ISSN:0093-7002    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

The optical characteristics of the vertebrate crystalline lens are reviewed in terms of environmental concerns and spherical aberration. Lens shape and relative size are determined by such factors as whether the eye is to be used in air or water and whether it is to be used under scotopic or photopic conditions. The continued growth of the lens through life can be related to whether the lens exhibits positive or negative spherical aberration. In general, spherical aberration, as measured using a split laser beam method with excised lenses, is minimized in species with life histories indicating superior resolution ability. In addition, lens optical quality, as indicated by zonular differences in focal length, deteriorates with lens age. Finally, the measurement of spherical aberration may be used to monitor lens integrity during lens culture experiments.

ISSN:0093-7002    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

The visual evoked potential (VEP) in four rhesus monkeys was used to assess the transient loss of visual function resulting from single 100-ms argon laser flashes (476.5 and 514.5 nm) whose energy levels did not exceed the maximum permissible exposure (MPE). VEP's were elicited by high-contrast square-wave test gratings which were phase-reversed at a frequency of 6 Hz, and were recorded using bipolar electrodes implanted in the foveal projection region of area 17. The parameters which were investigated included (1) flash size (focused vs. expanded), (2) position of the electrode's receptive field relative to the position of the flash (0, 1.5, 3.0, and 4.5-deg separation), (3) flash exposure level (50, 5.0, and 0.5% of the MPE), (4) peak wavelength of the test grating (454, 540, and 630 nm), and (5) spatial frequency of the test grating (1.0, 4.0, 6.0, and 12.0 c/deg). The results of the flash-size experiment revealed that the expanded flash, whose retinal diameter was approximately 750 μm, eliminated or severely attenuated the VEP for a longer duration than did the focused flash and also resulted in a more gradual recovery function. The combined results of the flash position and energy level experiments indicated that the effective energy of the focused flash declined rapidly beyond 1.5 deg, but still approximated 4% of its maximum value as far as 4.5 deg from its center. Few, if any, wavelength-specific effects were observed after exposure to either the 476.5− or 514.5-nm flashes, even when the energy of the flashes was reduced to a small fraction of the MPE. Finally, the flash effect was considerably longer in duration for the 12.0 c/deg grating relative to the low and intermediate frequency gratings. In general, the findings suggest that the focused and expanded argon laser flashes produce a VEP suppression whose time course and other characteristics correlate well with those associated with behaviorally observed flash-blindness in humans after exposure to intense noncoherent flashes.

ISSN:0093-7002    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

Mass should be considered as one of several clinically malleable physical properties of contact lens materials. Lenses with identical posterior surface designs and back vertex powers may have different front surface parameters and thicknesses when manufactured from materials of several refractive indices. Change in anterior surface design affects overall lens volume, which combines with differences in specific gravity to change overall lens weight or mass. Clinicalin situcontact lens performance may be affected in many ways by changes in anterior surface profile, volume, and overall mass, although back surface design and effective power is held constant. This study presents methodology for comparing the predicted mass of specific lens designs made from different rigid lens materials. Both theoretical and sample values are presented and discussed. Results suggest that specific gravity by itself may be a good clinical guide to the relative mass of identically designed lenses made of different materials. However, as lens mass can affect lens performance in several ways, it might be worthwhile for the clinician and/or manufacturer to develop methods whereby such calculations were automatically provided in each individual situation.

ISSN:0093-7002    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

The spectral transmittances of a sample group of tinted hydrogel contact lenses were analyzed to assess the reproducibility of tinted lenses of a given density. Transmittance data were used to assess permanency of the tint after a 14-day cycle of daily cleaning, sterilization, and storage using a variety of cleaning and sterilization treatments.One-way analysis of variance of the transmittance data has demonstrated significant variations in the density of tint for Cibasoft lenses of a given color and density. However, these variations are smaller than the manufacturer's stated criterion for acceptable differences in tint density at a given tint level, i.e., light, medium, or dark. The Cibatint is stable when the lenses are cleaned with the Septicon and Miraflow systems. However, tinted hydrogel lenses from other manufacturers demonstrated changes of tint which were dependent upon the cleaning and sterilization methods used.

ISSN:0093-7002    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

Evoked cortical potentials produced by flash pattern stimulation contain contrast- and luminance-dependent components. In order to elicit contrast-specific responses, reversing checkerboards used to elicit steady-state visually evoked responses (VER's) are designed to have luminance changes in adjacent checks that are equal and opposite so that the net change in the overall checkerboard luminance is zero. Data are presented which demonstrate that commercially available, electronically generated reversing checkerboards on television monitors may contain luminance artifacts sufficiently large to elicit flicker VER's closely resembling genuine contrast VER's. These hidden luminance contaminants may result in erroneous conclusions when assessing visual mechanisms or function.

ISSN:0093-7002    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

Restricted viewing time has previously been shown to produce a tritan classification for color normal observers on the City University Colour Vision Test (CUCVT). The present investigation, which uses the Moreland anomaloscope, studies the effect of restricted viewing time on mid-match point (MMP). It shows that a color normal observer requires more green in a match under these conditions. A study of the Rayleigh equation using the Pickford Nicolson anomaloscope shows that restricted viewing time does not affect the MMP for this metameric match for color normal observers.

ISSN:0093-7002    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

The purpose of this study was to assess (1) the clinical value of the standard Frisby stereotest with young children, and (2) the effects of modifying the standard Frisby to a two-item, forced-choice format. A description of the modified test is presented along with data that indicate (1) the standard Frisby and Random-Dot E (RDE) stereotests are appropriate for children as young as age 30 months; (2) both instruments yield similar results; and (3) the modified two-item Frisby extends the applicability of the test to even younger and/or less communicative children.

ISSN:0093-7002    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

There are a great number of causes of dislocated lenses. One such cause is the spontaneous dislocation of a mature or hypermature cataractous lens. The case of an 80-year-old black female with spontaneously dislocated lenses is reported. Because the woman was not aphakic from surgery, but rather from spontaneous dislocation of her lenses, she was not eligible for eyeglasses from Medicare.

ISSN:0093-7002    

出版商:OVID    

年代:1985

数据来源: OVID

ISSN:0093-7002    

出版商:OVID    

年代:1985

数据来源: OVID