Understanding Binocular Vision

Try and Locate Your Blindspot

• Near Triod includes accommodation and convergence, which are reasons for ambiocular vision.
• Miosis (pupillary constriction) is for stereopsis and better visual acuity.
• Aniseikonia refers to unequal retinal image sizes in both eyes.

Binocular Vision (BV)

• BV is having two coordinated eyes.
• Having two eyes is a prerequisite for BV, but doesn't guarantee it.
• Stereopsis is a specific depth sensation characteristic of ambiocular vision.
• BV is important for stereopsis.
• Stereopsis also allows judging distances with two eyes.
• Depth perception is usually monocular.
• Stereopsis is worse at a distance but better up close.
• Two-eyed vertebrate vision comes in two forms: utrocular (eyes work independently) and ambiocular (eyes work together).
• Binocular single vision means two eyes see separately, but the brain combines the images into one.
• Partial decussation is mentioned as a concept related to vision.
• BV is the coordinated behavior of two eyes in the perception of space.
• The visual field is the extent in space the eye can see while stationary.
• The blind spot is the spot in space where there is no perception of light.
• Anisometropia is an impairment to BV.

Panoramic View vs. Retinal Correspondence

• Panoramic view is being able to see at an angle of 360 degrees, like rabbits do.
• BV requires the overlap of two visual fields.
• Retinal correspondence means images must fall on the fovea of each eye, with corresponding foveas.
• Prey animals have eyes on the sides, while predators have eyes in the center.

Disadvantages and Conditions for Normal BV

• Disadvantages of BV include its complexity and susceptibility to anomalies and conflicts in convergence and accommodation.
• Abnormal head posture can counteract eye movement defects (ocular torticollis).
• Conditions for normal BV include clear ocular media in both eyes.
• There must be identical visual direction (retinal correspondence) and binocular fusion.

Advantages of BV

• Advantages include extended visual fields, a spare eye, enjoyment of BV, stereopsis.
• BV offers compensation for the blind spot and other interocular differences.
• If fovea points straight forward (ahead), and an object is located up, it falls below the retina.
• If it falls on the nasal retina, then something else occurs.

Leukocoria and Bruckner Test

• Leukocoria indicates a white pupil.
• The Bruckner test compares pupillary reflexes and helps to consider retinoblastoma or cataract.
• Homeopatrat pupils can be indicative of strabismus, retinoblastoma, or astigmatism; if one is seen, others should be suspected.

Binocular Fusion & Diplopia

• Binocular fusion's first step is motor alignment, followed by sensory confirmation.
• Depth perception involves perceiving distance using the visual system.
• Diplopia occurs when motor/sensory fusion fails.
• Sensory summation combines sensory inputs at different nervous system levels.
• Suppression occurs in binocular vision when the brain ignores the image from one eye.

Sensitive and Cortical Periods

• The sensitive period for vision is 6-9 years, offering maximal hope for intervention.
• The cortical period is 0-6 months, a period of rapid maturation.

Categories of Depth Perception

• Stereopsis, or seeing in 3D, is heightened depth perception arising from slight retinal disparity.
• "Stereo Sue" is a nickname for a professor who gained stereoscopic vision after 48 years, challenging beliefs about critical periods.
• Transient light adaptation is the rapid change in visual sensitivity responding to light alterations.
• Monocular depth perception uses visual cues from a single eye, including relative size, texture gradient.
• Occlusion happens when one object blocks another, which makes the blocked one seem farther away.
• Linear perspective: Parallel lines appear to converge in the distance.
• Motion parallax: Closer objects appear to move more quickly.

Eye Movements: Importance and Basics

• Eye movements help us have a wider field of view and to fixate on targets.
• The main reason for eye movement is to have the image of the object fall and remain on the fovea.
• Clear vision requires sharply focused and stationary images.
• The macula is darker and thinner than the surrounding retina.
• Eye movements help us maintain clarity.

Macula & Categories of Eye Movements

• The fovea is at the center of the macula.
• The macula has less blood vessels.
• Photoreceptors respond to light because of pigments; lutein and zeaxanthin are inside the macula.
• Two main categories shifting (tracking), gaze holding (stabilizing).

Gaze Shifting

• Gaze shifting involves tracking moving objects.
• Gaze holding (image stabilization) occurs during body movement, exemplified by the VOR (vestibulo-ocular reflex).
• Head movement triggers cancelling eye movement.
• VOR & OKR negate head/eye movement.
• If light does not fall on the fovea, the image will not be sharp.

Accommodation & Disjunctive Eye Movements

• Disjunctive eye movements involve eyes moving in opposite directions (vergences).
• Accommodation insufficiency is failing to bring enough accommodation relative to age.
• A presbyope cannot be as accommodative.
• Lead of accommodation uses more power than needed.
• It uses minimum effort to give clarity.
• Monocular movement toward the nose is adduction and away is abduction.
• Monocular rotation upward is supraduction, while downward is infraduction.

Terminology of Eye Movements & Rotation

• Incycloduction is rotation towards the nose, while excycloduction is rotation towards the temple.
• Eye rotations include left, right, up and down.
• Translation includes physical eye movement and shifting in position, having less impact than rotations.
• The limit to adduction is more than abduction.
• The limit of adduction is 50 degrees.
• The limit of abduction is 45 degrees.
• Supraduction is also known as sursumduction.
• The limit is 35 degrees.
• Infraduction is also known as deorsumduction and the limit is 50 degrees.

