Visual information processing in high-functioning individuals with autism spectrum disorders and their parents.

The authors assessed visual information processing in high-functioning individuals with pervasive developmental disorders (PDD) and their parents. The authors used tasks for contrast sensitivity, motion, and form perception to test visual processing occurring relatively early and late in the magnocellular-dorsal and parvocellular-ventral pathways. No deficits were found in contrast sensitivity for low or high spatial frequencies or for motion or form perception between individuals with PDD in comparison with a matched control group. Individuals with PDD performed equally with or better than controls on motion detection tasks. In addition, the authors did not find differences on any of the tasks between parents of the PDD group and matched control parents. These results indicate that high-functioning individuals with PDD and their parents are able to process visual stimuli that rely on early or late processing in the magnocellular-dorsal and parvocellular-ventral pathways as well as controls.

Measurement of stray light and glare: comparison of Nyktotest, Mesotest, stray light meter, and computer implemented stray light meter.

AIM: To evaluate the properties of devices for measuring stray light and glare: the Nyktotest, Mesotest, "conventional" stray light meter and a new, computer implemented version of the stray light meter. METHODS: 112 subjects, divided in three groups: (1) young subjects without any eye disease; (2) elderly subjects without any eye disease, and (3) subjects with (early) cataract in at least one eye. All subjects underwent a battery of glare and stray light tests, measurement of visual acuity, contrast sensitivity, refraction, and LOCS III cataract classification. Subjects answered a questionnaire on perceived disability during driving. RESULTS: Repeatability values were similar for all glare/stray light tests. Validity (correlation with LOCS III and questionnaire scores), discriminative ability (ability to discriminate between the three groups), and added value (to measurement of visual acuity and contrast sensitivity) were all superior for both stray light meters. Results of successive measurements are interrelated for the conventional but not the new stray light meter. This indicates a better resistance to fraud for the latter device. CONCLUSIONS: The new computer implemented stray light meter is the most promising device for future stray light measurements.

Light scattering by donor lenses as a function of depth and wavelength.

PURPOSE: To determine quantitatively dependence on the wavelength and angle, as a function of depth, of light scattering in the human lens. To compare the result for forward directions with psychophysical data. To derive candidate particle distributions that might be responsible for nuclear light scattering as significant in the psychophysical situation. METHODS: The amount of light scattered by donor lenses (n = 15, ages 48 to 82 years) from a 1-mm x 0.1-mm white slit beam was measured as a function of depth in the lens for seven angles from 10 degrees to 165 degrees, and for four wavelengths from 400 to 700 nm. Absolute values for light scattering (Rayleigh ratios) were derived. RESULTS: The light-scattering data are confounded by the short wavelength-absorbing pigments in the lens. After correction, backward light scattering in the nucleus followed wavelength to a power of -4. In the superior layers and for forward directions in the nucleus, light scattering was less dependent on wavelength. The nuclear data could be explained on the basis of a bimodal protein particle distribution: particles much smaller than wavelength, in quantitative accordance with the literature, and particles larger than wavelength, which control forward light scattering. CONCLUSIONS: The particles of significance for forward light scattering have, on average, a mean radius of 692 nm and constitute only 0.000003 of the volume. The wavelength dependence of retinal stray light is lessened by: the large sizes, the contribution of superficial lenticular layers, the lenticular pigments, and the contribution of other components of the eye.

Quantal and visual efficiency of fluorescence in the lens of the human eye.

PURPOSE: To document quantitatively the fluorescence in the human lens relevant to its interference with visual function. To explain quantitatively the experimental findings relative to loss of visual function. To study the relation between the fluorescence and the light transmission of the lens. METHODS: Three normal lenses, from 22-, 28-, and 69-year-old donors, were used. Fluorescent light was induced by a 4-mm diameter pencil beam of 380, 400, or 420 nm. It was measured as a function of the deflection angle from -10 to 150 degrees for different wavelengths. RESULTS: The shapes of the emission spectra were comparable to those reported in the literature. Total quantal efficiency of fluorescence was between 5% for 69 years and 380 nm excitation and 0.4% for 22 years and 420 nm excitation. The forward intensity was less than the backward intensity because of secondary absorption. CONCLUSIONS: Fluorescence of the lens causes light with wavelengths of 420 nm and lower to be much more visually effective. A marked homogeneous veil is added to the point spread function. The total increase in luminous efficiency was a factor 3 to 6 at 400 nm, and a factor 70 to 150 at 380 nm. For other visual effects (glare) the increase can be larger.

