This Pdf is about the physiology of binocular vision. It describes each grades of binocular vision namely; simeltaneous perception and superimposition, sensory and motor fusion and stereopsis. It describes different theories of development of binocular vision. It also describes principal visual direction, oculocenteric localization, egocenteric localization, normal retinal correspondence and anomalous retinal correspondence, horopter, panum's fusional area, crossed and uncrossed physiologic diplopia, types of suppression, retinomotor value, binocular rivalary, pathologic diplopia and confusion.
Presbyopia/ Methods of Presbyopic Addition Determination (healthkura.com)Bikash Sapkota
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Dear viewers Check Out my other piece of works at ❤❤❤ https://healthkura.com ❤❤❤
Presbyopia and techniques of measurement
A fantastic presentation in the topic "Presbyopia and techniques of measurement"
A detailed information about presbyopia, techniques of presbyopic add determination and different correction methods.
Informative slide presentation on presbyopia for ophthalmology residents, ophthalmologists, optometrists, ophthalmic assistants, ophthalmic technicians, ophthalmic nurses, medical students, medical professors, teaching guides.
Presentation Contents:
--Introduction to presbyopia
-Types of presbyopia
-Risk factors
-Symptoms and signs
-Refractive error and presbyopia
-Methods of determining near add.
-Management of presbyopia
In a nutshell..
- The evaluation and management of presbyopia are important because significant functional deficits can occur when the condition is left untreated
- Undercorrected or uncorrected presbyopia can cause significant visual disability and have a negative impact on the pt.'s quality of life
- Finally, every tentative addition should be adjusted according to the particular needs of the patient
For Further Reading:
-Clinical Procedures in Optometry by J.D. Bartlett, J.B. Eskridge, J.F. Amos
-Primary Care Optometry by Theodere Grosvenor
-Borish’s Clinical Refraction by W.J. Benjamin
-Clinical Procedures for Ocular examination by Carlson et al
-American Academy of Ophthalmology
-Optometric Clinical Practice Guideline by American Optometric Association
-Internet
Follow me to get in touch with optometric and ophthalmic updates.
Binocular single vision (BSV) is the ability to use both eyes together to achieve a single fused percept, even in the presence of disparity of the image seen by each eye. It is divided into five grades: simultaneous perception, superimposition, sensory fusion, motor fusion, and stereopsis.
The current study aimed to examine the contribution that motor fusion and stereoacuity make to visuomotor task performance, while addressing some of these confounding factors. Individual differences in task performance and adaptation to BSV deficits were minimized using a repeated measures design, in which participants with normal BSV and no amblyopia or strabismus had their fine visuomotor task performance assessed as their BSV was progressively degraded.
Presbyopia/ Methods of Presbyopic Addition Determination (healthkura.com)Bikash Sapkota
DIRECT DOWNLOAD LINK ❤❤https://healthkura.com/presbyopia-near-addition/❤❤
Dear viewers Check Out my other piece of works at ❤❤❤ https://healthkura.com ❤❤❤
Presbyopia and techniques of measurement
A fantastic presentation in the topic "Presbyopia and techniques of measurement"
A detailed information about presbyopia, techniques of presbyopic add determination and different correction methods.
Informative slide presentation on presbyopia for ophthalmology residents, ophthalmologists, optometrists, ophthalmic assistants, ophthalmic technicians, ophthalmic nurses, medical students, medical professors, teaching guides.
Presentation Contents:
--Introduction to presbyopia
-Types of presbyopia
-Risk factors
-Symptoms and signs
-Refractive error and presbyopia
-Methods of determining near add.
-Management of presbyopia
In a nutshell..
- The evaluation and management of presbyopia are important because significant functional deficits can occur when the condition is left untreated
- Undercorrected or uncorrected presbyopia can cause significant visual disability and have a negative impact on the pt.'s quality of life
- Finally, every tentative addition should be adjusted according to the particular needs of the patient
For Further Reading:
-Clinical Procedures in Optometry by J.D. Bartlett, J.B. Eskridge, J.F. Amos
-Primary Care Optometry by Theodere Grosvenor
-Borish’s Clinical Refraction by W.J. Benjamin
-Clinical Procedures for Ocular examination by Carlson et al
-American Academy of Ophthalmology
-Optometric Clinical Practice Guideline by American Optometric Association
-Internet
Follow me to get in touch with optometric and ophthalmic updates.
