To investigate the effect of visual field defects on driving performance, and to predict practical fitness to drive. Methods: The driving performance of 87 subjects with visual field defects due to ocular abnormalities was assessed on a driving simulator and during an on-road driving test. Outcome Measures: The final score on the on-road driving test and simulator indexes, such as driving speed, viewing behavior, lateral position, time-headway, and time to collision. Results: Subjects with visual field defects showed differential performance on measures of driving speed, steering stability, lateral position, time to collision, and time-headway. Effective compensation consisted of reduced driving speed in cases of central visual field defects and increased scanning in cases of peripheral visual field defects. The sensitivity and specificity of models based on vision, visual attention, and compensatory viewing efficiency were increased when the distance at which the subject started to scan was taken into account. Conclusions: Subjects with visual field defects demonstrated differential performance on several driving simulator indexes. Driving examiners considered reduced speed and increased scanning to be valid compensation for central and peripheral visual field defects, respectively. Predicting practical fitness to drive was improved by taking driving simulator indexes into account.

The RGS proteins are GTPase activating proteins that accelerate the deactivation of G proteins in a variety of signalling pathways in eukaryotes. RGS9 deactivates the G proteins (transducins) in the rod and cone phototransduction cascades. It is anchored to photoreceptor membranes by the transmembrane protein R9AP (RGS9 anchor protein), which enhances RGS9 activity up to 70-fold. If RGS9 is absent or unable to interact with R9AP, there is a substantial delay in the recovery from light responses in mice. We identified five unrelated patients with recessive mutations in the genes encoding either RGS9 or R9AP who reported difficulty adapting to sudden changes in luminance levels mediated by cones. Standard visual acuity was normal to moderately subnormal, but the ability to see moving objects, especially with low-contrast, was severely reduced despite full visual fields; we have termed this condition bradyopsia. To our knowledge, these patients represent the first identified humans with a phenotype associated with reduced RGS activity in any organ.

In a theoretical eye with spherical and aspheric surfaces, the retinal illumination is calculated if a Ganzfeld luminance field is used. The resulting retinal light distribution is nearly homogeneous over the whole retina. The homogeneity is not much influenced by the size of the optical surfaces. The corresponding retinal area and the luminous flux entering the eye are calculated as functions of the size of the visual field. The values of the length of the light path through the crystalline lens and of the angle of incidence on the retina are described as functions of the angle in the visual field.

We have examined the role of socio-demographic variables, cognitive and affective functioning, and personality in discrepancies between performance-based and self-report measures within three domains of physical limitations: motor functioning, hearing and vision. Data are drawn from a community-based sample of 624 persons of 57 years of age and older. The strength of the association between self-reported and performance-based levels of physical limitations is moderate. Socio-demographic variables and levels of cognitive functioning explained some of the discrepancies between self-reported and performance-based vision. Within the domains of motor functioning and hearing, discrepancies were substantially influenced by affective functioning and personality. The discrepancies may reflect bias in perception or true variation in the effect of limitations on daily functioning. Both self-report and performance-based measures seem to complement each other in providing useful information about physical limitations.

Practical fitness to drive was studied in 28 patients with homonymous hemianopia (HH). More specifically, visual performance during driving and neuropsychologica l visuospatial test performance were compared and related. Visuospatial tests were a priori classified in four visuospatial sets, and were evaluated on three measures, namely lateralisation, speed, and accuracy. Driving safety and fluency was assessed by means of a practical test-ride and scored using a structured protocol. It was concluded that HH cannot be considered a definite contraindication for holding a drivers' licence since not all patients failed the testride. The most frequent remark made by the driving expert was a lack of stability in steering. It was found that visual performance during driving was significantly related to visuospatial test performance, operationally defined as a function of typical visual HH disability. A specific combination of the lateralisation, speed and accuracy measures of the visuospatial sets explained 77% of the variance in visual performance during driving.