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Binocular Vision
Exam 1
| Question | Answer |
|---|---|
| Monocular system provides ____ and binocular system provides ____ | Position; depth |
| The visual system is ____ adaptable | highly; in this course we are going to see how the visual system adapts to lens and prism |
| Advantage of two eyes | 1. Stereopsis 2. Wider field 3. Increased spatial vision- ability to resolve or discriminate spatially defined features such as VA (Binocular VA is better than monocular VA) |
| Disadvantage of two eyes | Greater risk for problems |
| Compare frontal eye placement vs. lateral eye placement | Frontal eye placement: higher species, wider view, vergence system is "highly linked" and has "partial" decussation |
| Two basic problems that visual system needs to solve when interpreting visual space | 1.Convert 2D to 3D 2.Put together two different images of the world- the visual direction under binocular viewing condition does not match the individual monocular viewing direction (Most of time, it is from what's perceived monocular into binocular) |
| Objective visual space | 1. Infinite boundaries 2. Objects move without being deformed (measurable space which is not created by ourselves) |
| Image space | The image of space at the retina |
| Subjective visual space (perceived, phenomenal,experiential spaces) | The space of "perceived" things 1. Finite boundary 2. Objects being deformed |
| Three types of subjective visual space | 1. Body (personal) space 2. Reaching (peripersonal) 3. Far (extrapersonal) |
| Monocular or Oculocentric Visual Direction- two types | |
| First type- Principle Visual Direction | The direction signaled by the fovea (the direction as looking straight ahead) |
| Second type- Secondary Visual Direction | All directions other than principle visual direction |
| Eccentric Fixation | When principle visual direction is shifted from fovea.Typically develops in childhood with strabismus and amyblopia. Patients usually are not aware of the problem |
| Eccentric Viewing | Patients use a point other than the fovea when looking straight ahead. Usually develops in older patients with vision loss at the fovea. It's more like an adaptation to vision loss than abnormality. Patients are aware |
| Binocular Visual Direction- how do we combine two different views of the world | |
| Law of identical visual direction | When the foveas in each eye indicate the same principle visual direction, objects lying in the same visual direction will be seen in single visual direction under binocular viewing condition Ex Hering Window experiment |
| Egocentric localization | Objects from striking each fovea are perceived to fall on a single point "midway" between the two eyes like an imaginary single eye ball in the middle of two eyes- "cyclopean eye" |
| Common subjective principle direction | When foveas both fixate a common point and the common point is called "egocentric point" |
| Corresponding retinal points | pairs of points on each retina when stimulated simultaneously give rise to "a common visual direction" |
| Vieth Muller Circle (geometric horopter) | 1. a circle that passes thru fixation point and entrance pupil in each eye 2. predicts the location of objects that stimulate the corresponding retinal points 3. equal angular separation between two eyes |
| Binocular disparity (opposite to how to combine two different views) | 1. Difference in visual direction <--> law of identical visual direction 2. not lying on the V-M circle 3. non-corresponding points are stimulated 4. different angular separation |
| Which type of disparity gives rise to depth perception | Horizontal disparity |
| Crossed disparity | Points seen nearer than fixation point. The "temporal retina" is stimulated |
| Uncrossed disparity | Points seen farther than fixation point. The "nasal retina" is stimulated |
| Panum's area | Allow for small disparities to give rise to depth perception within and single vision within a certain range |
| Physiological diplopia | As images are outside of Panum's area and on non-corresponding points |
| Pathological diplopia | Occurs in strabismus. The fixation target is diplopic |
| Confusion | Fovea of two eyes point toward different subjects. Two different subjects are seen in one direction |
| Horopter | The locus of all points in space that are imaged on corresponding points in each eye when the eyes are converged at fixed location |
| Method of measurement of horopter and its principle (x5) | |
| 1. Identical visual direction horopter- hard to do | Law of identical visual direction- when two targets (one presented to each eye) are perceived as lying in "the same visual direction" |
| 2. Apparent frontoparallel plane horopter-easiest to do | The locations perceived as lying in "the same distance" from the subject as the fixation point |
| 3. Singleness- not very accurate | Take the advantage of Panum's area. Objects within the Panum;s area are seen as single |
| 4. Minimum stereoacuity threshold- not practical, more theoretical | Take the advantage of Panum's area. The region where you have the maximum depth perception |