Binocular single vision (BSV) is the ability to use both eyes together to achieve a single fused percept, even in the presence of disparity of the image seen by each eye. It is divided into five grades: simultaneous perception, superimposition, sensory fusion, motor fusion, and stereopsis.
The current study aimed to examine the contribution that motor fusion and stereoacuity make to visuomotor task performance, while addressing some of these confounding factors. Individual differences in task performance and adaptation to BSV deficits were minimized using a repeated measures design, in which participants with normal BSV and no amblyopia or strabismus had their fine visuomotor task performance assessed as their BSV was progressively degraded.
It details about the sensory development, theories and the neural aspects of binocular vision development along with various tests involved to assess stereopsis.
Anti ulcer drugs and their Advance pharmacology ||
Anti-ulcer drugs are medications used to prevent and treat ulcers in the stomach and upper part of the small intestine (duodenal ulcers). These ulcers are often caused by an imbalance between stomach acid and the mucosal lining, which protects the stomach lining.
||Scope: Overview of various classes of anti-ulcer drugs, their mechanisms of action, indications, side effects, and clinical considerations.
Couples presenting to the infertility clinic- Do they really have infertility...Sujoy Dasgupta
Dr Sujoy Dasgupta presented the study on "Couples presenting to the infertility clinic- Do they really have infertility? – The unexplored stories of non-consummation" in the 13th Congress of the Asia Pacific Initiative on Reproduction (ASPIRE 2024) at Manila on 24 May, 2024.
Lung Cancer: Artificial Intelligence, Synergetics, Complex System Analysis, S...Oleg Kshivets
RESULTS: Overall life span (LS) was 2252.1±1742.5 days and cumulative 5-year survival (5YS) reached 73.2%, 10 years – 64.8%, 20 years – 42.5%. 513 LCP lived more than 5 years (LS=3124.6±1525.6 days), 148 LCP – more than 10 years (LS=5054.4±1504.1 days).199 LCP died because of LC (LS=562.7±374.5 days). 5YS of LCP after bi/lobectomies was significantly superior in comparison with LCP after pneumonectomies (78.1% vs.63.7%, P=0.00001 by log-rank test). AT significantly improved 5YS (66.3% vs. 34.8%) (P=0.00000 by log-rank test) only for LCP with N1-2. Cox modeling displayed that 5YS of LCP significantly depended on: phase transition (PT) early-invasive LC in terms of synergetics, PT N0—N12, cell ratio factors (ratio between cancer cells- CC and blood cells subpopulations), G1-3, histology, glucose, AT, blood cell circuit, prothrombin index, heparin tolerance, recalcification time (P=0.000-0.038). Neural networks, genetic algorithm selection and bootstrap simulation revealed relationships between 5YS and PT early-invasive LC (rank=1), PT N0—N12 (rank=2), thrombocytes/CC (3), erythrocytes/CC (4), eosinophils/CC (5), healthy cells/CC (6), lymphocytes/CC (7), segmented neutrophils/CC (8), stick neutrophils/CC (9), monocytes/CC (10); leucocytes/CC (11). Correct prediction of 5YS was 100% by neural networks computing (area under ROC curve=1.0; error=0.0).
CONCLUSIONS: 5YS of LCP after radical procedures significantly depended on: 1) PT early-invasive cancer; 2) PT N0--N12; 3) cell ratio factors; 4) blood cell circuit; 5) biochemical factors; 6) hemostasis system; 7) AT; 8) LC characteristics; 9) LC cell dynamics; 10) surgery type: lobectomy/pneumonectomy; 11) anthropometric data. Optimal diagnosis and treatment strategies for LC are: 1) screening and early detection of LC; 2) availability of experienced thoracic surgeons because of complexity of radical procedures; 3) aggressive en block surgery and adequate lymph node dissection for completeness; 4) precise prediction; 5) adjuvant chemoimmunoradiotherapy for LCP with unfavorable prognosis.
Title: Sense of Smell
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the primary categories of smells and the concept of odor blindness.
Explain the structure and location of the olfactory membrane and mucosa, including the types and roles of cells involved in olfaction.
Describe the pathway and mechanisms of olfactory signal transmission from the olfactory receptors to the brain.
Illustrate the biochemical cascade triggered by odorant binding to olfactory receptors, including the role of G-proteins and second messengers in generating an action potential.
Identify different types of olfactory disorders such as anosmia, hyposmia, hyperosmia, and dysosmia, including their potential causes.
Key Topics:
Olfactory Genes:
3% of the human genome accounts for olfactory genes.
