The Visual System-compressed PDF

Sandra Shamseddine BS in Optics and Optometry MS in Clinical Optometry IPM - Actualités professionnelles 1 Fall 2023/2024  Course Outcomes - Introducing students to the field of binocular vision and oculomotricity. - Establishing a link between BV and psychomotor dev...

Sandra Shamseddine BS in Optics and Optometry MS in Clinical Optometry IPM - Actualités professionnelles 1 Fall 2023/2024  Course Outcomes - Introducing students to the field of binocular vision and oculomotricity. - Establishing a link between BV and psychomotor development. - Getting familiar with eye problems especially binocular vision and oculomotricity and relating them to different psychomotor fields. GEN ER A L EYE A N A TOM Y 16  EYE ANATOMY Cornea: The cornea is the transparent part of the eye that covers the front portion of the eye. The cornea’s main function is to refract, or bends light. The cornea is responsible for focusing most of the light that enters the eye. Pupil:The pupil is the opening in the center of the iris (the structure that gives our eyes their color). The function of the pupil is to allow light to enter the eye so it can be focused on the retina to begin the process of sight.  EYE ANATOMY Crystalline Lens: a nearly transparent biconvex structure suspended behind the iris of the eye, the sole function of which is to focus light rays onto the retina. The ability of the lens to adjust from a distant to a near focus, called accommodation, gradually declines with age (a condition called presbyopia), often requiring correction. Clouding or opacity of the lens, called a cataract, may also occur with age. Ciliary body: The ciliary body produces the fluid in the eye called aqueous humor. which is responsible for norishing the cornea and managing IOP.  EYE ANATOMY Retina: The retina is the sensory membrane that lines the inner surface of the back of the eyeball. It's composed of several layers, including one that contains specialized cells called photoreceptors. There are two types of photoreceptor cells in the human eye — rods and cones. The retina is actually an extension of the brain, formed embryonically from neural tissue and connected to the brain proper by the optic nerve.  EYE ANATOMY Optic nerve: Optic nerve, second cranial nerve, which carries sensory nerve impulses from the more than one million ganglion cells of the retina toward the visual centres in the brain. The vast majority of optic nerve fibres convey information regarding central vision.  EYE ANATOMY Common retinal diseases causing low vision: Retinal tear Solutions: Retinal detachment. Low vision aids Diabetic retinopathy. Vision Rehabilitation Macular degeneration. surgical intervention Retinitis pigmentosa. Glaucoma Optic Atrophy (partial or complete)  Six of the twelve cranial nerves directly innervate the eye & periocular tissues: CNII (optic nerve) CNIII (oculomotor) CNIV (trochlear) CNV (trigeminal) CNVI (abducens) CNVII (facial)  Extraocular muscles 6 Muscles responsible of eye movements: 1.Superior rectus 2.Inferior rectus 3.Medial rectus 4.Lateral rectus 5.Superior oblique 6.Inferior oblique Central Vs. Peripheral Retina Central retina close to the fovea is considerably thicker than peripheral retina.This is due to the increased packing density of photoreceptors, particularly the cones. Central retina is cone-dominated retina whereas peripheral retina is rod-dominated.  What are photoreceptors? - Phtoreceptors transform light into electrical energy by a chemical process - Impulses then travel along the visual pathway. - The distinctive names describe the shapes of the outer segments  Central Vs. Peripheral Retina -Central vision allows you to see details and colors -Peripheral vision allows us to identify contrasting shapes, size, direction and detect movement in our surroundings(catching an object, moving worms, avoid obstacles) - We use our central vision in parallel, which allows you to have a high definition image, and our peripheral vision, which allows us to have a broad and continuous vision,although less precise, of the world around us. Central Vs. Peripheral Retina  Key Differences Rods Cones -Very sensitive to light; so they are -Cone photopigment are of three sorts (each responsible for vision in very poor lighting having a distinctive spectral conditions (night vision) sensitivity - RED BLUE GREEN) -3 categories of cones (according to their -They produce colorless vision (because they photopigments): blue initiate the same sensation for all wavelengths sensitive (short wavelength); green sensitive; of light) red sensetive. 12 -Not sensitive to small amounts of light that’s why colors are not seen during night vision  Visual Acuity A measure of visual function by measuring a straight – ahead (central vision) or ability to see fine details. May help in detecting ocular diseases or injuries.e.g. cataract , corneal disorders,refractive errors, presbyopia..etc.  Visual acuity 10/10 (20/20, or 6/6) vision is a term used to express normal visual acuity (the clarity or sharpness of vision) measured at a distance of 20 ft (6m). If you have 20/20 vision, you can see clearly at 20 feet what should normally be seen at that distance. If you have 5/10 visual acuity, it means that this patient can read from 5 ft what a normal individual reads from 10 ft. Having 10/10 vision does not necessarily mean you have perfect vision. 10/10 vision only indicates the sharpness or clarity of vision at a distance. Other important vision skills, including peripheral awareness or side vision, eye coordination, depth perception, focusing ability and color vision, contribute to your overall visual ability.  