Psychophysical evidence for losses in rod sensitivity in the aging visual system.

Rod sensitivity was measured with a criterion-free psychophysical method at 10 deg in the horizontal meridian of the nasal field of the left eye on 26 young (mean age, 24.1 yr) and 14 older (mean age 72.6 yr) observers in good ocular health. A 1 deg, 90 msec stimulus was delivered by means of a free-viewing optical system under computer control. Stimulus wavelengths were chosen to have either significant (406 nm) or minimal (560 nm) absorption by the older lens. After correction for senile miosis and lens density, 0.39 log unit higher thresholds for the older observers remained and are interpreted as being due to neural factors.

Photophobia in patients with traumatic brain injury: Uses of light-filtering lenses to enhance contrast sensitivity and reading rate.

Patients who have sustained traumatic brain injury (TBI) often experience a new, intense and chronic photophobia. Photophobia, an intolerance to light, is an incompletely understood, subjective symptom, which has been divided into ocular and central types. Various commercial sources of light-filtering lenses have been developed, which have proven to be successful in diminishing visual symptoms expressed by patients who are photophobic. However, despite the many subjective reports of improved visual performance and comfort with use of these filters, there has been little documentation of actual enhanced visual sensitivity/efficiency. Letter contrast sensitivity (CS) and reading rate were measured in patients with TBI, who, despite good ocular health, experienced significant light intolerance. These patients exhibited up to two fold increases (0.3 log units) in binocular letter contrast sensitivity, as measured with the Pelli-Robson Letter CS Chart, in the presence of selected Corning Photochromic Filters (CPF), as compared to performance in the absence of CPF filters, or to that of similarly treated normal observers. These same patients demonstrated reading rates enhanced up to 39% above that measured in the presence of nearpoint optical correction alone. Reading performance of normal observers was unaffected by similar light filtration. These data provide objective evidence for improvement of visual function provided by light-filtering lenses in patients who become photophobic after TBI. Contrast sensitivity testing and assessment of reading rate add objective criteria for the clinical selection of light-filtering lenses in the treatment of TBI-induced photophobia.

Aging, background luminance, and threshold-duration functions for detection of low spatial frequency sinusoidal gratings.

PURPOSE: This study examined the temporal summation properties of the aging visual system under a wide range of background luminances. METHODS: Contrast thresholds for 0.5 cpd gratings for 12 younger (mean age 20.6 years) and 12 older (mean age 71.6 years) observers in good ocular health were measured for 6 stimulus durations (from 10 to 1000 ms) under 4 background luminances (from 0.44 to 249.50 cd/m2). Two-alternative forced-choice staircase method was used. RESULTS: We found significant main effects of age, background luminance, and stimulus duration on the contrast threshold. There were no age-related differences in the shape of the threshold-duration functions under all background luminances, although the shape changed significantly with background luminance. Age-related differences in contrast threshold were significant under the two lowest, but not under the two highest, background luminances. CONCLUSIONS: Age-related alteration in visual sensitivity may be attributed to sensitivity (amplitude) losses but not to changes in temporal characteristics of the visual system.

Performance of young and older drivers on a static acuity test under photopic and mesopic luminance conditions.

Sixty young (18-25 years) and 91 older volunteers (60-87 years) were tested for static visual acuity under six different luminance levels ranging from 245.5 cd/m2 (photopic) to 0.2 cd/m2 (mesopic). The results showed significant differences in log decimal acuity and in passing a 20/40 acuity criterion score as a function of age and luminance level. There were no differences, however, in comparisons between young subjects and those aged 60-64. It seems, therefore, that when using visual acuity measures, as is done for driver licensing, 65 years is the critical age after which visual acuity becomes significantly poorer under conditions of degraded illumination. The implications for issuing driver's licenses to individuals over age 65 based on standard visual acuity testing are discussed.

Temporal summation functions for detection of sine-wave gratings in young and older adults.

Temporal summation functions for 0.416 and 7.5 c/deg sinusoidal gratings were measured in young and old observers in order to test the hypothesis of a shift in sensitivity from "transient" to "sustained" channels in the aging visual system. Results failed to support the transient-shift hypothesis. Additional tests showed no age-related changes in temporal summation even within a single channel. When all observers were refracted for the test distance and matched for retinal illuminance, no age-related differences in contrast sensitivity were found.

Visual information processing speed in hypnotized and nonhypnotized subjects.

