Maxwellian View Research Articles

Iris color and age‐related changes in lens optical density⋆

Summary Purpose: Epidemiologic evidence indicates that dark iris color increases risk of age‐related cataract. No information is currently available, however, on the effects of iris color on the lens prior to cataract development. In this study, we relate iris color to lens optical density (OD) in individuals without frank cataract. Methods: 90 subjects with blue or green irises (light color) were compared with 87 subjects having hazel, brown, or black irises (dark color). Lens OD was measured psychophysically by comparing scotopic thresholds obtained at 410 (measuring) and 550 nm (reference). Stimuli were presented in Maxwellian view. Results: The groups with light and with dark iris color did not differ significantly in smoking habits, dietary patterns, or age. Despite other similarities between the groups, lens OD was significantly(p<0.024) higher in the group with dark irises. The higher OD of the dark iris group was due to differences in the older subjects (>45 years,p<0.005), rather than the younger subjects (20–45 years) who showed no differences in lens OD. Conclusion: Our data indicate that iris pigmentation may be directly related to age‐associated increases in lens OD.

Macular pigment optical density measurement: a novel compact instrument

SummaryA compact device to derive the optical density of human macular pigment (MP) using heterochromatic flicker photometry is described. The validity of the system is assessed by measuring the optical density spectra of MP in 12 healthy subjects and comparing this with well‐established previously published values. The mean spectral absorbance characteristics of MP across subjects corresponds well with accepted values. As reported in other studies, our measurements show a wide variation of MP optical densities between individuals. In our technique within‐subject variability is low; standard deviations are between 0.025 and 0.15 in most cases. The overall optical density of MP ranged from 0.08 to 0.84 with a mean of 0.496 and standard deviation of 0.257 at 460 nm. The stimulus size was 0.95 degrees. The unique feature of the technique is that it allows free viewing (not Maxwellian View) of the stimulus, it can be conducted easily and quickly and does not need frequent re‐calibration.

Macular pigment optical density measurement: a novel compact instrument

A compact device to derive the optical density of human macular pigment (MP) using heterochromatic flicker photometry is described. The validity of the system is assessed by measuring the optical density spectra of MP in 12 healthy subjects and comparing this with well-established previously published values. The mean spectral absorbance characteristics of MP across subjects corresponds well with accepted values. As reported in other studies, our measurements show a wide variation of MP optical densities between individuals. In our technique within-subject variability is low; standard deviations are between 0.025 and 0.15 in most cases. The overall optical density of MP ranged from 0.08 to 0.84 with a mean of 0.496 and standard deviation of 0.257 at 460 nm. The stimulus size was 0.95 degrees. The unique feature of the technique is that it allows free viewing (not Maxwellian View) of the stimulus, it can be conducted easily and quickly and does not need frequent re-calibration.

ホログラフィック素子によるマックスウェル視を用いたシースルーディスプレイ

ホログラフィック素子によるマックスウェル視を用いたシースルーディスプレイ

VISION RESEARCH: A PRACTICAL GUIDE TO LABORATORY METHODS.

One thing that is remarkable about this book is that no one has tried to produce a similar one before. Vision research is essentially a multidisciplinary activity embracing many aspects of science and technology. In the past, seminal contributions have arisen from individuals who had a fortuitous combination of knowledge, or from cross discipline co-operation. There has long been a need therefore for a basic text, which should provide an introduction to this multifaceted subject. Carpenter and Robson have attempted to fulfil this need with the co-operation of a dozen established researchers in the field. What they have provided is inevitably not a complete solution. It is, nevertheless, a book, which, to the beginner, is an invaluable source of information and to the experienced researcher is a reliable reminder of many of those things which one once knew but has temporarily forgotten or just neglected to learn. In the first chapter Makous reviews applications of optics and photometry, describing a useful range of components and techniques. Many relevant concepts, including transfer functions, Maxwellian view systems and optical relays are introduced and useful advice is given on divers aspects including the alignment of prisms and lenses, and checking linearity of photometric systems, particularly where flashes of light of short duration are concerned. In the second chapter, J. G. Robson provides an interesting review of light sources, which includes useful comments on the operation of the troublesome xenon flash tube, and the properties of light emitting diodes and ferroelectric shutters to provide visual stimuli. This is followed with a chapter by Tom Robson, …

Smoking and lens optical density.

