Scotopic Sensitivity Research Articles

Reading Disabilities and the Effects of Colored Filters

The efficacy of a controversial treatment, using colored filters to remediate reading disabilities, was measured empirically, with colored overlays placed over reading material on white paper. Irlen's (1983) method is to prescribe specific tinted filters as lenses that she claims filter specific light frequencies and remove a range of perceptual disorders that adversely affect reading and related learning performance. Irlen calls this condition "scotopic sensitivity" and claims it is a significant factor in a high percentage of people with learning disabilities. Ninety-two children with significant reading disabilities were classified as either scotopic or nonscotopic using the Irlen Differential Perceptual Schedule, and were randomly assigned to one of six treatment groups using colored or clear overlays. Reading performance (rate, accuracy, and comprehension) as measured by the Neale Analysis of Reading Ability (Neale, 1987) and the Formal Reading Inventory (Wiederholt, 1986) improved significantly when the scotopic children read with the preferred colored overlay filter compared to clear or different-colored overlay filters. Nonscotopic children showed no change.

The Effectiveness of Irlen Filters for Improving Reading Performance: A Pilot Study

The objectives of this pilot study were to investigate the effectiveness of Irlen filters for improving comfort and reading performance and to determine whether traditional optometric intervention would be effective in relieving the symptoms commonly reported by people seeking help through the use of Irlen filters. Thirty subjects were included in the study: 12 males and 18 females. The ages of the subjects ranged from 9 to 51 (mean = 23.6). They were randomly placed in either an Irlen filter treatment group (n = 11), a vision therapy treatment group (n = 11), or a control group (n = 8). Pre- and posttesting on all subjects included a vision evaluation, reading and intelligence testing, the Irlen scotopic sensitivity screening test, and a symptom questionnaire. Results revealed that subjects in both treatment groups were more comfortable after treatment, although only the vision therapy group showed improvement in vision functioning. The subjects in the Irlen filter group did not show any significant gains in reading rate, word recognition in context, or comprehension.

Behavioral studies of the sensitive periods of development of visual functions in monkeys

The age-dependent effects of monocular form deprivation on psychophysically determined visual functions were investigated in rhesus monkeys. Monocular form deprivation was initiated at various ages from 1 to 25 months and maintained for 18 months. The effects of form deprivation varied across the visual functions evaluated. Absolute scotopic sensitivity was depressed by form deprivation initiated only at 1 or 2 months of age. Photopic, increment-threshold spectral sensitivity functions showed alterations in sensitivity levels for monkeys treated at 5 months of age or earlier, with no effect thereafter. Monocular form deprivation at 1 to 5 months of age resulted in profound deficits in spatial modulation sensitivity. The effects on spatial vision decreased systematically as the age of onset was delayed from age 6 to 18 months. Finally, binocular summation measures revealed an absence of binocular vision even for the monkey form-deprived at 25 months of age, i.e. the experimental treatment series failed to define the upper limit of the age-range for the effects of monocular form deprivation on binocular summation mechanisms. Comparisons of the age-dependent effects of monocular form deprivation across the various functions demonstrated that the sensitive period, i.e. the period of life during which a visual function may be altered by monocular form deprivation, was different for each of the psychophysical measures of visual function.

Scotopic Sensitivity Syndrome

In 1983 Helen Irlen 1 described the scotopic sensitivity syndrome (SSS) as a visual defect related to difficulties with light source, glare, luminance, wave length, and black/white contrast. Since that time, tinted lenses have been offered as remediation for SSS, which Irlen links to reading deficiency and poor academic performance. On two occasions since May 1988 the tinted lens treatment for SSS received national exposure on the television program 60 Minutes. On this program it was stated that specially prescribed tinted lenses may be an effective method for the treatment of a variety of reading disorders, including dyslexia. The Irlen system for treatment of SSS begins with a client who complains of one or more of a long list of symptoms, including eye fatigue, blinking, blurred vision, difficulty with concentration, and skipping words. After being questioned about general health problems, clients are asked to respond to a series of visual

A Review of the use of Irlen (tinted) Lenses

Helen Irlen identified a syndrome defined as 'scotopic sensitivity' which it was claimed could be responsible for the inability of some people to read fluently and the symptoms of which could be ameliorated by the wearing of prescribed coloured lenses. The literature to date presents a confused and inconsistent picture concerning the use of the lenses. The literature (much of which is unpublished and difficult to obtain) is critically reviewed. Recent experimental evaluations of the lenses do not support the use of the lenses as a useful intervention for children with reading disabilities.