Types Of Visual Acuity 1. Detecting /Visibility Acuity: - simplest form of VA - represents the ability to see something. - ( minimum detectable) - by asking the patient do you see this or not 2. Resolution Acuity: - A measure of the minimum, inter-object separation that allow the patient to perceive that there are two , not one, objects. -It is mainly what we are measure in visual acuity testing  Types Of Visual Acuity 3. Recognition Acuity: - ability to identify and name what we are seeing by the action of the brain - It is dependent both on visibility acuity and resolution acuity 4. Direction acuity: where something is located in space , its orientation, tilt or alignment  Near Visual Acuity The near acuity test measures the patient’s ability to see clearly at normal reading distance. The test is usually performed if the patient complains of difficulty in reading or doing other close work  Conditions Affecting VA 1.Optics: refractive problems, myopia, hyperopia, astigmatism 2. Health: irregularity or opcification of the ocular media e.g. cataract 3. Retina: swelling or loss of cells , e.g. macular degeneration 4.Optic nerve or brain injury function of neurons e.g. stroke tumor 5.Beyond the visual system: mental retardation- autism- ADHD-Nystgamus  Myopia/Nearsightedness -Myopia, or nearsightedness, is a condition of the eye in which images are formed in front of the retina, resulting in a blurred image. -This occurs when the eye is relatively too long or the refractive powers of the corneaand lensof the eye are relatively too strong. -Myopia usually begins in childhood, and progressively worsens until adulthood is achieved, usually about 18 to 21 years of age Myopia/Nearsightedness  Hyperopia/Farsightedness -Hyperopia occurs when images are formed behind the retina, resulting in a blurred image. -This is due to an eye that is relatively too short, or the refractive powers of the corneaand lensof the eye are relatively too weak. -Depending on the degree of farsightedness and the age of the individual, some farsighted people may see clearly at both distance and near through the process of accommodation, or focusing of the lens in the eye. -This may cause significant eyestrain, however, and accommodative abilities are gradually lost with aging. Hyperopia/Farsightedness  Astigmatism The term astigmatism is used to describe a cornea that isn't round.Instead, it's shaped like a football rather than a round, spherical basketball. -Patients with astigmatism may notice blurred or ghost images close up or far away. -Astigmatism may be present in various degrees and is found in approximately 30 to 40% of individuals who wear glasses or contact lenses. Astigmatism  Presbyopia -In infancy and childhood the natural lensof the eye is soft and pliable andis easily altered in shape by the ciliary muscles of the eye through a process called accommodation. -Throughout life the lens of the eye gradually hardens, becomes less pliable, and progressively increases its resistance to change in shape. -This leads to greater difficulty in focusing at near and, by the age of about 45 years of age, most people require reading correction, assuming their vision is corrected for distance. This condition is known as presbyopia. Visual Pathway Optic nerve --> Optic chiasm --> Optic tract --> Lateral Geniculate Nucleas --> Optic radiation --> Primary Visual Cortex Visual Pathway: -Prechiasmal: optic nerve, chiasm. -Retrochiasmal: optic tract, the optic radiations, and the occipital cortex.  Parietal Association Cortex The parietal association cortex enables individuals to read, write, and solve mathematical problems. The sensory inputs from the right side of the body go to the left side of the brain and vice versa. same goes for the eyes. Visual Association Areas  Dorsal Root The Dorsal Stream: processes information through P-channel (parvocellular channel) information about object location and M-channel (Magnocellular channel) information about object movement. These dorsally located visual association neurons are responsible for producing our sense of Spatial orientation Binocular fusion/depth perception Location Movement direction and velocity of objects in space. The dorsal stream processes information about the “where” of the visual stimulus.Damage the dorsal visual association cortex results in deficits in spatial orientation, motion detection and in guidance of visual tracking eye movements.  Ventral Root The Ventral Stream: processes information about object color and form and is responsible for processing information necessary for our abilities to: Recognize objects and colors Read text Learn and remember visual objects (e.g., words and their meanings)This ventral stream processes information about the “what” of the visual stimulus. Damage to the inferior visual association cortex produces deficits in complex visual perception tasks, attention and learning/memory.  Alexia Alexia is a term describing a partial or complete inability to read. There are a number of different subtypes of alexia, but all have in common the feature that the affected patient cannot read normally, so that reading is slow or impossible, and comprehension is impaired. Treatment for alexia includes attempts to increase speed and accuracy of letter-by-letter reading and whole word recognition.  Alexia Alexia is associated with lesions that disconnect both visual association cortices from the dominant language-related temporoparietal cortices. Stroke is the most common cause of acquired alexia, though other forms of neurological disease can also cause alexia.  Vision and Learning Vision problems are the single most prevalent disabling condition among children. American Public Health Association statistics show that nearly 25% of all school-aged kids have vision problems serious enough to impede learning. Parents/therapists should know what signs to look for to make sure their child’s eyes are developing properly and that they have the best chance for success in school and throughout their lifetime.  