Epidemiological evidence indicates that smoking increases the risk of age-related cataract. No information is currently available, however, on the effects of smoking on the lens prior to cataract development. In this study, we relate smoking behavior to lens optical density (OD) in younger individuals without frank cataract. Fifty three never smokers and 41 current smokers were compared directly. Thirty one past smokers were tested to examine the relationship between years since smoking cessation and lens OD. Lens OD was measured psychophysically by comparing scotopic thresholds obtained at 410 (measuring) and 550 nm (reference). Stimuli were presented in Maxwellian view. The smokers in the sample smoked an average of 17.3 +/- 11.3 cigarettes/day for 20.4 +/- 12 years. No significant differences (other than in fat intake) were found between the smokers and nonsmokers in iris color, dietary patterns, or age. Despite their overall similarity, lens OD was significantly (p = 0.005) higher in the smokers. Moreover, we found a significant dose-response relationship (p = 0.02) between smoking frequency and lens OD. There was also a weak relationship between smoking frequency and lens OD for past smokers (p = 0.06), but no relationship between lens OD and years since smoking cessation. Our data indicate that smoking is directly related to age-related increases in lens OD throughout life and that these increases persist even after smoking cessation.

Smoking and lens optical density

Epidemiological evidence indicates that smoking increases the risk of age-related cataract. No information is currently available, however, on the effects of smoking on the lens prior to cataract development. In this study, we relate smoking behavior to lens optical density (OD) in younger individuals without frank cataract. Fifty three never smokers and 41 current smokers were compared directly. Thirty one past smokers were tested to examine the relationship between years since smoking cessation and lens OD. Lens OD was measured psychophysically by comparing scotopic thresholds obtained at 410 (measuring) and 550nm (reference). Stimuli were presented in Maxwellian view. The smokers in the sample smoked an average of 17.3+/−11.3 cigarettes/day for 20.4+/−12 years. No significant differences (other than in fat intake) were found between the smokers and nonsmokers in iris color, dietary patterns, or age. Despite their overall similarity, lens OD was significantly (p=0.005) higher in the smokers. Moreover, we found a significant dose–response relationship (p=0.02) between smoking frequency and lens OD. There was also a weak relationship between smoking frequency and lens OD for past smokers (p=0.06), but no relationship between lens OD and years since smoking cessation. Our data indicate that smoking is directly related to age-related increases in lens OD throughout life and that these increases persist even after smoking cessation.

Aging and the saturation of colors. 1. Colorimetric purity discrimination.

Colorimetric purity (Pc) discrimination functions were measured for 21 color-normal observers (11 younger and 10 older observers with mean ages of 30 and 74 years, respectively). On each two-alternative-forced-choice trial, observers saw two flashes of light, a broadband white light [CIE(x, y) = (0.33, 0.35)] and a mixture of broadband and monochromatic light (420-680 nm). The observer's task was to choose the flash that had a chromatic component. Foveally viewed, circular, 1.2 degrees-diameter stimuli were presented as 1.5-s flashes with 3-s interstimulus intervals in Maxwellian view. Stimuli [250 trolands (td) and 10 td] were equated on the basis of individual heterochromatic flicker photometry functions. Measured Pc discrimination sensitivity was lower in the older group than in the younger group at both light levels, and the performance difference between the age groups was approximately constant across the spectrum. The difference between discrimination at 10 and 250 td was relatively small for the younger group but larger for the older group, indicating a selective performance decrement for older observers at low light levels. The data were modeled as a sum of differential responses from S-cone and L/M-cone chromatic channels. The model and the data indicate similar age-related losses of sensitivity in the two channels, perhaps secondary to receptorial sensitivity losses.

Aging and the saturation of colors. 2. Scaling of color appearance.

