Joseph F. Sturr

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.

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 drivers licenses to individuals over age 65 based on standard visual acuity testing are discussed.

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.

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.

Spatial and Luminance Determinants of the Increment Threshold under Monoptic and Dichoptic Viewing

Increment thresholds for a 5-ms, 3.5′ test flash (TF) were measured as a function of conditioning-flash (CF diameter at four retinal positions for photopic and scotopic luminances. CF was either 200 or 50 ms, synchronized with TF onset (transient) or continuously exposed (steady state). TF was presented to the right eye, CF either concentrically to the right eye (monoptic), or to the homotopic contralateral retinal location (dichoptic). A four-channel maxwellian-view optical system was used. When TF luminance at threshold was plotted against CF diameter, inverted ∪-shaped functions were obtained for both monoptic and dichoptic conditions, the peaks occurring at progressively larger CF diameters with more peripheral stimulation. For any given retinal position, monoptic and dichoptic peaks occurred over the same CF diameter. Monoptic thresholds were higher than dichoptic, except for foveal photopic data where both showed over 10-fold maximum threshold change. The transient CF produced higher threshold elevation than the steady-state CF. Dichoptic stimulation with the transient CF often produced over 10-fold threshold changes, especially for scotopic stimulation. For any nonfoveal retinal position, the scotopic peak occurred over a larger CF diameter than the corresponding photopic condition. The results are discussed in terms of receptive-field organization.

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.

Spatial and Luminance Factors Determining Visual Excitability

Excitability functions were determined by measuring the threshold luminance of a circular test flash (43′, 5 msec) at various temporal intervals before and after the onset of a larger concentric 25-msec conditioning flash. The paired stimuli were presented in maxwellian view to the right eye, either centrally, or 7° or 15° in the nasal field. The conditioning flash was either 57′, 1°50′, 2°43′, or 3°30′ in diameter, and was either scotopic, or one of two photopic luminances. The results show that (1) luminance is the most powerful nontemporal determinant of the increment threshold, (2) as the conditioning diameter increases, test threshold decreases with central or 7° photopic stimuli, but with scotopic peripheral stimuli, the test threshold increases and then decreases. For photopic stimuli at 15°, increasing the CF diameter generally raises the increment threshold. In general, the diameter for maximal increment threshold becomes progressively larger as luminance is decreased or as stimulation occurs farther in the periphery. These results are discussed in terms of the neural organization under different conditions of luminance and retinal position.

Sensitization by annular surrounds: dichoptic properties.

Abstract Westheimer (1965) has shown that the rod threshold for a very small test flash at the center of a 45′ disk of light can be lowered by the presence of an annulus of light on the surrounding region of the retina. In the present paper we continue the comparison of the monoptic and dichoptic properties of such spatial influences on the threshold. The annulus was presented either steadily, or transiently in a masking paradigm, in which the changes in the threshold were traced for times near the onset of the annulus. Under steady presentation conditions, dichoptic spatial interactions were found to be small or non-existent. Under transient conditions, dichoptic and monoptic effects were remarkably alike. These results are similar to those of Fiorentini, Bayly and Maffei (1972) , and are consistent with their conclusion that steady-state disk-annulus interactions and transient diskannulus interactions probably occur at more peripheral and more central physiological locations respectively. The limitations on this conclusion are also discussed.

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.

Neural limitations of visual excitability VIII: Binocular convergence in cat geniculate and cortex

Abstract Excitability cycles for the lateral geniculate body and the visual cortex were obtained in 49 locally anesthetized-immobilized cats, by plotting the response changes to a test Mash ( F t ) against the time interval from a supraliminal conditioning flash ( F c ), presented either to the same (monocular stimulation) or to the contralateral (interocular stimulation) eye. For both forms of stimulation, the conditioning flash response disrupted the test flash response, either in amplitude or duration, depending upon the temporal interval. With monocular stimulation, increasing either F c duration or luminance prolonged the recovery cycle at both cortex and LG. With interocular stimulation, however, cortical recovery was more rapid, and only slightly affected by F c parameters. Interocular interaction could not be demonstrated at LG with closely spaced bipolar derivations. These findings suggest that both peripheral and central processes limit visual excitability, cortical rather than geniculate mechanisms being more significant in the latter instance.