Vision and driving: selective effect of optical blur on different driving tasks.

A test of static (high-contrast) visual acuity is the most prevalent vision test used to screen driver license applicants worldwide, even though research has largely failed to provide convincing empirical evidence for its role in traffic accidents. The purpose of this research was to evaluate the effect of visual acuity degradation on different components of the driving task. Participants were 24 young licensed drivers (15 men, 9 women) with normal vision. Driving performance was measured while participants wore modified swimmer's goggles to which blurring lenses were affixed in amounts necessary to produce binocular visual acuity levels of 20/20, 20/40 (the prevalent acuity standard for driving), 20/100, and 20/200. Driving performance was measured using the closed-road method of Wood and Troutbeck (1994). Acuity degradation produced significant decrements in road sign recognition and road hazard avoidance as well as significant increments in total driving time. Participants' abilities to estimate whether clearances between pairs of traffic cones were sufficiently wide to permit safe passage of the vehicle and to slalom through a series of traffic cones were relatively unaffected by acuity degradation. Thus the latter tasks appear to be mediated by aspects of central and peripheral vision that are relatively unaffected by optical blur. Potential applications of this type of research include the development of procedures for defining empirically justifiable vision standards for driver licensure.

Detection and identification of mirror-image letter pairs in central and peripheral vision.

Reading performance is poorer in the peripheral than in the central visual field, even after size-scaling to compensate for differences in visual acuity at the different eccentricities. Since several studies have indicated that the peripheral retina is deficient with respect to spatial phase discrimination, we compared the psychometric functions for detection (D) and identification (I) of size-scaled, mirror-symmetric letters (i.e. letters differing in the phase spectra of their odd symmetric components) at three inferior field eccentricities (0, 4, and 7.5 deg) using a two-alternative, temporal, forced-choice procedure and retinal image stabilization to control retinal locus. Each subject's data were fit with Weibull functions and tested for goodness-of-fit under several hypotheses. This analysis revealed that while the psychometric functions were of constant shape across eccentricity for the respective tasks, they showed statistically significant variations in the D/I threshold ratios. However, these variations were so small that poorer reading outside the fovea is unlikely to be due to reduced letter discriminability that might occur secondary to a loss of peripheral field phase sensitivity.

The effect of nonnutritive sucking on bottle-feeding stress in preterm infants.

OBJECTIVE: To examine the effects of nonnutritive sucking on the physiologic and behavioral stress reactions of preterm infants at early bottle feedings and to examine the effect of nonnutritive sucking on the feeding performance of preterm infants at early bottle feedings. DESIGN: Quasi-experimental with a matched sample. SETTING: A level III neonatal intensive-care unit in a large medical center. PARTICIPANTS: Twenty preterm infants whose gestational ages at birth ranged from 26 to 34 weeks. INTERVENTIONS: Ten infants were provided nonnutritive sucking for 5 minutes before and 5 minutes after an early bottle feeding. Ten infants served as controls. MAIN OUTCOME MEASURES: Physiologic stress was measured by heart rate and oxygen saturation rate. Behavioral stress was measured by observation of behavioral state. Feeding performance was measured by duration, percentage of formula taken by bottle, and behavioral state after feeding. RESULTS/CONCLUSIONS: Infants who received nonnutritive sucking before and after bottle feedings were more likely to be in a quiescent behavior state 5 minutes after the feeding (p = .01) and had higher feeding performance scores (p = .01) than infants who did not receive nonnutritive sucking.

Spatial contrast sensitivity: effects of age, test-retest, and psychophysical method.

Spatial contrast sensitivity was tested twice in normal subjects from five age groups by using each of two different psychophysical methods. Results obtained by the method of adjustment showed a decline in sensitivity with increasing age at all spatial frequencies. In contrast, the forced-choice procedure yielded results indicating an age-related decline predominantly at high spatial frequencies, with the magnitude of the decline being generally similar to that obtained earlier by a tracking method [Vision Res. 23, 689 (1983)]. The decline that we observed cannot be due to pupillary changes with age, since this factor was controlled. Moreover, we suggest that the high-spatial-frequency decline in contrast sensitivity, although it is comparatively small, is too large to be due to changes in lens density. We therefore suggest that a neural component is responsible. In addition, interactions among the age of the subject, the spatial frequency used, and the psychophysical method used suggest that the method of adjustment should be avoided for age-related studies of vision.

Age and illuminance effects in the Farnsworth-Munsell 100-hue test.

Seventy-five normal volunteers (20-78 yr) were tested on the Farnsworth-Munsell 100-hue test at each of five illuminance levels. Each cap score distribution was analyzed by fitting a two-cycle sine wave whose amplitude and phase characterize the polarity of the error distribution and its axis. Analysis of these parameters reveals a similarity between tritanlike defects in older groups and those of younger groups at lower illuminance levels. These data are also useful for specifying age norms for the polarity of the error distribution.

Clinical measurement of saturation discrimination.

In this paper, we describe how a circular reflective neutral-density wedge can be used to construct an apparatus which provides a relatively rapid procedure for the clinical measurement of saturation discrimination. Subsequent to an initial measurement of the patient's relative luminosity function, the patient need only turn a single control which varies the colorimetric purity of a test field which remains luminance matched to a white light reference field.

Retinal cotton-wool spots: an early finding in diabetic retinopathy?

Five insulin dependent diabetic patients are reported on who had a few small retinal cotton-wool spots or 'soft exudates' either totally isolated or associated with fewer than 10 microaneurysms. These observations suggest that cotton-wool spots may be an early finding in diabetic retinopathy. Significant biological abnormalities in these patients were high levels of glycosylated haemoglobin and mild increases in thrombin generation, indicating slight activation of the coagulation system. The possible significance of these clinical and biological findings is discussed.