Saturation of two sets of stimuli was scaled by 21 color-normal observers (ten younger and 11 older observers, mean ages: 30 and 73 years). Circular fields, 1.2 degrees in diameter, were presented in Maxwellian view as 1.5-s flashes with 3-s interstimulus intervals. Stimuli were mixtures of broadband light [CIE(x, y) = (0.35, 0.39), 200 trolands (td)] and monochromatic light (420-700 nm, 50 td). Monochromatic lights were equated by the 1978 2 degrees fundamental observer's luminosity function in one set of stimuli [J. J. Vos, Color Res. Appl. 3, 125 (1978) and by each observer's heterochromatic flicker photometry function in the other set of stimuli. Comparing the two age groups reveals no sizable differences in saturation for either set of stimuli, neither supporting nor refuting neural compensation for age-related increases in ocular media density (OMD). Examining short-wavelength saturation as a continuous function of estimated OMD reveals a more complicated pattern of results, however, suggesting substantial compensation over a certain range of OMD values but incomplete compensation for observers with the highest OMD values.

S-cone signals to temporal OFF-channels: asymmetrical connections to postreceptoral chromatic mechanisms.

Psychophysical tests of S-cone contributions to temporal ON- and OFF-channels were conducted. Detection thresholds for S-cone modulation were measured with two kinds of test stimuli presented on a CRT: a rapid-on sawtooth test and a rapid-off sawtooth test, assumed to be detected differentially by temporal ON- and OFF-channels, respectively. S-cone related ON- and OFF-temporal responses were separated by adapting for 5 min to 1 Hz monochromatic (420, 440, 450, 540, or 650 nm in separate sessions) sawtooth flicker presented in Maxwellian view. Circular test stimuli, with a sawtooth temporal profile and a Gaussian spatial taper, were presented for 1 s in one of four quadrants 1.0 degree from a central fixation point. A four-alternative forced-choice method combined with a double-staircase procedure was used to determine ON- and OFF-thresholds in the same session. Following adaptation, the threshold elevation was greater if the polarity of the test stimulus was the same as the polarity of the sawtooth adaptation flicker, consistent with separate ON- and OFF-responses from S-cones. This asymmetrical pattern was obtained, however, only when the adaptation stimuli appeared blue with a little redness. When the adaptation flicker had a clear reddish hue component, the threshold elevation did not depend on the polarity of the sawtooth test stimuli. These results are consistent with a model in which OFF-signals originating from S cones are maintained by a postreceptoral mechanism signaling redness, but not by a postreceptoral chromatic mechanism signaling blueness.

The area of complete scotopic spatial summation enlarges with age.

The maximal area of complete scotopic spatial summation (Ricco's area) was determined for 50 subjects ranging in age from 19 to 87 yr. Increment thresholds were measured for 10-ms, 520-nm circular test lights of varying diameters that were superimposed and concentric with a 10 degrees, 640-nm circular background. The test lights were imaged in Maxwellian view along the horizontal meridian, 6 degrees nasal from a foveal fixation point. The results demonstrate a statistically significant enlargement of Ricco's area with age. The average angular subtenses of Ricco's areas for the ten youngest (mean = 26 yr) and ten oldest (mean = 75 yr) observers were approximately 48 and 69 arc min, respectively. Model simulations based on a series of optical transfer functions of the eye and varying degrees of intraocular light scatter for younger and older observers show that preneural factors cannot account for these results. Therefore changes in neural mechanisms must be invoked to explain the enlargement in the size of Ricco's area under scotopic conditions.

Binary masks yielding Gaussian light distributions in Maxwellian view

Gaussian light distributions are important stimuli for vision research, but are difficult to produce for Maxwellian viewing conditions. In this study, two binary Maxwellian-view masks which produce smooth light distributions on the retina were considered: one was an out-of-focus circular aperture; the other was an in-focus pattern of opaque squares with a prescribed size distribution. The diffraction images of the two masks on the retina were computed numerically and shown to be well described by gaussian functions. As an experimental test, a mask with the desired pattern of opaque squares was manufactured by evaporation of chromium over a quartz substrate; its quality, as assessed by micro-transmittance measurements, was found to be adequate for most visual applications.