Depth-dependent forward light scattering by donor lenses.

PURPOSE: To determine quantitatively forward light scattering in the human lens as a function of depth. To use this to explain the psychophysical result, verified earlier in vitro, showing total light scattering in the human lens to decrease with scattering angle according to an approximate power law (power -2). METHODS: The amount of light scattered by donor lenses (n = 15; age range, 43 to 82 years) from a 1 mm x 0.1 mm white slit beam was measured as a function of depth in the lens for seven angles from 10 degrees to 165 degrees and for four wavelengths from 400 to 700 nm. Absolute values for light scattering (Rayleigh ratios) were derived. RESULTS: Light scattering of the total lens corresponded quantitatively to psychophysically determined in vivo stray light data. Powers were approximately -2.2. An important source of forward scattered light is located superficially at the anterior and the posterior poles. Nuclear forward light scattering varied over 2 log units, more or less in line with clinical assessment of nuclear opacity (LOCS III NO score). Nuclear powers were approximately -1.4. CONCLUSIONS: In vitro forward light scattering of donor lenses as a whole corresponded with in vivo data, but different depths in the lens contributed differently. Studies on functionally relevant light scattering by the human lens proteins should be conducted to explain true (in vivo) lenticular light scattering.

Conversion of lens slit lamp photographs into physical light-scattering units.

PURPOSE: To derive from lens slit lamp photographs by means of densitometry the physically defined quantity for light scattering (the Rayleigh ratio) and to expand the use of the Lens Opacity Classification System (LOCS III) to include clear lenses and also to calibrate the LOCS III Nuclear Opacity (NO) score in physical terms. METHODS: Series of slit lamp photographs were taken from 38 eyes from 29 subjects (age range 18 to 84 years old) including cataracts, for 0.1- and 0.2-mm slit width, using 200 ASA and 1600 ASA film speed (Kodak professional; Eastman Kodak, Rochester, NY) and different flash settings with a Topcon SL-6E (12 slit/speed/flash combinations; Paramus, NJ). Additionally 19 eyes were photographed with a Zeiss 40 SL/P (8 slit/speed/flash combinations; Carl Zeiss, Thornwood, NY). A calibrated suspension of latex spheres also was photographed at the same 20 conditions. Densitometry was performed on the nuclear area of all photographs including the LOCS III standards, using a photometrically corrected photocell. Slit width and flash intensity settings were photometrically calibrated. All eyes and the suspension were digitally "photographed" with the EAS-1000 (Nidek, Gamagori, Japan) Scheimpflug system. RESULTS: For each eye and the suspension, the series of 20 or 12 densities, corresponding to a range of about 1 log unit in the amount of light used, proved to follow closely a course common to all eyes (the two film characteristics), apart from a shift in the amount of light (because of the differences in light back scattering). CONCLUSIONS: From normal slit lamp photographs, the physical quantity for light (back) scattering can be derived using transformation graphs derived in this study. The LOCS III NO score also can be used for clear lenses and translated into physical units. In this way, slit lamp photography can be used better for more precise studies, provided some minimal calibration of the photograph slit lamp.

Relationship between spectral transmittance and slit lamp color of human lenses.

