bluuebunny/crossref_metadata_2025_split huggingface dataset:
New matrix formulation of spectacle magnification using pupil magnification. I. High myopia corrected with ophthalmic lenses
Authors: García M. , González C. , Pascual I. 
Published: July 2002

SummaryIn this paper we have applied the matrix method to calculating spectacle magnification (SM) and relative spectacle magnification (RSM) for myopic eyes corrected with ophthalmic lenses (OLs). We have been able to obtain very simple expressions of the magnifications and analogous values to the ones obtained using other geometric methods. Through the paraxial 2 × 2 object‐image matrix for spherical systems, we can calculate the correcting lens pupil matrix (ML) and the corrected ametropic eye pupil matrix (Mca). These two matrices, that is ML and Mca, directly provide the lateral magnification and the lens‐eye system's image focal parameters that enable us to easily calculate SM and RSM. The magnifications have been calculated for the case of myopic eyes corrected with OLs, which shows the validity of this method since its results are similar to the ones obtained using other methods. The analysis of other correcting systems such as contact intraocular lenses will be presented in two associated papers (to be published as parts II and III of this review).
The importance of clinical audit to optometrists in the Hospital Eye Service
Authors: Johns Steve 
Published: July 2002

SummaryIn 1989 the government published the white paper ‘Working for Patients’ and with it the requirement for the medical profession to carry out medical audit. In 1993 the Department of Health published its requirements for clinical audit in the recognition that other professionals, such as optometrists, have an integral part to play in the treatment and management of patients alongside medical practitioners. 1994 saw the publication of ‘Getting ahead with Clinical Audit’ which emphasized the commitment of the DoH to multidisciplinary non‐hierarchical clinical audit.It is the fundamental right of every patient who consults hospital optometrists, as with any healthcare professional, to expect the best quality of care to be delivered. It is the fundamental responsibility of all practitioners who work in hospital optometry, whether heads of departments or not, to ensure that the care that is delivered is to the very best standards that can be achieved. Clinical audit is the term given to the analysis process that reconciles these fundamentals.It is a common misconception that clinical audit is research and, although questions raised during the audit process can lead to the undertaking of research, in essence clinical audit uses current knowledge to set standards against which clinical practice is compared. Through a structured design not dissimilar to clinical research, various aspects of optometric care can be observed in order to ascertain whether a change in clinical practice will lead to an improvement in the healthcare delivered to patients. A good audit is cyclic in nature in that the observation of clinical practice is ongoing in order to ensure standards of care are continually met and as such should not result in a single ‘snap‐shot’ of the care provided.This area is becoming increasingly important within the purchaser/provider setup in that the purchaser is now responsible for allocating resources to clinical audit. Increasingly purchasers are looking at building in quality measures when contracting services along with initiating audit in specific areas.In the future, clinical audit both in terms of uniprofessional and multiprofessional will play an increasing part in Hospital Eye Service (HES) optometric practice. It is important that it is understood what can be achieved and how to use clinical audit to ensure that HES optometry can continue to provide the very best standards of optometric healthcare to its patients.
Panasil light body impression material study
Authors: Brammar R. , Bullock J. , Sunderland S. , Tromans C. 
Published: July 2002

SummaryThis study was undertaken to confirm that Panasil light body is a suitable replacement impression material for Panasil ‘C’, used for ocular impression procedures, which was withdrawn by the manufacturers in 1993. The damaging effects to the corneal and conjunctival tissues of alginate materials used in the past during impression‐taking procedures for artificial eye and cosmetic shell prostheses, is recognized by ocularists and optometrists.Modern silicone impression materials demonstrate:1. Minimal disruption to tissues.2. High accuracy.3. High strength in relation to thin section.4. Good flow characteristics prior to curing.Panasil light body impression material is polyvinyl siloxane based, low viscosity, addition curing silicone.Our trial investigated the effects of obtaining impressions from five groups of patients presenting with:1. Anophthalmia with hydroxyapatite implants.2. Phthisical eyes.3. Unsighted vascularized eyes.4. Clear corneas.5. Exenterated orbits with osseointegrated implants.Total number of patients examined was 30.In all cases where an eye was present, post‐procedural examination by Burton/slit‐lamp with fluorescein was carried out to determine the level of tissue damage/abrasion. A table of results is presented.We have shown that Panasil light body silicone impression material is accurate and stable when used for the purposes investigated. We would emphasize the minimal adverse effects to the corneal and conjunctival tissues observed during the course of this study.
Application of a modified keratometer in the study of corneal topography on Chinese subjects
Authors: Lam Andrew K. C. , Douthwaite William A. 
Published: July 2002