Using a backward-masking paradigm with a bias-free and ceiling-free psychophysical task, we tested hypnotized and control subjects for speed of visual information processing. Approximately half of each group received visual imagery suggestions in an attempt to influence attention. Imagery produced no significant differential effect. Although an absence of a hypnotizability-performance relationship was in keeping with findings of a previous study, those subjects in the present study who performed under hypnosis were, as a group, significantly superior to the other subjects in speed of information processing.

Selective attenuation in brightness for brief stimuli and at low intensities supports age-related transient channel losses.

A brightness estimation experiment was conducted on 10 old (ages 60 to 77) and 10 young (ages 22 to 27) volunteers. Participants were introduced to magnitude estimation by scaling the lengths of line stimuli, after which they dark adapted for 10 minutes. Stimuli for brightness estimation were presented binocularly via a free-viewing system and consisted of circular flashes of 2 degrees. Stimuli covered a 3 log unit range of luminance levels in 0.5 log unit steps, and 3 durations (10, 100, 1000 msec). Linear regression analysis yielded dual-branched functions with a low intensity segment which was significantly steeper in slope than the high intensity segment. The slope for the older group was significantly less steep than that of the younger observers only at the low intensity segment. Findings with respect to stimulus duration showed a significantly attenuated slope for the old as compared to the young group only at 10 msec. The results extend previous threshold results to suprathreshold levels, and are consistent with an hypothesis of a selective loss of transient channels with age.

Comprehension of informed consent information by young-old through old-old volunteers.

Comprehension of typewritten informed consent information was evaluated for young-old (60-69 years) through old-old (80-89 years) volunteers as a function of years of education (less than 12, 12, and greater than 12), readability of information (low [college level] vs high [7th grade]), and typeface used in the preparation of the materials (Prestige Elite 72, Letter Gothic, and Orator). All volunteers (N = 235) read a typewritten information sheet and retained it for review while answering eight multiple choice questions. Immediate feedback was provided, and a second test was administered if any answers were incorrect. The findings indicated that comprehension varied directly with education and inversely with age. Typeface and age interacted due to age-related differences with the two smaller (Prestige Elite and Letter Gothic), but not with the largest of the typefaces (Orator). These findings suggest that the observed age-related differences may have been due to visual and not cognitive deficits. Readability did not affect performance either by itself or in combination with any other variable.

Older observers have attenuated increment thresholds upon transient backgrounds.

Foveal increment thresholds were measured in young, middle-aged, and older observers. These thresholds, which involved the detection of a small test flash as a function of the intensity of a larger background adapting field (AF), were measured at the instant of onset of the AF (transient condition) and when the eye had been fully light adapted to the AF (steady-state condition). All stimuli were presented to the left eye in a free-viewing system through a 2 mm artificial pupil. For the steady-state condition for all age groups, the functions were similar, but for the transient condition, the slope for the older observers was significantly less steep than that for the younger observers. These findings are consistent with an hypothesis of a selective loss of transient (Y) channels in the aging visual system.

Reading disability: a hemispheric asymmetry--information processing approach.

A visual half-field task using a Sperling partial-report paradigm was presented to 10 reading disabled and 10 control subjects (7 to 14 yr. old). The design was very similar to that described in 1977 by Morrison, Giordani, and Nagy, examining performance of letters placed in a circular array at both the perceptual and short-term memory stage. The reading-disabled subjects performed significantly lower on letter-recognition during both the perceptual and short-term memory processing stages. A hemi-field analysis showed a left visual-field performance decrement for the reading-disabled group during the short-term memory stage. Contrary to previous findings which discount a perceptual deficit, this study indicates that such a deficit may exist and is further accentuated during the short-term memory stage by a decrement in right-hemisphere performance.

Informed consent for research. Effects of readability, patient age, and education.

Comprehension of informed consent materials from a study of psychological variables associated with chest pain was evaluated as a function of age (27 to 69 years), education (5 to 20 years), and readability of information [low (college level) versus high (7th grade)]. The potentially confounding effect of memory was eliminated by allowing patients to use the written information sheets to find answers to the multiple choice test. Feedback and a repeat test were provided if any answers were incorrect. The findings indicated that comprehension varied inversely with age and directly with education. It is suggested that while ensuring informed consent may be difficult for all volunteers, it may be a critical problem for elderly patients with low education. The effects of readability were not consistent, suggesting that simplifying informed consent materials by shortening words and sentences may not, by itself, be sufficient to improve comprehension.