<ul>
 <li>Most primary visual sensory responses are monocular</li>
 <li>
 When an observer moves, different retinal receptors are stimulated when viewing an object and
 yet the object does not appear to move
 </li>
 <ul>
 <li>This is due to &lsquo;image stabilisation&rsquo; at the cortical level</li>
 </ul>
</ul>
<HotTopic>
 <>
 Normal retinal correspondence: required for BSV
 <ul>
 <li>Retinal elements that share a common subjective visual direction</li>
 <li>Equal distance from the two foveal centres</li>
 <li>Connected to the same areas of the cortex</li>
 </ul>
 </>
</HotTopic>
<ul>
 <li>
 Horopter: imaginary line in space connecting corresponding retinal points with no binocular
 disparity.
 </li>
 </ul>
 <li>
 Panum&rsquo;s area: region bordering a horopter.{' '}
 Images in this area are seen as single despite falling on disparate retinal elements.
 </li>
 <ul>
 <li>Without Panum&rsquo;s fusional area, we experience physiological diplopia.&nbsp;</li>
 <li>
 Takes the shape of an ellipse: greater disparities can be fused in the horizontal compared to
 the vertical
 </li>
 <li>Panum&rsquo;s area is narrowest at fixation and broader in the periphery</li>
 </ul>
 <li>Fusional amplitudes</li>
 <ul>
 <li>
 The degrees of retinal disparities outside of Panum&rsquo;s area that can be overcome by eye
 movements (motor fusion)
 </li>
 </ul>
 <li>
 Visual direction: stimulus falls on corresponding retinal units and is perceived as being in the
 same direction regardless of which eye sees it
 </li>
 <ul>
 <li>Requires functioning extraocular muscles&nbsp;</li>
 <li>The visual direction is perceived relative to the fovea</li>
 <li>When the visual axis of the foveas intersects, binocular fixation is achieved</li>
 </ul>

<HotTopic>
 <ul>
 <li>Worth&rsquo;s classification of binocular vision (in order of increasing quality)</li>
 <ul>
 <li>
 Grade I: simultaneous macular perception. Visual cortex can perceive separate stimuli from
 the eyes simultaneously.&nbsp;
 </li>
 <ul>
 <li>Often absent in amblyopia</li>
 </ul>
 <li>
 Grade II: sensory fusion. The two images are fused with some capacity for
 superimposing the images despite obstacles eg. eye movements/object movements (so-called
 motor fusion).&nbsp;
 </li>
 <ul>
 <li>Required for BSV&nbsp;</li>
 <li>Occurs in the visual cortex</li>
 </ul>
 <li>
 Grade III: stereopsis. Images from each eye are blended to achieve higher perceptual
 synthesis.&nbsp;
 </li>
 <ul>
 <li>Achieves appreciation of depth</li>
 <li>
 Images fall on disparate retinal areas but within Panum&rsquo;s fusional area, otherwise
 diplopia occurs
 </li>
 </ul>
 </ul>
 </ul>
</HotTopic>
<ul>
 <li>
 Dichoptic presentation: different images in the same retinal area helps development of
 binocular rivalry
 </li>
 <ul>
 <li>
 Different contours presented to corresponding retinal elements makes fusion impossible and
 causes confusion
 </li>
 <li>
 To remove the confusion, the image from one eye is suppressed leading to
 dominance of the other eye.&nbsp;
 </li>
 </ul>
</ul>
<HotTopic>
 Retinal rivalry is necessary for binocular vision
</HotTopic>
<ul>
 <li>
 Suppression: this is a neuro-physiological mechanism to prevent confusion or diplopia (due to simultaneous
 stimulation of non-corresponding retinal elements).
 </li>
 <ul>
 <li>Foveal suppression prevents confusion&nbsp;</li>
 <li>Extrafoveal suppression prevents diplopia</li>
 <li>
 Obligatory suppression continues even under monocular conditions resulting in reduced VA
 (amblyopia)
 </li>
 </ul>
</ul>
<ul>
 <li>
 Driving standard field of BSV: 20 degrees above and below horizontal and 60 degrees either side
 of the vertical
 </li>
 <li>Normal BSV: bifoveal</li>
 <li>
 Anomalous BSV: images are projected from the fovea of one eye but an extrafoveal area of the
 other eye.
 </li>
 <ul>
 <li>
 The visual direction of the retinal elements has changed (manifest strabismus) and there is
 abnormal retinal correspondence (ARC)
 </li>
 <li>
 This is an attempt to regain binocularity: the one fovea and the extrafoveal point share a
 common subjective visual direction
 </li>
 </ul>
</ul>
<HotTopic>
 