| 5. Zero Vergence | Points in space seen as eqidistant will not stimulate motor fusion |
| Compensate for the perception | Arrange the horopter in a way that compensates the perception Ex If you perceive horopter rods as further away then you will move the rods closer to you |
| Spatial Spot of the horopter | Draw a Vieth-Muller circle, a fixation point on the circle and entrance pupil in each eye |
| Triangles with a "Common base" | Have 1. equal apical angle 2. equal external longitudinal angle (= angle separation) |
| R value | 1. R= tan(alpha2)/tan (alpha1) 2. relative magnification of the retinal images relative to the two eyes |
| R=1 | Point right on the circle |
| R>1 | 1. Point outside of the circle in the right field 2. Point inside of the circle in the left view |
| R<1 | 1. Point inside of the circle in the right field 2. Point outside of the circle in the left field |
| Convert spatial plot to analytical plot | R = H (tan alpha2)+ Ro |
| Ro | The relative magnification at the fixation point of the two eyes and result in "tilting of the horopter" - "Slope" of horopter on spatial plot |
| H | A measure of difference in "curvature" between the Vieth-Muller circle and the horopter |
| Changing H while keeping Ro constant (Y intercept is the same point) | 1. The curvature of horopter bends away from you, (deviation gets larger) H becomes more "positive," the slope becomes steeper 2. If the horopter bends toward you,(deviation gets smaller) H becomes less positive and the slope becomes less steep |
| Changing Ro while keeping H constant (slope is the same) | 1. If horopter is tilted toward right,(further from OD) Ro >1 2. If horopter is tilted toward left,(further from OS) Ro < 1 |
| Different fixation distance | The shape of horopter changes but the H value does not change |
| Abathic distance | The distance where the horopter matches an objective fronto parallel plane |
| Calculation at abathic distance | H=2a/b - 2a is IPD - b is fixation distance (abathic distance) |
| Nasal packing | Local signs in the nasal retina are spaced closer together |
| Monocular partition experiment | 1. Close right eye and partition a line into 2 parts where they appear equal-->majority of people have larger temporal field is than nasal field 2. compensate for what you perceived |
| Kundt asymmetry | Temporal field is larger - nasal angle is larger - H is more positive |
| Munsterburg deviation | Nasal space is larger - temporal angle is larger - H is less positive |
| Ro and perception | Uniform relative magnification. Influence on relative size and orientation of perceived images |
| H and perception | Non-uniform magnification. Influence on shape of perceived images |
| Effects of lenses on the Horopter | 1. Geometric effect 2. Induced effect 3. Adaptation 4. Aniseikonia 5. Prisms |
| Aniseikonia | Difference in magnification between the two eyes that affects the perception of size and shapes of objects |
| Four types of aniseikonia | 1. Optical aniseikonia 2. Induced aniseikonia 3. Neural- essential aniseikonia 4. Retinal aniseikonia |
| Optical aniseikonia | Caused by axial anisometropia or refractive anisometropia |
| Induced aniseikonia | Caused by size lens, which is a thick lens that change magnification but have no dioptric power |
| Neural or essential aniseikonia | Occurs when the images should be "optically equal" (so non-optical)but are perceived as different |
| Retinal aniseikonia | Caused by retinal stretching or contracting (everything related to retina) |
| Power factor (Mp) | Mp = 1/ 1-hFv - Mp is power factor in magnification - h is vertex distance - Fv is back vertex power - we usually manipulate power factor by changing h |
| Shape factor (Ms) | Ms = 1 / 1-(t/n)F - Ms is the shape factor of magnification - t is the lens thickness - n is refractive index - F is the front surface power - we can change any one of them |
| Geometric effect | A size lens with horizontal meridian (axis 90)creates a horizontal disparity. Patient would perceive the plane rotated "away from the eye with the size lens" |
| Degree of rotation | tan(angle)= (M-1/M+1)(d/a) -M is the magnification of the size lens - d is the viewing distance - a is 1/2 of IPD - the more magnification, the more tilt |
| Induced effect | A size lens with vertical meridian (axis 180) creates a vertical disparity which doesn't yield depth perception. The lens produces tilt as if an axis 90 lens is introduced on the other eye |
| Oblique magnification | Meridian at 45 or 135 degree creates a rotation around the x-axis |
| Three principles of Adaptation to aniseikonia | 1. Baseline before the lens is induced 2. Inducing and adaptation (measure how long it takes to go back to habitual state) 3. After effect/decay- when removing the lens, patient will show opposite error |
| Three types of adaptation | 1. Full 2. Partial 3. No adaptation |
| Why do we get adapted to size lens | Size lens creates a "cue conflict" between binocular and monocular cue to depth.Monocular cues predominate over stereo cues so everything we perceive go back to normal. We adapt! |
| Monocular cue is more ____ and ____ to recalibrate | plastic, easier |
| The more you move with size lens, the ____ the system recalibrate which ____ the adaptation | faster, speed up |
| Prism effect | Prism creates a "curve." The base of the prism creates a curve towards the patients |
| BO prism OU | Slope(H)becomes more positive, and Ro does not change |
| BI prism OU | Slope becomes less positive |
| Compare size lens and prism | Size lens creates a uniform magnification which causes changes in Ro, size, and orientation and no change in H, slope and the shape |
| (Continued) | Prism creates a non-uniform magnification which causes change in H and the shape (curvature) |
| Aniseikonia in clinic | -Every 1D difference of anisometropia causes 1-2% of aniseikonia - >7% disrupt binocular fusion and stereopsis |
| Static aniseikonia | When looking thru the center of the lens |
| Dynamic aniseikonia | When looking in different field of gaze and results in 1. asymmetrical vergence movement- the eye with higher prescription does not move that much as the eye with lower prescription 2. prismatic effect |
| Clinical tests (x4) | 1. Space Eikonometer 2. New Aniseikonia test (NAT) 3. Aniseikonia Inspector (AI) 4. Maddox Rod |
| Space Eikonometer | The best test cuz you can see the actual change in stereoposis |
| New Aniseikonia test | A book test, a direct comparison test. It underestimates the amount of aniseikonia compared with Eikonometer by a factor of 3 |
| Aniseikonis Inspector | A direct comparsion test. It underestimates that are greater in the horizontal meridian and has poor reliability |
| Maddox rod | need size lens to neutralize difference |
| Knapp's Law | When a correcting lens is placed in the anterior focal plane of an "axially ametropic eye" the retinal image will be the same as in the emmetropic eye |
| Axial aniseikonia is best corrected with ____ according to Knapp's law | spectacles |
| Refractive aniseikonia is best corrected with ____ | Contact lens |
| But in clininc, ____ is usually a better choice because of ____ | Contact lens, dynamic aniseikonia |
| Vertical horopter | -Vertical horopter is tilt away from the individual - Tilt away - (+) - Tilt towards - (-) - A small positive tilt is preferred - think of "the screen of laptop" |
| Horopter and strabismus | |
| Objective angle of deviation, H | what I measure from cover test |
| Subjective angle of directionalization, S | What I get when I create diplopia Ex what you get from red lens test |
| Angle of Anomaly | The difference of Objective angle and subjective angle A = H - S |
| To measure the angle of anomaly (x2) | 1. "Direct" measure A - after-image test Horizontal image is placed over the fixating eye 2. Indirect- red lens and use A=H-S Red lens is placed over the deviating eye |
| ESO is ___ value while EXO is ___value | +, - |
| Definition of Anomalous correspondence (AC) | Two foveas and other homologous retinal loci do not correspond to each other in regard to visual direction |
| Characteristics of AC | 1. Eccentric fixation 2. Binocular condition 3. |
| Classification of AC (x3) | 1. Normal correspondence 2. Harmonious AC 3. Unharmonious AC |
| Normal correspondence | H = S, then A=0 Two foveas hooked up |
| Harmonious AC | A = H so we know that S = 0 Fovea hooked up with point zero |
| Unharmonious AC | H > S and H > A (the objective angle is larger than the subjective angle. The angle of anomaly is still less than the objective angle) Fovea hooked up with some point between fovea and point zero |
| In red lens what we measure is ____ while in after image test we measure ____ | S, A |
| Theories of AC (x3) | 1. Sensory theory 2. Motor theory 3. Abnormal disparity detectors |
| Sensory theory | Adaptation to diplopia and confusion. The problem is patient has varied eye turn and according to sensory theory, brain needs to change constantly -- hard to explain co-variance |
| Motor theory | Use EOM (x2) - Registered- succades which strabismus patients use -non-registered- vergence - explain co-variance |
| Abnormal "disparity detector" | AC has "variable" disparity detector which change with disparity convergence (ESO) or disparity divergence (EXO) |
| Large vergence movement to prism | When placing a prism to correct strabismus, the disparity detector always like the biased amount of AC,therefore, large vergence movements are observed to re-establish the amount |
| Horopter in Strabismus | 1. difficult to measure 2. More variable in AC than NC 3. Horopter is excessively curved 4. Horopter changes with whether pt has ocular alignment or deviation |
| Intermittent exotrope (similar to BI) | Ocular alignment so horopter is at fixation point, bulges away and excessively curved |
| Esotrope (similar to BO) with NC | Ocular deviation so horopter passes thru where the visual axis cross, bulges towards you and excessively curved |
| Esotrope with AC | Notch horopter - use three lights test to verify the notch - notch is on the visual axis, normal correspondence -peripheral to visual axis is anomalous correspondence |
Created by:
yaya107