摘要:

Temporal modulation transfer functions (MTF's) were recorded from the macula of nine normal subjects using focal electroretinography (FERG). An array of light emitting diodes (LED's) was used to experimentally manipulate stimulus temporal frequency, modulation depth, and mean luminance values. Two techniques were used to derive FERG modulation thresholds at several temporal frequencies: conventional averaging with extrapolation to a criterion amplitude, and a swept stimulus lock-in retrieval method. These two methods produced comparable results. The electrophysiologically derived MTF's were similar in shape to those obtained psychophysically. Six patients with retinal disease were also examined; all patients showed sensitivity losses which were most marked at the higher frequencies. Such losses tended to be greater in patients with poorer visual acuity.

ISSN:0093-7002    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

Age-related macular degeneration (AMD) is an important cause of vision loss among the elderly. Because patients with early subretinal neovascular membranes due to AMD can be treated by laser photocoagulation it becomes critical to find tests which can detect early changes. Inasmuch as AMD involves the retinal pigment epithelium, one might expect the electro-oculogram (EOG) to be sensitive to AMD pathology, but the ganzfeld EOG has been found to be normal in most cases. We designed a focal EOG apparatus to try to emphasize the contribution of the central retina, where AMD is found, to the EOG. Seventeen patients with various stages of drusen and AMD were tested and compared with normals. The focal EOG did not separate the AMD patients from the normals, nor did it give different distributions for the various subgroups of AMD. The focal EOG, like the ganzfeld EOG, is not a sensitive test for AMD.

ISSN:0093-7002    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

Contrast sensitivity functions (CSF's) were measured for a group of 6-month-old infants using the visual evoked potential (VEP). Sine-wave luminance gratings were counterphase modulated at 12 contrast reversals per s and simultaneously swept in contrast. Each contrast sweep lasted 10 s, spanning a range of 0.5 to 40% contrast in 19 equal logarithmic steps. The amplitude and phase of the response at the second harmonic were determined by a discrete Fourier transform. Contrast thresholds were estimated from a linear extrapolation to zero-amplitude of the VEP amplitude vs. log-contrast function. Contrast sensitivity was found to be nearly adult-like at 1 c/deg, but was not yet mature at higher spatial frequencies.

ISSN:0093-7002    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

It is generally believed that some degree of defective color vision is frequently acquired along with certain ocular and systemic disorders. Precise definition of the nature and extent of the color defects has not been possible because of the limitations inherent in the tests currently available for clinical use. We undertook to define the defects in terms of thresholds of discrimination to each color, plotted on a color circle similar to Munsell's uniform chromaticity scale diagram. Furthermore, we were able to construct a symmetrical-type of colorimeter which plots thresholds directly on a printed circle without having to read and interpret scales or dials. Good correlation of subtle defects with certain disorders was confirmed, and may eventually be helpful in diagnosing and following some types. This system of threshold measurement was found to provide more information about color vision than any one of the conventional tests, or all of them combined.

ISSN:0093-7002    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

Retinitis pigmentosa (RP) frequently leads to a decrease in cone system sensitivity. A number of alternative explanations have been proposed for this decrease. Based on the results of a psychophysical technique, the probe-flash paradigm, the authors suggest that a decrease in responsiveness of retinal elements can account for much of this loss. In this paper the decreased responsiveness hypothesis is tested by obtaining data at two levels of steady adaptation. The results of the study indicate that sensitivity loss is greater for the dark adapted than the light adapted state. The data rule out the decreased responsiveness hypothesis coupled with a simple model of adaptation. More complicated adaptation models cannot be excluded. The importance of considering models of adaptation when testing models of disease-related sensitivity loss is underscored.

ISSN:0093-7002    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

Application of computer digitizing methods to conventional kinetic visual field test data permits mathematical analysis of these data. In some cases this provides more information than is available by a simple inspection of the field charts. This is demonstrated by analysis of multiple isopter data for a patient with open-angle glaucoma and a patient with retinitis pigmentosa.