SummaryA corneal topography study was carried out on Hong Kong Chinese subjects using a modified keratometer. The Chinese corneal topography measured by this modified keratometer was similar to other studies using the Wesley–Jessen Photo Electronic Keratoscopy (PEK) System 2000. The mean p‐values along the horizontal meridian and the vertical meridian were 0.82 and 0.87, respectively. A negative correlation was found between the p‐value and the central corneal radius along the horizontal meridian which may indicate that a steeper central cornea will have a greater p‐value. However, the correlation coefficient of 0.56 was not too certain for this conclusion to be drawn. A difference of 0.04 was found between the horizontal p‐value and the vertical p‐value, which may be a result of the tight lid tension along the vertical meridian. This modified keratometer can be considered as an inexpensive instrument for the study of corneal topography.
Proximal contribution to a linear static model of accommodation and vergence
Authors: Hung George K. , Ciuffreda Kenneth J. , Rosenfield Mark 
Published: July 2002

SummaryTo determine the influence of target proximity on accommodation and vergence under both open‐ (OL) and closed‐loop (CL) viewing conditions, a static interactive feedback model, which included proximal accommodation (PA) and proximal vergence (PV) inputs, was developed and analysed quantitatively. It was based on an earlier static dual‐interactive feedback model of accommodation and vergence. The proximal inputs were added to both the accommodative and vergence loops at the output of the respective controllers. The values of the PA and PV gains were obtained from experimental dual‐OL data. The model equations were analysed over a stimulus range of 1 to 6 D (or MA). It was found that under the dual‐OL condition, the contribution of PA to the overall accommodative output ranged from 42.5 to 81.6%, whereas the contribution of PV to the overall vergence output ranged from 56.1 to 88.5%. In contrast, under all other stimulus conditions, with the exception of the PA contribution to the accommodative output under the Aol, Vcl condition (26.5–41.0%), the relative contributions were much smaller, ranging from 0.04 to approximately 7.0%. In particular, under the dual‐CL condition, representing the normal binocular visual feedback condition, the relative contributions were only 4.0 and 0.04% for PA and PV, respectively. Thus, although the relative contributions of PA and PV were large under the dual‐OL condition, they were generally very small under the various CL conditions that simulated more naturalistic viewing situations. Nevertheless, proximity may still play an important role by providing cues for attaining coordinated and harmonious motor responses under specific viewing conditions.
Relative roles of resolution and spatial interference in foveal and peripheral vision
Authors: Latham Keziah , Whitaker David 
Published: July 2002

SummaryThe rate of change of visual performance with increasing eccentricity of fixation is known to be task dependent. In order to examine eccentricity‐related changes in visual performance when a combination of two different factors influence thresholds, visual acuity in the presence of flanking elements was investigated across the visual field. Interference zones increased in extent with eccentricity at a much faster rate than did resolution thresholds. E2 values, quantifying the eccentricity‐related magnification required, were 1–2° for resolution and 0.1–0.2° for spatial interference. E2 values for resolution in the presence of flanks depended on the proximity of the flanks and their ‘weighting’ in the task. From the results, the magnitude and extent of spatial interference across the visual field can be described quantitatively. Further, the results serve as an example of how observed variations in peripheral threshold gradients might be achieved as a combination of underlying factors with different E2 values.
Dark focus and dark vergence: an experimental verification of the configuration of the dual‐interactive feedback model
Authors: Bai‐chuan Jiang , Woessner William M. 
Published: July 2002