Critical issues associated with irlen lenses: A reply to robinson

Abstract While Robinson has raised a number of issues from our study and is concerned about its limitations (as he sees them), the most critical findings and their implications appear to have been completely overlooked. In particular, Robinson ignores the findings that children diagnosed as suffering from the “scotopic sensitivity” syndrome differ significantly on a number of personality variables from those diagnosed as not “scotopic sensitive,” and that for children diagnosed as “scotopic sensitive” there were no differences in performance with prescribed Irlen lenses compared with any other lens condition on standardised reading or objective perceptual tasks. This latter result is crucial in view of the fact that, as acknowledged by Robinson, Irlen lenses are prescribed on the basis of a diagnostic procedure which purports to demonstrate an immediate effect based on reading and perceptual tasks for each individual.

An evaluation of the irlen lenses as a treatment for specific reading disorders

Abstract Tinted lenses have been prescribed in recent years to ameliorate the “scotopic sensitivity” syndrome thought to underlie some reading disabilities (Irlen, 1983a). The present investigation revealed personality differences between scotopic sensitive (n = 38) and non-scotopic sensitive children (n = 22). The study also examined performance in reading, depth perception, and simple eye-hand coordination tasks for 22 children who were prescribed specific tinted lenses. There were no significant differences in performance between pre- and post-lens prescription on any measure of the Neale Analysis of Reading Ability (rate, accuracy, or comprehension). Performance with tinted lenses was also compared with that for random colour, plain lenses, and a no lens control condition. There were no significant differences in reading performance or performance on a simple eye-hand coordination task or on depth perception tasks with prescribed coloured lenses compared with any other lens condition. The study did no...

Detection of briefly flashed sine-gratings in dark-adapted vision

Scotopic contrast sensitivity was measured near 20 deg retinal eccentricity for briefly flashed (10 or 20 msec) sine-wave gratings presented in darkness to dark-adapted subjects. For very low spatial frequencies (0.2–0.5 c/deg), curves of contrast sensitivity vs luminous energy show evidence of a low rod plateau and a high scotopic region, with an intervening transition at around −2 to −2.5 log scot td sec. Similar measurements made using long flashed or flickering gratings do not show a plateau. The results suggest that vision in the low rod region is impaired for brief flashes. For the briefly flashed stimuli, curves of contrast sensitivity versus spatial frequency in the low region were best fit by simple Gaussian functions with a variable centre size ( σ c = 0.5 → 0.25 deg ), size decreasing with increasing flash energy. Difference-of-Gaussian functions with constant centre size ( σ c = 0.25 deg ) provided the best fit in the high region. Overt input from the cones and grating area artefacts are excluded by appropriate tests. Calculation of photon flux into the receptive field centres suggests that signal compression in Pα ganglion cells contributes to the low rod plateau.

Double-flash electroretinography in human eyes.

A tri-color Ganzfeld stimulator with light-emitting diodes as light sources is used to study the suppression of the second electroretinographic response in human eyes to double-flash stimulation. The mechanism suppressing the a- and b-waves of the response to the second (test) flash has a scotopic spectral sensitivity to the first (conditioning) flash. Responses to mild test stimuli are more sensitive to suppression by a conditioning flash than responses to strong test stimuli.

The photoreceptors in atypical achromatopsia.

1. The receptoral mechanisms underlying the vision of two atypical achromats of the complete variety were studied with standard psychophysical procedures. 2. Under scotopic conditions the spectral sensitivity of each achromat was well described by the CIE (Commission Internationale de l'Eclairage) scotopic sensitivity function and the recovery of sensitivity after a retinal bleach showed characteristic duplex behaviour with the time constant of recovery of the slower phase matching that of normal rod vision for both foveal and peripheral stimulation. 3. Their spectral sensitivity was measured under conditions of chromatic adaptation in order to reveal any residual middle or long wavelength cone activity. Only one photopic spectral responses was found and this was adequately described by the spectral sensitivity function of Stiles pi 3 mechanism of normal vision. 4. Increment threshold measurements as a function of background intensity revealed a double-branched function in the fovea. The lower branch was found to have the spectral sensitivity of the rods; the upper branch that of Stiles' pi 3 mechanism. Stiles-Crawford measurements of directional sensitivity confirmed that the branch with the rhodopsin action spectrum had the directional sensitivity of rods and that the branch with the action spectrum of pi 3 had the directional sensitivity of cones. 5. These was no evidence for hue discrimination under photopic conditions. Regions of apparently normal performance on hue discrimination tests on more careful examination could be explained by luminosity judgements mediated by short wavelength-absorbing receptors. 6. We reject the notion of there being rhodopsin-filled cones in the fovea of these subjects. The foveal and peripheral vision of each of these achromats can be adequately described in terms of the participation of only two types of receptor, namely normally functional rods under scotopic conditions and normally functioning short wavelength-absorbing cones under photopic conditions. They are therefore functional blue mono-cone monochromats, an explanation which was originally proposed by Blackwell & Blackwell (1957) over thirty years ago.

