Catharine M. Chisholm

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.

Cross-sectional sample of peripheral refraction in four meridians in myopes and emmetropes.

PURPOSE The study of peripheral refractive error is of growing interest as degradation of the retinal image quality in the periphery is known to affect central refractive error development and ocular shape in animal models. The purpose of this study was to measure peripheral refraction across the horizontal, vertical, and two oblique meridians in a group of myopic and emmetropic adults and to investigate retinal asymmetry in the human retina. METHODS Thirty-one myopes (spherical equivalent between -2.00 and -9.62 D) and 20 emmetropes (spherical equivalent between -0.50 and +0.50 D) with astigmatism less than -0.75 D, participated in the project. Noncycloplegic peripheral refraction measurements were captured with an autorefractor (NVision K-5001; Shin-Nippon, Tokyo, Japan) at the fovea and up to 30° eccentricity in the horizontal, vertical, and two oblique meridians in 10° steps. RPR was calculated by subtracting the foveal spherical equivalent refraction from that obtained at each eccentric location. RESULTS Along all measured meridians, myopic eyes showed a relative hyperopic shift in the periphery, with the superior-temporal portion of the retina exhibiting the smallest shift. Emmetropic eyes, however, exhibited a relatively consistent refractive profile across all meridians and eccentricities, confirming a spherical retinal shape for this group. In addition, off-axis astigmatism increased with eccentricity in all meridians. CONCLUSIONS These results suggest that the myopic eye tends toward an ellipsoid shape, rather than the globular shape of an emmetropic eye.

Assessing visual fields for driving in patients with paracentral scotomata

Background: The binocular Esterman visual field test (EVFT) is the current visual field test for driving in the UK. Merging of monocular field tests (Integrated Visual Field, IVF) has been proposed as an alternative for glaucoma patients. Aims: To examine the level of agreement between the EVFT and IVF for patients with binocular paracentral scotomata, caused by either ophthalmological or neurological conditions, and to compare outcomes with useful field of view (UFOV) performance, a test of visual attention thought to be important in driving. Methods: 60 patients with binocular paracentral scotomata but normal visual acuity (VA) were recruited prospectively. Subjects completed and were classified as “pass” or “fail” for the EVFT, IVF and UFOV. Results: Good agreement occurred between the EVFT and IVF in classifying subjects as “pass” or “fail” (kappa = 0.84). Classifications disagreed for four subjects with paracentral scotomata of neurological origin (three “passed” IVF yet “failed” EVFT). Mean UFOV scores did not differ between those who “passed” and those who “failed” both visual field tests (p = 0.11). Agreement between the visual field tests and UFOV was limited (EVFT kappa = 0.22, IVF kappa 0.32). Conclusions: Although the IVF and EVFT agree well in classifying visual fields with regard to legal fitness to drive in the UK, the IVF “passes” some individuals currently classed as unfit to drive due to paracentral scotomata of non-glaucomatous origin. The suitability of the UFOV for assessing crash risk in those with visual field loss is questionable.

Off-axis partial coherence interferometry in myopes and emmetropes

This study describes the axial and peripheral dimensions of myopic and emmetropic eyes in a wide range of retinal locations using a non‐contact optical biometer (Zeiss IOLMaster) based upon the principle of partial coherence interferometry. Understanding the optical properties of the peripheral eye may provide insight into myopia development and the possible effects on off‐axis visual performance.

Driving with homonymous visual field loss: Does visual search performance predict hazard detection?

Introduction Stroke often causes homonymous visual field loss, which can lead to exclusion from driving. Retention of a driving licence is sometimes possible by completing an on-road assessment, but this is not practical for all. It is important to find simple tests that can inform the assessment and rehabilitation of driving-related visual-motor function. Method We developed novel computerised assessments: visual search; simple reaction and decision reaction to appearing pedestrians; and pedestrian detection during simulated driving. We tested 12 patients with stroke (seven left, five right field loss) and 12 controls. Results The homonymous visual field defect group was split into adequately compensated or inadequately compensated groups based on visual search performance. The inadequately compensated group had problems with stimuli in their affected field: they tended to react more slowly than controls and in the driving task they failed to detect a number of pedestrians. In contrast, the adequately compensated group were better at detecting pedestrians, though reaction times were slightly slower than controls. Conclusion We suggest that our search task can predict, to a limited extent, whether a person with stroke compensates for visual field loss, and may potentially identify suitability for specific rehabilitation to promote return to driving.

