block 5-eyes Flashcards
Pathological Nystagmus (abnormal eye movements )
- involuntary constant to and for movement of the eyes
- two types: infantile or developed in later life due to a neurological disease
- reduced visual acuity
-cosmetics- has physcho/social impacts of life
importance of classifying nystagmus
- can lead to predictions of future diseases so it’s important to know if it’s infantile or accrued
- Infantile albinism, retinal disease etc…
- acquired brain disorders such as = oscillopsia ( perceive the world is moving around)
multiple scelerosis, brain tumours, strokes
Recording eye movements of Nystagmus
Qualitative= video
Quantitative= 2D so horizontal and vertical movement of eyes
E.g. 2D- electroculography
- 3d sagitoonal something as well
2D-Electrooculography (EOG)
-measure the corneo-retinal potential= difference in electrical charge between the cornea and retina
2D- limbus tracker
-measures reflected infrared light shone onto limbus
-measures the border of dark iris and light sclera
-high temporal resolution
2d-video oculography
-ifrared tracks pupil movement, while screen markers track head movement.
-high temporal and spatial resolution recordings, but does not record during blinks
idiopathic Infantile nystagmus
- hereditary
-onset in the first few months of life - no other problems with the visual System
-vision is good - nystagmus amplifier use and waveform changes with age
- sometimes head nodding
-horizontal,conjugate,abnormal head turn
Albinism
- absent or decreased tissue melanin cause visual systems abnormalities
-occurs in all species
Visual system abnormalities in albinism
- hypopigmentation
- retinal abnormalities. fovea underdeveloped
-chiasmal abnormalities - similar to characterisic to infantile nystagmus
Retinal diseases associated with nystagmus
- congenital stationary night blindness (rod photoreceptor abnormalities)
-achromatopsia (cone photoreceptor abnormality)
-leads to poor vision, sensitivity to light/night blindness
-abnormal pupil responses etc….
Multiple sclerosis
-demyelination disease
- myelin sheath in the brain and spinal cord are damaged
- usually diagnosed between 20-40 years
-oscillopsia
Wernicke Encephalopathy
lesions in the central nervous system due to lack of vitamin B
-usually due to alcohol or drug abuse or pregnancy
-vertical nystagmus
-oscillopsia
-reversible with vitamin d / thiamine supplements treatments and get off the drugs and alcohol lol
Why is there no oscillopsia in infantile Nystagmus
- maybe due to the plasticity of the brain until about 7 years - parental cortex
eye journey to the brain
-eye
-optic nerve
-optic chiasm
-optic tract
-LGN
-optic radiation
-visual cortex
The optic chiasm
-where some of the nerve fibers from your eyes cross over to the opposite side of the brain. About 55% of these fibers, specifically from the nasal side of each retina, cross to the other side.
-The left side of your brain processes what you see in your right visual field (what’s on the right side of your view).
The right side of your brain processes what you see in your left visual field.
Both sides of your brain get input from both eyes, so they work together to create a complete picture of what you see.
importance of optic chiasm
-improve signal noise
-so that we see our hands on the same side of the brain that controls it. = improves the speed of control
-for 3D vision.it helps create 3D vision and depth perception.
Each eye sees a slightly different image (this difference is called retinal disparity).
The optic chiasm combines and processes these differences, allowing us to judge how near or far things are.
horoptor
-surface where no disparity
between two eyes (images correspond)
Everything nearer =
crossed disparity
Everything further away
= uncrossed disparity
primary visual cortex
-The primary visual cortex (V1) is the brain’s main area for receiving and processing visual information. Here’s what happens:
Retina Map: V1 is organized like a map of the retina, with each part of the retina linked to a specific spot in V1.
Fovea Focus: V1 gives extra attention to the fovea (the sharp vision center), helping us see details.
Combining Inputs: V1 has ocular dominance columns—stripes that process input from each eye. These combine to create a full view of the world.
ocular dominance columns
-They are alternating stripes or columns in V1. Some stripes process input from the left eye, and others process input from the right eye.
Why They Matter:
These columns help the brain combine information from both eyes to create a single, clear image. This is key for depth perception and seeing in 3D.
abnormalities of the optic chiasm
-in albinism, around 80% of the fibres cross at the chiasm instead of 55%
-can measure connections from the eyes to the brain using FMRI or other methods
-Achiasm = no crossing over or less so the left visual field is processed on the left side of the brain and vice versa
strabismus
- the eyes are not looking in the same direction
-input from one eye is suppressed to prevent double vision. It causes reduced stereopsis =the brain’s ability to perceive depth and see in 3D by combining the slightly different images from each eye.
-leads to a lazy eye (amblyopia)
amblyopia
-very common
-vision in one eye is stronger than the other
-can be reversed by patching when the child is young.
ventral pathway
-WHAT pathway (what object?)
-runs from the primary visual cortex (V1) to the inferior temporal cortex
-It helps identify and recognize objects, focusing on what you’re looking at. For example: Recognizing faces, shapes, colours, and objects.
-mainly receives inputs from the fovea
-allocates salience to objects (how important an object is)
Dorsal pathway
-WHERE pathway (vision processing action)
-It runs from the primary visual cortex (V1) to the intraparietal parietal lobe.
-Where objects are located in space (spatial awareness).
How to interact with objects (e.g., reaching, grasping, or avoiding them)..