400 genes for odorant receptors.
Olfactory Membrane:
Located in the superior part of the nasal cavity.
Medially: Folds downward along the superior septum.
Laterally: Folds over the superior turbinate and upper surface of the middle turbinate.
Total surface area: 5-10 square centimeters.
Olfactory Mucosa:
Olfactory Cells: Bipolar nerve cells derived from the CNS (100 million), with 4-25 olfactory cilia per cell.
Sustentacular Cells: Produce mucus and maintain ionic and molecular environment.
Basal Cells: Replace worn-out olfactory cells with an average lifespan of 1-2 months.
Bowman’s Gland: Secretes mucus.
Stimulation of Olfactory Cells:
Odorant dissolves in mucus and attaches to receptors on olfactory cilia.
Involves a cascade effect through G-proteins and second messengers, leading to depolarization and action potential generation in the olfactory nerve.
Quality of a Good Odorant:
Small (3-20 Carbon atoms), volatile, water-soluble, and lipid-soluble.
Facilitated by odorant-binding proteins in mucus.
Membrane Potential and Action Potential:
Resting membrane potential: -55mV.
Action potential frequency in the olfactory nerve increases with odorant strength.
Adaptation Towards the Sense of Smell:
Rapid adaptation within the first second, with further slow adaptation.
Psychological adaptation greater than receptor adaptation, involving feedback inhibition from the central nervous system.
Primary Sensations of Smell:
Camphoraceous, Musky, Floral, Pepperminty, Ethereal, Pungent, Putrid.
Odor Detection Threshold:
Examples: Hydrogen sulfide (0.0005 ppm), Methyl-mercaptan (0.002 ppm).
Some toxic substances are odorless at lethal concentrations.
Characteristics of Smell:
Odor blindness for single substances due to lack of appropriate receptor protein.
Behavioral and emotional influences of smell.
Transmission of Olfactory Signals:
From olfactory cells to glomeruli in the olfactory bulb, involving lateral inhibition.
Primitive, less old, and new olfactory systems with different path
These simplified slides by Dr. Sidra Arshad present an overview of the non-respiratory functions of the respiratory tract.
Learning objectives:
1. Enlist the non-respiratory functions of the respiratory tract
2. Briefly explain how these functions are carried out
3. Discuss the significance of dead space
4. Differentiate between minute ventilation and alveolar ventilation
5. Describe the cough and sneeze reflexes
Study Resources:
1. Chapter 39, Guyton and Hall Textbook of Medical Physiology, 14th edition
2. Chapter 34, Ganong’s Review of Medical Physiology, 26th edition
3. Chapter 17, Human Physiology by Lauralee Sherwood, 9th edition
4. Non-respiratory functions of the lungs https://academic.oup.com/bjaed/article/13/3/98/278874
The prostate is an exocrine gland of the male mammalian reproductive system
It is a walnut-sized gland that forms part of the male reproductive system and is located in front of the rectum and just below the urinary bladder
Function is to store and secrete a clear, slightly alkaline fluid that constitutes 10-30% of the volume of the seminal fluid that along with the spermatozoa, constitutes semen
A healthy human prostate measures (4cm-vertical, by 3cm-horizontal, 2cm ant-post ).
It surrounds the urethra just below the urinary bladder. It has anterior, median, posterior and two lateral lobes
It’s work is regulated by androgens which are responsible for male sex characteristics
Generalised disease of the prostate due to hormonal derangement which leads to non malignant enlargement of the gland (increase in the number of epithelial cells and stromal tissue)to cause compression of the urethra leading to symptoms (LUTS
TEST BANK for Operations Management, 14th Edition by William J. Stevenson, Ve...kevinkariuki227
TEST BANK for Operations Management, 14th Edition by William J. Stevenson, Verified Chapters 1 - 19, Complete Newest Version.pdf
TEST BANK for Operations Management, 14th Edition by William J. Stevenson, Verified Chapters 1 - 19, Complete Newest Version.pdf
New Directions in Targeted Therapeutic Approaches for Older Adults With Mantl...i3 Health
i3 Health is pleased to make the speaker slides from this activity available for use as a non-accredited self-study or teaching resource.
This slide deck presented by Dr. Kami Maddocks, Professor-Clinical in the Division of Hematology and
Associate Division Director for Ambulatory Operations
The Ohio State University Comprehensive Cancer Center, will provide insight into new directions in targeted therapeutic approaches for older adults with mantle cell lymphoma.
