[A simple apparatus for evaluating stereoscopic vision in near vision].
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The development of ocular motilities, convergence, form perception and depth perception were studied for 128 infants at the ages of 18, 24 and 30 months of age. Developmental trends were evident in ocular motilities and form perception. Convergence ability was relatively good at 18 months and remained constant. Depth perception did not show a specific trend over the period studied.
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Interocular transfer of two figural aftereffects was examined in orthotropes and strabismic subjects. Within both groups there were persons with an appreciable degree of stereoacuity and others who had little or none. Experimental evidence from a variety of sources has suggested that stereopsis depends upon binocularity of units in the geniculostriate system. For the tilt aftereffect, interocular transfer correlated with stereoacuity among both orthotropes and strabismics. For the spiral motion aftereffect, interocular transfer did not correlate with stereoacuity; it was present among orthotropes and absent among strabismic individuals. The correlation of stereoacuity with interocular transfer of the tilt aftereffect agrees with previous observations and is consistent with the interpreation that this effect is mediated at a cortical level. The lack of a correlation between stereoacuity and interocular transfer of the spiral motion aftereffect suggests that this effect is mediated by units other than those responsible for stereopsis. Richards and Smith, on the basis of certain phenomenal differences between the spiral motion aftereffect and other figural aftereffects, have suggested that the former is mediated at a midbrain level. If strabismic persons lack binocular units in midbrain, the present results are consistent with their hypothesis.
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With the increasing popularity of periodic gratings in vision research, the effects of ocular defocus, such as spurious resolution and the presence of more than one maximum in the contrast - defocus level function, are very important. Optical transfer function theory is used to develop graphs and formulae that can be used to predict the presence of spurious resolution for given levels of defocus and spatial frequency in aberration-free optical system. Geometrical optical approximations are used extensively, as these lead to very simple formulae. These general equations, applying to any optical system, are extended to the particular case of ocular defocus. Formulae are presented that can be used to predict the presence of spurious resolution, in terms of such variables as pupil size and longitudinal focus error. Conditions for the observation of spuriously resolved gratings are also discussed. An example is presented for observing spurious resolution and contrast reversal and this example can be presented as a "pseudo" visual illusion.
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Patients complaining of reduced acuity in the absence of a clearcut diagnosis present a challenge to the eye care practitioner. It is important to differentiate retinal disease from optic nerve disease as the etiology of the decrease in vision. This differentiation can have significant ramifications and must be determined for patient welfare and management. Several procedures may be used in making the differential diagnosis of macular or retinal from optic nerve disease. Some of these procedures are easy to perform and include Amsler grid, color vision testing, pupillary reflexes, light-brightness comparison, and macular dazzle. Other procedures require a greater degree of sophistication and include fluorescein angiography, the Visual Evoked Potential (VEP) and simultaneous VEPs and ERGs (Electroretinograms). The clinician should be aware of all of these procedures and how each may be useful in this differential diagnosis.
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The test made use of a rotating chair mounted in a striped cylindrical enclosure, 4.6 m in diameter. The subject was exposed to the following motion profile: With eyes covered he was accelebrated at 15 degrees/s2 to clockwise volocity of 300 degrees/s and maintained at that velocity for 30 s. The chair was then decelerated to a stop within 1.5 s and maintained at rest for 30 s while physiological parameters and motion sickness symptoms were recorded. This procedure was repeated until a pre-selected motion sickness endpoint was reached or 20 stops had been made. If the endpoint was not reached, testing continued without the blindfold while the subject passively viewed the striped enclosure; if the endpoint was still not reached after 20 stops, the direction of rotation was reversed. The subject's score represented one-half the number of stops with eyes covered plus the number of stops with eyes open plus twice the number of stops after reversal of direction of rotation. Fourteen subjects were each assessed four times; the average interval between tests was 3 d. The first test was usually a poor indicator of alter performance. The second test provided a satisfactory ranking of susceptibility to motion sickness, and the results of the four sessions provided an indication of the rates of acquisition and decay of adaptation. Some advantages and uses of this new test are summarized.