Visual Perception Definition of perception: -the way that one thinks about or understand someone or something using his senses -the ability to understand or notice something easily -  Visual Perception Perception is an active process of locating and extracting information from the environment aided by visible light. There are various physiological components involved in Visual Perception are referred to collectively as the Visual System. healthy functional vision is the result of the well performance of psychology, cognitive science, neuroscience, and molecular biology, in the study of visual perception.  Visual Perception Visual Perceptual Skills involve the ability to organize and interpret the information that is seen and give it meaning.  Visual Perceptual Processing Categories -Visual Discrimination -Visual Figure ground -Visual Closure -Visual Memory -Visual Sequential Memory -Visual Form Constancy -Visual spatial relationships - Visualization -Visual sequencing -Visual attention/ Attention span  Visual Discrimination - recognize similarities and differences between images (hot/hut) -essential elementary reading skill for phonics and sight word proccessing Visual Figure Ground locate and identify an item within a busy background without confusion (discard crowing effect)  Visual Closure Visual Closure is the ability to recognize a complete feature from fragmented information.  Visual Memory recognize or recall chracteristics of previously seen image Visual form constancy Visual form constancy is the ability to recognize objects as they change size, shape, or orientation. - mentally visualize and manipulate images  Visual Spatial Skills - ability to understand directional concepts that organize external visual space. - recognize forms regardless of their orientation  Visual Sequencing Visualization: -visualize the whole image in ones percieve,organize and remember a mind and manipulate it specific order - the most highly developed form of visual memory  Visual attention/attention span: - select or attend to a subset of visual information for more indeoth proccessing- simultneous proccessing of multi-element displays (relevant vs. irrelevant) - span: number of letters/visual information one can take in and accurately proccess in one look  Visual analysis Dysfunction: Difficulties in: 1. Visual discrimination: - confuse letters, shapes, colors, positions and objects (p/q 6/9 d/b o/0 -difficulty in gaining information from maps,charts,graphs and text - difficulty in matching and sorting objects -difficulty in dressing (matching shoes and socks) -difficulty in self correcting error in homewrok - difficulty in matching 2d with 3d objects  Visual analysis Dysfunction: Difficulties in: 2. Form perception/spatial relationship: - difficulty in distinguishing differences in size, shape,objects, space. - difficulty in plan action in relation to objects around you -difficulty in spatial concepts (in, out, under,over, next to, down, up, left right) - difficulty in math - poor sight vocabulary - losing place on page and difficulty in finding what is asked to look for - difficulty in attending to a task  Visual analysis Dysfunction: Difficulties in: 3. Form Consistancy: -difficulty in recognizing letters and numbers in different fonts - slow alphabet and number mastery - difficulty in recognizing errors - assuming size of objects regardless of their distance - difficulty in looking at objects from different angles -difficulty in understanding volumetric concepts (mass, amount, quantity, density) -difficulty in recognizing familiar objects when environmental conditions change  Visual analysis Dysfunction: Difficulties in: 4. Figure ground: - difficulty in pulling out shape from background (find specific piece of info from the board) -difficulty in locating a friend in the playground - difficulty in copying from the board or worksheets - tendencay to overlook details and misses important information(skips pages, puncuations..) -difficulty in filtering out distractions  Visual analysis Dysfunction: Difficulties in: 5. Visual attention/ Attention span: - slow reading speed - mistaking word with similar beginnings -difficulty in reading fluently - difficulty in reading comprehension -difficulty in counting - difficulty in moving from task to task (don't finish the first to start the second) -difficulty in focusing on sublexical units resulting ins serial processing (sounding out words) instead of parallel proccessing (sight word reading)  Visual analysis Dysfunction: Difficulties in: 6. Visual memory / Visualization: - difficulty reproducing figures (math and geometry) -mix up lowerand upper case - difficulty in copying more than one letter at a time from the board - difficulty in phone number memorization -difficulty in reproducing information from memory - academic regression  Visual analysis Dysfunction: Difficulties in: 7. Visual Closure: - difficulty in art - difficulty in writing -difficulty in dot-to-dot wroksheets/puzzles - leave out parts or entire words Accommodation  Main struggles of school-aged children with Accommodative problems: Eye discomfort and/or headaches (usually frontal headaches) with sustained close work like reading Squinting, blinking and rubbing eyes Trouble copying from the chalkboard Blurred vision when reading small print Vision becomes worse by the end of the day Reduced attention in the classroom, work and/or independent reading Poor reading comprehension  TYPES OF ACCOMMODATIVE DISORDERS Ill-sustained accommodation Accommodative excess Accommodative insufficiency Accommodative in facility Paralysis of accommodation Spasm of accommodation  Types of Accommodative disorders Ill-sustained accommodation Accommodative excess Accommodative Insufficiency The most common sign or Tendency to focus closer in than Insufficient amplitude of symptom of ill-sustained the page being read, the individual accommodation to clear an object accommodation is blurred vision will focus as if the book is closer at a specific distance. after prolonged near work. than it really is. Blurred vision at near It occurs because the an excessive, over-focusing error Symptoms worsen by the end of accommodative system fails to of near visual tasks the day sustain long-term Difficulty with attention when accommodative effort. reading  Types of Accommodative disorders Accommodative infacility Accommodative paresis Accommodative spasm In school aged children this is of Accommodative paresis (also concern as it both reduces visual called accommodative palsy) is efficiency the absence of an ability to a condition in which the eyes focus but also delays ability to shift produce an accommodative constantly or automatically. It can focus between distance and near response. occur after an activity, like reading, tasks. (board in which a person is using their near and copy book) The disorder is usually the vision. consequence of disease or poor/sluggish eye focusing trauma. flexibility from near to far Ocular Motor skills  Eye movements and reading In order to be able to read, the subject performs different eye movements: progressive, regressive and back-to-line accesses allowing to orientate a look at new letters of submissions fixing micromovements allowing the extraction of visual information Fixation and reading  Saccades Saccades refer to fast conjugate eye movements that shift the eyes from one target to another, bringing an object of interest into focus on the fovea, where visual acuity is highest. Saccades are the fastest eye movements (up to about 500 degrees per second) and they are very brief in duration (typically less than 100 msec) Saccades can be clinically tested in a self-paced or verbally-guided manner.  Saccades and reading Precise jerks / start of learning Imprecise jerks / start of learning For example:Pe can examine self-paced saccades by asking the patient to make repeated saccades between two visual targets without verbal commands (such as looking quickly back and forth between two pencils placed to the right and left of central fixation), vs. examining verbally- guided saccades by asking a patient to look at the examiner’s nose and then at a target (such as the examiner’s finger) to the left or right of central fixation only upon verbal command.  Pursuits: Smooth pursuits movements allow clear vision of a moving target by holding the image steady on the fovea. Pursuit performance requires focused attention to track a particular object. Pursuit capabilities decline with age and can be particularly affected by medications. If smooth eye pursuits movement do not match the movement of the target, corrective saccades are needed to get the eyes back on target.  Pursuits testing: Test smooth pursuit by having the patient follow an object moved across their full range of horizontal and vertical eye movements. Observe the eyes at rest to see if there are any abnormalities such as spontaneous nystagmus , dysconjugate gaze (eyes not both fixated on the same point) resulting in diplopia (double vision)  Fixation Fixation is the ability to aim the eyes to a particular spot accurately. Static fixation is the ability to focus on a stationary object when reading a word or working a math problem. Fixation occurs monocularly or binocularly. The goal of visual fixation is to then trigger the accommodative and vergence systems to identify what the object is, and where it is in space.  Saccadic fixation Saccadic fixation dysfunction can cause a number of symptoms to the patient. Not being able to accurately and surely plant the eye or eyes in one particular place can make it very challenging to read. 80% of what we learn comes through the visual system, if any part of the visual system is not functioning at an operating standard then, learning becomes more difficult.  Pursuits fixation: Pursuit fixation is the ability to follow a moving object with the eyes. These complex operations require split-second timing for the brain to process the information received and to track the path of the moving object. Problems in these areas can impact someone's ability to read, drive a car, or participate in sports. An example of a pursuit is when a person is following a moving car with their eyes while also not moving their head. Video youtube of Righteye Technology Vergence and going back to the line  Interpretation: foveal and parafoveal treatment The identification of words is done thanks to a fovea which is supported by the cones allowing a high acuity around the position fixed by the eye the programming of the eye movements, is done thanks to the parafoveal and peripheral treatment which is ensured by the Rods, giving information on the length of the words. These two kinds of processing (foveal and parafoveal) are done within the framework of a visual-attentional window, also called "perceptive span"  The areas of the visual span In a fixation, the set of perceived letters is called the "visual span". The latter can vary from 2 to 20 characters and would be composed of three zones: - foveal zone which has about 3 characters to the left and to the right of the point of fixation - parafoveal zone which goes from 6 to 12 characters to the right and that one uses as preprocessing by using the information of the letters of the following word. -peripheral zone, which contains 18 to 20 characters on the right and where one will seek information concerning the size of the words in order to program the saccades to come up. Visual span: 3 zones Perceptual span: child / adult  Role of attention in foveal and parafoveal treatment -An attentional filter would have the role of reducing the influence of parafoveal information on foveal information. Foveal treatment therefore becomes optimal. -Visuo-attentional processes play an important role in guiding eye movements, especially in determining the position of arrival in words.  Remedies / Readings Avoid any parasitic element: colored background Use an enlarged font: Arial for example Space the lines: line spacing of 1.5 minimum Space the words: put a double space Enlarge: use A3 formats if necessary Courtesy sentences requiring no newlines Alternation of colors on the lines which helps them to follow their line to the end and to go to the next line => so that the children organize their saccades and use the fixation time to analyze visually. Vergence system (eye- teaming)  Symptoms for binocular disorders: Eye strain (especially with or after reading) Headaches Blurred visionDiplopia (double vision) Difficulty reading and concentrating Short attention span Frequenting losing their place while reading Avoidance of near work Poor sports performance Dizziness or motion sickness Trouble remembering what was read Words appear to move, jump, swim or floatSquinting, rubbing, closing or covering an eye  In order for you to look at an object as it moves closer to your face, the eyes must rotate inward (converge) toward the object. When looking at a faraway object, they move by rotating outwards towards the ears or diverge.  Convergence and divergence are unique eye movements as these are the only eye movements that are not conjugate (meaning the eyes move in the same direction) but are instead termed disconjugate. The brain is constantly rapidly sampling the visual environment, quickly altering between convergence and divergence, then just as quickly holding eye posture so that the image of interest is stabilized on the retina  Types of Vergence disorders Convergence insufficiency: Convergence Insufficiency is a common problem with the development of these skills. When convergence is insufficient, it means that the eyes do not come together closely enough when looking at a near object, so the eyes are essentially looking "past" the target It is not unusual for a person with convergence insufficiency to cover or close one eye while reading to relieve the blurring or double vision. Symptoms will be worsened by illness, lack of sleep, anxiety, and/or prolonged close work.  Types of Vergence disorders Convergence insufficiency:  Types of Vergence disorders Convergence insufficiency: Convergence Insufficiency disorder has often gone undetected because testing is not included in pediatrician's eye tests, school screenings, basic eye exams. A person can pass the 20/20 eye chart test and still have convergence insufficiency.If untreated, in some cases, convergence insufficiency can lead to an outward eye turn that comes and goes. This is called intermittent exotropia.  Treatment Methods Treatments range from passive (prism lenses) to active (office-based vision therapy). Scientific research by the National Eye Institute has proven that office-based vision therapy is the most successful treatment. Home-based pencil pushups therapy appears to be the most commonly prescribed treatment, but scientific studies have shown that this treatment is ineffective so its important to refer to specialists to do the right intervention.  Types of Vergence disorders Convergence excess Convergence excess describes a condition where the eyes do not exactly aim together; rather, they aim too close or in front of the object. As a consequence, blur, confusion or fatigue may result. Convergence excess will effect near work tasks, especially reading and writing. Rapid changes in convergence demands such as copying from the blackboard are often very difficult for children with convergence excess. 1. Some children may move their book closer or forward to ‘see better’, when in fact what they are doing is trying to relieve their convergence excess difficulties.  Types of Vergence disorders Convergence excess  Treatment methods: Management of convergence excess requires therapeutic prescription lenses to enhance the focus efficiency thus reducing the need to pull the eyes closer in. The lenses are typically worn for close work tasks such as reading, writing, computer work and copying from the blackboard. This is a therapeutic treatment that requires monitoring over time to ensure the excessive demand is reduced to within a normal range of focus and convergence.Usually over time prescriptions can be reduced and wearing time reduced. In some cases, vision therapy may be required in addition to the glasses.  Types of Vergence disorders Divergence Insufficiency: when one is looking at far object, the eyes tend to diverge for both eyes to fixate on the target of regard. Divergence insufficiency is an unusual form of strabismus and diplopia only at distance and single binocular vision at near inhibiting the eyes to diverge equally  Types of Vergence disorders Divergence Insufficiency:  Treatment methods: Prisms Vision therapy Surgical intervention Types of Vergence disorders Divergence Excess Divergence excess is prevalent in 0.03% of the population and is found to be more common in women, making up 60-70% of cases. when the eyes look into the distance and diverge, they relax and can wander off to the side. This is often noticeable in children less than 18 months of age, progressing throughout life if not treated. At first, parents may notice an eye that rarely turns outward, usually only when their child is tired or sick. Then the eyes start to spontaneously deviate outwards but straighten moments later. Eventually, the eye is constantly turned outward Types of Vergence disorders Divergence Excess  Treatment methods: Usually the operation is done to shorten the medial rectus muscle of the eye, which is closest to the nose, to prevent the eye from turning outwards. Glasses with special lenses that are over-minused or contain a prism can help, but must always be worn to prevent the outwards turn of the eye Vision therapy  Types of Vergence ACCOMMODATIVE VERGENCE If an object of interest is located nearer to the person than the fixation point, it will be blurred.Accommodation is required to focus on the near material, and when attention is shifted to the near object, reflex accommodation is unconsciously stimulated. TONIC VERGENCE: Simply being conscious, even without a visual stimulus (i.e., in the dark, or with the eye closed), will cause innervation to the muscles that brings the eyes to a nearly parallel (or slightly eso) orientation. This is known as tonic vergence. It is also called dark vergence.  Types of Vergence PROXIMAL VERGENCE is an oculomotor mechanism, distinct from the other types of vergence, which is stimulated by the perceived distance to a near object. VOLUNTARY VERGENCE this is the vergence that a person can apply consciously.Can be useful in vision therapy, because it allows the patient to start fusing certain training targets when their other vergence mechanism may still be weak.  Phorias and Tropias Direction of Misalignment Ortho - the eye(s) shows no misalignment. Exo - the eye(s) tends to turn outwards. Eso - the eye(s) tends to turn inwards. Hyper - the eye(s) tends to turn upwards relative to the fellow eye. Hypo - the eye(s) tends to turn downwards relative to the fellow eye. Incyclo - the eye(s) tends to rotate inwards.  Tropias/ Strabismus  Tropias Strabismus is the term to describe when one’s eyes are misaligned. The degree of misalignment can vary, ranging from small to large angle deviations. It can always be present, which we call “constant,” or can occur some of the time, which we call “intermittent.” ] The different types of strabismus are as followed: 1. Exotropia: Eyes are deviated outwards 2. Esotropia: Eyes are turning inwards towards the nose 3. Hypertropia: Eyes are deviated upwards 4. Hypotropia: Eyes are deviated downwards.  Phorias -A phoria is a latent (hidden) eye deviation. -The eyes appear to be straight, but when covering an eye and breaking fusion, the eyes assume a position away from normal alignment. -Most people have a very small phoria if tested, but a large phoria makes it hard to keep the eyes aligned, especially after a long day or when stressed. - Phorias are also named with the exophoria, esophoria, hyperphoria, hypophoria convention.  Phorias vs. Tropias Phoria is normal and it won’t disrupt everyday life. If the two eyes can work together in the end with the brain to achieve binocular vision, there is nothing to be concerned about. On the other hand, tropia is not normal and can lead to double vision since the misaligned eye won’t correct itself. If it is left untreated, impaired binocular depth perception can occur and the brain will begin to ignore the abnormal eye, resulting in a lazy eye. In some cases, individuals experienced permanent vision loss  Patient Education Patients should be aware that many accommodative and vergence anomalies are neuromuscular problems and not refractive problems. Thus, the most effective treatment relies on not only spectacles, but active vision therapy to eliminate neuromuscular dysfunction. Patients should also be told that treatment improves accommodative and vergence reflexes. Proper management usually results in improvement, due to changes in the slow vergence system.  Stereopsis The binocular appreciation of depth. The eyes are separated in the horizontal plane of the head and thus each eye has a slightly horizontal disparate view of the world. The sensory fusion of these horizontally disparate unequal retinal images results in a 3-dimensional percept. Stereopsis  Stereopsis Stereopsis is considered the most important benefit of binocular vision. Among the different levels of binocular fusion (Worth’s degrees of fusion), the highest is stereopsis. Stereopsis provides us with extremely fine depth perception at near and significantly enhances our space perception. The stereo acuity test is one of the most important tests you can do in a pediatric eye exam, because it provides much information about the development of a child’s visual system.  Amblyopia Amblyopia is a condition in which the patient has poor vision due to incomplete development of the visual system. It is caused by some kind of deprivation during the sensitive period. Amblyopia is diagnosed by the presence of a subnormal best-corrected visual acuity, with no sign of ocular disease or damage to the visual system. In some cases it may be possible to have amblyopia in both eyes. Normal visual development requires good image quality on both retinas and good correlation between the images during the sensitive period. With this in mind, amblyopia may be classified according to the type of visual deprivation that led to the amblyopia. Amblyopia  Amblyopia Three categories of deprivation that may cause amblyopia: Pattern deprivation (light but no image such as in infantile cataract) Optical defocus (poor image quality such as uncorrected refractive errors) Strabismus (poor correlation and brain's lack of capacity to fuse two images)  Amblyopia Therapy In order to be effective, amblyopia therapy must be performed as early as possible within the sensitive period, which is thought to extend up to about age 8 or 9 in humans. In some individuals, treatment after age 9 may still help restore some visual function to the amblyopic eye.  Amblyopia Therapy In theory, treatment should include both of the following. Optical correction to provide a high quality retinal image to the amblyopic eye. Reverse occlusion of the better eye. Vision therapy The objective is to stimulate stronger synaptic connections in the visual cortex for neurons associated with the amblyopic eye, and give them a competitive edge by weakening input from the dominant eye..  