STATEMENT OF NEED
Mantle cell lymphoma (MCL) is a rare, aggressive B-cell non-Hodgkin lymphoma (NHL) accounting for 5% to 7% of all lymphomas. Its prognosis ranges from indolent disease that does not require treatment for years to very aggressive disease, which is associated with poor survival (Silkenstedt et al, 2021). Typically, MCL is diagnosed at advanced stage and in older patients who cannot tolerate intensive therapy (NCCN, 2022). Although recent advances have slightly increased remission rates, recurrence and relapse remain very common, leading to a median overall survival between 3 and 6 years (LLS, 2021). Though there are several effective options, progress is still needed towards establishing an accepted frontline approach for MCL (Castellino et al, 2022). Treatment selection and management of MCL are complicated by the heterogeneity of prognosis, advanced age and comorbidities of patients, and lack of an established standard approach for treatment, making it vital that clinicians be familiar with the latest research and advances in this area. In this activity chaired by Michael Wang, MD, Professor in the Department of Lymphoma & Myeloma at MD Anderson Cancer Center, expert faculty will discuss prognostic factors informing treatment, the promising results of recent trials in new therapeutic approaches, and the implications of treatment resistance in therapeutic selection for MCL.
Target Audience
Hematology/oncology fellows, attending faculty, and other health care professionals involved in the treatment of patients with mantle cell lymphoma (MCL).
Learning Objectives
1.) Identify clinical and biological prognostic factors that can guide treatment decision making for older adults with MCL
2.) Evaluate emerging data on targeted therapeutic approaches for treatment-naive and relapsed/refractory MCL and their applicability to older adults
3.) Assess mechanisms of resistance to targeted therapies for MCL and their implications for treatment selection
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4. Objective
At the end of this seminar we should be able to discuss:
• the definition of binocular vision and its development
• different theories of binocular vision
• the definition and physiology of each grade of binocular vision
• horopter and panum’s fusional area
• definition and types of suppression
• definition of retinomotor value, binocular rivalry
• the difference between diplopia and confusion
10/18/2022 4
5. Binocular vision
• is the ability to use both eyes simultaneously so that each eye
contributes to a common single perception
• the state of simultaneous vision, which is achieved by the coordinated
use of both eyes, so that separate and slightly dissimilar images arising
in each eye are appreciated as a single image by the process of fusion
10/18/2022 5
6. • highly coordinated organization of series of sensory and motor
processes that culminate in perception of singleness and stereoscopic
depth enabling the eye to attain single vision from 2 retinal images
• normal binocular single vision results due to the presence of bifoveal
fixation and normal retinal correspondence and vice versa
10/18/2022 6
7. BV depends on normal functioning of underlying vision processes
including:
• central fixation with normal visual acuity in each eye
• accurate oculomotor control to obtain bifoveal fixation
• normal inter-retinal correspondence of visual directions
• sensory mechanisms to produce haplopia (single vision)
• neural mechanisms to extract selective depth signals from objects that
are nearer or farther than the plane of fixation
10/18/2022 7
8. Origin and Development of Binocular Vision
Theory of empiricism:
• describes that binocular vision depends on ontogenetic development
• describes that humans are born without binocularity or spatial
orientation and these functions are acquired as a result of experiences
from everyday life
• acquisition of this function is aided by all other sensations especially
kinesthetic sense
10/18/2022 8
9. Theory of nativistic teaching:
• states that simultaneous perception and binocular vision occur as result
of innate process i.e anatomicophysiological arrangement of
components of visual system
• binocular vision is acquired phylogenetically and not ontogenetically
10/18/2022 9
10. Development of binocular vision
• during the initial few years of life certain normal anatomical and
physiological conditions are required for the development of binocular
vision
10/18/2022 10
11. Anatomical factors:
• the eyes are spruced up in the orbit in such a way that the visual axis
of both eyes is aligned
• this occurs as a result of multiple anatomical factors:
i. architecture/shape of the orbit
ii. ligaments, muscles and connective tissue
10/18/2022 11
12. Physiological factors:
• normal physiological binocular reflexes determine the development of
binocular vision
• these physiologic reflexes can be either innate or acquired as a result
of appropriate environmental stimulation
Fixation reflex
Refixation reflex
Accomodation convergence reflex
10/18/2022 12
13. Fixation reflexes
a. compensatory fixation reflex (gravitational reflex) - the function of
this reflex is to keep the eyes in a fixed position i.e. looking in the
required direction compensating for the movement of the body,
head, limbs etc
b. orientation fixation reflex -it can be demonstrated by the eye
following a moving object or panorama, thus exhibiting a