PURPOSE: To study the relationship between subjective lens color as observed with slit lamp biomicroscopy and spectral transmittance of the lens. To propose a model for this relationship to derive quantitative information on lens pigmentation from slit lamp observation. METHODS: Twenty-nine normal lenses, from donors aged 14 to 86 years, were used. The fraction of light transmitted from a narrow beam was measured as function of wavelength. The spectra were fitted with the one-parameter TL model of Pokorny et al. The relationship between this parameter and the color grading from Chylack et al. (lens opacity classification system III nuclear color score) was established. RESULTS: After slight adaptation of the TL model, the shapes of the transmittance spectra corresponded closely to the TL model (average residual error 0.05 log units). Log transmittance and lens opacity classification system nuclear color score were closely related (r = 0.90, 0.77, and 0.55 for 400, 500, and 602 nm, respectively). CONCLUSIONS: A mathematical relationship between TL parameter and lens opacity classification system nuclear color score could be established to predict lens transmittance from lens opacity classification system nuclear color score. This relationship was successful in predicting the correction for lens absorption needed in blue-on-yellow perimetry.

Intraocular light scattering in age-related cataracts.

Intraocular light scattering was studied in 34 controls and 65 patients with cortical, nuclear, or posterior subcapsular cataracts by measuring forward scatter and backscatter. Forward scatter was measured by the psychophysical direct compensation method. Backscatter was determined with the Lens Opacity Meter of Interzeag. Contrast sensitivity loss caused by forward scatter was assessed with a glare tester (Vistech MCT 8000). Mean forward scatter was in the upper range for subcapsular cataracts compared to nuclear and cortical cataracts. Experimental results of the glare test (the contrast loss) deviated systematically from expected results based on measured forward scatter. Mean backscatter was largest for nuclear, intermediate for posterior subcapsular, and almost zero for cortical cataracts. Thus, each cataract has a characteristic mean ratio between forward scatter and backscatter. However, this ratio varied considerably among individuals, especially for cortical and posterior subcapsular cataracts. As a rule, forward scatter cannot be derived from backscatter (or the slit-lamp image).

Functional characteristics of blue-on-yellow perimetric thresholds in glaucoma.

PURPOSE: Blue-on-yellow (B-on-Y) perimetry assesses the S-cone visual field under yellow adaptation. Glaucomatous field defects have been shown to appear earlier and to be larger in B-on-Y perimetry than in standard perimetry. An upper limit to the use of B-on-Y perimetry is set by the separation of the S-cones from the M- and L-cones. But, because the S-cones may also input to the luminance channel, the actual separation of the color and luminance channels is unknown. Here, the relative sensitivities of the color and luminance channels under B-on-Y test conditions are measured. METHODS: In 15 eyes with early glaucoma, 19 risk eyes, and 10 normal eyes, B-on-Y thresholds were measured from 0 degrees to 20 degrees eccentric and were compared to pure chromatic (B-in-Y) and achromatic (Y-on-Y) thresholds, obtained under identical yellow adaptation. RESULTS: In normals, B-on-Y thresholds were found to coincide with B-in-Y thresholds; Y-on-Y values were 0.5 log (at 20 degrees) to 0.9 log (at 0 degrees) higher. In the pathologic groups, the differences between B-in-Y and Y-on-Y thresholds were smaller. Pathologic threshold elevation is on average 1.8 times larger for chromatic than for achromatic stimuli. In some cases, the luminance channel takes over detection of the B-on-Y stimulus. CONCLUSIONS: In normals, the B-on-Y stimulus is mediated by the color channel. Takeover of detection by the luminance channel might impose limits on following color defects with B-on-Y perimetry. This takeover may occur before the S-cones become less sensitive than the M- and L-cones and might indicate S-cone input to the luminance channel.

Quantitative analysis of iris translucency in Fuchs' heterochromic cyclitis.

