locus of points in space which are imaged on corresponding retinal points, which when stimulated give rise to identical visual direction

-functions as a reference for points having zero disparity

-due to photoreceptor packing

-Hering-Hillebrand deviation

-oculocentric visual direction

-egocentric visual direction

-retinal position

-proprioceptive information

-head and body position

-vestibular apparatus

-disparate points

-do not have same visual direction

-theoretical horopter

-all points on this circle should stimulate corresponding points on retina and lead to single vision

-assumes that there is angular symmetry of the corresponding points

1. position of all points appear to lie in an AFPP that includes point of fixation

2. position of points will lie in the center of the region of BV

3. positions of points will be such that the stereoscopic sensitivity to changes in position will be a maximum

4. none (points) provide a stimulus for fusional movement of eye's (Ogle's crieria)

The horopter varies with viewing distance. How does it vary?

at short distances appears convex towards observer

-at long distances will appear convex towards observer

-at a certain distance (termed abathic distance) will appear flat

-greater than 0, usually 1

-less than 0, usually -1

-apparent and real frontoparralel planes coincide.

-horopter is truly flat

-horopter will tilt towards right eye

-image percept will tilt away from right eye (towards left eye)

-geometric effect

-image percept (visual) move toward right eye

-horopter moves toward left eye

-induced effect

-x axis: tan alpha 2

-y axis: R (ratio of tan alpha 2/tan alpha 1)

-H is the slope

-Ro is the y intercept

-the origin is (0, 1)

analytical plot: ordinate intercept of straight line 

spatial plot: slope (skew) of the horopter at the fixation point. Curve is symmetrical when Ro = 1

analytic plot: slope of the straight line plot or the asymptote

spatial plot: curvature of the horopter at the fixation point. Represents deviation from vieth muller circle

it is the smallest near the fovea, 6-10 min arc on either side of horopter

-stereopsis begins about 2-10 arc seconds on either side of the horopter, near centre of panums space

-panum's space expands to around 30-40 min arc at 12 degrees fixation

-width of Panum's space is not fixed, can vary depending on conditions

-psycho-physical methods of measurment

-training

-retinal eccentricity

-illumination

-temporal (exposure time)

-direction (crossed or uncrossed)

-spatial frequency

-proximity of other targets

-relative colour

-relative brightness

-bernell test lantern

-AO vectographic slide

-Borish card

-Wesson card

-y intercept: fixation disparity (eso/exo)

-x intercept: associated phoria (BO/BI)

-type 1

-type II: eso

-type III: exo

-type II is more resistant to change

type III curves sometimes change to typeI

-images in two eyes can be equal in size so due to neural causes (small amount seen in emmetropes)

-may persist after a difference in image size has been corrected optically.

-retinal receptor distribution effect

-stretching or compression seems to be the cause

-if there is a stretching or compression of the retina, photoreceptors are displaced creating macropsia or micropsia

epiretinal membrane, vitreomacular traction, re-attached retinal detachment, macular hole, retinoschisis

-seen in amsler grid

-epiretinal membrane

-all the rest cause micropsia

-vertical magnification in one eye is equal to the same magnification applied horizontally to the other eye

-not as robust as geometric effect, diminishes around 7%

-unequal saccades (violation of hering's law)

-due to each eye's retinal image being in a different location

-sets of afocal lenses whose surface curves are chosen to give mag (1-8%)

-mag not related to vertex distance and power factor does not contribute

-it is the aniseikonia induced due to eccentric fixation

-it is when anisometric spectacle correction not only produces aniseikonia, but as the visual axis moves across lenses, produces varying differential prism

-is a source of fusional stress

space eikonometric method (based on binocular perception)

direct comparison method (directly compare perceived image sizes)

-most accurate and successful measuring device

-measures of three components of aniseikonia, horizontal mag, vertical mag and oblique mag

-must have good BV and stereopsis

-3-5%

-aniskeikonia will interfere with stereopsis over this limit

-field-dependant aniskeikonia

-varies with field angles

-there is no one value of aniskeikonia anymore since it varies with gaze

-HAs

-ashenopia

-photophobia

-reading difficulty

-nausea

-diplopia

-those arising from structures in the ocular media

-those arising from structures in the retina

-droplet of tears and mucus on corneal surface

-folds in corneal epithelium (horizontal bands)

-lacrimal fluid adhering to the upper lid margin

-folds and channels in corneal stroma

-structure of crystalline lens (star figure of a point source of light

-opacities

-phosphenes: visual sensation resulting from inadequate stimulation to the eye

-purkinje tree due to retinal vessels on top of photoreceptors and cast shadows (not normally viewed due to adaptation)

-capillary circulation

-maxwell spot: due to selective absorption of blue light by yellow pigment of macula

-haidingers brushes

-blue arcs

-best seen with blue light, evenly illuminated field with polarizer, they appear as bundles of wheat or propeller.

-due to dichroism of macular pigment or birefringence of henle fiber layer

-do not appear in edematous lesions of macula, early stages of ARMD, or in degeneration of papillomacular bundle

-central retinopathy

-eccentric fixation

-retinal disparity

-convergence

-use an after image to keep retinal image size constant

-if you keep constant but change perceived distance should change the perceived size

-perception of an objects size remains relatively constant, even if the size of the object on the retina changes

-two object of different retinal images sizes can be perceived as being same physical size if these objects are judged at different distances

-maintained by  a perceptual scaling of the perceived size of an object according to its estimated distance

-obstruction of a distant object by a closer object

-images may lie in same plane but brain will interpret simplest image possible (linear object)

-direction of light and shadow can tell us about depth. Shadow falls behind the object, so sense of depth created

-objects with shadows are farther away

-shading from illuminated convex or concave shape (shape from shading)

-objects with depth cast their own shadow)

-we perceive objects near to the horizon as more distant than points that are farther away from horizon

-below the horizon objects higher in VF appear farther

-above horizon object lower in VF appear farther

results when a moving observer fixates on an object while noticing relative motion of surrounding object

-due to objects closer to us moving farther across our field of view than objects in distance

-velocity proportional to the seperation of the object from fixation point

-helps animals with limited BV to see depth

-almost as good as binocular disparity

motion parralax produces image displacements on the retina equivalent to those produces by disparity

6-10 arc seconds

-good source of information about relative distance of objects and only monocular cue that rivals stereopsis

-some non binocular animals use it as a substitute for stereopsis

-how fast the images of these objects move across the retina is partially a function of how distant they are

-law of proximity

-law of similarity

-law of figure-ground

-law of symmetry

-law of closure

-law of continuity

What is the law of proximity. What about law of similiarity?

the law of proximity posits that when we perceive a collection of objects, we will see objects close to each other as forming a group

-items that are similar tend to be grouped together (things that are similar tend to be perceived as belonging as a unit)

-holds that points that are connected by straight or curving lines are seen in a way that follows the smoothest path

-innate tendency to perceive incomplete objects as complete and to close or fill gaps

-when we perceive objects we tend to perceive them as symmetrical shapes