e−0.0283t where t is the period of thread insertion.
Deceptive discs ..!
Authors: Pawson Pete 
Published: July 2002

Discrimination between normal and glaucomatous optic discs is notoriously difficult, even for ophthalmologists specialising in glaucoma. This poster will present optic disc photographs, together with their corresponding visual fields, in order to highlight this difficulty. The various possible disc, field and intraocular pressure combinations will be explored, and potential explanations for non‐correlation between these variables will be offered. Emphasis will again be placed upon:1. The value of visual field examinations when screening for glaucoma (Tuck and Crick, 1993).2. The relevance of disc size in the interpretation of C : D ratios (Jonas and Dichtl, 1995).3. The fact that raised intraocular pressure is a risk factor for glaucoma, rather than a diagnostic criterion (Sommer, 1989).
Biographical and clinical characteristics of a low vision population
Authors: Doorduyn Katie , Harper Robert 
Published: July 2002

A retrospective survey of the optometry clinics at Manchester Royal Eye Hospital was undertaken in order to define the biographic and clinical characteristics of the population being provided with low vision rehabilitation. For the year quarter July‐September 1994, 288 patients were identified as having attended the low vision clinic. The hospital case notes were available for examination in 273 cases (94.8%). The results presented here relate to this latter sample of patients.Analysis of the records revealed that the major diagnostic categories were ARMD (55.7%), glaucoma (10.6%), diabetic retinopathy (8%), other macular disorders (5.9%) and myopic degeneration (5.5%). The median age of patients was 78 years (range 7–104) and the male : female ratio was 0.87 (i.e. 53.4% female). Distance visual acuities on entry to the clinic were 6/60 or better in 72.5% of the sample. A total of 141 patients (51.6%) were known to be registered as blind or partially sighted.A new spectacle prescription was issued to 21.6% of patients. The most frequent low vision aids (LVAs) issued were stand magnifiers (147 illuminated and 46 non‐illuminated), hand‐magnifiers (67 issued) and distance monocular/binoculars (51 issued). With appropriate low vision provision, 84.5% of the sample achieved a near acuity of N8 or better. A total of 371 LVAs were issued, representing an average number of 1.36 LVAs per patient. The total cost of all LVAs issued amounted to £7818.81, giving an average cost of £28.64 per patient.This survey has provided a useful insight into the characteristics of both the population our service provides and the LVAs prescribed. Studies to measure the outcomes of our low vision provision are presently being carried out.
The effect of an artificially elevated intraocular pressure on the central corneal curvature
Authors: Douthwaite William A. , Lam Andrew K. C. 
Published: July 2002

SummaryTwenty‐three optometry students with normal corneal condition were recruited. The intraocular pressure and central corneal curvature of the right eye were measured in a sitting and a 30° head‐down posture. The mean (standard deviation) IOPs before and during posture change were 1 5.6 (2.4) mmHg and 22.1 (2.3) mmHg respectively. This 6.5 mmHg mean rise in IOP was found to be statistically significant which is similar to the results from previous studies. The mean changes in radius of corneal curvature and the orientation of the axis of the vertical principal meridian were 0,02 mm (SD 0.025 mm) and 2.4° (SD 10.4°) respectively. No significant variation was demonstrated on these keratometric results due to the 30° head‐down posture. The maximum change in radius of curvature was only 0.055 mm for one subject. Perhaps this amount of pressure rise was not sufficient enough to distort the corneal surface centrally. Another possibility could be an even distribution of the elevated pressure around the cornea, or the distribution of pressure is not even but could not be revealed by a conventional keratometer.
The light scattering characteristics of the eye
Authors: Hennelly M. L. , Barbur J. L. , Edgar D. F. , Woodward E. G. 
Published: July 2002

Aim: To validate a new method for the measurement of scattered light in the eye. In addition, normal values and results of subjects with keratoconus, cataract and corneal dystrophy will be demonstrated.Method: The scatter programme is implemented on the P__Scan 100 system. The system involves the use of high luminances and extended stimuli modulated sinusoidally. It reveals three parameters; n the scatter index which describes the distribution of scattered light from the scattering source; k, which describes the overall light scattered and a new index k′ known as the integrated straylight parameter. k′ provides an alternative to the commonly used straylight parameter, k.Results: Preliminary results in a small sample of normals showed k′ to be affected by age, diurnally, and by the menstrual cycle. Little variation in k′ was found between the ages of 16 and 42 years, with an increase found after the age of 60. A diurnal variation was found, with increased values of k′ on waking, which may be related to variation in corneal thickness. A variation in k′ with the menstrual cycle was noted. All values, i.e. n,k, k′ were found to be affected by keratoconus, cataract and corneal dystrophy.Conclusion: k′ is an important parameter in the quantification of scattered light. The results obtained give an insight into the patient's symptoms of glare, essential in the timing of conducting penetrating keratoplasty.Acknowledgement: M. L. Hennelly was supported by a College of Optometry Studentship.
Reproducibility of topographic measurements of the optic nerve head with the Heidelberg Retina Tomograph using separate and imported contour lines
Authors: Roff E. J. , Hosking S. L. , Barnes D. A. , Gibson J. M. 
Published: July 2002

