Term
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Definition
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 |
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Term
| Why don't theoretical and empirical horopters coincide? What is the deviation called? |
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Definition
-due to photoreceptor packing
-Hering-Hillebrand deviation |
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Term
| retinal image disparity occurs occurs to what type of displacement of the eyes? |
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Definition
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Term
| which areas around pannums fusional area are in physiologic diplopia? |
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Definition
| areas in front and behind (but diplopia is suppressed) |
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Term
| What are two terms describing visual direction sense? |
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Definition
-oculocentric visual direction
-egocentric visual direction |
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Term
| What is the oculocentric visual direction? |
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Definition
| -determined by using the line between and object and fovea as a reference. Based on this principle visual direction, all direction of all other objects in persons VF is determined |
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Term
| What is the egocentric visual direction? |
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Definition
| -refers to direction of an object in space relative to one's self, rather than eyes |
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Term
| In egocentric fixation, what factors help us determine if a change in retinal position is due to object movement or head/eye movement |
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Definition
-retinal position
-proprioceptive information
-head and body position
-vestibular apparatus |
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Term
| What are corresponding points? |
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Definition
| -points on the retina which give rise to same visual direction |
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Term
| What are non corresponding points referred to as? |
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Definition
-disparate points
-do not have same visual direction |
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Term
| What happens when corresponding points are stimulated at the same time? |
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Definition
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Term
| Why do we need the horopter? |
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Definition
| -to deal with mutliple points in visual space to have single vision. |
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Term
| What is the vieth muller circle? What does it assume? |
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Definition
-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 |
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Term
| What is Tschermak's Criteria for measuring the horopter? (5) |
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Definition
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) |
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Term
| What are the two most common methods of measuring the horopter? |
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Definition
| -AFPP and identical visual direction (or Nonius) Horopter |
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Term
| How is the IVD (Nonius) horopter tested? |
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Definition
| -involves setting two vertical rods one below the other. Each rod seen by each eye |
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Term
| What is considered the most accurate and true horopter? |
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Definition
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Term
| How does low luminance and low contrast affect pannums area? |
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Definition
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Term
The horopter varies with viewing distance. How does it vary? |
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Definition
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 |
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Term
| What are the two types of plots used to describe H (herring hillebrand deviation)? |
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Definition
| -spatial plot and analytical plot |
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Term
| When H = 0, how does the analytic plot look like? |
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Definition
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Term
| If your actual horopter lies off, and is larger than theoretical what is slope on analytic plot? If it is smaller? |
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Definition
-greater than 0, usually 1
-less than 0, usually -1 |
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Term
| What does the analytical plot allow us to see? |
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Definition
| -horopter changes as function of viewing distance |
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Term
| What happens at the abathic distance? |
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Definition
-apparent and real frontoparralel planes coincide.
-horopter is truly flat |
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Term
| What are size (iconic lenses)? |
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Definition
| -changes size without changing vergence |
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Term
| What happens to horopter when you place a 2% size lens in front the right eye? |
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Definition
| horopter will tilt towards right eye* |
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Term
| How does aniseikonia relate to pannums area? |
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Definition
| -it identifies with reshaping of visual space within panum's fusional area |
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Term
| What happens to horopter and image percept if you put an axis 90 meridonial magnifier in front of right eye? What is this called? |
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Definition
-horopter will tilt towards right eye
-image percept will tilt away from right eye (towards left eye)
-geometric effect |
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Term
| What happens to the image percept and horopter when an axis 180 meridonial magnifier place in front of right eye? What is this called? |
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Definition
-image percept (visual) move toward right eye
-horopter moves toward left eye
-induced effect |
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Term
| What does the horopter look like for intermittent exotropes? |
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Definition
| -excessively curved (may lie within VM) |
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Term
| What might an abnormal horopter cause? |
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Definition
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Term
| What is special about esotrope horopters? |
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Definition
| -do not follow smooth curves, have a large notch near the fixation point, lies between two visual axis |
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Term
| What are the parameters of the analytic plot? |
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Definition
-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) |
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Term
| What does the analytic plot appear like when the horopter does not intercept the fixation point (like fixation disparity) |
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Definition
| -hyperbole with asymptotes |
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Term
| What does the Ro point tell you in terms of perception? |
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Definition
| -uniform relative magnification across the visual field. Influences the relative size and orientation of perceived image |
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Term
| What does H tell you in terms of perception of image? |
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Definition
| -the non uniform relative magnification. Influences shape of perceived images in the visual field. |
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Term
| What does Ro demonstrate on the analytical plot and the spatial plot? |
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Definition
analytical plot: ordinate intercept of straight line
spatial plot: slope (skew) of the horopter at the fixation point. Curve is symmetrical when Ro = 1 |
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Term
| What does H mean on the analytic plot and spatial plot |
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Definition
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 |
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Term
| What are the dimensions of the pannums area? |
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Definition
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Term
| What occurs in fixaiton disparity in terms of corresponding points? |
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Definition
| -images of objects do not stimulate exact corresponding retinal points, but still fall within pannum's fusional areas, thus the object still being seen singly |
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Term
| What marks the limit of panum's? |
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Definition
| -when retinal disparities becomes too large for the visual system to fuse, diplopia will begin (images will fall on non corresponding points) |
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Term
| What are some characteristics of Panum's area? |
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Definition
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 |
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Term
| What are the factors affecting Panum's areas |
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Definition
-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 |
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Term
| What would you use to give a precise measurment of FD? |
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Definition
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Term
| Which techniques give you a rough estimate of the associated phoria? |
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Definition
-bernell test lantern
-AO vectographic slide
-Borish card
-Wesson card |
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Term
| On the fixation disparity curves define the parameters. Which type of fixation disparity curve is ideal? |
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Definition
-y intercept: fixation disparity (eso/exo)
-x intercept: associated phoria (BO/BI)
-type 1 |
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Term
| typically what are normal ranges for fixation disparity? |
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Definition
| -6 arc minutes exo or 4 arc minutes eso |
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Term
| What are type II and III curves associated with? Which curve type is more resitant to change? |
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Definition
-type II: eso
-type III: exo
-type II is more resistant to change
type III curves sometimes change to typeI |
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Term
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Definition
| -difference in optical image (perceptual) sizes between the eyes |
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Term
| What is regular aniseikonia? |
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Definition
| -due to optical differences |
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Term
| What is irregular aniseikonia? |
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Definition
| -due retinal or media based distortions, prism induced effects, surface distortions, visual problems encountered due to change in angle of gaze |
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Term
| What is optical aniseikonia |
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Definition
| -due to physically measured differences in sizes of the retinal images that typically arise in axial anisometropia or in corrected refractive anisometropia |
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Term
| What is neural aniseikonia? |
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Definition
-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. |
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Term
| What type of aniseikonia is possible in uncorrected axial anisometropia? |
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Definition
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Term
| What type of aniseikonia present in corrected axial anisometropia? |
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Definition
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Term
| What type of aniseikonia is possible in uncorrected refractive anisometropia |
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Definition
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Term
| What type of aniseikonia is present in corrected refractive anisometropia? |
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Definition
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Term
| What are reasons for neural aniseikonia? |
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Definition
-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 |
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Term
| What are some retinal conditions that cause neural aniseikonia? |
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Definition
epiretinal membrane, vitreomacular traction, re-attached retinal detachment, macular hole, retinoschisis
-seen in amsler grid |
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Term
| Which type of retinal condition causes macropsia? |
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Definition
-epiretinal membrane
-all the rest cause micropsia |
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Term
| What is aniseikonia of eccentric gaze? |
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Definition
| -occurs for objects displaced to one side of the median plane of the head. Object is closer to one eye than the other - projects a larger image to that eye |
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Term
| What is induced aniseikonia and how is it produced? |
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Definition
| -produced by wearing a magnifying lens in front of one eye. Use a size lens |
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Term
| Explain how horizontal magnification happens in the induced effect? How does it compare to geometrical effect? |
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Definition
-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% |
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Term
| Describe the apparent tilt in the geometric effect? |
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Definition
| -increases linearly with magnification until about 10% |
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Term
| What type of eye movement failure can result in in aniseikonia? |
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Definition
-unequal saccades (violation of hering's law)
-due to each eye's retinal image being in a different location |
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Term
| What can be said about binocular vision and aniseikonia? |
|
Definition
| binocular visual system can tolerate small amounts of aniseikonia without loss of function |
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Term
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Definition
| measurement of aniseikonia using a device that can change the size of one retinal image wrt the other, by a known percentagel without affecting vergence of light or clarity |
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Term
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Definition
-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 |
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Term
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Definition
-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 |
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Term
| What are the two methods to test for aniseikonia? |
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Definition
space eikonometric method (based on binocular perception)
direct comparison method (directly compare perceived image sizes) |
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Term
| What is the space eikonometer and what does it measure |
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Definition
-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 |
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Term
| What three quantities define the aniseikonic ellipse? |
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Definition
| -vertical and horizontal mag, and declination error |
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Term
| Besdies date from eikonometer what data is needed to calculate the aniseikonic spectacle Rx? |
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Definition
| -spectacle Rx, vertex distance, thickness and curve of trial lenses |
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Term
| What amount of aniseikonia is compatible with good normal stereopsis? |
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Definition
-3-5%
-aniskeikonia will interfere with stereopsis over this limit |
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Term
| What does a measure of -5% aniseikonia OD mean? |
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Definition
| -means that image in right is perceived to be 5 times larger than left, therefore corrected by minifying right eye by 5% (or magnifying left eye by 5% |
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Term
| How do you describe optically induces aniseikonia? |
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Definition
| -aniseikonic ellipse (consists of overall aniseikonia and meridional aniseikonia) |
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Term
| How is retinal induced aniseikonia described? |
|
Definition
-field-dependant aniskeikonia
-varies with field angles
-there is no one value of aniskeikonia anymore since it varies with gaze |
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Term
| What are the main symptoms of aniseikonia? |
|
Definition
-HAs
-ashenopia
-photophobia
-reading difficulty
-nausea
-diplopia |
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Term
| What might be a reason to misdiagnose aniseikonia? |
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Definition
| -optically induced anisophoria |
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