The optical quality of the human eye revisited

A subjective assessment of the optical quality of the human eye may be derived from a comparison between the contrast sensitivities obtained in response to a refracted grating display and a non-refracted grating display. The former may be generated on a cathode ray tube (CRT) while the latter may be obtained with laser interference fringes observed in the Maxwellian view. With this method, the rate of decline of the contrast ratio of the optical media with increasing spatial frequency has been shown to be appreciably less than the rate of decline of the neural performance represented by the laser contrast sensitivities. However, this comparison has been based on results in response to a green CRT display and red (Helium-Neon) interference fringes. In the present study, we have confirmed this result with respect to comparisons between a green CRT display and a green laser display, although the absolute value of the contrast ratio of the optical media for the green laser display was reduced compared with values for the red laser display.

Spatial Extent of Masking by Sine-Wave Gratings

The contrast threshold for detection of a target consisting of 1.5 periods of a sine wave was determined as a function of the number of cycles in a sinusoidal mask with the same spatial frequency and orientation. The test frequencies were 2, 4, and 8 cycles deg−1. The masks were spatial-frequency modulated so as to equate their spectral extent. Stimuli were seen monocularly in Maxwellian view at a mean luminance of 10 cd m−2. The contrast threshold in a backward masking paradigm was determined by a 2AFC staircase. Data were obtained from three subjects with normal vision. It was found that as the number of cycles in the mask was increased, the contrast threshold fell, but only to a certain level. The full range of the threshold decrement was about 2 dB. At all the spatial frequencies tested, the final threshold level was reached with 3 cycles in the mask and then remained unaffected by a further increase in the number of cycles. The results implicate frequency-tuned mechanisms of very restricted spatial extent. It is suggested that these may underlie processing of spatially distributed information at the post-striate stages.

Spectral mechanisms of spatially induced blackness: data and quantitative model.

Spectral efficiency functions and tests of additivity were obtained with three observers to identify possible chromatic contributions to spatially induced blackness. Stimuli consisted of a series of monochromatic (400-700 nm; 10-nm steps), 52-arcmin circular test lights surrounded by broadband (x = 0.31, y = 0.37), 63-138-arcmin annuli of fixed retinal illuminance. The stimuli were imaged on the fovea in Maxwellian view as 500-ms flashes with 10-s interstimulus intervals. Observers decreased the intensity of the test center until it was first perceived as completely black. Action spectra determined for two surround levels [2.5 and 3.5 log trolands] had three sensitivity peaks (at approximately 440, 540, and 600 nm), However, when monochromatic surrounds were adjusted to induce blackness in a broadband center, action spectra were unimodal and identical to functions obtained by heterochromatic flicker photometry. Tests of additivity revealed that when blackness is induced by broadband surround into a bichromatic center, there is an additivity failure of the cancellation type. This additivity failure indicates that blackness induction is influenced, in part, by signals from opponent-chromatic pathways. A quantitative model is presented to account for these data. This model assumes that blackness induction is determined by the ratio of responses to the stimulus center and the annulus, and while signals form the annulus are based only on achromatic information, responses from the center are based on both chromatic and achromatic properties of the stimulus.

Safety norms for Maxwellian view laser scanning devices based on the ANSI standards.

Standards for safe use of lasers like those of the American National Standard Institute (ANSI) do not give specific guidelines regarding the safety norms for a Maxwellian view laser scanning device (for example, the scanning laser ophthalmoscope). In this note it is shown that a pulsed extended source ocular exposure system, which is described by the ANSI standards, can be used as a conservative model of such a laser scanning device. With some adjustments to this model, the Maxwellian character can be included and the maximum permissible corneal power also can be normalized independently of the field size.

The effect of anti-epileptic drugs on visual perception in patients with epilepsy.

We investigated the influence of the antiepileptic drugs carbamazepine (CBZ), phenytoin (PHT) and valproic acid (VPA) on different aspects of visual perception in patients with epilepsy by three different methods. (i) The colour arrangement test Farnsworth Munsell D100. (ii) A monitor system generating 24 different Gaussian dots and 24 different vertical sinusoidal gratings. Luminance increments and decrements for achromatic discrimination and four different colours for chromatic discrimination were investigated with four different sizes each adding up to 24 stimuli. (iii) A Maxwellian view system providing a foveal blue test light either superimposed on a yellow adaptation field (increment threshold) or after switching off this field (postadaptation threshold). Five different adaptation levels were investigated. Patients on PHT offered the most abnormalities, particularly in the D100 and in all Gaussian dots recordings. The individual differences between increment and postadaptation threshold (transient tritanopia effect) were significantly elevated at the four higher adaptation levels, whereas no change was found in the increment thresholds and only for the highest luminance level in the postadaptation thresholds. With VPA, chromatic and achromatic increment discrimination was impaired particularly for larger Gaussian stimuli on the monitor system. Valproic acid also induced a consistent increment threshold increase on the Maxwellian view system, an increase of the postadaptation threshold at the highest luminance level and, like PHT, an increase of the threshold differences at level 3 and 4, but not at the highest background level 5. Patients on CBZ provided normal results in all investigations, with the exception of a slight but significant increase in the D100 error score. Sinusoidal gratings turned out to be much less sensitive than Gaussian dots since they remained unchanged in patients on all three drug groups.