 When the normal eye is closed, the fovea of the other eye retains control over the extrafoveal
 element and in this monocular condition, central fixation is retained by the fovea. This is the principle underlying the cover test.
 
</HotTopic>
<ul>
 <li>Confusion vs diplopia</li>
 <ul>
 <li>
 Confusion: different images stimulating corresponding points (images on top of each other) eg.
 different image on the two foveas
 </li>
 <li>
 Diplopia: same image stimulating non-corresponding points eg. same image on fovea of one eye
 and extrafoveal region of other eye.
 </li>
 <li>
 Central suppression: almost always present. Prevents confusion by suppressing one foveal image
 </li>
 <li>
 Peripheral suppression: occurs in undeveloped visual systems. Prevents diplopia by suppressing
 the extrafoveal image.&nbsp;
 </li>
 <ul>
 <li>Adults with new strabismus complain of diplopia rather than confusion</li>
 </ul>
 </ul>
</ul>
<HotTopic>
 Normal fusional reserves
 <div>
 <table>
 <tbody>
 <tr>
 <td>
 Normal fusional reserves
 </td>
 </tr>
 <tr>
 <td>&nbsp;</td>
 <td>
 Near
 </td>
 <td>
 Far&nbsp;
 </td>
 </tr>
 <tr>
 <td>
 Convergence&nbsp;
 </td>
 <td>25 PD</td>
 <td>15-20 PD</td>
 </tr>
 <tr>
 <td>
 Divergence&nbsp;
 </td>
 <td>9-12 PD</td>
 <td>6-10 PD</td>
 </tr>
 <tr>
 <td>
 Vertical&nbsp;
 </td>
 <td>2-3 PD</td>
 </tr>
 <tr>
 <td>
 Torsional&nbsp;
 </td>
 <td>2-3 degrees</td>
 </tr>
 </tbody>
 </table>
 </div>
</HotTopic>

## Stereopsis
<ul>
 <li>
 The perception of distance/depth in the third dimension of space using binocular
 disparities.&nbsp;
 </li>
 <ul>
 <li>
 Note: not required for binocular single vision.
 </li>
 <li>Occurs in the cortex and requires fusion of images within Panum&rsquo;s area.</li>
 </ul>
 <li>Poor beyond 20 degrees from the fovea (Panum&rsquo;s area is narrowest here)</li>
 <li>
 Objects on the horopter are seen as flat (stereoacuity of zero)
 because the image projects to corresponding retinal regions with no horizontal disparity.
 </li>
 <ul>
 <li>Stereoacuity increases approaching the horopter but is zero on the horopter itself</li>
 </ul>
 <li>Varies with object size: disparities will be more easily detected in larger objects</li>
</ul>
<ul>
 <li>Requirements:</li>
 <ul>
 <li>Images have some corresponding points on both retinal</li>
 <li>Some proportion of points are non-corresponding (&ldquo;binocular disparities&rdquo;).</li>
 <ul>
 <li>These points also need to be fused</li>
 </ul>
 </ul>
 <li>
 Convergence contributes to stereopsis
 </li>
</ul>
<HotTopic>
 
 Stereoscopic acuity: the smallest binocular horizontal disparity that can be detected as depth
 
 <ul>
 <li>Normal stereoacuity is about 60 arcseconds or better</li>
 <li>Maximum stereoacuity is within the macula</li>
 <li>
 A stereoacuity of better than 250 arcseconds is thought to exclude significant amblyopia
 </li>
 </ul>
</HotTopic>