Amblyopia Therapy If the patient has strabismus, it will also be necessary to restore correct ocular alignment to recover normal binocular vision. Vision therapy may help to restore alignment. If these fail, surgery may also be needed. Complete reverse occlusion may be accomplished by physically patching the better eye. Another option is to degrade the better eye’s image by putting semi-transparent tape over the spectacle lens of the better eye. Some doctors believe that it may be beneficial to stimulate the amblyopic eye with flashing lights or highcontrast moving patterns.  Suppression Suppression essentially refers to the brain ignoring the visual signal provided by one eye. Let's start with a normal pair of eyes. When the eyes are aligned and pointing towards the same object in space and have an equally clear image, the brain uses small cues to determine the depth, size, shape, etc. of the object and combines the images of each eye together to see. If one eye has a very blurry image (amblyopia, specifically refractive amblyopia due to an unequal glasses prescription) the brain struggles to combine the images of each eye together into a single image. To compensate, the brain suppresses or ignores visual input from the blurry eye.  Starbismus and suppression This same concept occurs if one eye is turned (strabismus or squint). In this example, the brain sees multiple images, which would be confusing. Again, the brain suppresses (ignores) visual input from the deviating eye and utilizes input from the fixating eye.  Suppression At its core, suppression is the visual system's method of compensating or adapting for a defect. To avoid the confusion of a blurry image superimposed on a clear image, or seeing two of one image in space, the brain simply ignores the abnormal image. Suppression is rather easily "learned" by the brain at an early age when the visual system has a higher degree of neuroplasticity. In contrast, a patient that suddenly acquires a strabismus or squint later in life may have trouble suppressing and constantly see double.  Suppression For amblyopic patients, a critical issue stems from long-term suppression. Suppression can be difficult to "unlearn". One of the key components of visual rehabilitation for patients that have amblyopia or strabismus is to teach the brain to use both eyes together. Tests of suppression check for the presence of suppression and, in some cases, quantify the amount of suppression the visual system is experiencing  Suppression Signs: Trouble catching balls and other objects thrown through the air Avoidance of tasks that require depth perception (games involving smaller balls traveling through the air, handicrafts, and/or hand-eye coordination, etc.) Frequent mishaps due to misjudgment of physical distances due to possible suppression, such as: -Trips and stumbles on uneven surfaces, stairs, and curbs, etc. -Frequent spilling or knocking over of objects -Bumping into doors, furniture and other stationary objects -Sports and/or car parking accidents Poor posture while doing activities requiring near vision Problems with motion sickness and/or vertigo Suppression  Vision Therapy A therapy program designated to help a patient learn to use his visual system more effectively, whether to aid visual development, enhance or remediate skills and abilities, or rehabilitate the visual process after brain injury. Possibilities for conditions needing therapy include: A binocular disorder which is slowing down academic learning or causing physical discomfort A loss of binocularity such as strabismus or amblyopia Developmental and perceptual difficulties Needs for enhancing or developing a finer tuned system to aid in activities such as sports and learning Rehabilitation after the loss of visual processing skills due to closed head injury, whether traumatic or acquired, such as stroke. Vision Therapy Vision Therapy  Color Vision Color vision deficiency is the inability to distinguish certain shades of color. The term "color blindness" is also used to describe this visual condition, but very few people are completely color blind.  Color Vision Color vision is possible due to photoreceptors in the retina of the eye known as cones. Found in the macula (the central part of the retina), each cone is sensitive to either red, green or blue light (long, medium or short wavelengths). The cones recognize these lights based on their wavelengths. Normally, the pigments inside the cones register different colors and send that information through the optic nerve to the brain. This enables us to distinguish countless shades of color. But if the cones don't have one or more light-sensitive pigments, they will be unable to see all colors.  Color Vision Deuteranomaly is the most common type of red-green color blindness. It makes green look more red. Protanomaly makes red look more green and less bright. Protanopia and deuteranopia both make you unable to tell the difference between red and green at all.  Color Vision Ishihara Test:  Contrast Sensitivity A contrast sensitivity test measures your ability to distinguish between finer and finer increments of light versus dark (contrast). This differs from common visual acuity testing in a routine eye exam, which measures your ability to recognize smaller and smaller letters on a standard eye chart. Contrast sensitivity is a very important measure of visual function, especially in situations of low light, fog or glare, when the contrast between objects and their background often is reduced. Driving at night is an example of an activity that requires good contrast sensitivity for safety.Even if you have 20/20 visual acuity, you can have eye or health conditions that may diminish your contrast sensitivity and make you feel that you are not seeing well. Contrast Sensitivity  Perception of Movement The perception of movement is accompanied by a set of eye movements eye