ISSN:0093-7002    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

Multi-flash campimetry is a computer-implemented technique used for the rapid assessment of temporal resolving power across the visual field. On the basis of previous reports that glaucoma patients exhibit impaired temporal sensitivity earlier than conventional per-imetric field loss, the question of whether multi-flash campimetry might also be sensitive to the visual consequences of glaucoma was explored. Of the 27 patients that were tested, only one had normal temporal resolving power in both eyes, suggesting that multi-flash campimetry might be a useful aid in determining whether a patient should be diagnosed and treated as a glaucoma suspect or as a confirmed glaucoma patient.

ISSN:0093-7002    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

The P-300 is a positive polarity electroencephalographic (EEG) signal occurring about 300 ms after a surprising, novel, or unique stimulus. The amplitude of the P-300 is dependent on the degree of attention and importance the subject has assigned to the stimulus and on its relative novelty. P-300 latency is dependent on the time it takes the subject to mentally process the stimulus and determine if the information it carries is novel. In Experiment I, the latencies of P-300's for 40 and 80 column size video display characters were compared. The effect of dioptric blur (mean add power +2.44 D) on latency was also determined. It was found that 40 column size characters could be interpreted more quickly than 80 column size characters and that blur increased the processing time equally for both character sizes. In Experiment II, P-300 latencies for green and amber display screens were compared. Display screen color did not significantly affect latency, neither did the addition of lens powers ranging from a mean of −1.15 D to a mean of +1.15 D over the subjects' habitual lenses. However, it was found that latencies significantly increased when a mean add of +2.29 D for the green display or a mean add of +2.57 D for the amber display were used. (Chromatic aberration accounted for the difference in lens power for the green vs. amber display.) These results demonstrate that character size and clarity are significant factors in determining the time required to mentally process a stimulus. They also demonstrate that there is no clear advantage to using an amber vs. a green screen when speed of mental processing (as measured by P-300 latency) is used as a criterion.

ISSN:0093-7002    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

Nonius horopter measurements were made on three normal subjects using both physically displaced (real viewing) and stereogrammetrically displaced (projected viewing) test objects. Three subjects with ocular anomalies were tested using the projected viewing arrangement with and without 5% overall magnifier before the right eye, and seven complete measurements of the projected viewing horopter were made on a fourth subject with an ocular anomaly over the period of 1 month. These latter individual plots showed large irregularities that changed location from day to day. Plotting the mean and standard error of the means of these seven sets of data produced a smoothing out of the horopter locus. Plotting each individual horopter setting in the sequence of measurement and monitoring eye position indicated that all of the irregularities and regional horopter changes found are most likely introduced by changes in fixation disparity (vergence eye movements).

ISSN:0093-7002    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

It is well-known that the accommodative response of the visual system to Snellen letters and other targets of wide spatial bandwidth becomes less accurate as the luminance is lowered from photopic to scotopic levels, a constant state of “night myopia” eventually being reached. The present study seeks to understand this behavior in terms of the responses to the single-frequency, sinusoidal grating, Fourier components of such targets, for a constant, 80% object modulation. The focal range over which sinusoidal gratings can be detected is first investigated as a function of grating frequency and luminance; this range diminishes as the luminance is lowered. These data are then related to measurements of the accommodative response to similar gratings in the mesopic luminance range (10−25to 10 cd/m2). The response is less accurate for gratings of low spatial frequency. It appears that, provided that any grating can be detected, changes in luminance generally have only a relatively small effect on the associated accommodative response. However, low spatial frequency gratings can be detected at much lower luminance levels than higher spatial frequency gratings. The effects observed with targets of wide spatial bandwidth may thus be largely ascribed to the inability of the visual system to use higher spatial frequency information as the luminance is lowered.

ISSN:0093-7002    

出版商:OVID    

年代:1986

数据来源: OVID