PURPOSE: To measure intraocular stray light and to quantify translucency of the iris and the surrounding ocular wall in both eyes of patients with Fuchs' heterochromic cyclitis; to investigate whether differences in paired eyes could be measured in patients without heterochromia or with a minimal degree of iris atrophy. METHODS: Intraocular stray light was measured by means of the direct compensation technique. A modification of this technique was used to quantify translucency of the iris and the surrounding ocular wall. RESULTS: Intraocular stray light proved to be significantly higher in all patients with Fuchs' heterochromic cyclitis (both eyes) than in normal control subjects. Translucency of the iris and the ocular wall around it were increased in the patients with Fuchs' heterochromic cyclitis, including patients without heterochromia or with a minimal degree of iris atrophy. CONCLUSIONS: Quantitative analysis of translucency was used to determine iris depigmentation in vivo in patients with Fuchs' heterochromic cyclitis. This technique showed that the process of atrophy and depigmentation in patients with Fuchs' heterochromic cyclitis is probably not restricted to the iris, but also occurs in the surrounding ocular wall. More studies, including other uveitis groups, are necessary to investigate if this technique can be used as a diagnostic tool in Fuchs' heterochromic cyclitis.

A comparison of retinal and choroidal hemodynamics in patients with primary open-angle glaucoma and normal-pressure glaucoma.

PURPOSE: To quantify, compare, and assess differences between retinal and choroidal hemodynamics in normal control subjects and patients with ocular hypertension, primary open-angle glaucoma, and normal-pressure glaucoma. METHODS: Video fluorescein angiograms were made in 20 normal subjects, 11 patients with ocular hypertension, 45 patients with primary open-angle glaucoma, and 43 patients with normal-pressure glaucoma. Choroidal dye build-up curves were analyzed using an exponential model. The model time constant tau reflected the local blood refreshment time, the time needed to replace the blood volume in a tissue volume. Retinal arteriovenous passage time was estimated from the time lapse between retinal arterial and venous dye curves. RESULTS: The retinal arteriovenous passage time was longer in patients with primary open-angle glaucoma compared with normal subjects and patients with normal-pressure glaucoma; the average arteriovenous passage times (+/-SEM) in normal subjects and in patients with ocular hypertension, primary open-angle glaucoma, and normal-pressure glaucoma were, respectively, 2.44 +/- 0.19, 2.90 +/- 0.37, 3.02 +/- 0.17, and 2.55 +/- 0.15 seconds. Choroidal tau was longest in the normal-pressure glaucoma group but not as long in the primary open-angle glaucoma group; tau values in normal subjects and patients with ocular hypertension, primary open-angle glaucoma, and normal-pressure glaucoma were, respectively, 4.6 +/- 0.29, 5.6 +/- 0.69, 6.2 +/- 0.39, and 7.1 +/- 0.33 seconds. CONCLUSIONS: Whereas choroidal circulation is especially slower in patients with normal-pressure glaucoma, retinal circulation is delayed in patients with primary open-angle glaucoma. The choroidal and retinal vascular systems behave differently in primary open-angle and normal-pressure glaucoma, which may be important in the management of glaucoma.

Stray light in radial keratotomy and the influence of pupil size and straylight angle.

Glare is a major sequela of the radial keratotomy procedure. We used the straylight meter to measure intraocular light scatter, which is the cause of glare, in eyes after radial keratotomy. This apparatus uses a direct compensation method to assess the amount of intraocular light scatter. Nineteen patients were tested. Nine individuals served as controls. The mean postsurgery time was 60 months. The influence of the number of radial incisions, the pupil size, and the angle of light entering the eye were evaluated with the straylight meter. The results showed straylight values for normal pupil size (mean, 4 mm) to be statistically significantly higher (P = .0044) only for the smallest angle of light deflection studied (3.5 degrees). For dilated pupils (mean, 8 mm), straylight values were statistically significantly higher (P = .00005) for all three angles of light deflection studied. The number of incisions showed no statistically significant relationship to straylight values. Average stray light values were increased by a factor of 1.4 for 4-mm sized pupils and 2.0 for 8-mm sized pupils. There was an overlap in straylight values between the patient population and the control population.

Grading of retinal nerve fiber layer with a photographic reference set.

