摘要:

Purpose.The purpose of this investigation was to determine whether new experimental multifocal optical designs incorporating diffractive/refractive optics for correction of presbyopia in a soft contact lens would compromise binocular contrast sensitivity at distance while achieving 20/20 binocular visual acuity at near.Methods.Thirty presbyopic volunteers were fitted with Acuvue Bifocal soft lenses, two (FO1 and 3B1) experimental diffractive/refractive multifocal soft lenses separately and in combination as a pair and soft spherical lenses. Visual performance was evaluated via binocular contrast sensitivity and binocular distance high- and low-contrast visual acuity after 1 week of lens wear.Results.The experimental lenses FO1 and the combination FO1/3B1 performed as well for binocular contrast sensitivity, binocular distance high-contrast visual acuity, and binocular distance low-contrast visual acuity as the habitual presbyopic correction and the spherical soft distance correction. A strong correlation (r = 0.73 and 0.53, respectively) was found between binocular contrast sensitivity and binocular distance low-contrast visual acuity with experimental FO1 and FO1/3B1 lenses. However, the correlation (r = 0.37 and 0.60, respectively) between binocular contrast sensitivity and binocular distance high- and low-contrast visual acuity with FO1 was weaker than that with the combination FO1/3B1 lenses. Subjective responses support the objective data.Discussion.The data show that experimental FO1 lens and the experimental combination of the FO1/3B1 lenses can be prescribed to not compromise distance binocular contrast sensitivity.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Background.Crossing the street is a complex task that involves gathering, processing, and acting on information that is time dependent. The gaze behavior of subjects has been previously studied on increasingly complex and dynamic tasks such as making tea, walking indoors, and driving. The purpose of this study was to assess how normally sighted people use their vision to cross a street safely. Specifically, we identified the environmental features people look at when crossing two types of intersections.Method.We measured the eye movements and head directions of 12 normally sighted people as they approached, evaluated, and crossed a light-controlled “plus” intersection and a roundabout. The primary measures were percentage of fixations and head direction.Results.Crossing the street can be divided into three phases, walking to the curb, standing at the curb, and crossing the street. We found that while moving, subjects fixated primarily on crossing elements and when standing at the curb, they fixated primarily on vehicles. At the plus intersection, fixation behavior corresponded with crossing strategy; the subjects who crossed early fixated on cars, and the subjects who waited for the light to change fixated on traffic controls. At the roundabout, all subjects determined an appropriate time to cross from vehicular traffic flow by directing the majority of their fixations on cars. When moving, the head position of subjects was predominately centered. Subjects also made head turns in both directions before crossing and directed the head toward the danger zone while crossing.Conclusion.Crossing the street is a complex task that can be described in three phases. Common head and eye behaviors were found near the critical moments of crossing the street. Fixation behavior was closely related to street crossing behavior.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Purpose.The Scheimpflug principle, as a method of performing biometry on the anterior segment, has not been widely used in the clinical setting compared with ultrasonography. The purpose of this study was to examine the agreement in anterior chamber length and lens thickness measurements between A-scan ultrasonography and Scheimpflug photography.Methods.A total of 252 children aged between 6 and 12 years participated in this study. All subjects had instillation of cycloplegic eye drops before measurement. Scheimpflug photography and A-scan ultrasonography were performed in this sequence on the same day. The anterior segment length on the Scheimpflug images was taken as the axial corneal thickness added to the anterior chamber depth. A-scan ultrasonography was performed by placing the probe on the corneas after topical anesthesia. Differences were obtained by subtracting the A-scan ultrasonography measurements from the Scheimpflug measurements. Data were analyzed using difference vs. mean plots.Results.For anterior chamber length, the mean difference between the two methods was −0.03 ± 0.16 mm, with 95% limits of agreement of −0.35 to +0.30 mm. However, Scheimpflug readings were greater than that of ultrasonography for smaller measurements, and the opposite was true for larger measurements. For lens thickness, the mean difference was −0.2 ± 0.10 mm, with 95% limits of agreement of −0.40 to +0.00 mm. For the measurement of lens thickness, adding a correction factor of 0.2 mm to Scheimpflug’s readings should replace that of A-scan readings reasonably well.Conclusions.The readings obtained from these two methods of biometry must be used with the knowledge of the instruments. We discuss the possible reasons for the difference in readings obtained using these two instruments.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Background.Subjects with absolute central visual field loss use eccentric fixation and magnifying devices to utilize their residual vision. This preliminary study investigated the importance of an accurate eccentric correction of off-axis refractive errors to optimize the residual visual function for these subjects.Methods.Photorefraction using the PowerRefractor instrument was used to evaluate the ametropia in eccentric fixation angles. Methods were adapted for measuring visual acuity outside the macula using filtered optotypes from high-pass resolution perimetry. Optical corrections were implemented, and the visual function of subjects with central visual field loss was measured with and without eccentric correction.Results.Of the seven cases reported, five experienced an improvement in visual function in their preferred retinal locus with eccentric refraction.Conclusions.The main result was that optical correction for better image quality on the peripheral retina is important for the vision of subjects with central visual field loss, objectively as well as subjectively.

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