Densitometric measurement of human cone photopigment kinetics

We measured the radiance response function for steady state bleaching lights and the regeneration of the cone visual photopigments using the continuous recording densitometer described by v. Norren and v.d. Kraats. Measurements made on 5 deuteranopes, 1 protanope and 2 color-normal observers were similar. The radiance response function was steeper than the function predicted by a simple first-order kinetic equation. For a measured density (ca 0.3) we evaluated whether high stray light (ca 47.5%) and high two-way optical density (ca 1.3) could account for the deviation from the prediction of a first-order equation. Such a model was rejected because these parameters predicted different estimates of the time course of regeneration for different test wavelengths (554 and 605 nm). Statistical analysis of the regeneration data revealed a highly significant non-linearity. A model in which the rate of regeneration increases as the proportion of bleached photopigment decreases is required to explain both the radiance function and the regeneration data.

Brightness of equal-luminance lights

The brightness of lights defined by heterochromatic flicker photometry as being of equal luminance was determined by direct comparison with a white standard. Stimuli included mixtures of white and colored lights. Eight different colorimetric purities were tested for each of eleven primaries. Adaptation to a known white was maintained. Resulting brightnesses were expressed in terms of the ratio of the amount of light required for a brightness match to the amount required for a flicker photometric match (B:F). B:F ratios varied with the primary, being largest for red and blue primaries. The variation of B:F ratio with colorimetric purity differed depending on the primary, although for any given dominant wavelength the highest-purity stimulus always had the largest B:F ratio. The data qualitatively exclude a number of simple models of brightness generation.

Classification of complete and incomplete autosomal recessive achromatopsia

We studied color vision in 32 patients with autosomal recessive achromatopsia. Color matching revealed complete achromatopsia (rod monochromasy) in ten patients (Group I) and incomplete achromatopsia in the remaining twenty-two patients. Amongst the incomplete achromats, were three groups distinguishable by their color matching. Patients in Group II were dichromats; their color matches were mediated by rods and MWS (middle-wavelength sensitive) cones. Patients in Groups III and IV were trichromats. Color matches of patients in Group III were mediated by rods, LWS (long-wavelength sensitive) cones and MWS cones. Group III patients showed no evidence of SWS (short-wavelength sensitive) cones. Color matches of patients in Group IV were mediated by rods, LWS cones and SWS cones; color matching did not reveal MWS cones.

Color matching in autosomal dominant tritan defect

We evaluated color matching in 39 observers with an autosomal dominant tritan defect. Eleven tritans were dichromats with 1 degrees field, and only two were dichromats with an 8 degrees field. Twenty-one of the tritan observers ahd normal blue-green equations with an 8 degrees field, indicating that autosomal dominant tritans have short-wavelength-sensitive cones. Some of the tritan observers showed a shifted blue-green equation, which was ascribed to rod activity.

Structure of the granular layer of the rat dentate gyrus. A light microscopic and Golgi study

The rat dentate gyrus was examined with the Golgi method. Cell counts were performed in Nissl-stained serial sections. The number of granule cells was 635,000 +/- 33,000. The number of basket cells in the granular layer was 3600 +/- 570. In whole dentate gyrus, the average ratio between granule and basket cells was 160-220:1. The ratio was higher in the caudal part of the dorsal and ventral blades and significantly less basket cells were found in the ventral than in the dorsal blade of dentate gyrus. 60% of all the basket cells were found at the margin between the granular layer and hilus, 35% were found in the lower half of molecular layer and 5% within the granular layer. Five types of basket cells were differentiated in Golgi sections on the basis of their location and cell morphology. The granule cells in their early development stages sent dendrites in every direction even in the hilus, but the developed granule cells never had basal dendrites. Spines were seen on the 5 days old granule cell dendrites, but the spine density was found to grow until adulthood. As a rule several axon collaterals could be seen on the granule cell axons. The whole length of granule cell dendrites totaled 2400 micron +/- 331, those of the basket cell dendrites totaled 1100 micron +/- 144. The possible role of basket cells in the regulation of the dentate gyrus granular layer was considered.