The effect of instrument alignment on peripheral refraction measurements by automated optometer

Citation information: Ehsaei A, Chisholm CM, Mallen EAH & Pacey IE. The effect of instrument alignment on peripheral refraction measurements by automated optometer. Ophthalmic Physiol Opt 2011, 31, 413–420. doi: 10.1111/j.1475‐1313.2011.00838.x

Central and peripheral visual performance in myopes: Contact lenses versus spectacles

PURPOSE Myopia is known to degrade visual performance with both optical and retinal changes implicated. Whether contact lenses or spectacles provide better visual performance for myopes is still under debate. The purpose of this study was to examine central and peripheral visual function in myopic subjects corrected with contact lenses versus spectacles. METHODS Size thresholds were measured at 13 locations for 20 myopic subjects (mean spherical equivalent refractive error (SE): -6.43±1.22 D and cylinder power: -0.23±0.22 D) corrected with contact lenses (new etafilcon A contact lens, fitted 15 min prior to measurements) versus spectacles. Measurements were taken at both low (δl/l=14%) and high (δl/l=100%) contrast levels. The data were analysed using one way repeated-measures ANOVA. RESULTS Size thresholds increased with eccentricity in a similar manner for both forms of optical correction. Repeated-measures ANOVA showed no statistically significant difference in central and peripheral visual performance between the two forms of correction for both low and high contrast tasks. The outcome remained the same following correction for spectacle magnification. CONCLUSION Eye care practitioners can be confident that modern soft contact lenses do not impair visual performance compared to spectacle lenses for the majority of myopes.

Addressing inequalities in eye health with subsidies and increased fees for General Ophthalmic Services in socio-economically deprived communities: a sensitivity analysis

OBJECTIVES Poor knowledge of eye health, concerns about the cost of spectacles, mistrust of optometrists and limited geographical access in socio-economically deprived areas are barriers to accessing regular eye examinations and result in low uptake and subsequent late presentation to ophthalmology clinics. Personal Medical Services (PMS) were introduced in the late 1990 s to provide locally negotiated solutions to problems associated with inequalities in access to primary care. An equivalent approach to delivery of optometric services could address inequalities in the uptake of eye examinations. STUDY DESIGN One-way and multiway sensitivity analyses. METHODS Variations in assumptions were included in the models for equipment and accommodation costs, uptake and length of appointments. The sensitivity analyses thresholds were cost-per-person tested below the GOS1 fee paid by the NHS and achieving break-even between income and expenditure, assuming no cross-subsidy from profits from sales of optical appliances. RESULTS Cost per test ranged from £ 24.01 to £ 64.80 and subsidy required varied from £ 14,490 to £ 108,046. Unused capacity utilised for local enhanced service schemes such as glaucoma referral refinement reduced the subsidy needed. CONCLUSIONS In order to support the financial viability of primary eye care in socio-economically deprived communities, income is required from additional subsidies or from sources other than eye examinations, such as ophthalmic or other optometric community services. This would require a significant shift of activity from secondary to primary care locations. The subsidy required could also be justified by the utility gain from earlier detection of preventable sight loss.

Occupational colour vision requirements for police officers

Inclusion of public service professions in the UK Disability Discrimination Act in 2004 prompted a review of occupational colour vision requirements for police officers. Changes in the regulations which existed prior to 2003 were proposed. The aim of this study was to obtain the views of serving police officers in Northern Ireland on the importance of good colour discrimination in everyday police work and on the recruitment regulations for patrol constables introduced in 2003 in mainland UK. These views were obtained by means of a questionnaire and informal discussions. More than 65% of police officers who responded to the questionnaire considered that good colour vision was very important for effective policing. Fewer than 2% considered that colour vision was unimportant. Experienced police officers agreed that the employment of colour‐deficient patrol constables, as permitted in the new regulations, would lead to reduced efficiency and organisational difficulties at the local level. A number of everyday activities were described which showed the need for accurate colour discrimination. The change in recruitment policy and the lack of clarity in the new regulations show inadequate appreciation of the needs of the occupation, of different types of colour vision anomalies and of the diagnostic function of colour vision tests. Failure to provide guidance on appropriate colour vision tests, examination procedures and counselling services is likely to result in inconsistent employment policies in different police forces. It is recommended that the colour vision standard in place prior to 2003 is reinstated at the recruitment stage. The Ishihara test should be used for screening, and colour‐deficient applicants further examined with the Farnsworth D15 test as a replacement for the City University Test 2nd edition.

Distance and near visual performance in pseudophakic eyes with simulated spherical and astigmatic blur.

Increased depth‐of‐focus after cataract surgery is dependent on various ocular characteristics, including refractive astigmatism. This work studied the influence of meridional blur produced by astigmatism, and spherical blur, on distance and near visual performance in pseudophakic eyes.