## Adaptive mechanisms
<ul>
 <li>Suppression: remove one image causing either confusion (central) or diplopia (peripheral)</li>
 <ul>
 <li>Leads to amblyopia if not treated</li>
 </ul>
 <li>
 Abnormal retinal correspondence: cortical process to remap non-corresponding retinal points to
 produce single perception.
 </li>
 <ul>
 <li>Allows BSV despite a manifest deviation</li>
 </ul>
 <li>Abnormal head posture: behavioural mechanism to move image into a more useful position</li>
</ul>
<ClinicalCorrelate>
 <>
 Microtropia
 <ul>
 <li>Demonstrates adaptive measures</li>
 <li>
 A small manifest deviation with BSV achieved through abnormal retinal correspondence,
 eccentric fixation and a central suppression scotoma
 </li>
 <li>
 May be no movement on cover test (see Part 2 package for further exploration of microtropia)
 </li>
 </ul>
 </>
</ClinicalCorrelate>

## Monocular depth cues
<ul>
 <li>Some perception of depth is possible without BSV</li>
 <li>Illumination</li>
 <li>Relative position of objects situated at different distances</li>
</ul>

## Diplopia
<ul>
 <li>Sensation caused by stimulating two points outside Panum&rsquo;s area</li>
 <li>Physiological vs non-physiological (heterotropias)</li>
 <li>Heterotropias: manifest deviations</li>
 <ul>
 <li>May be horizontal, vertical or torsional</li>
 </ul>
 <li>Heterophorias: latent deviations</li>
</ul>

## Tests of stereopsis
<ul>
 <li>Frisby:</li>
 <ul>
 <li>Three clear plates of different thicknesses</li>
 <li>
 Four squares on each plate with one containing a hidden circle printed on the back surface
 </li>
 <li>The test is three-dimensional</li>
 <li>Viewed at 40cm generally&nbsp;</li>
 <li>Measures a range from 15-600 arcseconds by altering the viewing distance</li>
 </ul>
 <li>Random dot stereograms</li>
 <ul>
 <li>Lang stereotest</li>
 <ul>
 <li>Fine vertical lines viewed through cylindrical lens elements</li>
 <li>Displacement of the random dot images creates disparity between 550-1200 arcseconds</li>
 </ul>
 <li>TNO stereotest: computer generated random dot anaglyphs</li>
 <ul>
 <li>
 Anaglyphs: stereogram in which disparate views are printed in red and green respectively on
 a white background
 </li>
 <li>Viewed through red-green spectacles</li>
 <li>The eye behind the red lens sees the green picture as black and vice versa</li>
 <li>The two views can be fused&nbsp;</li>
 <li>Range from 15-450 arcseconds</li>
 </ul>
 </ul>
 <li>
 Linear polarisation stereotests: require polaroid filter glasses so that each eye views a
 disparate image emitting vertical or horizontal light
 </li>
 <ul>
 <li>Titmus test</li>
 <ul>
 <li>
 Vectographs: two superimposed views presented so that the light is polarised. The light from
 each image travels at right angle to that of the other
 </li>
 <li>Viewed through a polarising visor or spectacles at 40 cm</li>
 <li>
 Wirt fly tests for gross stereopsis: if the wings of the fly are perceived standing out from
 the body
 </li>
 <li>Range from 40 to 3000 arcseconds with different plates</li>
 </ul>
 </ul>
 <li>Synoptophore:&nbsp;</li>
 <ul>
 <li>Measures all aspects of binocular single vision</li>
 <ul>
 <li>Simultaneous perception</li>
 <li>Fusion</li>
 <li>
 Stereopsis, but cannot quantify it
 </li>
 <li>Can measure the degree of any misalignments</li>
 <li>Detects suppression and abnormal retinal correspondence</li>
 </ul>
 <li>If the patient can see both images: simultaneous perception</li>
 <li>
 &ldquo;Put lion in cage&rdquo;: patient can adjust angle of one eyepiece to create a
 subjective measure of angle of deviation
 </li>
 <li>Examiner can also measure objectively by corneal reflections or alternate cover test</li>
 <li>The angle of anomaly (AOA) is the objective angle (OA) minus the subjective angle (SA)</li>
 <ul>
 <li>Normal retinal correspondence: SA = OA and AOA is 0</li>
 <li>Unharmonious ARC: SA &lt; OA and SA &gt; 0</li>
 <li>Harmonious ARC: SA = 0 so that the AOA = OA</li>
 </ul>
 </ul>
</ul>

## Tests of suppression
<ul>
 <li>Worth&rsquo;s four dot test: subjective test of retinal correspondence</li>
 <ul>
 <li>Four circular lights typically mounted in the Snellen light box</li>
 <li>Patient views them through red-green goggles creating partial dissociation</li>
 <ul>
 <li>Red goggle in front of the right eye</li>
 </ul>
 <li>Two green, one red and one white light</li>
 <li>Right eye sees the red light and left eye sees the green</li>
 <li>Four lights seen</li>
 <ul>
 <li>Normal retinal correspondence, or;</li>
 <li>Abnormal retinal correspondence (in presence of a heterotropia)</li>
 </ul>
 <li>Two red lights seen (red and white): left suppression</li>
 <li>Three green lights seen (two greens and white): right suppression</li>
 <li>Five lights seen (two red and three green): diplopia with no BSV.</li>
 <ul>
 <li>Two red lights to the left of the three greens: exotropia</li>
 <li>Two red lights to the right of the three greens: esotropia</li>
 </ul>
 </ul>
 <li>Synoptophore</li>
 <li>Friend test</li>
 <li>Amsler grid</li>
 <li>Bagolini&rsquo;s striated glasses&nbsp;</li>
 <li>4PD base out prism test</li>
 <ul>
 <li>
 When placed in front of the suppressed eye, no movement is detected (eg. in microtropia)
 </li>
 <li>
 When placed in front of the normal fellow eye, it moves towards the apex (normal response)
 </li>
 <ul>
 <li>The suppression eye also then moves as a conjugate movement</li>
 <li>But there is no re-fixation movement of the affected eye</li>
 </ul>
 </ul>
</ul>

Vision

Binocular Vision

Intro

FRCOphth Part 1 Study Notes

Orbit and ocular adnexae

Orbit

Extraocular Muscles

Orbital Blood Vessels

Paranasal Sinuses

Lacrimal Glands

Tear Film

Eyelids

Blinking

Anterior segment - ocular surface

Conjunctiva

Conjunctivitis

Sclera

Cornea

Corneal Structure And Development

Corneal Physiology

AC to Lens

Angle

Ciliary Body

Aqueous Humour Dynamics

Iris

Pupil

Lens

Posterior segment

Choroid

Vitreous

Retinal Macrostructure

Neurosensory Retina

Retinal Pigment Epithelium

Neuroanatomy

Venous Sinuses

Cerebral Ventricles

Cerebral Blood Supply

Supranuclear Gaze Pathways

Head And Neck Autonomic Nervous Supply

Head And Neck Glands

Osteology

Nerves

Muscles And Pharyngeal Arches

Extraocular Nerves

Sensory Nerves

Physiology

Physics Of Blood Flow

Neuronal Control Of Blood Vessels

Oxygen-Haemoglobin Dissociation Curve

Cytochrome p450

Pituitary Gland

Thyroid Hormone Production

Insulin

Glucagon

Parathyroid Hormone

Corticosteroids

Catecholamines

Cardiac Cycle

Renal Physiology

Fluid Balance

Acid-Base Balance

Muscle Physiology

Sensory Fibres

Cutaneous Receptors

Endocytosis

Glycosaminoglycans

Condensed Ocular Biochemistry

Eye Movements

Accomodation

Visual Cycle And Phototransuction

Visual Pathway

Visual Acuity

Colour Vision

Pathology

Collagen

Tissue Damage

Inflammation

Disease Entities

Wound Healing

Thrombosis / Atherosclerosis

Cell Growth

Neoplasia

Histopathology

Nystagmus

Free Radicals And Antioxidants

Immunology

Ocular Immunology

Microbiology

Viral Infections

Bacterial Infections

Fungal Infections

Protozoa

Nematodes

Antimicrobials

Genetics

Chromosomes

Mitosis

Meiosis

Genes

Polypeptide Synthesis

Histones

MicroRNA

Hardy-Weinberg Equilibrium

Mutations

Chromosome Defects

Autosomal Inheritance

X-Linked Inheritance

Mitochondrial Inheritance

Multifactorial Inheritance