摘要:

Purpose.To compare measured visual field extent for a 6° stimulus (typical size used in studies of infants) with a 1.5° stimulus (similar to the largest size used in Goldmann perimetry) in young infants.Methods.A total of 120 infants (60 each at 3.5 months and 7 months of age) and 24 adults were tested monocularly with a kinetic perimetry procedure using a black double-arc perimeter. Each subject was tested with either a 6° or 1.5° white sphere, which was mounted on a black wand and moved smoothly toward the intersection of the perimeter arms at 3.4°/s. Visual field extent along each perimeter arm was defined as the median of 2 to 3 measurements of the position of the leading edge of the stimulus when the subject made an eye movement toward the stimulus.Results.The 6° stimulus produced larger measured visual field extent than the 1.5° stimulus in 3.5-month olds (temporal field only) and in 7-month olds (nasal and temporal field), but not in adults.Conclusions.Using the testing conditions of the present study, increasing stimulus size beyond the largest used in a Goldmann perimeter (∼2°) increases measured visual field extent in young infants, but not in adults. This may relate to differences in peripheral summation areas or to differences in attentional factors between infants and adults.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Purpose.To study the effect of coatings on the resistance of CR-39 industrial plano lenses to ballistic impacts and abrasion from fine particles.Methods.Twelve groups of CR-39 lenses with various scratch-resistant (SR) or combinations of scratch-resistant and antireflective (SR-AR) coatings were mounted in metal industrial spectacle frames. The ZEST protocol was used to determine the mean impact speed for breakage of each lens group using the Canadian Standards Association ballistic test protocol. One pair of lenses from each group was tested for abrasion resistance using the falling sand method. Abrasion resistance was ranked by the degree of haze observed by three independent observers.Results.Uncoated lenses had the best impact resistance and worst abrasion resistance. SR-coated lenses showed mild to moderate reductions in impact resistance, with no correlation between impact and abrasion resistance. SR-AR-coated lenses had very good abrasion resistance, but severely reduced impact resistance.Conclusions.Most SR-coated CR-39 lenses have a high probability of meeting the high-velocity impact resistance requirement of industrial lenses, whereas CR-39 lenses with SR-AR coats are too fragile to be used in industrial spectacles. As a group, the SR-AR coating tended to be more resistant to abrasion by fine particles and less resistant to ballistic impacts, but the abrasion resistance of the SR-coated lenses was more variable, and, thus, overall there was no significant correlation between impact resistance and abrasion resistance.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

During off-axis viewing through an anisometropic spectacle correction, the two eyes must diverge to fuse. This can cause great discomfort, especially in the vertical meridian. To consider a correction for the problem, one must know the amount of forced divergence induced by the spectacles. Because the eyes select ray entry points that do not coincide with the object point projections on the lens planes, the exact directions of gaze are difficult to determine with conventional ray-tracing methods. The methods previously developed for determining the visual directions of gaze through anisometropic spectacle corrections are limited to hypothetical thin lenses and require complicated trigonometric constructs that are not suitable for clinical work. A recently developed method for solving the problem applies the dynamic spectacle magnification to find the visual direction of an image of a given object point. The method, referred to as the theory of object and image eccentricities, is based on projections of object and image from the rotation center onto a common plane, such as the back vertex plane. The theory can be applied to many situations in ophthalmic optics previously difficult to analyze. It does not require ray tracing, and because it considers base curves and thickness, it is more accurate than previous methods. A major advantage is that it considers the two eyes as an integrated system rather than separately and in isolation from each other.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID