Noninvasive techniques for assessing the effect of environmental stressors on visual function.

Visual acuity, a standard measure of visual function, is affected by a variety of physical and toxic stressors. In anesthetized animals, the acuity may be determined by the visual-evoked potential (VEP). We compared two evoked potential methods: the steady-state VEP, elicited with a fixed stimulus, and the sweep VEP, elicited by a dynamic stimulus. The steady-state VEP is a conventional electrophysiological technique for determining acuity, although its signal-to-noise ratio declines at high spatial frequencies and introduces a source of error for acuity determinations. Moreover, it is unsuited for repeated or rapid measurements. The sweep VEP is elicited by a dynamic stimulus which sweeps through a series of spatial frequencies. Response amplitude is measured with a sensitive, synchronous filter. The sweep VEP can be completed in as little as 10 s and may be used for repeated measures. On the other hand, waveform data is lost with the sweep VEP. The two techniques yield fairly similar acuity measures, generally agreeing within a factor of two.

Binocular neurons and binocular function in monkeys and children.

Electrophysiologic studies have shown that binocular neurons of the striate cortex of monkeys are irreversibly lost when the visual axes of the eyes are optically dissociated during the first weeks of life. The present study was a behavioral investigation of monkeys reared with optical dissociation. After brief periods of experimental strabismus, the monkeys showed poor binocular summation performance and were unable to see random dot stereograms even after two years of post-treatment normal binocular vision. These monkeys' performance on the stereopsis task was virtually identical to the stereoperformance of clinically diagnosed stereoblind children.

Behavioral measurement of laser flashblindness in rhesus monkeys.

Flashblindness was measured in rhesus monkeys performing a visual detection task. Stimulus field subtense was 3.5 degrees, and mean luminance was 10 cd.m-2. Single-pulse laser exposures (doubled Nd:glass, 530-nm wavelength, 20-ns pulsewidth) were presented in Maxwellian-view and formed a 12.5 degrees diameter spot centered on the fovea. The independent variables were: test grating contrast (10% and maximum contrast); test grating spatial frequency (1, 4, 12 c.deg-1); and averaged laser exposure energy (1-94% retinal maximum permissible exposure). The dependent variable was flashblindness, operationally defined as the time between a laser exposure and the first response in a pair of consecutive correct responses (referred to as "time to criterion"). Time to criterion decreased as the contrast of the grating increased. The longest times to criterion were at a spatial frequency of 12 c.deg-1, next longest at 1 c.deg-1, and shortest at 4 c.deg-1. Both the mean and S.E.M. of times to criterion increased with the laser exposure energy.

Effectiveness of letters to Cape Breton women who have not had a recent Pap smear.

Nova Scotia, and especially Cape Breton, has high cervical cancer incidence and mortality rates. Letters were sent to 15,691 unscreened and 6,995 under-screened women from Cape Breton Island encouraging them to obtain a Pap test. Controls were 61,510 unscreened women and 32,996 under- screened women in mainland Nova Scotia who were not sent letters. For this cohort study, the provincial Health Card Number database and Provincial Cytology Registry were linked. Having a Pap smear was associated with having received a letter (OR = 1.64), having been previously under-screened rather than unscreened (OR = 1.85), with youth and with higher income (OR = 1.13). After receiving a letter, women in Aboriginal, Mixed Black, Acadian, and rural communities had smear rates similar to those of other women. Being previously unscreened, rather than under-screened, was associated with higher rates of abnormalities (OR = 1.62), indicating greater need for early detection and treatment to prevent invasive cancer. While one-time letters to women improved the Pap smear screening rates, multiple, continuous interventions are needed to make a more substantive improvement in these rates.