tracking keeps an object moving on the fovea (it is the slowness of the chasing movements that allows this foveal seizure) What stimulates and guides the chase: it is this retinal stimulus and more precisely the retinal slip ("retinalslip") that the chase tries to reduce to zero  Perception of Movement At a higher level the perception of visual movements does not result from the analysis of successive displacements of the image but from the extraction of some of the elementary characteristics specific to the movements: direction and speed  Impact of proper assessment and optometric intervention Elimination of associated visual signs and symptoms Improvement of visual comfort and efficiency Improvement of visual attention and concentration Increase in stamina and strength of the patient’s visual system Strengthening of visual information processing and efficiently translating them into everyday tasks Positive change in the patient’s academic performance, confidence and self esteem Model of Visual Perceptual Processing Adaptation through vision Visual Cognition Visual memory, pattern recognition Visual scanning, visual attention Accommodation,Binocular vision,VA,Visual Field, oculomotor dysfunction Model of Visual Perceptual Processing A person cannot make decisions or adapt to their envirnment through the information he/she have gathered visually unless they have analyzed the visual info first (frontal lobe) Visual Cognition: Ability to manipulate and integrate visual inputs with ones sensory information to gain the knowledge, solve problems,formulate plans, and make decisions.visual cognition/analysis cannot occur without an intact visual memory. visual memory: while visual analysis is occuring, person must be able to create and retain a picture of the object/visual field in the mind. Model of Visual Perceptual Processing before and image can be stored in memory,we must recognize the pattern that makes up the image via pattern recognition(distignuish a particular object from another and from it surrounding - like figure ground) pattern recognition cannot be performed without proper visual scanning/saccades. visual scanning (performed using organized search patterns to visually search through the envornment) is a PRODUCT of visual attention. Model of Visual Perceptual Processing Visual attention can be : 1- Automatic-reflexive level: protective reflex controled by the brainstem and activated with suddenly appearing object in the visual field or initial occurance of a movement. 2- Voluntary level: volantary saccaed movements controlled by the cotrex and untilized for information gathering. Model of Visual Perceptual Processing ability to maintain visual focus and attention on an object for a period of time determines how visual input is analyzed in the cortex, and it is the basis for decision making if i don't attend to visual info--> don't initiate a search for visual info or pattern recognition--> don't produce visual memory for that image-->dont use that visual input for decision making higher level processes cannot occur unless the cortex recieves clear and concise visual info from the eyes (VA,VF, Oculomotor skills, Accommodation and Binocular vision)  Visual spatial skills - ability to tell where of the objects including your body in space. - ability to know how objects relate to each other in space (how internal and external visual space is organzied ) Visual Spatial Skills can be divided to 3 subdivisions : 1- Laterality: knowldege of own Right and Left. 2- Directionality: knowledge of other people's/object's right and left. 3-Bilateral Integration: awareness of both sides of the body and ability to use both sides separately and togetjer unilaterally and bilaterally.  Visual spatial skills Visual Spatial Skill Dysfunction can lead to difficulties in: - Manipulation of visual information such as mazes,maps,navigations) -Gross motor functions. -Recognizing position of objects and their dept perception - telling time - left right confusion (was,saw) - coordination and balance are poor Pediatric eye problems  Pediatric Cataract A cataract is a cloudiness or opacification of the normally clear lens of the eye. Cataracts are typically associated with older adults, but cataracts can occur at birth or duringchildhood. Early detection and treatment of cataracts are critical in infants and young children in order to restore normal visual development. Often, pediatric cataracts result in some degree of lazy eye (amblyopia).  Pediatric Glaucoma Glaucoma is a condition that is associated with high pressure within the eye. This pressure can damage the optic nerve, which is critical for vision, resulting in permanent vision loss. Pediatric glaucoma is a rare condition that can present in the newborn or during childhood. Signs and symptoms of pediatric glaucoma include cloudy cornea, tearing, frequent blinking, light sensitivity, and redness of the eye. Cortical visual impairment (CVI) is vision loss due to any abnormality of the visual center in the brain. The eyes are normal, but the visual interpretation center in the brain does not function properly and prevents normal vision.  Developmental Abnormalities During development of the fetus, abnormalities in the visual system can occur. Some developmental abnormalities include coloboma, microphthalmia (small eye), and optic nerve hypoplasia. These abnormalities often result in vision impairment. Vision and tests NEPSY FLECHES : -Visual figure ground - Pursuits - Peripheral awareness -Discrimination acuity NEPSY MAISON: -Recognition -Pursuits -Crowding effect  NEPSY CUBES and Stereopsis  TEA-CH: -Contrast -Saccadic ability -Recognition  REY : -Visual spatial capacity(orientatio n in space) -Visual Memory  DTVP3: -Visual figure ground -Recognition -Crowding effect  DTVP3 : Visual and Motor coordination Pursuits Crowding effect Contrast