comparatively slow movement of continued fixation and not a rapid
jerk fixation
10/18/2022 13
14. The refixation reflex
• the aim of this reflex is to bring the eye back to the original orientation
point or to the new orientation point
Accomodation convergence reflex
• it is aimed at correctly aligning the eyes and keeping them focused on
the object. It includes vergence fixation reflex, accommodation reflex
and fusional vergence reflex
10/18/2022 14
15. Development of BV in infant
First 2–3 weeks: follows light uniocularly
6 weeks to 6 months: follows light binocularly
1-6 months: convergence reflex develops
6 months: accommodation develops
• the sensitive period of development of binocular vision in human
beings begins at about 4 months of age, peaks at 2 years, it is well
developed by 4 years of age and slowly stops by 9 years of age
10/18/2022 15
17. • any obstacle in the reflex pathway is likely to hamper the development
of binocular vision and the obstacles can be in the form of:
Sensory obstacles
• dioptric obstacles – e.g. media opacities, uncorrected r/e
• prolonged uniocular activity- e.g. severe ptosis, anisometropia
• retinoneural obstacles – lesions of retina, optic nerve
• proprioceptive obstacle
10/18/2022 17
18. Motor obstacles
• congenital craniofacial malformations
• conditions effecting extra-ocular muscles
• CNS lesions- involving the nerve trunks, root of nuclei
10/18/2022 18
19. • the presence of these obstacles gives rise to various sensory
adaptations to binocular dysfunction especially if the disruptive factor
is present in the sensitive period
• this can be in the form of:
ARC
suppression
amblyopia
10/18/2022 19
20. Theories of Binocular Vision
• Correspondence and disparity theory
• Neurophysiological theory
• Alteration theory
• Projection theory
• Motor theory
• Theory of isomorphism
10/18/2022 20
21. Correspondence and disparity theory
• most widely accepted theory
• according to this theory sensory binocular cooperation is based on
system of correspondence and disparity
• it assumes the presence of one to one retinocortical relationship
between the two eyes
• simultaneous stimulation of the corresponding points by one object
transmits single visual impression with no depth quality
• simultaneous stimulation by two objects points that differ in character
results in binocular rivalry
10/18/2022 21
22. • diplopia occurs when disparate elements are stimulated by one object
point
• however, BSV with stereopsis results when the horizontal disparity
remains within the limits of panums area
10/18/2022 22
23. Neurophysiological theory
• approximately 80% of the neurons in the striate cortex can be
stimulated from either eye in response to a visual stimulus, assuming
there is a precise and orderly arrangement of connections along the
retino-geniculate striate pathway
• of these 75% represented graded response from either left or right eye
while 25% are binocularly driven cells and are equally stimulated from
each eye
• these 75% cells that could be driven by stimulation of either eye had
receptive fields of nearly equal size and in corresponding positions of
visual field
10/18/2022 23
24. • retinal field disparity is detected by sensitive binocular neurons giving
rise to binocular vision and stereopsis which occurs as a result of the
difference in direction or distance of the fields in each retina, forms the
basis of Panum’s fusion area
10/18/2022 24
25. Alteration theory
• states that sensory fusion is perceptual unification of images perceived
in corresponding location in the two retinae
• this theory fails to explain many phenomena of binocular vision
particularly stereopsis
10/18/2022 25
26. Projection theory
• according to this theory visual stimuli are exteriorized(projected to
physical space) along the lines of direction
• this is an obsolete theory
• the basic reason for the failure of the projection theory is that the
distinction between physical and subjective space is disregarded and it
fails to explain physiologic diplopia
10/18/2022 26
27. Motor theory
• this theory conceptualizes that spatial orientation is obtained from the
movement of the head, conjugate movements of the eye and
convergence
• the eyes are made aware of their movements by muscle sense
• it is this awareness that produces spatial localization
• the sensations arising from the convergence effort determine whether
one object is nearer or further away than the others
• this theory fails to explain many sensory aspects of the binocular
vision especially stereopsis
10/18/2022 27
28. Theory of isomorphism
• states that there exists a one to one relationship between the retina and
cortex and strict conformity or isomorphism between the distribution
of objects in space and cortical events forms the basis of spatial
orientation
• based on a rigid retinocortical relationship
• there is no evidence of physiological rigidity of the retinocortical
relationship or the convergence of the pathways on which this theory
is based
10/18/2022 28
29. Grades of Binocular Vision
• binocular single vision can be classified into three grades according to
Worth’s classification
1. Simultaneous perception and superimposition
2. Fusion
3. Stereoscopic vision
10/18/2022 29
31. Simultaneous perception and superimposition
• simultaneous perception: the ability of both eyes to perceive
simultaneously two images, one formed on each retina
