David F. Edgar

Supplementation with the carotenoids lutein or zeaxanthin improves human visual performance

Background:  Macular pigment (MP) is found in diurnal primate species when vision spans a range of ambient illumination and is mediated by cone and rod photoreceptors. The exact role of MP remains to be determined. In this study we investigate two new hypotheses for possible MP functions.

Exploring eye movements in patients with glaucoma when viewing a driving scene.

Background Glaucoma is a progressive eye disease and a leading cause of visual disability. Automated assessment of the visual field determines the different stages in the disease process: it would be desirable to link these measurements taken in the clinic with patients actual function, or establish if patients compensate for their restricted field of view when performing everyday tasks. Hence, this study investigated eye movements in glaucomatous patients when viewing driving scenes in a hazard perception test (HPT). Methodology/Principal Findings The HPT is a component of the UK driving licence test consisting of a series of short film clips of various traffic scenes viewed from the drivers perspective each containing hazardous situations that require the camera car to change direction or slow down. Data from nine glaucomatous patients with binocular visual field defects and ten age-matched control subjects were considered (all experienced drivers). Each subject viewed 26 different films with eye movements simultaneously monitored by an eye tracker. Computer software was purpose written to pre-process the data, co-register it to the film clips and to quantify eye movements and point-of-regard (using a dynamic bivariate contour ellipse analysis). On average, and across all HPT films, patients exhibited different eye movement characteristics to controls making, for example, significantly more saccades (P<0.001; 95% confidence interval for mean increase: 9.2 to 22.4%). Whilst the average region of ‘point-of-regard’ of the patients did not differ significantly from the controls, there were revealing cases where patients failed to see a hazard in relation to their binocular visual field defect. Conclusions/Significance Characteristics of eye movement patterns in patients with bilateral glaucoma can differ significantly from age-matched controls when viewing a traffic scene. Further studies of eye movements made by glaucomatous patients could provide useful information about the definition of the visual field component required for fitness to drive.

The effect of age on the light scattering characteristics of the eye

The rising mean age of our population has increased the need for understanding the physiologic consequences of ageing on visual function. Changes due to age were evaluated using a new scatter test implemented on theP_SCAN 100 pupillometer apparatus (Barbur, 1991). The test yields the full scatter function of the eye and also permits simultaneous measurement of pupil size (Barbur et al., 1995). In addition, contrast sensitivity was measured using sine wave gratings. The 28 subjects had a spherical refractive error between +0.50 DS and −0.25 DS, and astigmatism of less than −0.50 DC, V.A. of at least 6/6, and were ophthalmologically normal. To facilitate statistical analysis, subjects were classified into five groups according to age. For younger subjects (under 45 years),k′, the integrated straylight parameter, varied little with age. For this group,k′ ranged from 4.9 to 8.1. For subjects aged over 45 years,k′ increased with age, ranging from 10.7 to 19.7. One way analysis of variance showed Group 5 (60 year olds) to have significantly greaterk′ than 20, 30, 40 and 50 year olds (P=0.000). A slight downward shift in the contrast sensitivity function was seen over the age of 45. Significant differences between older and younger subjects were found at spatial frequencies of 3, and 10 cpd (P=0.081,P=0.002, respectively). Pupil diameter was found to reduce with age, but there was no significant difference between groups. Therefore, above 45 years, the ageing eye reveals a more rapid increase in forward scatter, and a reduction in contrast sensitivity, despite apparently good visual acuity.

Acquired colour vision defects in glaucoma-their detection and clinical significance.

Colour vision defects associated with ocular disease have been reported since the 17th century. Kollner1 in 1912 wrote an acute description of the progressive nature of colour vision loss secondary to ocular disease, dividing defects into “blue-yellow” and “progressive red-green blindness”.2 This classification has become known as Kollners rule, although it is often imprecisely stated as “patients with retinal disease develop blue-yellow discrimination loss, whereas optic nerve disease causes red-green discrimination loss”. Exceptions to Kollners rule3 4 include some optic nerve diseases, notably glaucoma, which are primarily associated with blue-yellow defects, and also some retinal disorders such as central cone degeneration which may result in red-green defects. Indeed, in some cases, there might be a non-specific chromatic loss. Colour vision defects in glaucoma have been described since 18835 and although many early investigations indicated that red-green defects accompanied glaucomatous optic neuropathy,1 later studies suggested that tritan defects predominate.6-9 This change of view largely reflected improved experimental design over time—in early studies no distinction was made between the various types of glaucoma, nor was any allowance usually made for the age distribution of subjects in the sample. A summary of the early research can be found in Drance et al .7 Although modern studies control for confounding factors such as increasing lens density and decreasing pupil size with age, some controversy still surrounds the nature of colour vision defects in primary open angle glaucoma (POAG). Comparing previous research evaluating chromatic discrimination in POAG is complicated by wide variations in methodology and experimental conditions. In recent years, computer generated colour tests have provided the means for isolating the processing of chromatic signals from the accompanying achromatic cues.10-15 In these tests, typically, the subject is asked to report the presence of a coloured target such …

Image processing of computerised visual field data.

BACKGROUND--Computerised perimetry is of fundamental importance in assessing visual function. However, visual fields are subject to patient response variability which limits the detection of true visual loss. METHODS--A method of improving the repeatability of visual field data was demonstrated by applying techniques used in image processing. An illustrative sample of nine normals and nine patients with field loss was used. Two successive Humphrey fields were selected for each subject. Repeatability was defined as the standard deviation of the pointwise differences between sensitivity values of the reference field and repeat field. The field data were then separately subjected to Gaussian and median image processing filters and the repeatability was compared with the unprocessed field results. RESULTS--Improvement in repeatability, by a factor of approximately 2, was demonstrated by both processes. CONCLUSION--These techniques may improve the reliable detection of loss of visual function using computerised perimetry.

