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At least 901 records · Page 50Linked to original sources
PubMed1997

Is myopia related to amplitude of accommodation?

PURPOSE: To report the association between amplitude of accommodation and refractive error. METHODS: Refractive error and amplitudes of accommodation were measured in 1,148 eyes of 696 patients as part of the Early Treatment Diabetic Retinopathy Study. RESULTS: Eyes with myopia, defined as those with a refractive error of -0.75 diopter or more, have lower accommodative amplitudes (P = .005). After multivariate logistic regression analysis adjusting for age, occupation, and white race, lower amplitudes of accommodation remained associated with myopia (P = .03). CONCLUSIONS: Eyes with lower amplitudes of accommodation must use more of their accommodative reserve for near work. Myopia may be an adaptation that develops in eyes with reduced accommodative amplitudes.

Accommodation, Ocular↗
PubMed2003

Recovery of the rod photoresponse in infant rats.

We tested the hypothesis that the kinetics of recovery of the rod photoresponse differ between mature and immature rods. A paired flash paradigm was used. The effect of a test flash on the ERG a-wave response to a probe flash presented 60 to 2 s after the test flash was studied. The functions summarizing the interaction between the test and probe flash did not differ significantly between infants and adults if the stimuli were equated for estimated proportion of rhodopsin isomerized/rod/flash. The kinetics of rod cell recovery are likely the same in infants and adults.

Adaptation, Ocular↗
PubMed2006

Cone phototransduction and growth of the ERG b-wave during light adaptation.

The purpose of this study was to determine whether cone redepolarization accounts for the amplitude increase of the b-wave of the human electroretinogram (ERG) during light adaptation. The time course of the b-wave amplitude increase was compared to the time course of the change in the activation phase of cone phototransduction, as derived from a delayed Gaussian model applied to the leading edge of the ERG a-wave. ERG recordings were obtained from five visually normal subjects, alternately in the presence of the adapting field (adapt-on condition) and 300ms after its temporary extinction (adapt-off condition). The proportional increase in amplitude was less for R(mp3) (maximum amplitude of P3, the massed cone photoreceptor response) than for the b-wave for both adaptation conditions, and the time course of the amplitude increase for R(mp3) was faster than that for the b-wave in the adapt-off condition. The results demonstrate that time-dependent changes in the activation phase of cone phototransduction have only a minimal role in governing the increase in the amplitude of the human cone-derived ERG b-wave during light adaptation. In addition, the systematic increase in b-wave amplitude and the decrease in b-wave implicit time in the adapt-off condition indicates that the ERG response measured shortly after adapting field offset does not necessarily represent the waveform of the dark-adapted cone ERG.

Adaptation, Ocular↗
PubMedDate not supplied

Noise and light adaptation in rods of the macaque monkey.

Membrane voltage was recorded in rod photoreceptors in retina isolated from macaque monkey. The size of the single photon response and the magnitude of membrane voltage fluctuations were assessed in dark- and light-adapted retina. The "dark light" rate I(D), defined as the rate of spontaneous photopigment isomerizations that would produce a variance equivalent to that of the noise measured in the dark, was calculated after matched filtering. The average value of 0.08 s(-1) fell at the higher end of psychophysical estimates of dark light in human observers. In light-adapted rods the photon response decreased in amplitude and duration, and the magnitude of the voltage fluctuations increased with increasing background light intensity. The signal-to-noise ratio (SNR) for single rods was defined as the ratio of the peak amplitude of the photon response to the standard deviation of the noise fluctuations. The signal-to-noise ratio for dark-adapted rods SNR(D) was about 7. With increasing background intensity I, the SNR fell as SNR(D)(1 + I/I(D))(-1/2). This function may account for the increment thresholds measured with small brief test flashes in human psychophysical experiments.

Adaptation, Ocular↗
PubMed1999

Electroretinographic profile in emmetropic Singaporean eyes.

OBJECTIVES: To characterise the electroretinographic (ERG) profile in 70 Singaporean emmetropic eyes. METHOD: Seventy eyes of thirty-five patients with refractive error of -1.00D or less and with a normal ophthalmic examination were chosen. They were subjected to three flash patterns generated with a Nihon-Kohden Flash Stimulator. The results were captured on a Nihon-Kohden Neuropack 8. RESULTS: The mean age of the patients was 25 years (range 20 to 30). The mean spherical refractive error was -0.3D (range 0D to -1.00D). For the scotopic dim flash, the mean amplitude for the 'b' wave was 304.6 +/- 69.2 mu v (range 175 mu v to 469 mu v) and the mean latency was 47.56 +/- 4.87 ms (range 41.2 ms to 62.0 ms). For the scotopic bright flash, the mean amplitude for the 'b' wave was 469.54 +/- 127.15 mu v (range 257 mu v to 750 mu v) and the mean latency was 40.54 +/- 3.91 ms (range 32.0 ms to 48.9 ms). In the flicker response, the mean amplitude for the 'b' wave was 34.19 +/- 12.97 mu v (range 14 mu v to 64 mu v) with mean latency at 34.46 +/- 0.58 ms (range 33.1 ms to 35.9 ms). CONCLUSION: With ERG normal values so generated, comparisons with these can then be made for abnormal cases.

Adaptation, Ocular↗
PubMed1995

Short-term adaptation of the phase of the vestibulo-ocular reflex (VOR) in normal human subjects.

We investigated the effects of short-term vestibulo-ocular reflex (VOR) adaptation on the gain and phase of the VOR, and on eccentric gaze-holding in darkness, in five normal human subjects. For 1 h, subjects sat in a chair that rotated sinusoidally at 0.2 Hz while surrounded by a visual stimulus (optokinetic drum). The drum was rotated relative to the chair, to require a VOR with either a phase lead or lag of 45 deg (with respect to a compensatory phase of zero) with no change in gain, or a gain of 1.7 or 0.5 with no change in phase. Immediately before and after each training session, VOR gain and phase were measured in the dark with 0.2 Hz sinusoidal rotation. Gaze-holding was evaluated following 20 deg eccentric saccades in darkness. Adaptation paradigms that called only for a phase lead produced an adapted VOR with 33% of the required amount of phase change, a 20% decrease in VOR gain, and an increased centripetal drift after eccentric saccades made in darkness. Adaptation paradigms that called for a phase lag produced an adapted VOR with 29% of the required amount of phase change, no significant change in VOR gain, and a centrifugal drift after eccentric saccades. Adaptation paradigms requiring a gain of 1.7 produced a 15% increase in VOR gain with small increases in phase and in centripetal drift. Adaptation paradigms requiring a gain of 0.5 produced a 31% decrease in VOR gain with a 6 deg phase lag and a centrifugal drift. The changes in drift and phase were well correlated across all adaptation paradigms; the changes in phase and gain were not. We attribute the effects on phase and gaze-holding to changes in the time constant of the velocity-to-position ocular motor neural integrator. Phase leads and the corresponding centripetal drift are due to a leaky integrator, and phase lags and the corresponding centrifugal drift are due to an unstable integrator. These results imply that in the short-term adaptation paradigm used here, the control of drift and VOR phase are tightly coupled through the neural integrator, whereas VOR gain is controlled by another mechanism.

Adaptation, Psychological↗