• superimposition: simultaneous perception of the two images formed
on corresponding areas, with the projection of these images to the
same position in space
10/18/2022 31
32. Fusion
• is the cortical unification of 2 images of an object, 1 from each eye,
into a single percept
• for fusion of macular images (central fusion) to occur, there can be
very little dissimilarity between the images in each eye, because of the
small receptive fields in the area near the fovea; otherwise, diplopia
results
• more image dissimilarity is tolerated in the periphery (peripheral
fusion), where the receptive fields are larger
10/18/2022 32
33. Sensory fusion
• the hallmark of retinal correspondence
• defined as the ability of both eyes to perceive two similar images, one
formed on each retina, when interpreted as one single visual image
• the images not only must be located on corresponding retinal areas but
also should be sufficiently similar with respect to size, brightness and
sharpness (prerequisites for sensory fusion)
• a severe obstacle to fusion are unequal images
10/18/2022 33
34. Motor fusion
• is the ability to align both the eyes in such a way that sensory
fusion can be maintained
• unlike sensory fusion, motor fusion is a function of the extrafoveal
retinal periphery
• fusion, whether sensory or motor, is always a central process, i.e., it
takes place in the visual cortex
10/18/2022 34
35. Stereopsis
• is a binocular sensation of relative depth caused by horizontal disparity
of retinal images
• is the ability of both eyes to fuse images that lie within Panum’s
fusional area resulting in three dimensional perception of the object
• is the highest form of binocular cooperation and adds a unique quality
to vision
• is the means by which we determine the relative depth of objects by
virtue of the fact that our two eyes view the world from a slightly
different angle
10/18/2022 35
36. Stereoscopic acuity
• the smallest relative binocular disparity that can generate a sensation
of depth
• can be defined as the disparity beyond which no stereoscopic effect
can be produced
• is the smallest binocular disparity that can be readily detected
• stereopsis cannot work beyond critical distance of 125-200 meters
10/18/2022 36
38. • the stereo-acuity threshold for static targets is 2-10 arc sec; for targets
in motion towards and away from the observer the threshold increases
to about 40 arc sec
• stereo-acuity is maximal about 0.25 degrees off dead center in the
foveola, and diminishes exponentially with increasing eccentricity
along the x-axis
• stereopsis is nil beyond 15 degrees eccentricity
• stereo-acuity diminishes in similar exponential fashion when the target
is moved in front or behind the horopter along the y-axis
10/18/2022 38
39. Monocular cue for depth perception
• the brain can achieve depth perception with a single eye through
simulated stereopsis and the use of monocular cue including
texture variations and gradients
linear perspective
monocular movement parallax
shade and shadows
relative size which enable the cortex to estimate the distance and
depth of the object
10/18/2022 39
40. Advantages of binocular vision
• stereopsis
• binocular summation- vision sharper, clearer and more sensitive
• larger field of view
• single vision
• any image distortion due to optical or pathological defects in one eye
can be masked by a normal image in the other eye
10/18/2022 40
41. Visual direction
• is a two dimensional localization of an object and it is represented by a
straight line which connects any given point on the retina to points in
the physical space
Principal visual direction/ visual axis
Oculocenteric visual direction
Egocentric visual direction
10/18/2022 41
42. Principal visual direction
• visual direction of an object that can be represented by a line that joins
the fovea and the object of the regard
10/18/2022 42
43. Oculocenteric visual direction
• when eye fixes an object through principal visual axis the other objects
around the fixation point focus around the fovea; those visual
directions are called oculocenteric visual direction
10/18/2022 43
44. Egocenteric localization
• when we see with one eye the direction of the object is judged in
relationship to the visual axis of that eye but when we see with both
eyes we localize the objects in the visual space in relation to an
imaginary eye centered between the two eyes, the cyclopean eye- this
is called egocentric localization
10/18/2022 44
46. Sensory binocular correspondence
• the retinal receptors and subsequent local retinal neurones responding
to the visual stimulus are known as a retinal element
• for most of each retina, every retinal element or ‘retinal point’ shares a
common relative subjective visual direction with an associated retinal
point in the other eye
• there are some peripheral retinal elements that never actually share a
common visual direction because they receive images from objects in
the monocular visual field of each eye
10/18/2022 46
47. • retinal elements of each eye that do have the same common subjective
visual directions are called corresponding retinal points
• for a given retinal element in one eye, all retinal elements in the other
eye except the corresponding retinal point are non corresponding
points
10/18/2022 47
49. Types of retinal correspondence
• Normal retinal correspondence is defined when fovea of one eye
corresponds to the fovea of the other eye and they both share a