Visual function abnormalities in macular heterotopia caused by proliferative diabetic retinopathy

In seven patients with displacement of the macula in one eye caused by vitreoretinal traction from proliferative diabetic retinopathy, the macula was displaced toward the optic disk in all but one eye. The eyes with macular heterotopia showed (1) reduced visual acuity (ranging from 6/6 (20/20) to 6/24 (20/80), (2) reduced static perimetry sensitivity (particularly in the temporal field) with displacement of the peak sensitivity toward the blind spot, (3) loss of hue discrimination, and (4) metamorphopsia. In two eyes with macular heterotopia, Stiles-Crawford data provided evidence for photoreceptor disorientation; one eye had mixed orientation, and the other a displaced peak suggesting regular photoreceptor tilting. The proposed mechanisms of visual loss in eyes with macular heterotopia secondary to traction from proliferative diabetic retinopathy include detachment of the macula, disorientation of photoreceptors in the macula, and disturbance of normal neural connections within the retina caused by stretching of the retina.

Photoreceptor misalignment accompanying a fibrous scar

A 9-year-old boy with dense fibrous scars at the macula had visual acuities of 6/12 and 6/9 and an abnormal color match (pseudoprotanomaly). The Stiles-Crawford effect functions were abnormal in both eyes, showing maximal sensitivity at the nasal edge of each pupil. The data suggest that the foveal photoreceptors, although spared destruction by an adjacent focus of healed chorioretinitis, have been distorted by fibrous traction arising from that defect.

Autosomal recessive incomplete achromatopsia with deutan luminosity

Four patients in three different families had a form of autosomal recessive incomplete achromatopsia not previously described. The visual acuity was 6/18 to 6/60 (20/60 to 20/200) with minimal ophthalmoscopic abnormality and normal fluorescein angiogram. The photopic electroretinographic responses were present in all four patients; the fusion rate of 60 Hz was only slightly subnormal. The high-intensity scotopic response was subnormal. The patients failed color screening plates and accumulated over 400 errors with scotopic axis on the Farnsworth-Munsell 100-hue test. The Rayleigh match was abnormal, displaced toward the red primary, but with normal luminance. The photopic luminous efficiency function was similar to that of the deuteranope. Color matching revealed a trichromatic form of color vision mediated by long wavelength and short wavelength cones, and a rhodopsin receptor.

Chromatic information processing

The investigation of visual processing mediated solely by chromatic information requires conditions preventing a subject's use of the luminance differences normally accompanying a chromatic change. In Experiment 1, which involved a discriminative reaction time (RT) task, chromatic and white stimuli of the same luminance were presented on a dimmer achromatic background. Subjects were instructed to respond only to the chromatic stimuli. RT was slowest at 570 nm and somewhat faster to short wavelengths than to long wavelengths. In Experiment 2, which compared two discriminative RT tasks, RT was faster when subjects responded to color than when they responded to white. Experiments 3 and 4 demonstrated that a brighter white surround decreased the perceived brightness of chromatic stimuli as well as their perceptual similarity to white, but did not affect RT. The results are discussed in terms of the response strength of the chromatic processing channel.

Duration thresholds for chromatic stimuli

The duration necessary to detect chromatic stimuli was measured for wavelengths between 463 and 620 nm. Stimuli were presented either in hue substitution (replacement of white by a chromatic stimulus of matched luminance) or as increments. Two observers viewed a 1 degrees 45' homogeneous white field. A trial consisted of replacement of the central 40' of the field by a chromatic stimulus. In substitution mode the white field was 2.4 cd/m2., the chromatic replacement was of matched luminance using heterochromatic flicker photometry (HFP). In increment mode, the white field was decreased to 1.2 cd/m2., the chromatic replacement remained at 2.4 cd/m2. In substitution mode, duration threshold varied from approximately 3--4 ms for the spectral extremes to 45--66 ms at 570 nm. Detected stimuli were always seen as a change in chromaticity. In increment mode, thresholds were in the 2--4 ms range with no dependence upon spectral composition. Detected stimuli were seen either as changes in chromaticity or brightness. A control experiment indicated that HFP did establish equivalent luminance for the hue substitution mode. We conclude that duration thresholds in substitution mode reveal chromatic processing channels; duration thresholds in increment mode are mediated by chromatic and/or achromatic processing channels.