Purpose: To investigate whether topographical measurements of the optic nerve head are more reproducible when the contour line is redrawn for each image as opposed to imported using the Heidelberg Retina Tomograph (HRT).Introduction: Optic nerve head topography can be measured in vivo using Confocal Scanning Laser Ophthalmoscopes such as the HRT. Image analysis requires that the area of the optic disc is defined by subjectively drawing a contour line around Elschnig's ring. The HRT software can export this contour line between images for a subject, or the contour line can be redrawn.Method: Ten eyes of ten normal volunteers (40–60 years) were analysed with the HRT. Seven 10° images of the optic disc were taken by one observer for each randomly selected eye. Focus and scan depth settings were kept constant. All available stereometric parameters were analysed using three methods: (1) with a separately drawn contour line for each individual image, (2) with a contour line imported from the first image into subsequent images of the series, (3) by repeatedly redrawing the contour line for a single image from each eye. All contour lines were drawn by one observer. Mean co‐efficients of variation were calculated for each parameter for the three methods.Results: The mean co‐efficient of variation for the parameters ranged from 1.7–23.4% (method 1), 0–20% (method 2) and 1.6–13.4% (method 3).Conclusion: These results show that redrawn contour lines increase variability. Topographical measurements of the optic nerve head are more reproducible if the contour line is imported across subsequent images rather than redrawn for each individual image.
Longitudinal studies of visual and cognitive development in young children with Down's syndrome
Authors: Cregg M. , Woodhouse J. M. , Parker M. , Pakeman V. H. , Fraser W. I. , Sastry P. , Lobo S. 
Published: July 2002

As part of a long‐term study of visual and cognitive development in children with Down's syndrome, we are monitoring visual functions, including visual acuity, accommodation, refractive error, as well as scores on Bayley Scales of Infant Development in a cohort of 64 children throughout South and West Wales. Cross‐sectional data, presented at a previous meeting, suggest a remarkable similarity between acuity and cognitive scores, in that both progress rapidly in the early months, and undergo a sudden rate change at the age of 2 years.We now have a sufficient longitudinal data to re‐examine the progress of these two functions. Results for 12 children, each seen four times at similar ages, were analysed. Those children whose visual acuity falls outside the normal range at later ages, also show significantly lower cognitive scores, when compared to the children with normal visual acuity.
Symmetry detection in amblyopia
Authors: Barrett B. T. , Herbert A. M. 
Published: July 2002

Purpose: It has been suggested that the term tarachopia, meaning ‘distorted sight’, provides an accurate description of the visual deficit in amblyopia. This follows psychophysical findings of spatial inaccuracy in amblyopia, as well as subjective reports of perceptual distortions by amblyopic observers. Mirror symmetry is a salient feature in normal human vision and its detection is critically dependent upon the spatial relations between the elements of the pattern. This study investigates whether the perceptual distortions in amblyopia extend to mirror symmetry detection.Methods: Three strabismic and three non‐strabismic amblyopes participated in the experiment (acuity range 6/9 to 6/90). Symmetric and random dot patterns were briefly presented (<250 msecs) at three retinal locations (centred at fixation, and 4° to the left and right of fixation). The patterns were generated and displayed on a Macintosh computer. After each stimulus presentation the subject was required to press one of two keys to indicate whether the pattern was symmetrical or random. The d′ statistic was computed for three symmetry orientations (H, V, and 45°) for each of the three retinal locations.Results: Amblyopic‐eye performance was equivalent to fellow‐eye performance in 5 of the 6 amblyopes tested. In the remaining amblyope symmetry detection in the amblyopic eye. This is likely to have resulted from reduced visibility of the dot pattern since the acuity in this eye was 6/90.Conclusions: The ability to detect mirror symmetry in briefly presented dot patterns is not affected by amblyopia.
Measuring the outcomes of ophthalmic healthcare: low vision rehabilitation
Authors: Harper Robert 
Published: July 2002