Contribution of the retinal ON channels to scotopic and photopic spectral sensitivity

Visual information encoded by the middle-wavelength-sensitive (MWS) and long-wavelength-sensitive (LWS) cones in the primate retina are processed by both depolarizing (ON) and hyperpolarizing (OFF) bipolar cells. In contrast, signals from the short-wavelength-sensitive (SWS) cones and dark-adapted rod photoreceptors are thought to be carried almost exclusively by ON bipolar cells (Gouras & Evers, 1985). Consequently, it would be expected that functional inactivation of the retinal ON channels at the bipolar cell level would produce selective deficits in visual functions mediated by rods and SWS cones. We have examined this hypothesis by injecting rhesus monkeys with 2-amino-4-phosphonobutyric acid (APB), a pharmacological agent that reduces the responsiveness of retinal ON neurons, and psychophysically measuring the changes in spectral sensitivities. Under adaptation conditions that isolated rod function, APB caused, as expected, a substantial loss in rod-mediated spectral sensitivity. However, under photopic conditions, cone-mediated spectral sensitivity, including that associated with the SWS cones, was relatively unaffected. These results demonstrate distinct organizational differences between the rod and cone systems; specifically, they indicate that the rod system is more dependent upon retinal ON channels than the cone system. Our failure to find a selective visual deficit related to SWS cone function under photopic viewing conditions suggests that the OFF system can mediate stimulus detection throughout the visible spectrum and that the ability of the OFF system to process signals from the SWS cones has been underestimated.

Dark Adaptation and Recovery from Light Adaptation: Smokers versus Nonsmokers

Because the published data concerning the effects of smoking on visual sensitivity at night are inconsistent, a new study was initiated to obtain ground level comparison data from smoking and nonsmoking Army aviators. Blood samples also were analyzed to compare serum levels of nicotine, cotinine, and carboxyhemoglobin with the visual measures. The present data show no differences in visual sensitivity between smokers and nonsmokers and no significant correlations between the blood and visual measures. The conclusion from these results is that the ability to see the dimmest lights at night is independent of smoking history when scotopic sensitivity is assessed at ground level.

Spatial organization of sensitivity regulation in rod vision

To investigate whether scotopic sensitivity is set locally or in neural “pools”, we have tested the spatial variation in sensitivity after bleaching with gratings using 3 different methods. One experiment circumvented the influence of involuntary eye movements by deliberately randomizing the horizontal position of a fine test line on the area bleached by the vertical gratings. The spatial variation of threshold across the bleached area is reflected in the width of the frequency-of-seeing curve. A clear difference between the probability-of-seeing curves following a grating bleach and a uniform bleach was seen only up to between 4.2 and 6.3 c/deg, suggesting that adaptation signals are pooled so as to almost obliterate the contrast in finer gratings than this. In a second experiment the lowest bleaching-grating contrast (for a space-averaged initial rhodopsin bleach of 10%) that produced a patterned afterimage stayed close to the scotopic threshold contrast for frequencies from 1 to 6.4 c/deg, but it rose above the contrast threshold at high spatial frequencies. This slight loss of sensitivity at the high frequencies is more evidence for pooling in adaptation. A third experiment assessed the sensitivity profile at the adapting site without any influence of later stages of neural integration. Bleaching and test gratings of slightly different spatial frequency were flashed successively. If the effect of bleaching is restricted to the bleached rods, the observer will effectively be looking at the test grating through a grid of sensitive and insensitive stripes in his own retina. The two gratings come in and out of register at the difference frequency, and a corresponding low-frequency grating should be visible even when the test and bleaching gratings are not themselves resolved by the later stages. We could not see the difference frequency unless the test and bleach gratings were themselves coarse enough to be resolvable in rod vision. This is very strong evidence against any model in which each rod has its own sensitivity-regulating mechanism, and instead supports (for these conditions) Rushton's view that adaptation is entirely the work of a neural pool. The estimated pool size is about 10 min arc of visual angle.

Spectral sensitivity and chromatic discriminations in 3- and 7-week-old human infants.