SummaryBased on the dual‐interactive feedback model, dark focus and dark vergence designate a point on a line describing the response AC/A ratio. In order to verify the relationship between dark focus and dark vergence, we predicted the dark vergence from the measured dark focus when the measurements were based on the response‐based calculated and gradient AC/A ratios. For 10 subjects, the correlations between predicted and measured dark vergence values were high. The prediction was better when using the gradient AC/A ratio.
Le Grand eye for the study of ocular chromatic aberration
Authors: Villegas E. R. , Carretero L. , Fimia A. 
Published: July 2002

SummaryIn this technical note we study the prediction of ocular chromatic aberration which provides Le Grand's complete theoretical eye model. Theoretical computations of the longitudinal chromatic aberration are lower than experimental results. However, we show that experimental results of the chromatic difference of position (CDP) agree with theoretical predictions. The fit of the CDP for this model is practically the same as the one obtained for the Thibos reduced eye.
Low contrast letter acuity in age‐related maculopathy
Authors: Abadi Richard V. , Pantazidou Mary 
Published: July 2002

SummaryDistance low contrast letter acuity (LCLA) was assessed in six subjects with age‐related maculopathy (ARM) and 12 subjects with normal visual function using a series of eight Regan charts ranging in contrast from 4% to 96%. Mean logMAR acuities for letters of 96% contrast were −0.205, −0.053 and 0.748 for the young control group (mean 23.3 years), the age‐matched control group (mean 70.3 years) and the ARM subjects (mean 72.3 years), respectively. The LCLA function was found to be significantly better for the six in the young control group compared with the six age‐matched controls (P < 0.05). The ARM subjects performed significantly poorer (P < 0.05) at each contrast level down to 20% compared with the age‐matched subjects. A constant 0.8 logMAR difference was found between the LCLA function of the age‐matched controls and that of the ARM subjects. These results show that, since the low contrast test charts revealed similar differences in visual acuity between the ARM and the age‐matched groups, the use of low contrast letter charts do not appear to give any additional information of acuity loss.
A new matrix formulation of spectacle magnification using pupil magnification. II and III: High myopia corrected with contact lenses and intraocular lenses
Authors: García M. , González C. , Pascual I. 
Published: July 2002

SummaryIn this paper we use the matrix method to calculate spectacle magnification (SM) and relative spectacle magnification (RSM) using pupil magnification for myopic eyes corrected with contact lenses (CLs), and intraocular lenses (IOLs). For myopic eyes corrected with contact lenses, the calculation is very similar to the one done for myopic eyes corrected with ophthalmic lenses (OLs) since both OLs and CLs are external correcting systems. For myopic eyes corrected with intraocular lenses, the calculation is different from the ones carried out for myopic eyes with external correcting systems. In this paper we show the differences that exist between the matrix calculations for these two correcting systems, external and internal. The magnifications are calculated for specific myopic eyes corrected with CLs and IOLs. By comparing the results obtained with three correction types, namely, OLs, CLs and IOLs, we will be able to choose the best correction system for each case.
An integrated system for measuring static and dynamic accommodation with a Canon Autoref R‐1 refractometer
Authors: Wetzel Paul A. , Geri George A. , Pierce Bryon J. 
Published: July 2002

SummaryAn integrated system is described which we have found useful for efficiently collecting and analyzing both static and dynamic accommodation data using the Canon Autoref R‐1 refractometer. The system consists of hardware modifications and software designed to both facilitate the measurement of accommodation and to process the resulting data. Several features of the Canon R‐1, which may not be evident to some users, are also described. A program written in Microsoft C/C++ running under DOS, and designed for use on a PC, is available from the authors upon request.
Visual functions and acute ingestion of alcohol
Authors: Watten R. G. , Lie Ivar 
Published: July 2002