The measurement of health status and medical outcomes is becoming a major requirement for all providers of healthcare services. There is a need to measure the outcomes of healthcare, not only to demonstrate the effectiveness of care, but also to assess the relative (and possibly competing) worth of different forms of care. At the same time, there is a growing awareness of the limitations of clinical outcomes in contrast to those measured by patients themselves. There is, therefore, considerable interest in the use of generic and disease specific ‘Quality of Life’ (Qol) instruments.Within ophthalmic healthcare, clinical outcomes include, for example, measures of visual function or the gradings of images of ocular structure. Other outcome measures used may include specific disease scales or indices, including questionnaire measures of visual disability (e.g. the VF14, ‘Activities of Daily Vision Scale’ and TyPE scales, designed to assess the impact of cataract and cataract surgery on self‐rated visual disability). In contrast to disease specific measures, generic measures are designed to provide an overall measure of an individuals health status. These measures are classified into profile measures (e.g. the SF36) or indices (e.g. the Rosser index or the EuroQol).There have been a number of studies which have evaluated the effectiveness of low vision rehabilitation, although these have mainly been small cross sectional surveys which have used a single definition of ‘success’, including for example, the visual acuity/visual performance achieved with the LVA or the usage of the LVA. More recently questionnaire approaches have been used to measure ‘success’, but as with clinical outcomes, the validity and reliability of the outcomes used has not been established. Given the considerable scale of the low vision population and the current debate about optimal models of low vision care, there is a pressing need to (1) define an appropriate set of outcome measures and (2) carry out randomised controlled trials comparing the effectiveness and cost‐effectiveness of different forms of care.If we as clinicians fail to inform the debate about appropriate outcomes in ophthalmic healthcare, this may result in such care being incorrectly valued by others.
Optometric referrals to an ophthalmology outpatients department: classification and sensitivity
Authors: Weed Kathryn H 
Published: July 2002

The rationale of this study was to find the answers to the following questions:1. The number of optometric new patient referrals in a month period.2. The reason for referral.3. The number of false positives.Of a total of 267 new patients referred to Sunderland Eye Infirmary, 104 were optometrically derived (39%). In this group the most common reason for referral by optometrists was cataract assessment (23%) followed by suspected glaucoma (21%). In the latter group of 22, 15 (68%) were actually diagnosed as suffering from primary open angle glaucoma, or were listed for further assessment. In the former group of 24, 19 patients (83%) were listed for surgery. The three remaining patients were deemed untroubled by any visual symptoms and despite lens opacities maintained 6/12 Snellen visual acuities.The other reasons for referral were macular degeneration (13), decreased visual acuity (8), orthoptic management (7), visual defects (6), corneal (4), central vein occlusion (3), posterior vitreous detachment (3), migraine symptoms (2), epiphora (2), irritation symptoms (2), capsular opacification (2), caruncle cyst (1), retinal haemorrhage (1), pupil irregularity (1), diplopia (1), narrow angles (1) and ptosis with conjunctivitis (1).There appeared to be an inconsistency on the number of tests used for referral criteria and baseline information for all referrals. A guide line on the minimum information that should be included in a referral is discussed for cataract assessment, suspected glaucoma and macular degeneration.
Penetrating keratoplasty, corneal topography and the optometrist
Authors: Macalister Graham 
Published: July 2002

The success rate for penetrating keratoplasty in non‐vascularised corneas is now in the region of 95%. However corneal clarity alone can no longer be considered as the sole criteria for success, and the quality of the visual outcome is now receiving much more attention. This is often compromised by high astigmatism and topographic irregularity.A prospective longitudinal trial involving 108 eyes with transplanted corneas was carried out. The longest follow‐up was for 10 years, and data was available for 60 patients at the 5 year stage. Healing and improvement in corneal topography are dynamic processes, and it was decided to use sequential observations taken from the same eye to investigate changes in corneal topography over time. The results were then related to patient characteristics and to variables in the surgical technique, and multivariate analysis carried out to determine which factors have the most influence on the outcome.A photokeratoscope was used and an analysis technique was developed which enabled clinically meaningful topographical components to be derived from measurements of each keratograph. These components were spherical equivalent, asymmetry, axis of asymmetry, regular astigmatism and its axis, and an irregularity component. The changes in astigmatism and irregularity were analysed using Multilevel Modeling. The results of this study will be presented and the implications discussed.Computerised video‐keratoscopes are capable of revealing a great deal of information about corneal irregularity and are therefore useful in the management of post‐keratoplasty astigmatism. Colour topography maps will be presented which demonstrate commonly encountered features. These will include the effect of individual tight sutures and the changes brought about by suture removal and refractive surgery. The potential of video‐keratography as a guide to the optometrist in refraction and contact lens fitting for the post‐keratoplasty patient will be discussed.
Contour interaction for high and low contrast optotypes in normal and amblyopic observers
Authors: Simmers Anita J. , Gray Lyle S. , McGraw Paul V. , Winn Barry 
Published: July 2002

SummaryWe investigate the influence of stimulus contrast upon contour interaction in normal and amblyopic subjects. Using a computer generated acuity task, flanked and unflanked acuities were measured psychometrically at both high contrast (80%) and low contrast (6%), in a group of 19 normal and 11 amblyopic subjects. The crowding ratio for high contrast letters was found to be significantly higher than that for low contrast letters. The extent of the crowding zone was measured at high and low contrast by varying the separation of the optotype and flanking bars. The crowding zone measurement was repeated for the high contrast optotypes using dioptric blur. The position of the flanking contours was found to have a significant effect on letter resolution at high contrast but no significant effect was demonstrable at low contrast. With the addition of dioptric blur the effect of contour interaction became negligible at high contrast. These findings support the hypothesis that the crowding effect is: (1) similar in normal and amblyopic eyes when tested at threshold; (2) is contrast dependent appearing only for high contrast optotypes.