Download OPT 219 Horopters Exam Questions and Answers: A Comprehensive Guide to Binocular Vision and more Exams Advanced Education in PDF only on Docsity!
OPT 219 HOROPTERS EXAM QUESTIONS AND CORRECT ANSWERS!!
Retinal Stimulus Pattern is dependent upon - ANSWER -photometry: how an object is illuminated and how it reflects light -lens design: how an external lens transmits light -how internal media (e.g., cornea, crystalline lens, vitreous, etc.) transmit light -entoptic phenomena: how retina transmits light
Horopter - ANSWER -location of objects whose images lie on corresponding points -when corresponding points are stimulated, they give rise to same visual direction -zero disparity plane -theoretical (Vieth-Muller circle) and empirical horopters do not coincide due to photoreceptor packing -this difference is called Hering-Hillebrand deviation -important because multiple points in space give rise to single vision -empirical horopter is convex behind abathic distance (distance between face and V-M circle) due to stereopsis -empirical horopter is concave in front of abathic distance due to stereopsis -in normal BV, all changes in horopter that are caused by changes in fixation distance and/or application of lenses/prisms can be explained by optics -in abnormal BV, arrangement of corresponding points may be altered -> Anomalous Retinal Correspondence -> can cause changes in horopter
Oculocentric Visual Direction - ANSWER -object we look at directly falls on the fovea -> it is along the principal visual direction (i.e., visual axis) -direction of all other objects is determined in reference to visual axis (e.g., those imaged above fovea are perceived as "below")
Egocentric Visual Direction - ANSWER -refers to direction of object in space relative to
one self rather than the eyes -determined via position of retina and proprioception info about eye, head, and body position as well as vestibular system -helps determine whether a change in retinal position is due to object movement or eye/head movement
Ocuocentric vs Egocentric Direction change - ANSWER -if oculocentric direction changes but egocentric direction does not -> eye moved -if oculocentric direction does not change but egocentric direction does -> object moved (i.e., object tracking)
Crossed vs Uncrossed Diplopia - ANSWER crossed: image on the right is perceived to be on the left (exo) uncrossed: image on the right is perceived to be on the right (eso) Crossed diplopia occurs when an object is imaged on temporal retinas of both eyes because it is located closer than the fixation point. Uncrossed diplopia occurs when an object is imaged on nasal retinas of both eyes because it is located further than the fixation point.
Vieth-Muller Circle - ANSWER -theoretical horopter -assumes that the eye rotates around its nodal point (instead of its centre of rotation) -assumes there is angular symmetry of each pair of corresponding points
AFPP (Apparent Fronto-Parallel Plane) criterion (aka OFPP percept) - ANSWER -actual location of objects when images appear equidistant from the base line -objects are not actually equidistant here -helps measure empirical horizontal horopter -most used experimentally -easiest and most accurate -e.g., rod exercise in Lab 4 (272)
Analytic plot continued - ANSWER When horopter passes through fixation point, (i.e., P coincides with F): R = Ro + [H * tan(alpha2)] where Ro is the point where horopter crosses y axis (i.e., y-intercept; tells us the uniform relative magnification across the visual field) Ro = 1 means the curve is symmetrical; y-intercept is at x & y axis intersection (aka origin) H is the slope of the line (tells us the non-uniform relative magnification across the visual field) When Ro = 1, H represents Hering-Hillebrand deviation from V-M circle -if no deviation, H = 0 -if horopter is less curved than V-M circle, H > 0 (positive slope) -if horopter is more curved than V-M circle, H < 0 (negative slope) Ro influences size and orientation of perceived images, while H impacts their shape.
B term - ANSWER -indicates asymmetry of the curve with respect to the y axis -disappears when Ro = 1 -if (B2 - 4AC) = 0, horopter curve is a parabola or straight line (if H = 2a/b) -if (B2 - 4AC) > 0, horopter curve is a hyperbola (with asymptotes) -if (B2 - 4AC) < 0, horopter curve is an ellipse (or circle if A = C and B = 0)
Vertical horopter - ANSWER -straight vertical line passing through fixation point in midsaggittal plane -Helmholtz claimed that the empirical vertical horopter is top-back slanted, so the plane appears inclined
Eso vs exo fixation disparity and analytical plot - ANSWER -in normal bv, EVERY horopter intersects y-axis at fixation point (Ro = 1) -in eso fixation disparity, the horopter intersects y-axis in front of the fixation point, the
hyperbola in the analytic point approaches the ordinate asymptote in quadrants II (upper left) and IV (lower right) -in exo fixation, the horopter intersects y-axis behind fixation point, the hyperbola approaches the ordinate asymptote in quadrants I (upper right) and III (lower left)
Nonius (aka Identical Visual Direction) horopter - ANSWER -alternative criterion -the "true" horopter -tested using a 1 meter distance, Vernier targets on white background (for noise reduction), and polaroids (to get a dichoptic view of the slits - OS sees lower slit, OD sees upper slit) -Lab 1 (219)
Vengu's study of Nonius horopter - ANSWER -plotted nonius horopter in central 40 min of arc (beyond 40 min of arc, subjects tended to converge) for different wavelengths in ~25 subjects -found correlation between chromostereopsis direction and horopter curves -for 18 subjects, red horopter was in front of blue -> positive chromostereopsis (red perceived to be in front of blue) -for 5 subjects, blue horopter was in front of red -> negative chromostereopsis (blue perceived to be in front of red)
Panum's Fusional Area - ANSWER -region of single binocular vision -measured by fixating on and moving test rod until it is seen as double -range in which the rod is seen as single represents Panum's Fusional Area -centre of the range is the location of haplopia horopter (aka singleness horopter) -haplopia horopter is another criterion -Panum's Fusional Areas are smallest when fixating with fovea and get larger in periphery
Maximum stereosensitivity horopter - ANSWER measured by fixating on central rod and moving it until it is in 3D
Leaf Room - ANSWER -aka Ames Room -no cues to depth -tilt and distortion of the world via uniocular magnification
Abnormal BV and horopter - ANSWER -in intermittent exotropes, when Px fuses, horopter may lie within V-M circle -abnormal horopter might be cause of strab, not vice versa
Flom Notch - ANSWER -in constant strab patients (esp. esotropic), horopter shifts towards origin but does not follow a smooth curve -there is a notch within the region of the two eyes' visual axes -if measured using continuously visible nonius lines (Mallett), no notch; if measured using alternating stimuli (Flom et al.), notch present
Monocular asymmetries - ANSWER -Kundt: equal distances in temporal half of VF are overestimated as compared to equal distances in nasal half of VF -Munsterberg: reverse asymmetry; in the right VF, apparent size is less for the right than for the left eye; in the left VF, the reverse is true
Analytic plot purpose - ANSWER shows us that horopter changes as function of viewing distance
What happens at abathic distance - ANSWER -apparent and real frontoparallel planes coincide -horopter is truly flat
Spatial plot - ANSWER Ro: slope (skew) of the horopter at the fixation point; curve is symmetrical when Ro = 1 H: curvature of the horopter at the fixation point; represents deviation from VM circle