common visual direction
• points located nasal to the fovea in one eye correspond to the points
located temporal to the fovea of the other eye
10/18/2022 49
50. • Anamolous retinal correspondence is a type of sensory adaptation in
which fovea of one eye shares a common visual direction with the
extra foveal point of the other eye
• this is an adaptation in manifest squint resulting in BSV
• it is known as anomalous because extra foveal point of one eye
corresponds to foveal point of the other eye
10/18/2022 50
51. Theories on anomalous retinal correspondence
• the 1st theory states that, with anomalous correspondence the two eyes
perceive space independently. Each eye computes egocentric visual
direction from its own sense of eye position and oculocentric retinal
image location. In effect, there is a lack of correspondence
• the 2nd theory proposes that there is a shift in retinal correspondence so
that retinal points that are normally disparate are shifted to acquire an
anomalous coupling in the striate cortex
• the 3rd theory proposes that strabismics who have no suppression are
able to perceive space singly due to enlarged Panum’s fusional areas
10/18/2022 51
52. Horopter
• derived from Greek words, horos-boundary, opter-observer
• is a curved line formed when all the corresponding points are
projected in space at a particular distance from the observer
• hence it is the locus of all points in the space that stimulates the
corresponding points of the retina leading to a BSV
• it can be plotted by joining the points of intersection of the lines drawn
from the corresponding points through the nodal points
10/18/2022 52
53. Geometric horopter (Vieth Muller
circle)
• it is a geometrically constructed
circle which passes through the
corresponding points of the two
eyes; but actually it is not
spherical, it is flatter
• is a theoretical horopter
10/18/2022 53
54. Empirical or longitudinal horopter
• when the horopter is determined experimentally, the locus of points
that are seen singly falls not on a circle but on a curve called the
empirical horopter
• is slightly flatter than vieth muller circle i.e. it has a greater radius of
curvature
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56. • the difference between the geometric and the empirical horopter is
known as the Hering-Hillebrand deviation
• if the horopter includes all points in space that stimulate corresponding
retinal points, double vision would be expected when the target does
not lie on the horopter
• however, the visual system can combine slightly disparate points
within a limited area surrounding the horopter, called Panum’s area of
single binocular vision
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57. Panum’s area
• the field infront of and behind the horopter in which the expected
diplopia does not occur
• objects within Panum’s area do not result in diplopia
• objects outside Panum’s area stimulate widely disparate retinal points,
resulting in physiologic diplopia
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59. Physiologic diplopia
• when an object is located closer than the horopter it is imaged
temporal to the fovea in each eye resulting in crossed
diplopia/heteronymous
• when an object is located beyond the horopter it is imaged nasal to the
fovea in each eye resulting in uncrossed diplopia/homonymous
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61. Binocular disparity
• images of a single object that do not stimulate corresponding retinal
points in both eyes are said to be disparate; binocular disparity is
defined as the difference in position of corresponding points between
images in the two eyes
• the horizontal component of binocular disparity is the unique stimulus
for stereoscopic depth perception and is quantified by the difference in
the longitudinal visual angles, also called horizontal disparity angles
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62. Suppression
• is the alteration of visual sensation that occurs when an eye’s retinal
image is inhibited or prevented from reaching consciousness during
binocular visual activity
• physiologic suppression is the mechanism that prevents physiologic
diplopia (diplopia elicited by objects outside Panum’s area) from
reaching consciousness
• pathologic suppression may develop because of strabismic
misalignment of the visual axes or other conditions resulting in
discordant images in each eye, such as cataract or anisometropia
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63. • if a patient with strabismus and normal retinal correspondence (NRC)
does not have diplopia, suppression is present, provided the sensory
pathways are intact
• classification of suppression
central versus peripheral
nonalternating versus alternating
facultative versus constant
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64. Central suppression
• is the mechanism that keeps the foveal image of the deviating eye
from reaching consciousness, thereby preventing visual confusion
Peripheral suppression
• eliminates diplopia by preventing awareness of the image that falls on
the peripheral retina in the deviating eye, which corresponds to the
image falling on the fovea of the fixating eye
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65. Non-alternating suppression
• if suppression always causes the image from the dominant eye to be