Visual function in acute posterior multifocal placoid pigment epitheliopathy

We examined a 19-year-old woman with acute posterior multifocal placoid pigment epitheliopathy one week after she noted blurring of central vision. Her corrected visual acuity was R.E.: 6/7.5 (20/25), and L.E.: 6/12 (20/40). The visual fields showed 10-degree pericentral scotomas. A color vision defect and an abnormal Stiles-Crawford effect were present. Dark adaptation showed a delayed time course, with normal final thresholds. The electro-oculogram was subnormal, suggesting widespread abnormality of the retinal pigment epithelium. Active lesions resolved within three weeks, but fluorescein angiography showed characteristic widespread residual changes. Within three weeks, she had normal visual acuity and a normal electro-oculogram. Other tests of visual function showed recovery with a slower time course. By one year, the visual fields, color matching, Stiles-Crawford effect, and dark adaptation were almost normal. Analysis of the color-matching data and Stiles-Crawford effect indicated that the abnormalities of macular function were caused by an underlying lesion of the pigment epithelium and photoreceptors. This caused a physical distortion of the photoreceptor layer and metabolic disfunction of the photoreceptors.

Autosomal recessive incomplete achromatopsia with protan luminosity function

A unique form of dichromatic color vision is described in a family with incomplete achromatopsia. In 1966, incomplete achromatopsia was diagnosed in 4 of 14 children of a consanguineous marriage. The 4 affected had best visual acuities of 6/60 or 6/180, pendular nystagmus, and aversion to bright lights. The ERG showed minimal photopic responses. No abnormality of rod function was present. There was a severe color vision defect. In 1976, one of the patients returned for further color testing. Color tests included measurement of the luminous efficiency function using heterochromatic flicker photometry and colorimetric evaluation. The luminous efficiency function resembled that of the protanope. From the colorimetric measurements, we conclude that the patient has a unique form of dichromatic color vision mediated by two visual photopigments: the normal MWS cone photopigment and a photopigment with the spectral characteristics of rhodopsin.

Transscleral electroretinography

We studied the electroretinogram in normal patients, patients with opacities of the anterior segment, and patients with vitreous hemorrage, using a high-intensity light stimulus delivered either through the sclera or through the pupil. We found the response obtained with transscleral stimulation a consistent indicator of gross retinal function. Since the stimulus entered the eye through the sclera, it provided a method for studying the retinal responses independent of opaque or translucent media.

Evaluation of single-pigment shift model of anomalous trichromacy

The spectral sensitivity of the visual photopigments, the interobserver variability in color judgments, and the spectral locus of unique yellow provide three major problems for accounts of X-chromosomal-linked anomalous trichromacy. According to the single-pigment hypothesis, the primary defect in anomalous trichromacy is a wavelength shift in the peak sensitivity of one of the three visual photopigments. We show that this shift results in reduction of the anomalous trichromat's r-g opponent chromatic channel. The distribution of response variability in Rayleigh equation match widths due to factors other than the spectral characteristics of the photopigments is similar in normal and anomalous trichromats. When normal and anomalous trichromats make hue estimations of sets of stimuli designed to contain similar chromatic information, their judgments show similar variability. Calculation of the r-g opponent chromatic channel can provide correct predictions of the spectral loci for unique yellow for anomalous trichromats.

Large-field trichromacy in protanopes and deuteranopes

Protanopes and deuteranopes do not accept the classical dichromatic matches when field size extends to 8 degrees visual angle. Their unique matches of spectral yellow to a mixture of red and green are then mediated by the photoreceptors of small-field dichromacy interacting with a photoreceptor with the spectral sensitivity of rhodopsin. Our data suggest that large-field trichromacy is a general feature of protanopia and deuteranopia.

Volatile degradation products of l-dehydroascorbic acid

Volatile degradation products were isolated from a solution of L-dehydroascorbic acid in phosphate buffer solution of pH 2,4,6 and 8 heated under reflux for 3 h or left at 25 degrees C for 200 h. The products were identified by comparison of their gas chromatographic retention data, infra-red and mass spectra with those of authentic compounds. Fifteen products were identified, among which 12 had not yet been reported as degradation products of L-dehydroascorbic acid. Concentrations of 5 main degradation products, i.e. 3-hydroxy-2-pyrone, 2-furancarboxylic acid, 2-furaldehyde, acetic acid and 2-acetylfuran depended on the pH values and temperature; the presence of oxygen had no pronounced effect.

Effect of field size on red--green color mixture equations

Red-green color mixture equations were measured in 10 color-normal observers for fields of view varying from 30' to 10 degrees. The G/R mixture decreases continuously as field size is increased. The data are consistent with the interpretation that the cone visual photopigments decrease exponentially in effective optical density as the field size is increased.