Vision and Eye Function Quiz

Student Information

• Sandra Shamseddine is the student
• She has a Bachelor of Science (BS) in Optics and Optometry
• She has a Master of Science (MS) in Clinical Optometry
• This is for a Fall 2023/2024 class

Course Outcomes

• Students will learn about binocular vision and oculomotricity.
• Course connects binocular vision (BV) to psychomotor development.
• Students learn about eye problems, especially binocular vision and oculomotricity, and how they relate to other psychomotor skills.

General Eye Anatomy

• Cornea: Transparent front part of the eye; refracts light, focusing on the retina
• Pupil: Opening in the center of the iris; controls the amount of light entering the eye
• Crystalline Lens: Transparent biconvex structure behind the iris; focuses light onto the retina; Accommodation ability declines with age (presbyopia)
• Ciliary body: Produces aqueous humor, fluid nourishing the cornea
• Retina: The sensory membrane lining the back of the eyeball, contains photoreceptors
• Rods and Cones: Retinal photoreceptors (two types), responsible for light detection.
• Optic Nerve: Carries sensory impulses from the retina to the visual centers in the brain; part of the second cranial nerve
• Parts of the Eye: Image displays parts of eye - superior rectus, inferior rectus, optic disc, optic nerve, retina, fovea centralis, optic nerve, central retinal vein, central retinal artery, vitreous body, Ora serrata, ciliary body, posterior chamber, anterior chamber, cornea, lens, pupil, iris, zonules and sclera

Eye Anatomy Details

• Cornea: Transparent outer layer of the eye that refracts light.
• Pupil: Opening in the center of the iris that controls the amount of light that enters the eye.
• Crystalline Lens: Transparent structure that focuses light onto the retina.
• Ciliary Body: Structure that controls the shape of the lens.
• Retina: Sensory membrane at the back of the eye; contains photoreceptors.
• Optic Nerve: Carries visual signals from the retina to the brain.

Common Retinal Diseases Causing Low Vision

• Retinal tear
• Retinal detachment
• Diabetic retinopathy
• Macular degeneration
• Retinitis pigmentosa
• Glaucoma
• Optic Atrophy (partial or complete)

Cranial Nerves

• Six of the twelve cranial nerves directly innervate the eye and periocular tissues: CNII (optic nerve) CNIII (oculomotor) CNIV (trochlear) CNV (trigeminal) CNVI (abducens) CNVII (facial)

Extraocular Muscles

• Six muscles responsible for 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 thicker than peripheral retina due to higher packing density of photoreceptors (especially cones).
• Central retina is primarily cone-dominated, while peripheral retina is rod-dominated.

What are Photoreceptors?

• Photoreceptors convert light into electrical energy through a chemical process.
• Signals move along the visual pathway

Central Vs. Peripheral Retina (cont.)

• Central vision: Details and colors
• Peripheral vision: Shapes, size, direction, movement of surroundings; helps us avoid obstacles

Key Differences (Rods and Cones)

• Rods: Highly sensitive to light, responsible for night vision, detect grayscale (no color)
• Cones: Less sensitive to light; responsible for color vision & detailed perception in bright light; three types (red, green, blue) to detect different colors.

Visual Acuity

• A measure of visual function by how well one sees details.
• Measures the patient's ability to see fine details; used to identify eye diseases.

Types of Visual Acuity

1. Detecting/Visibility Acuity: simplest form; the ability to detect something
2. Resolution Acuity: Measures the smallest separation the patient can perceive between two objects.
3. Recognition Acuity:Ability to name what is seen by the action of the brain; dependent on visibility and resolution acuity
4. Direction Acuity: Understanding an object's location, orientation, and tilt in space.

Near Visual Acuity

• Measures patients' ability to see at a typical reading distance
• Performed if a patient has difficulty reading or doing close-up work

Conditions Affecting Visual Acuity

1. Optics: Refractive problems (myopia, hyperopia, astigmatism)
2. Health: irregularities or clouding of ocular media (e.g., cataracts)
3. Retina: swelling or loss of cells (e.g., macular degeneration)
4. Optic nerve or brain: injury to neurons (e.g., stroke, tumor)
5. Outside the visual system: mental retardation, autism, ADHD, nystagmus

Myopia/Nearsightedness

• Images are focused in front of the retina
• Caused by an elongated eye or strong refractive powers
• Usually begins in childhood and progressively worsens until adulthood.

Hyperopia/Farsightedness

• Images are focused behind the retina
• Caused by a shortened eye or weak refractive powers
• Individuals may still have clear vision at either distance or near depending on the degree of farsightedness and age.
• Can cause eyestrain

Astigmatism

• Cornea is not perfectly round
• Results in blurred vision at various distances
• Impacts about 30-40% of individuals who wear spectacles or contact lenses

Presbyopia

• Declining ability of the lens to focus on near objects; the lens hardens
• Usually develops around age 40 or 45, leading to the need for reading glasses

Visual Pathway

• Optic nerve --> Optic chiasm --> Optic tract --> Lateral Geniculate Nuclei --> Optic radiation --> Primary Visual Cortex

Parietal Association Cortex

• Enables individuals to perform reading, writing, and solving mathematical problems
• Sensory inputs from one side of the body are processed by the opposite side of the brain in the same way as from the eyes.

Visual Field Defects (Diagram)

• Types and cause of vision loss

Visual Association Areas

• Visual information from the primary visual cortex is relayed to other areas for further processing. The dorsal and ventral streams process spatial and object features, respectively.

Dorsal Stream

• Processes information about where visual objects are in space (location) in combination with object movement

Ventral Stream

• Processes information about the characteristics of visual objects (form, identification, and color) -recognizes objects and colors, reads text, learns and remembers visual objects, and processes information about "what" of a visual stimulus

Alexia

• Partial or complete inability to read
• Subtype distinctions exist, but all typically involve slow or impossible reading with impaired comprehension.
• Stroke is the commonest cause but other forms of neurological disease can also cause alexia

Vision and Learning

• Vision issues are the most common cause of learning problems in children
• Approximately 25% of school-aged children have significant vision-related learning problems

Visual Perception

• Ability to organize visual information from one's surroundings to understand it
• Active process of extracting information aided by visible light. Visual system is comprised pf many physiological components and is a complex interaction of cognitive science, psychology, neuroscience and molecular biology

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/span

Visual Discrimination

• Ability to recognize similarities and differences in shapes, letters, colors, and settings (ex: hot vs. hut)
• Fundamental component of elementary reading skills and identifying and separating visual patterns

Visual Figure Ground

• Ability to distinguish an object from its background despite clutter or distractions.
• Separates the stimuli and allows us to understand details in a visual field

Visual Closure

• Recognizing a complete object/image from incomplete or partial information.
• Completing the image via mental filling in of missing pieces.

Visual Memory

• Recognizing and recalling characteristics of previously viewed images

Visual Form Constancy

• Ability to recognize objects regardless of their size, shape, or orientation

Visual Spatial Skills

• Understanding spatial concepts and organizing visual space
• Recognizing shapes/characters without regards to their orientation

Visual Sequencing

• Perceiving visual information that's arranged in a sequence and recalling the order of events

Visualization

• Creating a mental image of objects/information
• Recognizing the complete image from incomplete data

Visual Attention/Attention Span

• Ability to process information within complex visual fields
• Selecting important data and ignoring irrelevant information by focusing on the required/relevant data within the visual space.