Ultraviolet and Green Light Cause Different Types of Damage in Rat Retina

Purpose. To assess the influence of wavelength on retinal light damage in rat with funduscopy and histology and to determine a detailed action spectrum. Methods. Adult Long Evans rats were anesthetized, and small patches of retina were exposed to narrow-band irradiations in the range of 320 to 600 nm using a Tenon arc and Maxwellian view conditions. After 3 days, the retina was examined with funduscopy and prepared for light microscopy. Results. The dose that produced a change just visible in fundo was determined for each wavelength. This threshold dose for funduscopic damage increased monotonically from 0.35 J/cm 2 at 320 nm to 1600 J/cm 2 at 550 nm. At 600 nm, exposure of more than 3000 J/cm 2 did not cause funduscopic damage. Morphologic changes in retinas exposed to threshold doses at wavelengths from 320 to 440 nm were similar and consisted of pyknosis of photorecep tors. Retinas exposed to threshold doses of 470 to 550 nm had different morphologic appearances. Retinal pigment epithelial cells were swollen, and their melanin had lost the characteristic apical distribution. Some pyknosis was found in photoreceptors. Conclusions. Damage sensitivity in rat increases enormously from visible to ultraviolet wavelengths. Compelling evidence is presented that two morphologically distinct types of damage occur in the rat retina, depending on the wavelength. Because two types also have been described in monkey, a remarkable similarity seems to exist across species

The source of disparity vergence innervation determines prism adaptation

A physiological model of prism adaptation argues that adaptation magnitude and rate are functions of the magnitude of reflex vergence innervation. It has also been shown that there is reduced prism adaptation magnitude for a given disparity stimulus where only peripheral sensory fusion is present (the ‘eccentricity effect’). This study attempted to determine whether the eccentricity effect is attributable to reduced reflex vergence innervation in peripheral fusion. Experiments were run in a Maxwellian view haploscope. Convergence and divergence adaptation to 6Δ disparity stimuli were quantified for seven binocularly normal subjects using subjective heterophoria measurements. Vergence response during central or peripheral fusion was quantified objectively by infrared oculography. Six of seven subjects revealed an eccentricity effect. However, in three of seven subjects the eccentricity effect was not predictable from the manifest vergence response. The results suggest that the source of reflex vergence innervation affects prism adaptation. A model is proposed whereby different sources of reflex disparity vergence innervation stimulate prism adaptation by way of separate neurological pathways of differing responsiveness.

The source of disparity vergence innervation determines prism adaptation

SummaryA physiological model of prism adaptation argues that adaptation magnitude and rate are functions of the magnitude of reflex vergence innervation. It has also been shown that there is reduced prism adaptation magnitude for a given disparity stimulus where only peripheral sensory fusion is present (the ‘eccentricity effect’). This study attempted to determine whether the eccentricity effect is attributable to reduced reflex vergence innervation in peripheral fusion. Experiments were run in a Maxwellian view haploscope. Convergence and divergence adaptation to 6 Δ disparity stimuli were quantified for seven binocularly normal subjects using subjective heterophoria measurements. Vergence response during central or peripheral fusion was quantified objectively by infrared oculography. Six of seven subjects revealed an eccentricity effect. However, in three of seven subjects the eccentricity effect was not predictable from the manifest vergence response. The results suggest that the source of reflex vergence innervation affects prism adaptation. A model is proposed whereby different sources of reflex disparity vergence innervation stimulate prism adaptation by way of separate neurological pathways of differing responsiveness.