PURPOSE: We developed a new quantitative approach for the evaluation of diffuse atrophy of the retinal nerve fiber layer. METHODS: A simultaneous, visually supported grading system was designed, which consisted of a set of 25 reference photographs, numbered from 25 (broad, clearly striated nerve fiber bundles) to 1 (no nerve fibers visible). We prospectively evaluated this method by matching 60 retinal nerve fiber layer photographs of patients with glaucoma or ocular hypertension and normal subjects to the reference photographs twice by three observers with varying experience levels in evaluating retinal nerve fiber layer RESULTS: Intraobserver and interobserver reliability, evaluated by the intraclass correlation coefficient statistics, was excellent (intraclass correlation coefficient > 0.8). Intraclass correlation coefficients within observers were from 0.89 to 0.98 (lower limits 905% confidence interval, 0.84 to 0.97), and intraclass correlation coefficients between observers were from 0.81 to 0.91 (lower limits 95% confidence interval, 0.50 to 0.87). Clinical validity, in which the scores for upper and lower halves of photographs were compared with the mean deviation of the Humphrey 30-2 visual field program by using the Spearman correlation coefficient, was substantial (r = -.68, P < .01 for upper photo score and lower field mean deviation, r = -.53, P < .01 for lower photo score and upper field mean deviation). CONCLUSIONS: By using a reference set of of photographs of the retinal nerve fiber layer, we defined a method to derive a quantitative measurement of retinal nerve fiber layer with good reliability and to extend evaluation of retinal nerve fiber layer photographs to nonspecialists.

Retinal nerve fiber layer assessment by scanning laser polarimetry and standardized photography.

PURPOSE: To determine whether, in a clinical setting, scanning laser polarimetry and retinal nerve fiber layer photography provide equivalent information on the retinal nerve fiber layer. METHODS: We prospectively studied 60 patients with glaucoma or ocular hypertension and 24 healthy subjects. With scanning laser polarimetry, an estimate of the cross section of the retinal nerve fiber layer was obtained. By using a photographic reference set, we quantified photographs of the retinal nerve fiber layer. Visual fields were used to relate the results of both methods to functional damage. RESULTS: The scanning laser polarimetry measurements yielded reproducible cross-section values (coefficient of variation, 6.6%). Comparison of cross-section values and photograph scores gave Pearson correlation coefficients smaller than r = .4 (P < .01), improving to a maximum of r = .53 after compensation for offset. When cross-section values were compared to the mean deviation of the visual field, the Spearman correlation coefficients varied from an r of -.34 to -.53 (P < .01). Correction for offset resulted in an r of -.54 to -.65. When photograph scores and mean deviation of the visual field were compared, the Spearman correlation coefficients varied from an r of -.65 to -.71 (P < .01). CONCLUSIONS: Because r was maximal at .53, the information on the retinal nerve fiber layer obtained with scanning laser polarimetry and photography seems not equivalent. This result could not have been because of lack of reproducibility. Although the results suggested possible offset in scanning laser polarimetry, other methodologic differences must be considered to explain the differences between the two techniques.

Forward light scatter at one month after photorefractive keratectomy.

BACKGROUND: Although it is known that backward light scatter increases transiently following most excimer laser photorefractive keratectomies (PRKs), it is not clear that there is a significant increase in forward light scatter, which is of primary concern for the patient. The object of this study was to determine if there is a significant change of forward light scatter at 1 month after (PRK) with an ablation zone diameter of 6 mm. METHODS: Overlapping subsets of 24 normal myopic eyes were tested before (on the day of surgery) and 1 month after PRK, using three instruments: a Stray Light Meter (16 eyes); a Computerized Stray Light Meter (14 eyes); and a mesopic Increment Threshold-Glare Paradigm (six eyes). Differences between the two eyes before PRK were compared with the differences between the same eye before and after PRK, using repeated measured analysis of variance. In addition, increment threshold data obtained from 22 eyes after PRK were compared with those of 60 controls of the same age range and distribution by a t test. RESULTS: None of the statistical comparisons approached significance at the alpha = 0.05 level. Changes in light scatter as small as a factor of 1.95 (Stray Light Meter) and 1.55 (Increment Threshold-Glare Paradigm) could be detected as significant with a high power (0.8). Changes larger than a factor of 21 could be detected with a power of 0.8 for the Computerized Stray Light Meter. CONCLUSIONS: In these data, there is no support for the hypothesis that forward light scatter increases significantly 1 month after PRK with an ablation zone of 6 mm. Any increases in forward light scatter are unlikely to be greater than a factor of 1.5 to 2 under daytime or nighttime illumination conditions.

