Purpose Fundus autofluorescence was quantified (qAF) in subjects with healthy retinae using a standardized approach. The objective was to establish normative data and identify factors that influence the accumulation of RPE lipofuscin and/or modulate the observed AF signal in fundus images. Methods AF images were acquired from 277 healthy subjects (age range: 5-60 years) by employing a Spectralis confocal scanning laser ophthalmoscope (cSLO; 488-nm excitation; 30°) equipped with an internal fluorescent reference. For each image, mean gray level was calculated as the average of eight preset regions, and was calibrated to the reference, zero-laser light, magnification, and optical media density from normative data on lens transmission spectra. Relationships between qAF and age, sex, race/ethnicity, eye color, refraction/axial length, and smoking status were evaluated as was measurement repeatability and the qAF spatial distribution. Results qAF levels exhibited a significant increase with age. qAF increased with increasing eccentricity up to 10° to 15° from the fovea and was highest superotemporally. qAF values were significantly greater in females, and, compared with Hispanics, qAF was significantly higher in whites and lower in blacks and Asians. No associations with axial length and smoking were observed. For two operators, between-session repeatability was ± 9% and ± 12%. Agreement between the operators was ± 13%. Conclusions Normative qAF data are a reference tool essential to the interpretation of qAF measurements in ocular disease.

/pdf/quantitative-fundus-autofluorescence-in-healthy-eyes-2z42pbc61z.pdf

Quantitative fundus autofluorescence in healthy eyes

The purpose of this study was to determine how responses in the normal human electroretinogram (ERG) change with subject age. We studied 62 children, 10 days to 15 years old, and 30 subjects 15–37 years old, using the standard protocol established by the International Society for Clinical Electrophysiology of Vision, with Burian-Allen bipolar contact-lens electrodes. We measured rod response, maximal response, oscillatory potentials (OPs), cone response, flicker response, and b-wave amplitude/log intensity (V/log I) curve. A logistic growth curve was used to describe the developmental changes. Dark- and light-adapted ERG a- and b-wave amplitudes reached adult levels by three to five years of age, although b-wave amplitudes of scotopic rod-mediated responses were slower to reach maturity than mixed rod-cone mediated responses. In early infancy OPs were the most immature of the ERG responses, although the rate of development thereafter exceeded that of the other responses such that OP amplitudes were within adult levels by two years of age. Amplitudes of the ERG responses in 21 children sedated with chloral hydrate did not differ significantly from 21 who had not been sedated. ERG responses developed at varying rates, reflecting different developmental stages in photoreceptors, middle retinal layers and more proximal retina.

Time courses for maturation of electroretinogram responses from infancy to adulthood

In visual masking, visible targets are rendered invisible by modifying the context in which they are presented, but not by modifying the targets themselves. Here I summarize a decade of experimentation using visual masking illusions in which my colleagues and I have begun to establish the minimal set of conditions necessary to maintain the awareness of the visibility of simple unattended stimuli. We have established that spatiotemporal edges must be present for targets to be visible. These spatiotemporal edges must be encoded by transient bursts of spikes in the early visual system. If these bursts are inhibited, visibility fails. Target-correlated activity must rise within the visual hierarchy at least to the level of V3, and be processed within the occipital lobe, to achieve visibility. The specific circuits that maintain visibility are not yet known, but we have deduced that lateral inhibition plays a critical role in sculpting our perception of visibility, both by causing interactions between stimuli positioned across space, and also by shaping the responses to stimuli across time. Further, the studies have served to narrow the number of possible theories to explain visibility and visual masking. Finally, we have discovered that lateral inhibition builds iteratively in strength throughout the visual hierarchy, for both monoptic and dichoptic stimuli. Since binocular information is not integrated until inputs from the two eyes reach the primary visual cortex, it follows that the early visual areas contain differential levels of monoptic and dichoptic lateral inhibitions. We exploited this fact to discover that excitatory integration of binocular inputs occurs at an earlier level than interocular suppression. These findings are potentially fundamental to our understanding of all forms of binocular vision and to determining the role of binocular rivalry in visual awareness.

Visual masking approaches to visual awareness.

To check differences in visual function between Wistar (albino) and Long-Evans (pigmented) rats. The animals were born in our facilities and reared under identical light conditions avoiding bright light. Visual electrophysiology was performed at the ages of 1.5, 4, 7 and 10 months (electroretinography, ERG) and at 1.5 and 7 months (visual evoked potentials, VEP). ERG measurements showed that: 1) The amplitudes of both scotopic and photopic b-waves were markedly larger in Long-Evans rats than in Wistar rats, and also the amplitudes of scotopic oscillatory potentials and photopic 30 Hz Flicker amplitudes, 2) scotopic a-wave amplitudes were larger in Wistar rats at low light intensities, whereas they were smaller in bright light, 3) both a-wave and b-wave latencies were shorter in Wistar rats, 4) the maximum response RmP3 was larger in Long-Evans rats, 5) the sensitivity parameter S was larger in Wistar rats, and 6) the post-receptoral response of cones was smaller in Wistar rats. In the VEP measurements, amplitudes of both photopic and scotopic visual evoked potentials of Long-Evans rats were only slightly larger than those of Wistar rats. ERG b-wave amplitudes are markedly decreased in Wistar rats, which requires further investigation. As the b/a and OP/a ratios were also decreased in Wistar rats, it can be suggested that post-receptoral processing, in particular, is impaired in albino animals.

Comparison of visual function in pigmented and albino rats by electroretinography and visual evoked potentials

The International Society for Clinical Electrophysiology of Vision (ISCEV) standard for full-field electroretinography (ERG) describes a minimum protocol for clinical testing but encourages more extensive testing where appropriate. This ISCEV extended protocol describes an extension of the ISCEV full-field ERG standard, in which methods to record and evaluate the growth of the dark-adapted (DA) ERG b-wave with increasing stimulus energy are described. The flashes span a range that includes the weakest flash required to generate a reliable DA ERG b-wave and that required to generate a maximal b-wave amplitude. The DA ERG b-wave stimulus–response series (also known historically as the “intensity–response” or “luminance–response” series) can more comprehensively characterize generalized rod system function than the ISCEV standard ERG protocol and may be of diagnostic or prognostic value in disorders that cause generalized rod system dysfunction.

/pdf/iscev-extended-protocol-for-the-stimulus-response-series-for-3osijon5u5.pdf

ISCEV extended protocol for the stimulus–response series for the dark-adapted full-field ERG b-wave

Dark-adapted electroretinograms were obtained over a 3.6-log range of stimulus intensities from 17 black and 15 white normal subjects. Subjects were grouped on the basis of light or dark fundus pigmentation, determined from digitized fundus photographs. B-wave amplitudes for each group were fitted by the Naka-Rushton equation, and the measures Vmax, log K, and n were determined. The luminance-response functions revealed that subjects with light fundi had larger b-wave amplitudes at all luminance levels. There was a significant difference between groups for Vmax and n but not for log K. A comparison of b-wave implicit times showed no significant difference between subjects with dark and light fundi. Ancillary tests and multiple regression analysis suggested that the relationship between Vmax and fundus pigmentation could not be attributed to age, gender, refractive error, axial length or intraocular pressure. The results have implications for the collection of normative electroretinographic data and for the interpretation of electroretinogram results.

Fundus pigmentation and the dark-adapted electroretinogram.

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Fundus pigmentation and the dark-adapted electroretinogram.