Training compensatory viewing strategies:feasiblity and effect on practical fitness to drive in subjects with visual field defects

Fifty-one subjects with visual field defects were trained to use compensatory viewing strategies.The subjects were referred to the training program by an official driving examiner of the Dutch Central Bureau of Driving Licenses. Three training programs were compared: laboratory training, mobility training, and motor traffic training. Viewing behavior, visual attention, and practical fitness to drive were assessed before and after training. Practical fitness to drive was assessed on the road as well as in a driving simulator. It was observed that compensatory viewing behavior and practical fitness to drive could be improved by training. Subjects in the motor traffic training showed a small advantage with regard to practical fitness to drive, suggesting that training is task-specific and that generalization is limited. The effect of visual field defect on viewing behavior and practical fitness to drive was analyzed separately for subjects with central or peripheral visual field defects. It was observed that none of the outcome measures differed between the central and peripheral visual field defect groups

Changes in spherical aberration after lens refilling with a silicone oil

PURPOSE. It may be possible to restore accommodation to presbyopic human eyes by refilling the lens capsular bag with a soft polymer. In the present study, optical changes were measured that occurred in a pig eye model after the refilling of the capsular bag. METHODS. The optical power and spherical aberration in 10 isolated pig lenses were measured under different conditions. They were first determined by using a scanning laser raytracing technique over an effective pupil size of 6 mm. Second, the contours of the anterior and posterior lens surface were photographed, and a mathematical ray-tracing was performed by using a polynomial fit through the digitized surface contours, to determine optical power and spherical aberration. Third. the lenses were refilled with a silicone oil until their preoperative lens thickness was reached, and scanning laser ray-tracing, contour photography, and mathematical ray-tracing were repeated. Comparisons between the measurements were made to determine how the change from a gradient refractive index to a homogeneous refractive index influenced spherical aberration. The influence of the change in lens contour on spherical aberration after lens refilling was also studied. RESULTS. The natural lenses had a higher lens power than the refilled lenses (49.9 +/- 1.5 D vs. 36.8 +/- 1.5 D; P <0.001). Moreover, there was a change in sign from negative spherical aberration before lens refilling (-3.6 D) to positive spherical aberration after lens refilling (7.9 D; P <0.001). The comparison between scanning laser ray-tracing of the natural lens and mathematical ray-tracing of the photographed surface contours of the natural lens to determine the effect of refractive index substitution (i.e., replacement of a gradient refractive index by a homogeneous refractive index) showed a significant change in spherical aberration from -3.6 +/- 2.0 to 11.0 +/- 2.1 D (P <0.001). The change in lens contour did not result in a significant change in spherical aberration (P = 0.08) before and after lens refilling with an equal refractive index. CONCLUSIONS. The lower lens power of refilled pig lenses compared to natural lenses was due to the lower refractive index of the refill material. Refilling pig lenses with the silicone oil used in this study resulted in an increase in spherical aberration. This increase was mainly caused by the change from a gradient refractive index to a homogeneous refractive index. The change in lens curvature after lens refilling did not result in an increase in spherical aberration. The influence of lens refilling on spherical aberration of human lenses must be determined in similar experiments in human eyes

Design and Evaluation of a Protocol to Assess Electronic Travel Aids for Persons Who Are Visually Impaired

This study evaluated a protocol that was developed to assess how beneficial electronic travel aids are for persons who are visually impaired. Twenty persons with visual impairments used an electronic travel device (Trekker) for six weeks to conform to the protocol, which proved useful in identifying successful users of the device.</p