Binocular Movement Types & Eye Movement Testing

• Two types of binocular movement are conjugate (eyes go in same direction) (version) and disjunctive.
• Stimuli That Drives Accommodation: tonic (muscle tone), blur-driven, proximity, convergence.
• Tonus of muscle is lost when a person is dead.
• Accommodation is never totally abolished, as muscles remain alive.
• Accomodation can be abolished with cycloplegics.

Additional Eye Movement & Testing Info

• Paralysis of the ciliary muscles (cycloplegia).
• Ophthalmoplegics is paralysis of the extraocular muscles.
• Tonic accommodation is resting stage accommodation, existing even with closed eyes.
• After cycloplegia, if +15.00 is obtained, that has to be taken from it to compensate for tonic accommodation.
• Tonic accommodation is the baseline/resting stage accomodation due to muscle strength.
• Ability to rotate horizontally is easier than vertically.
• Vergence is inversely proportional to distance and accommodation.
• Vergence is influenced by pupillary distance.
• Arms length is an important indicator of the start of presbyopia.

Blur Driven Accommodation, Retinopic, Spatiotopic

• Blur-driven accommodation’s proponents claim it is an all-or-none phenomenon.
• If you accommodate you will see clearly in the RE (Right Eye)
• If you accommodate both eyes will too.
• Proximity: Driven by the awareness of a near object (nearness).
• It is connected to being spatiotopic
• Convergence accommodates
• To converge leads to accommodation.
• It is due to retinal blur.
• Accommodation requires a minus or plus lens to stimulate accommodation.
• Retinotepic: blur driven an convergence accommodation
• Spatiotopic: higher brain centers
• proximal accommodation

Convergence and Accommodation

• Convergence is directly proportional to accommodation.
• Esotropia can be managed by relaxing accommodation, which leads to a loss of some amount of convergence.
• If the person has divergence and uses minus lenses which they do not need it reduces the divergence.
• You can tap into accommodation through convergence or divergence.
• Types of Convergence: tonic, disparity driven fusional, proximal, and accommodation driven.

Vergence Facility & Binocular Vision

• For vergence facility, do not look for clarity but singularity.
• Convergence Insufficiency: When one does not have enough convergence
• Normal Accommodative Facility with expected value, may be aged or task biased
• Additional convergence can be obtained through accommodation -Since accommodation is accompanied by convergence.

More Anomalies

• Treating anomaly with AC Ratio gives them plus or minus lenses when it is not needed
• AC/A 4Δ/1D for most people
• When one accommodates by 1D you converge by 4Δ so relax accommodation to reduce convergence
• And induce accommodation to gain convergence in AC/A
• If AC/A is very low, modifying the spherical Rx is a problem and results include: . Testing fixation.
• Tests the ability to maintain steady fixation on an object!
• Every body should be able to maintain fixation for at least 10 seconds.
• Nystagmus is a disorder of fixation

Clinical Testing & What Triggers Eye Movement

• Facility - The ease with which we do something. Accommodation
• Accommodation Insufficiency: Facility
• How to Trigger Eye Movement with Test and Measure
• Push up to blur
• Minus to blur -target is held at a habitual near distance (40cm), Starting from +4.00D are introduced in front of the patient's plus/minus lenses that the patient can clear before target becomes blurry is the amount /number of is the AoAof the working distance is used for lens testing How to measure test Accommodations is used for testing Ampitutde Maintenance, flexibility and fluidity

More Testing for Accommodation and Vision

• Testing lens and accommodation are tested by: Lens flippers are used for measuring cycle per minute
• One cycle - is aten the lowering eye cycle
• Accommodation is testing Amplitude, Flexibility, Facility, and
• Results for test with the Proximal & accommodation being constant.
• Vision will be measured in days to measure testing

Assessing Accomodation & Vergence

• push up to Blur: for less accommodation or the ability to measure them accurately
• -Minus lens To test the degree of accuracy
• irls one eye
• Measure limited dipeth perception , it makes it Challenging to jucuige clotrmess da si2os accurately and potentially reduced by having the visual twks like diving Navigating stair catching

Direction: Seeing, Touching & Hearing

• Oculocentric direction - where things are located based on retinal signals.
• Each retina location has a unique direction that has been assigned to it.
• Retinal signals from oculo centric and from extra-ocular muscles- Extra retinal signals

Retina Direction and Function

• Retina + Extraretina signals = Egocentric
• Proprioception is use from ocular
• For the eye it the information in the a retinetopic map.
• The dominant eye state says it combines the information and imaging for both

More Functions

• Dominant Eye Theory: The best way to combine the images is for the eye to have more power than the other.

Direction & Retinal Correspondance

• Direction & Retinal visual half field left - right etc
• And visual field for both
• the smaller the area the the magnification. The brain link of retinal that the connect during stimulation that both link, not

Additional Retinal

• Binocular Ocular Direction Direction is the average of the two eyes that can come from a and B directions
• Direction is = alpha =average of the two eyes
• O the brain If it is is of small area