Improving the Prediction of Visual Field Progression in Glaucoma Using Spatial Processing

PURPOSE The authors show how the predictive performance of a method for determining glaucomatous progression in a series of visual fields can be improved by first subjecting the data to a spatial processing technique. METHOD Thirty patients with normal-tension glaucoma, each with at least ten Humphrey fields and 3.5 years of follow-up, were included. A linear regression model of sensitivity against time of follow-up determined rates of change at individual test locations over the first five fields (mean follow-up 1.46 years; standard deviation = 0.08) in each field series. Predictions of sensitivity at each location of the field nearest to 1 and 2 years after the fifth field were generated using these rates of change. Predictive performance was evaluated by the difference between the predicted and measured sensitivity values. The analysis was repeated using the same field data subjected to a spatial filtering technique used in image processing. RESULTS Using linear modeling of the unprocessed field series, at 1 year after the fifth field, 72% of all predicted values were within +/- 5 dB of the corresponding measured threshold. This prediction precision improved to 83% using the processed data. At the 2-year follow-up field, the predictive performance improved from 56% to 73% with respect to the +/- 5 dB criterion. CONCLUSIONS Predictions of visual field progression using a pointwise linear model can be improved by spatial processing without increased cost or patient time. These methods have clinical potential for accurately detecting and forecasting visual field deterioration in the follow-up of glaucoma.

Measuring clinical practice

The goals of this paper are to review techniques for measuring clinical practice within healthcare professions and to discuss possible applications of these techniques to primary care optometry. A review of the literature suggests a lack of systematic research investigating standards of clinical practice within optometry. It is argued that evidence‐based research to determine the content of typical optometric eye examinations would be valuable for several reasons: to evaluate the service provided to the public by the profession; setting priorities and assessing the outcomes of continuous education and training; to influence governmental and professional policy decisions; National Health Service General Ophthalmic Services issues; the equitable management of clinicolegal matters and consumer complaints; setting appropriate professional guidelines and developing undergraduate training. Evidence‐based studies within other healthcare professions have evaluated the content of clinical consultations. The literature reviewed reveals three main approaches: (1) abstraction of medical records, (2) use of clinical vignettes and (3) use of standardized patients (SPs) who present unannounced to clinics. In this review, we compare and contrast the use of these different methods in assessing the content of clinical consultations. It is clear from the literature reviewed that the use of SPs is the ‘gold standard’ methodology. Clinical vignettes can also provide useful data, especially if computerized.

Comparison of the effectiveness of two enhanced glaucoma referral schemes

Citation information: Parkins DJ & Edgar DF. Comparison of the effectiveness of two enhanced glaucoma referral schemes. Ophthalmic Physiol Opt 2011, 31, 343–352. doi: 10.1111/j.1475‐1313.2011.00853.x

A national survey of diagnostic tests reported by UK community optometrists for the detection of chronic open angle glaucoma

Citation information: Myint J, Edgar DF, Kotecha A, Murdoch IE & Lawrenson JG. A national survey of diagnostic tests reported by UK community optometrists for the detection of chronic open angle glaucoma. Ophthalmic Physiol Opt 2011, 31, 353–359. doi: 10.1111/j.1475‐1313.2011.00844.x

Nonlinear behavior of certain optic nerve head parameters and their determinants in normal subjects

OBJECTIVE To investigate the relationship between the absolute area of certain optic disc parameters and a number of ocular dimensional characteristics and demographic factors in young, healthy subjects. DESIGN Cross-sectional study. PARTICIPANTS One hundred twenty-one subjects, aged 16.5 to 35.4 years participated, encompassing a wide range of refractive error from +4 diopters (D) to -25.75 D. One eye from each subject was randomly selected for examination. MAIN OUTCOME MEASURES Absolute size of the optic disc parameters: optic disc area (DA), neuroretinal rim area (NRA), optic cup area (CA), and peripapillary atrophy area (PA). METHODS Absolute sizes of optic disc parameters were determined from digitized photographic color transparencies, taking into consideration the magnification of the fundus camera and human eye. Relationships between the absolute size of the optic disc features and axial length, crystalline lens thickness, anterior chamber depth, ocular refraction, front surface keratometry, age, and gender were examined. RESULTS Axial length, lens thickness, front surface keratometry, and age demonstrated positive associations with all optic disc parameters, and anterior chamber depth and ocular refraction demonstrated negative associations in all cases. Multiple regression analysis revealed that the associations observed univariately for age, anterior chamber depth, lens thickness, front surface keratometry, and ocular refraction were confounded by axial length for all disc parameters. After taking logs, DA and NRA exhibit an exponential relationship with axial length, whereas PA and CA exhibit a linear relationship with axial length. DA and NRA increase by approximately 3% per millimeter increase in axial length at 20 mm and up to 40% for DA and 50% for NRA at an axial length of 35 mm. PA and CA are estimated to increase by 26% (10%-44%) and 10% (5%-16%), respectively, per millimeter increase in axial length. Females have approximately 5% smaller DA and 7% smaller NRA than males, but these effects are not statistically significant (P > 0.2). From the multiple regression analysis, females have 31% larger optic cup areas (1%-57%, P = 0.03) and 24% smaller PA (42% smaller to 5% larger P = 0.06) than males, but these effects are of borderline statistical significance at 5%. CONCLUSIONS Of the ocular biometric factors considered, axial length seems to be the most important predictor of the absolute area of the optic disc parameters. No association exists between any disc parameter and age in this sample of subjects less than 40 years of age. Females exhibited smaller values for DA, NRA, and PA than did males, differences that were not statistically significant, and larger CA (P = 0.03).