Temporary loss of foveal contrast sensitivity associated with panretinal photocoagulation.

Snellen visual acuity and spatial contrast sensitivity measurements were used to monitor changes in foveal vision in two patients undergoing argon laser panretinal photocoagulation (PRP) in both eyes for proliferative diabetic retinopathy. Foveal edema developed in one of the four eyes. The remaining three eyes showed no signs of foveal edema, but developed temporary losses in high spatial frequency contrast sensitivity during the closely spaced PRP treatments. Since Snellen visual acuity remained stable at the prelaser level, these results indicate the need for more sensitive measures of visual resolution to monitor foveal integrity in patients undergoing PRP.

Clinical spatial contrast sensitivity measurement: implications of artificial scotoma experiments.

Measurement of spatial contrast sensitivity in normal subjects showed that the change produced by an artificial central scotoma depended on temporal factors associated with grating presentation. Minimizing temporal transients produced a predominantly high spatial frequency loss. Accentuating temporal transients produced an additional low spatial frequency change in sensitivity.

Spatial contrast sensitivity. Importance of controlling the patient's visibility criterion.

Clinical spatial contrast sensitivity measurements are typically made using psychophysical methods that do not specify the response criterion being used by the patient in judging grating visibility. Results of this report show the necessity of such methods for (1) maximizing detectability of early contrast sensitivity deficits by minimizing normal sample variance, and (2) ensuring that changes in an individual's contrast sensitivity reflect changes in vision and not simply fluctuations in the patient's criterion for judging grating visibility.

Tritan pedigree without optic-nerve atrophy.

Results of several previous reports have questioned the occurrence of the tritan color deficiency independently of dominantly inherited optic atrophy. This report describes the results of testing 34 members of a pedigree (including four tritans) for whom optic atrophy can be ruled out according to criteria previously described by Krill et al.

Effect of artificial central scotoma on the spatial contrast sensitivity of normal subjects.

Spatial contrast sensitivity was measured in normal subjects with and without a retinally stabilized artificial scotoma (either circular or rectangular), which precluded foveal vision. Our results indicate that the type of contrast sensitivity loss obtained (predominantly high frequency or overall) depended on temporal factors associated with grating presentation. A predominantly high frequency loss was obtained when grating contrast was turned on and off gradually. An additional low frequency difference was obtained when grating contrast was turned on and off abruptly.

Long-term stability of the dark focus of accommodation.

For 1 year we monitored the stability of the accommodative state assumed in darkness (the dark focus) of five subjects. Our results are similar to previously reported individual mean values. The magnitude and pattern of the variability in the dark-focus also demonstrate individual differences. Despite this individual variability, all five subjects oscillated around a stable mean dark-focus value throughout their respective measurement periods. This study indicates the feasibility of using the dark-focus as a basis for correcting the anomalous myopias, in particular night and empty-field myopia.

Amblyopic contrast sensitivity: insensitivity to unsteady fixation.

Functional amblyopia (a typically unilateral loss of visual acuity of unknown origin) is frequently accompanied by unsteady fixation. Measurements taken under conditions of retinal-image stabilization indicate that this fixation problem does not contribute to the currently measured losses in spatial contrast sensitivity of the amblyopic eye. Indeed, retinal image motions recorded from unsteadily fixating eyes do not produce spatial contrast sensitivity losses when superimposed on the central field of a normal subject, indicating that such losses are not an immediate consequence of unsteady fixation.

Monocular performance of functional amblyopes: another look at the scotoma hypothesis.

The traditional scotoma hypothesis for functional amblyopia is modified to state: whereas the central visual field of a normal visual system and that of an organic amblyope become increasingly scotomatous as light level is decreased from high to low photopic levels, the reverse is true for the central field of a functionally amblyopic visual system. An attempt is made to show how this hypothesis provides a unifying explanation for several seemingly different visual performances observed in functional amblyopes. The paper deals with (1) field inhomogeneities and threshold measures, and (2) threshold changes with light adaptation level. Implications of the modified scotoma hypothesis are discussed for (1) the neutral-density-filter test to distinguish functional from organic amblyopia, (2) the reduced CFF threshold for amblyopic eyes, (3) expectations of stereopsis for amblyopes, and (4) possible mechanisms for amblyopia.

Color vision testing: an alternative 'source' of Illuminant C.

The objective of this project was to evaluate an alternative procedure for administering reflective-type color vision tests. In this procedure, the tests are illuminated by a low color-temperature, 100 W, incandescent lamp (i.e. an improper illuminant) and the patient then views the illuminated test elements through an inexpensive gelatin filter placed before his eye (e.g. a Wratten 78AA costing about $4). Since the relative transmittance of this filter is quite similar to that used in the Macbeth Easel Lamp, the tests should still be valid. In fact, this alternative procedure yields test performances for normal and deficient subjects on the 100-hue, panel D-15, and AO H-R-R tests that are virtually identical to those obtained using a standard Macbeth Easel Lamp.

Validity of Pinckers' 100-Hue version of the Panel D-15.

Fifteen normal and 18 red-green-deficient subjects were tested with the Farnsworth Dichotomous Test of color vision (Panel D-15) and with an alternative version of the dichotomous test consisting of selected color chips from the Farnsworth-Munsell 100-Hue Test. Results indicate that the 100-Hue version of the dichotomous test is equivalent to the standard Panel D-15 with respect to detecting and differentiating among the more severe red-green deficiencies. These results confirm A. Pinckers' previous suggestion that the 100-Hue Test contains the components necessary for a Farnsworth Panel D-15.