SummaryIn a placebo‐controlled experiment comprising 22 healthy men (mean age 27.4 years), we investigated the influence of three breath levels of blood alcohol (BrAC; 0.0%, 0.05% and 0.1%) upon distant visual acuity, stereoacuity, contrast sensitivity, accommodation, resting focus of accommodation and binocular vision. Positive (PRA) and negative accommodation (NRA) and resting focus of accommodation showed no significant changes with increasing BrAC. Compared to the placebo condition, visual acuity and refraction were only significantly affected at a breath alcohol level of 0.1%. Contrast sensitivity, stereoacuity and binocular vision were affected both at BrAC 0.05% and BrAC 0.1%. Only the higher spatial frequencies of contrast sensitivity were affected.
Arabic near test chart for partially sighted patients
Authors: Oduntan Alabi O. 
Published: July 2002

SummaryThis paper describes the design of an Arabic alphabet near acuity chart for examination of partially sighted patients. The alphabets used have similar legibility values (0.92 to 1.05) (Mean = 1.00) (SD = 0.05) and each row of the chart has similar legibility values as the others. The LogMAR method of acuity scaling was used, therefore each row is larger in size than the preceding row by a constant value of 1.26 (0.1 log unit). The inter‐letter space in a row is equal to the breadth of each letter in the row and the inter‐row spacing is equal the height of letters in the subjacent row. The chart has 10 rows and visual acuity values range from 9.6 to 1.2 M (LogMAR 1.4 to 0.5) at 40 cm, corresponding to Snellen 6/144 to 6/18, 20/480 to 20/60. The chart will be useful for examining Arabic‐speaking partially sighted subjects.
Therapeutic contact lenses in the management of anterior segment pain relief
Authors: Sinton J. E. , Jackson A. J. , Frazer D. G. 
Published: July 2002

Therapeutic contact lenses have been used extensively in the management of pain relief in patients with both primary and secondary corneal pathology (McDermott and Chandler, 1989). Despite this, many ophthalmologists and contact lens practitioners underestimate the benefits achievable through this mode of treatment. The authors believe that many of the negative perceptions associated with therapeutic lenses arise through the inappropriate selection of cases and the use of unsuitable lenses. In this study subjective responses of patients wearing therapeutic lenses were sought and comments concerning case management requested.Thirty‐nine patients with a variety of painful corneal epitheliopathies (recurrent erosion syndrome, bullous keratopathy, chemical burns, ocular cicatricial pemphigoid, etc.) were fitted with a range of hydrogel and silicon rubber therapeutic contact lenses. Each patient was asked to complete a questionnaire on pain relief and the advantages and disadvantages of lens wear. A six‐point ordinal pain relief scale was used to quantify pain relief.Questionnaires were returned by 30 patients (10 male and 20 female, mean age 59.3 ± 18.4 years, range 24–85 years) and the results analysed. Twenty‐seven patients (90%) reported pain relief associated with lens wear over a 3–18 month period (P < 0.001). Twenty‐five patients (83%) felt that the benefits of lens wear outweighed the inconveniences (P < 0.05). Many patients commented on the fact that lens wear provided a marked improvement in quality of life, when compared to other methods of treatment. Of those experiencing complications, most reported these to be short‐lived and of relatively minor significance. These complications often related to episodes of lens movement or displacement and resolved within 48 hours of commencing lens wear. In only two cases were more serious complications noted (infective keratitis) and in both cases lenses had been used to manage underlying pathology which presented a high risk of infective complications.The results of this study show that with appropriate case and lens selection a high proportion of patients with painful corneal pathology benefit significantly from therapeutic lens wear.
Evaluation of the role of gas permeable scleral contact lenses
Authors: Tromans Cindy , Bullock John M. 
Published: July 2002