Visual Analysis Dysfunctions

• Difficulties with visual discrimination
• Difficulties with form perception/spatial relationships
• Difficulties with form constancy
• Difficulties with figure-ground segregation
• Difficulties with visual attention/attention span
• Difficulties with visual memory/visualization

Accommodation

• The process by which the eye adjusts its focus to clearly see objects at different distances

Accommodative Problems (Symptoms)

• Eye discomfort/headaches, especially frontal headaches when performing close-up work
• Squinting, blinking, and rubbing eyes
• Difficulty copying written material from a board
• Blurred vision when reading small print
• Visual acuity worsening as the day progresses
• Reduced attention span while performing close-up tasks
• Poor reading comprehension

Types of Accommodative Disorders

• III-sustained accommodation
• Accommodative excess
• Accommodative insufficiency
• Paralysis of accommodation
• Spasm of accommodation

Types of Accommodative Disorders (cont)

• Ill-sustained accommodation
• Accommodative excess: focusing on objects closer than they should be.
• Accommodative insufficiency: problems with focusing objects closer than they should be.

Types of Accommodative Disorders (cont.)

• Accommodative infacility:
• Accommodative paresis:
• Accommodative spasm:

Ocular Motor Skills

• Coordination of eye movement, including tracking, fixation, and saccades

Eye Movements and Reading

• Progressive, regressive, and back-to-line movements for orienting to new letters/sentences
• Micromovements for extracting and analyzing the visual information during fixation

Fixation and Reading

• Maintaining steady gaze on a point to extract visual details from that particular spot/area

Saccades

• Rapid eye movements that shift the eyes from one target to another
• Bring objects of interest into focus on the fovea
• Clinically tested by having the patient make eye movements

Saccades and Reading

• Precise eye movement jerks are important in visual processing and reading

Pursuits

• Smooth eye movements that tracking a moving object and maintaining the image on the fovea
• Affected by age and medication
• Corrective saccades needed to get the eyes back on target

Pursuits Testing

• Testing smooth pursuit by having a patient follow a moving object
• Observe eyes at rest to look for anomalies.

Fixation

• Ability to accurately aim the eyes at a particular spot (monocularly/binocularly)
• Essential for tasks requiring focusing on stationary objects

Saccadic Fixation

• Saccadic fixation dysfunction can cause symptoms to the patient.
• Important for reading in which the eyes must be accurately focused at a specific spot

Pursuits Fixation

• Ability to follow moving objects with eyes.
• Requires split-second timing for the brain to process and track the movement of the object

Vergence and Going Back to the Line

• Includes eye movements to look at objects at different depths/depths. Visual system movement for different depths

Interpretation (Foveal and Parafoveal Treatment)

• Foveal and parafoveal treatment
• Fovea (cone supported): high-acuity vision at the center
• Parafoveal and peripheral (Rods supported): processing the length of words

Areas of Visual Span

Perceptual Span (Child/Adult)

• Foveal vision is clear to allow quick visual fixations of nearby objects.

Role of Attention in Foveal and Parafoveal Treatment

• Attentional filters help reduce the impact of parafoveal information on foveal information

Remedies/Readings

• Methods of enhancing readings, including adjustments to fonts, spacing, and lines.

Symptoms for Binocular Disorders

• Eye strain with prolonged reading
• Headaches, blurred or double vision
• Difficulty concentrating
• Short attention span
• Avoiding near work
• Poor sports performance
• Dizziness or motion sickness
• Trouble remembering what was read
• Words may appear to move, float, jump

Convergence and Divergence (Eye Teaming)

• Convergence: Inward movement of the eyes when looking at nearby objects
• Divergence: Outward movement of the eyes when looking at faraway objects
• The brain constantly samples the visual environment and adjusts the eye movements for optimal focus

Convergence Insufficiency

• A common problem with the development of these skills, eyes not coming together when looking closely.
• Can lead to blurriness, difficulty focusing, and eye strain

Convergence Excess

• Eyes aim too close or in front of objects, resulting in blurred vision, confusion, or fatigue
• Common in near-work tasks, such as reading and writing.

Types of Vergence Disorders (Cont.)

