Retinal densitometer with the size of a fundus camera

Norren, Dirk van; Kraats, Jan van de

doi:10.1016/0042-6989(89)90085-0

Cited by 42 publications

(20 citation statements)

References 14 publications

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“…The regeneration of cone photopigment has been measured by reflection densitometry for many years (see for example, Rushton & Henry, 1968; Hollins & Alpern, 1973; van Norren & van de Kraats, 1989; Coile & Baker, 1992), though generally only following near‐total bleaches. Those recoveries have usually been described by a single exponential with a time constant of 1–2 min (but see below for exceptions).…”

Section: Discussionmentioning

confidence: 99%

Recovery of the human photopic electroretinogram after bleaching exposures: estimation of pigment regeneration kinetics

Mahroo

Lamb

2004

The Journal of Physiology

112

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We used a fibre electrode in the lower conjunctival sac of the human eye to record the a-wave of the photopic electroretinogram elicited in response to dim red flashes, delivered in the presence of a rod-saturating blue background, before and after exposure of the eye to bright white illumination that bleached a significant fraction of cone photopigment. Responses were recorded from two normal subjects whose pupils were maximally dilated. A range of intensities of bleaching light were used, from 500 to 3000 photopic cd m −2 , and exposures were made sufficiently long in duration to achieve a steady-state bleach. In addition, responses were also recorded following shorter durations of exposures to the highest intensity (3000 cd m −2 ); these durations ranged from 5 to 60 s. The amplitude of the a-wave response to dim flashes was reduced following the exposures, with brighter or longer exposures causing greater reduction. The amplitude then recovered within about 4 min to the prebleach level. The amplitudes measured at ca 15 ms after the flash were used to derive the effective intensity of the flashes, thereby quantifying the fraction of photopigment available at the time of delivery of each flash. Recovery from all exposures in both subjects followed a common time course, which could be described well by a model of pigment kinetics based on rate-limited regeneration, where the initial rate of recovery following a total bleach was ca 50% of the total pigment per minute, and the residual pigment level for half the maximal rate was ca 20% of the total pigment. The same parameters, together with a fixed photosensitivity, could account for the steady-state pigment levels seen at each bleaching intensity, and also for the fraction of pigment bleached following exposures of different duration at the highest intensity. The dim-flash ERG thus provides a novel method for assessing pigment regeneration in vivo. Our finding that pigment regeneration follows rate-limited kinetics may explain previous reports of pigment regeneration deviating from first order kinetics. We present a model of regeneration in which the rate limit arises from a limitation in the delivery of 11-cisretinoid to the photoreceptor outer segments.

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Section: Discussionmentioning

confidence: 99%

Recovery of the human photopic electroretinogram after bleaching exposures: estimation of pigment regeneration kinetics

Mahroo

Lamb

2004

The Journal of Physiology

112

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“…Reflection measurements were performed with a slightly modified version (Van de Kraats et al 1996) of the Utrecht Retinal Densitometer (Van Norren & Van de Kraats, 1989a). We used an illumination field of 1P9 deg and a detection field of 1P6 deg.…”

Section: Methodsmentioning

confidence: 99%

Foveal cone mosaic and visual pigment density in dichromats.

Berendschot

Kraats

Norren

1996

The Journal of Physiology

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1. Optical reflectance spectra of the fovea were measured in ten subjects with normal colour vision, ten protanopes and seven deuteranopes. Four conditions were used: perpendicular and oblique angle of incident and reflected light on the retina, both in a dark-adapted and a fully bleached state. 2. The spectra were analysed to assess the effects of dichromacy on the cone mosaic. A replacement model, i.e. one where the total number of cones remains unchanged and all cones are filled with a single type of pigment, was found to fit our data best. 3. The analysis of the spectral fundus reflectance also provided estimates for densities of photo-labile and photo-stable retinal pigments and fraction of long wavelength-sensitive (LWS) cones. Visual pigment density was 0 39 for protanopes and 0f42 for deuteranopes, significantly lower than the 0 57 found for colour normals. Macular pigment density was 0 54 for colour normals, 0f46 for protanopes and 0-42 for deuteranopes. 4. For colour normals the LWS cone fraction was 0-56, in agreement with psychophysical literature. The LWS cone fraction for protanopes was -0'04, and for deuteranopes 0-96, consistent with their Rayleigh matches.

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“…Van Norren and Van de Kraats presented an instrument that could measure 15 wavelengths quasi-simultaneously. 4 The instrument was again optimized for the directional reflection, and it used low light levels to enable retinal reflection spectra with the nearly full complement of visual pigments. A new model was derived by Van de Kraats et al with better funded trajectories of light in the receptor layer.…”

Section: Introductionmentioning

confidence: 99%

Directional and nondirectional spectral reflection from the human fovea

Kraats

Norren

2008

J. Biomed. Opt.

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A model of the directional and nondirectional reflection spectrum of the human fovea is developed, incorporating reflectors, absorbers, and a wavelength-dependent optical Stiles-Crawford effect (OSCE). Data from 102 healthy subjects between 18 and 75 years obtained with the fundus reflection analyzer (FRA), an imaging spectrograph that measures the directional reflection profile of the human fovea in the pupil plane from 400 to 950 nm, were analyzed. Subgroups of young (<40 years) and old (>50 years) observers were defined. Mean results of the young group defined a template for directionality versus wavelength. For the whole group, mean reflection at 550 nm from the cones was 2.12%, from the retinal pigment epithelium 0.56%, and from the choroid 7.92%. Lens density, cone disc reflection, and blood layer thickness showed significant trends versus age. The model for the first time simultaneously describes the spectra of the directional and nondirectional reflection of the human fovea. Rayleigh scatter losses of the media and in preretinal layers were assumed zero in the nondirectional pathway. Mean density of the macular pigment of a subgroup (53 subjects, 19 to 75 years) correlated significantly with independent data from reflectance and autoflourescence images obtained by scanning laser ophthalmoscope (SLO) and data from flicker photometry.

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Retinal densitometer with the size of a fundus camera

Cited by 42 publications

References 14 publications

Recovery of the human photopic electroretinogram after bleaching exposures: estimation of pigment regeneration kinetics

Recovery of the human photopic electroretinogram after bleaching exposures: estimation of pigment regeneration kinetics

Foveal cone mosaic and visual pigment density in dichromats.

Directional and nondirectional spectral reflection from the human fovea

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