Purpose: To evaluate visual outcome and wearing times in eyes fitted with a gas permeable scleral contact lenses (GPSCL) and to assess the role of these lenses in therapeutic contact lens practice.Methods: The criteria for selection of eyes for GPSCL assessment were:1. Previous PMMA scleral lens wearers with poor wearing times due to hypoxia.2. Unsuccessful rigid gas permeable (RGP) corneal lens fitting.3. Intolerance to RGP corneal lenses.4. Ocular surface disease (bandage).Of 20 patients, 24 eyes with corneal ectasia, corneal grafts, aphakia and ocular surface disease were assessed for GPSCLs. The GPSCLs used were sealed, controlled clearance lenses produced by Innovative Sclerals, Hertford, UK.Results: Fitting was achieved in 21 of 24 eyes assessed. Of these, 66% achieved VA better than 6/9. All eyes achieved VAs better than 6/18. Wearing times ranged from 6 to 16 hours with all previous PMMA scleral wearers reporting increased comfort and wearing time. Five patients (5 eyes) discontinued wear for reasons discussed.Conclusions: GPSCLs have a role in therapeutic contact lens fitting, especially in instances of highly irregular corneal topography where conventional corneal lens fitting has failed and in these cases a GPSCL is a realistic alternative to surgical intervention. Previous PMMA scleral lens wearers with hypoxic symptoms benefit from refitting with GPSCLs.
Frequency of seeing
Authors: Evans Jane , Henson David 
Published: July 2002

Frequency‐of‐seeing curves were found to be a useful tool for the investigation of the variability inherently seen in the visual field results of glaucoma patients. The frequency‐of‐seeing curve is the fundamental function which describes the patient's response behaviour to liminal light stimuli. A number of previous researchers have used the frequency‐of‐seeing technique for measuring local variability (Chauhan and House, 1991; Weber and Rau, 1992; Olsson et al., 1992/93). This technique is used in preference to the index short‐term fluctuation, which has classically been used to measure variability in visual field results, as this index makes an assumption that variability is constant across the whole visual field.In this particular study, frequency‐of‐seeing curves were plotted at two different locations in the same eye of 15 established glaucoma patients. One location was relatively normal and the other glaucomatous. There was a significant difference in the appearance of the two curves; the normal location showed little variability, whereas the defective location showed a much larger degree of variability. One suggested reason for this increased variability in glaucoma patients has been that of poor fixation (Henson and Bryson, 1990/91).The frequency‐of‐seeing curve was used again to compare the variability of each location when the errors of fixation were removed. In those cases removing the errors of fixation did not have a significant effect on the variability of the frequency‐of‐seeing curve indicating that fixation errors were not a major cause of the variability seen in glaucoma patients.
Effects of age‐related cataract on obstacle avoidance strategies
Authors: Elliot D. B. , Patla A. E. , Adkin A. L. , Furniss M. 
Published: July 2002

Purpose: To examine the effects of age‐related cataract on obstacle avoidance strategies. A key health issue facing the elderly population is an increase in the incidence of falls, which can be attributed to tripping over obstacles.Methods: Subjects with age‐related cataract (n = 9; 75.2 ± 4.7 years; 1.71 ± 0.07 m height) and normal, healthy eyes (n = 23; 72.5 ± 4.3 years; 1.71 ± 0.09 m height) were recruited. Subjects were required to repeatedly walk a straight path and step over one of two low contrast foam obstacles (6.7 cm and 26.8 cm high). Detailed locomotor changes were assessed using four infra‐red diodes affixed to the various points on the subject's lower limbs and the OPTOTRAK motion analysis system.Results: Cataract subjects had an increased incidence of tripping with both the leading (3.2 vs. 0%) and trailing limbs (4.0 vs. 0.7%). Lead limb toe clearance was higher (∼19 vs. 15 cm) and horizontal toe velocity lower (∼2.5 vs. 3.0 m/sec) in the cataract subjects compared to the controls.Conclusions: Cataract patients adapted their obstacle avoidance strategies in order to minimize the chances of tripping. However, significantly greater occurrences of tripping still occurred. We hope to present additional post‐surgery and second eye surgery data.