• Divergence insufficiency
• Divergence excess

Treatment Methods (Convergence Insufficiency)

Treatment Methods (Convergence Excess)

Divergence Insufficiency

• Eyes tend to diverge excessively when looking at distant objects, causing blur or double vision
• Unusual form of strabismus and diplopia only at distance

Treatment Methods (Divergence Excess)

Stereopsis

• Binocular depth perception
• The ability of the two eyes to fuse separate images to create a 3-dimensional image

Stereopsis (cont.)

• Important component of binocular vision; crucial for depth perception

Amblyopia

• Poor vision due to incomplete visual system development
• Caused by an imbalance in the eyes, or by damage causing a blurry image

Amblyopia Categories

• Pattern deprivation: Light enters but no clear/focused image
• Optical defocus (poor image quality): e.g. poor prescription of spectacles
• Strabismus (poor eye coordination): eyes do not align properly

Amblyopia Therapy

• Early intervention during the sensitive period is important or it will result in poor vision in one or both eyes.
• Therapy and glasses may be effective

Suppression

• Brain ignores signals from a blurry eye to avoid confusion

Suppression (cont.)

• Common in amblyopia, specifically refractive amblyopia
• If left untreated, can lead to permanent vision loss

Suppression (cont.)

• Suppression involves the brain ignoring the visual input from one eye to avoid the confusion of two separate images from different eyes.

Vision Therapy

• A therapy program designated to help patients learn to use the visual system more effectively
• Conditions needing therapy may include binocular disorders, loss of binocularity, and/or developmental/perceptual difficulties.
• May help restore proper visual function following loss of brain function if a closed-head injury, or other traumatic events such as a stroke.

Color Vision

• Involves the perception of colors via photoreceptors called cones
• Detected based on wavelengths

Color Vision (cont.)

• Cone types: Red, green, blue

Color Vision (cont.)

• Ishihara color test for identifying color blindness and deficiencies

Contrast Sensitivity

• Ability to discriminate subtle differences in light/shadow.
• Important for situations involving low light, fog, or glare

Perception of Movement

• The visual system processes and recognizes movements through eye tracking.

Impact of Proper Assessment and Optometric Intervention

• Improving visual comfort, efficiency, and concentration.
• Visual system improvement that results in improved daily visual tasks
• Increase in strength and stamina regarding the visual system that impact the individual academically, confidently, and positively regarding their self-esteem.

Model of Visual Perceptual Processing

• A hierarchical model outlining the steps for visual information processing and visual perception
• This multi-step process begins with input via the eyes for visual information which then moves through the brain.

Visual Spatial Skills

• Understanding the locations of objects and relations with the body (laterality, directionality, and bilateral integration)

Pediatric Eye Problems (Overview)

• Cataracts
• Glaucoma
• Cortical Visual Impairment (CVI)
• Developmental abnormalities

Pediatric Cataracts

• Cloudiness or opacification of the eye lens; occurs in children (infants/young children)
• Early identification and correction are key to prevent vision impairment

Pediatric Glaucoma

• High eye pressure can damage the optic nerve, leading to permanent vision loss.
• Common in newborns/children

Cortical Visual Impairment (CVI)

• Abnormalities in the brain's visual processing centers
• Eyes may function normally but interpretation is lost or impaired due to issues in the visual processing areas within the brain.

Developmental Abnormalities (Eye Problems)

• Coloboma, microphthalmia (small eye), optic nerve hypoplasia

Vision and Tests

• Visual tests to evaluate different components of the eye

NEPSY Fleches and NEPSY Maison tests for visual functions

• NEPSY Fleches: evaluates visual figure ground, pursuits, and peripheral awareness, and visual discrimination acuity.
• NEPSY Maison: evaluates recognition tasks, pursuits, and the crowding effect

NEPSY Cubes and Stereopsis tests - for visual functions.

TEA-CH tests - for visual functions (contrast, saccadic ability, and recognition)

REY tests: tests Visual Spatial capacity and visual memory.

DTVP3 tests (Visual and Motor coordination, Pursuits, Crowding effect, and Contrast)

Visual Processing Model Summary