Drugs online research references
Am J Ophthalmol. 1975 Feb;79(2):292-304.
Ocular torsion and the function of the vertical extraocular muscles.
Jampel RS.
The vertical corneal meridia are not kept perpendicular to the horizon in human and nonhuman primates when the head or body is tilted, i.e., compensatory counter-rolling of the eyes does not occur. The slight torsional displacement of the vertical corneal meridia noted by many observers may be the result of rotation around an axis or to translation of the globe. The neurologic and structural systems that control the actions of the vertical muscles in human and nonhuman primates do not appear to provide a mechanism for wheel-rotation of the eyes around the pupillary axis. Ocular torsion is not a normal function of the vertical extraocular muscles. Their function is probably the reverse, i.e., the inhibition or prevention of ocular torsion and the stabilization of the eyes when the head or body inclines. Torsional displacement of a vertical corneal meridian occurs only when there is an abnormal muscle imbalance. Wheel-like movements (cycloduction) around the pupillary axis or visual line do not occur. Torsional displacement of a vertical corneal meridian occurs only with a simultaneous vertical movement. The vertical rectus and the oblique muscles in man work together to produce vertical ocular movements regardless of head position of body posture while maintaining the vertical corneal meridia parallel to the sagittal plane of the head. The vestibular apparatus may be responsible for distributing innervation among these muscles, enabling them to function in this manner.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=803789&dopt=Abstract
Vision Res. 1994 Jan;34(2):163-77.
Monocular discrimination of the direction of motion in depth.
Regan D, Kaushal S.
Department of Psychology, York University BSB, North York, Ontario, Canada.
The direction of motion in depth of a monocularly-viewed rigid sphere can be quantified in terms of the distance by which the sphere's centre will miss the centre of the pupil of the observing eye. If we express this distance as ns (where s is the sphere's radius and n is a scaling factor), then n approximates the ratio (d phi/dt)/(d theta/dt) between the translational velocity (d phi/dt) and the rate of expansion (d theta/dt) of the object's retinal image. To use this monocular information alone as a basis for motor action, prior knowledge of s would be necessary. (However, the value of s is available from binocular information, so that the distance by which the sphere's centre would miss the eye is, in principle, available from retinal image information alone and, in particular, without knowing the object's size or distance from the eye). We measured the just-discriminable difference in the direction of motion in depth for a monocularly-viewed simulated object. Thresholds were measured for trajectories contained within the horizontal, vertical and two oblique meridia. The translational speed of the retinal image was removed as a reliable cue to the direction of motion in depth by randomly varying the simulated object's speed on a trial to trial basis. The direction of translational motion was also removed as a reliable cue. Discrimination threshold for the stimulated direction of motion ranged from 0.03 to 0.12 deg for our seven subjects, and did not vary appreciably with the direction of motion relative to the line of sight over the range investigated, nor did it depend on whether trajectory was contained within the horizontal, vertical or oblique meridia. We conclude that subjects are able monocularly to discriminate differences in the direction of motion in depth, even when both the direction and speed of retinal image translation are removed as reliable cues.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8116276&dopt=Abstract
Ophthalmic Physiol Opt. 1994 Jan;14(1):71-8.
Spatial summation of the differential light threshold as a function of visual field location and age.
Latham K, Whitaker D, Wild JM.
Department of Vision Sciences, Aston University, Birmingham, UK.
Static differential light thresholds were measured as a function of stimulus size (Goldmann sizes I-V) along four visual field meridia (75, 165, 255 and 345 degrees) with the Humphrey Field Analyzer 640. Data were obtained for both young (n = 10, age 23.6 +/- 2.9 years) and elderly (n = 10, age 72.0 +/- 5.2 years) normal subjects. The resulting peripheral spatial summation curves could be equated to the foveal data simply by a change in size scale, which increased linearly with eccentricity. E2 values, expressing the eccentricity at which stimulus size must double for performance to remain comparable to the fovea, were in the order of 3-9 degrees. Whilst the rate of scale change is approximately the same for both young and elderly observers, differences in performance can be explained by a combination of lower sensitivity and a bias in sensitivity towards larger stimulus sizes with increasing age.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8152824&dopt=Abstract
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