The effect of an interrupted daily period of normal visual stimulation on form deprivation myopia in chicks.

The aim of this study was to determine whether an integrator of neural activity influences the amount of myopia and axial elongation resulting from deprivation of form vision. The effects on ocular parameters of a continuous period of 30 min per day of normal vision was compared to two exposures of 15 min duration each, or three exposures of 10 min each. For the remaining time, chicks had monocular translucent occlusion in a 12 hr light/12 hr dark diurnal cycle, for either 2 or 3 weeks. Fellow eyes and the eyes of bilaterally unoccluded chicks were used as controls. We found that several short periods of normal visual stimulation per day were more effective in preventing the development of form deprivation myopia and axial elongation than was one single period of the same total duration, after both 2 and 3 weeks of treatment. This study suggests that the level of neural activity in the retina may have a cumulative effect in influencing ocular growth.

Neuropsychological characterization and detection of subclinical hepatic encephalopathy.

OBJECTIVE: To elucidate the nature of the neuropsychological deficits associated with subclinical hepatic encephalopathy. DESIGN: Prospective study comparing the performance of patients with liver disease and carefully matched normal controls on a short but comprehensive neuropsychological test battery. SETTING: A university medical center. PARTICIPANTS: Twenty patients with cirrhosis (10 alcoholic and 10 nonalcoholic) and 20 controls carefully matched on the basis of age, sex, education, and alcohol history. RESULTS: The cirrhotic patients exhibited relatively selective deficits in complex attentional and fine motor skills, with preservation of general intellectual ability, memory, language and visuospatial perception. CONCLUSIONS: This pattern of neuropsychological deficits suggests a subcortical pathophysiology, possibly reflecting involvement of the basal ganglia. These neuropsychological findings are consistent with recent neuroradiological, electrophysiological, and neurophysiological research implicating basal ganglia involvement in cirrhosis.

The duration of normal visual exposure necessary to prevent form deprivation myopia in chicks.

The aim of this study was to determine the minimum daily period of exposure to normal visual stimulation required to prevent occlusion induced myopia in chicks. Chicks were treated with monocular translucent occlusion in a 12 hr light/12 hr dark cycle. Occluders were removed for 0 (constant occlusion), 15, 20, 30, 40, 60, 75, 90, 120, 150, 240 or 720 (no occlusion) minutes each day for either 2 or 3 weeks. Fellow eyes and the eyes of normal chicks (bilaterally unoccluded) were used as controls. Occlusion-induced myopia and axial elongation were found to decrease significantly (P < 0.01) with increasing daily exposure to normal visual stimulation. Application of a time series equation to the data estimates that 30 and 130 min of normal visual exposure per day reduces myopia by 50 and 95% respectively. This study demonstrated that the regulation of ocular growth is affected strongly by short periods of normal visual stimulation in the presence of long periods of abnormal stimulation.