Near infrared light absorption in the human eye media.

Available literature on the spectral transmittance of the eye media in the infrared (IR) is insufficiently accurate to estimate the deposited doses, e.g. in view of light damage risks. Analysis of the data of Boettner and Wolter [Investigative Ophthalmology and Visual Science, 1, 776-783 (1962)] for cornea, anterior chamber, lens and vitreous separately, shows that they can be explained on the basis of the pure water content. The transmittance spectrum of Geeraets et al. [Archives of Ophthalmology, 64, 606-615 (1960)] for all eye media combined is found to be impossible. It is concluded that in the near-IR, light losses in the eye media are best estimated with the absorption coefficient for pure water. A table is given from 700-2500 nm in steps of 10 nm.

Light scattering model for donor lenses as a function of depth.

The amount of light scattered by normal donor lenses (n = 15, ages 43-82 years) from a 1 x 0.1 mm white slit beam was measured as a function of depth in the lens for seven angles from 10 to 165 degrees, and for four wavelengths from 400 to 700 nm. Apart from the most superficial layers, the data could be described with a model that consisted of three components. (1) small sized protein particles (alpha-crystallin), (2) large sized protein particles and (3) spectrally neutral rough surface reflectance ('zones of discontinuity'). Component (1) and (3) dominate backward scattering. Component (2) dominates forward scattering, but occupies only around 0.000006 of the lens volume, with the lowest values in the nucleus. Component (3) is important for a small range of backward directions only, being much stronger in extranuclear areas than in the nucleus.

Light transmittance of the human cornea from 320 to 700 nm for different ages.

In vivo relative corneal transmittance was estimated using Tan's [(1971) Vision in the ultraviolet, thesis, University of Utrecht, The Netherlands] data on scotopic spectral sensitivity in aphakic eyes. This was combined with in vitro corneal transmittance data and in vivo light scattering data to arrive at absolute data. All data combined, the following function (no age dependence is found) resulted: log(transmittance) = -0.016-c*lambda-4 (lambda = wavelength in nm, lambda > 310 nm). c = 85*10(8) nm4 for direct transmittance (acceptance angle of the order of 1 deg) and c = 21*10(8) nm4 for total transmittance (acceptance angle close to 180 deg).

Light scattering in donor lenses.

Light scattering for normal and cataractous lenses from 21-86 yr old donors was measured in vitro. As expected, scattering increased with severity of cataract. Scattering decreased with angle according to a power law. This corresponded to the power law finding for functional straylight measurements in early-cataract patients using white light (power around -2). In vitro, straylight increased monotonically from 700 nm (power around -2.3) towards 400 nm (power around -2.0). For extreme cataracts the angular dependence flattened at small angles. The present results suggest that the structures dominating in light scattering differ not by scattering type but by number, and that they are not very small compared to wavelength. The present results were used to specify the separate effects of light absorption and light scattering on lenticular light transmission.

The spectral shape of A2 visual pigments.

A mathematical description is proposed for the shape of absorption spectra of A2 visual pigments in which the shape continuously varies with peak wavelength lambdamax. The description consists of two parts: (a) the peak and short wavelength region is described by the sum of three lognormal curves and (b) the long wavelength region is derived from an existing physical model, including temperature dependence. The resulting function can be used as a basis for action spectra, also if a large long wavelength tail is present. The parameters of the functions as a function of lambdamax were assessed by fitting experimental goldfish rod and cone spectra. By interpolation of these parameters spectra can be calculated for lambdamax values all over the visual spectrum.