predominant over the image from the deviating eye
• this may lead to amblyopia
Alternating suppression
• if the process switches between the 2 eyes
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66. Facultative suppression
• if the suppression is present only when the eyes are deviated and is
absent in all other states. Patients with intermittent exotropia, for
instance, often experience suppression when the eyes are divergent but
may experience high-grade stereopsis when the eyes are straight
Constant suppression
• denotes suppression that is always present, whether the eyes are
deviated or aligned. The suppression scotoma in the deviating eye may
be either relative (permitting some visual sensation) or absolute
(permitting no perception of light)
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67. Retinomotor values
• the appearance of an object in the periphery of the visual field attracts
attention, and the eye is turned toward the object so that it may be
imaged on the fovea
• the resulting eye movement is called a saccade and is extraordinarily
precise
• it is initiated by a signal from the retinal periphery that transmits to the
brain the visual direction, relative to the foveal visual direction, where
the peripherally seen object has appeared
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68. • corresponding impulses are then sent to the extraocular muscles to
perform the necessary ocular rotation
• this function of the retinal elements may be characterized by saying
that they have a retinomotor value
• retinomotor value of the retinal elements increases from the center
toward the periphery
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69. • the retinomotor value of the fovea itself is zero: once an image is on
the fovea, there is no incentive for ocular rotation.
• the fovea, then, in addition to its other functions, is also the
retinomotor center or retinomotor zero point
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70. Retinal rivalry/ Binocular rivalry
• when dissimilar contours are presented to corresponding retinal areas
fusion becomes impossible since two dissimilar objects localized in
the same place give rise to conflict and confusion
• the conflict which results when contradictory and incompatible signals
are transmitted from corresponding points to the visual cortex is
termed retinal rivalry
• the visual system responds to retinal rivalry by suppression
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71. Abnormalities of Binocular Vision
• when a manifest deviation of the eyes occurs, the corresponding
retinal elements of the eyes are no longer directed at the same object
• this places the patient at risk for 2 distinct visual phenomena: visual
confusion and diplopia
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72. Visual Confusion
• is the perception of a common visual direction for 2 separate objects
• the 2 foveal areas are physiologically incapable of simultaneous
perception of dissimilar objects
• the closest foveal equivalent is retinal rivalry, wherein there is rapid
alternation of the 2 perceived images
• clinically significant visual confusion is rare
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73. Diplopia
• usually results from an acquired misalignment of the visual axes that
causes an image to fall simultaneously on the fovea of one eye and on
a nonfoveal point in the other eye
• the same object is perceived as having 2 locations in subjective space,
and the foveal image is always clearer than the nonfoveal image of the
nonfixating eye
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74. • the loss of normal binocular fusion in an individual unable to suppress
disparate retinal images results in intractable diplopia, referred to as
central fusion disruption (horror fusionis)
• this condition is typically seen in adults or visually mature children
and can occur in a number of clinical settings, including prolonged
visual deprivation due to monocular occlusion or a mature cataract,
traumatic brain injury, or long-standing strabismus
• management is challenging
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76. Summary
• binocular vision is the ability to use both eyes simultaneously to bring
about single perception
• there is continued development of visual system during the initial few
years of life
• correspondence and disparity theory is the most accepted theory of BV
• there are 3 grades of BV
• retinal correspondence can be NRC and ARC
• horopter is a curved line formed with locus of all points in the space
that stimulates the corresponding points of the retina leading to a BSV
and the field in front and behind it is called panum’s area
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77. • suppression occurs when an eye’s retinal image is inhibited or
prevented from reaching consciousness during binocular visual
activity
• physiologic Vs pathologic diplopia
• confusion Vs diplopia
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78. References
• Adler’s physiology of the eye, 11th edition
• BCSC 2020-2021, Section 6: Pediatric ophthalmology and Strabismus
• Duane’s Ophthalmology 2012 edition
• Normal Binocular Vision Theory, Investigation and Practical Aspects,
Pdf
• Binocular Vision and Ocular Motility, Pdf
• Binocular Functions, Pdf
• Binocular Vision , Rahul Bhola, MD
• Different online videos
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