The chromatic discrimination capabilities of 3- and 7-week-old infants were tested using 8 degrees, 417-, 448-, 486-, 540-, and 645-nm test fields embedded in a 547-nm surround and 486-nm test fields in a broadband red surround. In corroboration of earlier studies, few 3-week-old infants demonstrated chromatic discriminations, although their performance was somewhat better when one of the lights was long wavelength. Most 7-week-old infants could make chromatic discriminations, but they still demonstrated performance minima. The radiances of the test lights at the infants' performance minima were used to generate a spectral luminous efficiency curve. This curve agreed with both the adult heterochromatic brightness matches measured at 30 degrees of visual eccentricity in situ and the standard adult scotopic sensitivity curve V(lambda) over the short- and mid-wavelength range but deviated from both adult curves for the 645-nm test stimulus on a 547-nm surround. The results suggest that rod-initiated signals play a major role in infants' visual performance under the conditions tested.

Effects of Yellow Filter Glasses on the Results of Photopic and Scotopic Photometry

I measured the luminosity of a white surface with seven different yellow filter glasses and a photometer with two different sensitivities, which resembled the photopic and scotopic sensitivity of a Commission Internationale d'Eclairage standard observer. When measured with filters GG 400, GG 420, GG 435, and GG 455, there was a small and almost equal reduction in the relative photopic and scotopic luminosities. Measured with filters GG 475, GG 495, and OG 515, there was a more marked reduction in the scotopic luminosities than in the photopic luminosities.

The Relation of Rhodopsin and Scotopic Retinal Sensitivity in Sector Retinitis Pigmentosa

We used reflection retinal densitometric, psychophysical, and electroretinographic techniques to study the scotopic retinal function of a mother and her three daughters who had clinical evidence of a sectoral type of retinitis pigmentosa. Retinal regions with, and those without, ophthalmoscopic signs of degeneration were investigated. During dark adaptation, the time courses of rhodopsin regeneration and recovery of scotopic sensitivity were similar to normal as was the relation of rhodopsin to scotopic threshold. In dark-adapted eyes, threshold increases were not proportional to rhodopsin loss. The results of psychophysical tests of background adaptation and temporal summation, and analysis of the relation of electroretinographic a- to b-wave amplitudes, led to the conclusion that abnormalities of photoreceptor cell function central to the rhodopsin-bearing outer segments accounted for the increased thresholds.

The Relation of Rhodopsin and Scotopic Sensitivity in Choroideremia

We examined two patients who had clinical characteristics typical of choroideremia using psychophysical and reflection retinal densitometric techniques. In the dark-adapted state, sensitivity was more compromised than would be predicted on the basis of the modest losses of rhodopsin. In the dark-adapted state, studies of spatial and temporal summation suggested that postreceptoral processes are similar to normal. The kinetics of rhodopsin regeneration after bleaching exposures were abnormal in some retinal regions.

The Use of Coloured Overlays to Improve Visual Processing ‐ A Preliminary Survey

Abstract Forty volunteers reporting consistent reading problems were divided into three groups on the basis of an assessment of degree of scotopic sensitivity. Four speeded visual processing tasks involving word matching and letter and number identification were administered to all subjects using three plastic overlays, one of a colour maximizing visual efficiency, one chosen at random and one with no colour. For subjects with high scotopic sensitivity, the use of optimal coloured overlays yielded significantly better results on some visual tasks than the other two overlays. Implications of these findings are discussed.

Scotopic and Photopic Spectral Sensitivities of Boobies

AbstractThe day and night visual capacities (photopic and scotopic spectral sensitivity) of several species of boobies (family Sulidae) were analyzed using a behavioral psychophysical testing technique. On the basis of these data there is evidence for sensitivity to near‐ultraviolet light in the order Pelecaniformes. The scotopic spectral sensitivity functions of three booby species conform closely to the spectral absorption characteristics of avian rhodopsin. There are marked differences between the photopic sensitivities of a coastal booby species with that of a pelagic species; these differences appear correlated with their respective feeding ecologies. Lastly, a brief review of avian spectral sensitivity and a consideration of individual variation in avian vision studies are presented.

The relationship of retinal sensitivity and rhodopsin in human infants

During dark adaptation after full field, ⩾90% bleaches recovery of sensitivity and regeneration of rhodopsin were studied using electroretinographic and pupillographic techniques in both 10-week-old infants and adults. The courses of scotopic sensitivity recovery and rhodopsin regeneration of infants and adults were similar and were reasonably well fit by single exponentials having τ = 400sec. For both infants and adults log scotopic sensitivity was linearly related to the proportion of rhodopsin present during dark adaptation. It is concluded that by age 10 weeks human distal retinal processes that occur after photolysis are equivalent to those of adults.