-Helps you track moving objects or navigate through your environment.
-helps with eye movements and hand movements etc…
Bottom-up processes
- sensory (exogenous)information
- Information comes from the environment (like sights, sounds, smells) and flows up to the brain.
top-down processes
-internal (endogenous) information-Your past experiences, knowledge, and expectations influence how you interpret sensory information.
: interpretation of visual information is heavily influenced by - expectation, context, learning
advantages of using information already in the brain
-makes sense of fragmented incoming information
-improves the speed of visual processing
Charles Bonnet syndrome
- condition where people with significant vision loss experience visual hallucinations, even though they are mentally healthy.
-The brain creates the hallucinations to “fill in the gaps” left by reduced visual input.
damage to the inferior temporal cortex (extrastriate areas)
-visual agnosia 2 types:
-aperceptive= cannot copy or match objects (cannot integrate visual features) e.g. name it but not describe it
-associative: cannot interpret , understand or assign meaning to object e.g can describe it but not name it
damage to the intraparietal cortex (extrastriate areas)
-damage to the right parietal lobe leads to Hemi-neglect of the left visual field
-The right parietal cortex sees the whole visual field whereas the left parental cortex only sees the right visual field
-thereforefore becausethe right see everything damage to the lef6t wouldn’t cause a loss in vision
binding
-binding is the integration of highly diverse neural information to form a cohesive experience
e.g. allows you to see on person as a whole and not several people
-binding problem questions how this is possible ?
damage to binding
-synesthesia= stimulation of one sense automatically triggers another unrelated sense. It’s like a “blending” of senses that most people experience separately.
Key Features:
Cross-Sensory Experiences:
A person might see colors when hearing music, taste flavors when reading words, or associate numbers with specific colors.
Consistent and Automatic:
The associations are involuntary and consistent. For example, someone might always see the number “3” as green.
sclera
-white of the eye within the retina
-protective, outer layer comprised of collagen and elastin fibres
choriod
-vascular layer providing nutrients and oxygen to outer retna especially fovea
retinal pigment epithelium
-pigmented layer for light absorption and reducing oxidative stress
-tight junctions form blood brain (retina) barrier
photoreceptors of the retina
-cones: concentrated in the fovea, high acuity,day vision and colour vision
-rods= dark vision . not in the central retina
horizontal cells
-interneurons connecting photoreceptors laterally
bipolar cells
-connect photoreceptors to retinal ganglion cells
-faciliates sensory processing through horizontal and anacrine cells
amacrine cells
-laterally connect bipolar cells
retinal ganglion cells
-output cells from the retina
the fovea
-The fovea is a small, central pit in the retina of the eye. It is the point of sharpest vision and is responsible for seeing fine details.
Key Features of the Fovea:
High Cone Density:
-the fovea is packed with cone cells (light-sensitive cells) but has no rod cells.
Cone cells are responsible for color vision and work best in bright light.
The absence of rod cells means the fovea isn’t good at detecting light in dim conditions.
why move the eyes?
- bring the image onto the fovea
-keep the imagine on the fovea
saccades
-saccades = bring the image onto the fovea. voluntary as they are in response to stimuli. conjugates both eyes moving at same time in the same direction,fast. When you’re reading, your eyes make quick saccades from one word to the next
fixations
-are moments when your eyes pause on a specific point to take in detailed visual information.
-When you’re reading a word, your eyes will stop and fixate on it for a brief moment to process the letters and meaning.
microsaccades
-small saccades to bring the image back torwards fovea
drift
-slower than microsaccades and more random
tremor
-fine oscillations superimposed on the drift
smooth pursuit
Smooth pursuit eye movements are slow, controlled movements that allow your eyes to follow a moving object smoothly without jerking. Unlike saccades, which are quick jumps, smooth pursuit helps you track objects like a moving car or a ball in flight, keeping the target in focus. These movements are essential for activities like reading or watching a moving object in your environment.
-conjugate eye movements
Optokinetic Nystagmus (OKN)
-a type of eye movement that helps you track a moving visual scene. It involves a combination of smooth pursuit (tracking the movement) and saccades (rapid eye jumps to reorient the gaze). OKN occurs when you follow something like a passing train, where your eyes smoothly track the movement, and then quickly reset to the starting point when the object moves out of view. It helps maintain stable vision during continuous motion. involuntary and conjugate
-slow build up
vestibulo -ocular reflex (
A reflex that keeps your vision stable while your head moves. It works by moving your eyes in the opposite direction of your head movement, so the image you’re looking at stays steady on your retina. For example, if you turn your head to the left, the VOR moves your eyes to the right to maintain focus. This reflex is essential for clear vision during activities like walking or turning your head quickly.
-involuntary and conjugate
YThe vestibular system
The vestibular system is the inner ear’s balance system, crucial for detecting motion, head position, and maintaining equilibrium. It consists of:
- Semicircular Canals:
Detect Rotational Movements: These three canals are oriented in different planes (horizontal, vertical, and diagonal) to sense head rotation in all directions.
How They Work: Fluid inside the canals moves when you turn your head, stimulating sensory hair cells to detect the direction and speed of rotation. - Utricle and Saccule:
Detect Linear Movements and Gravity: These structures are part of the otolith organs.
Utricle: Senses horizontal motion (e.g., moving forward or side to side).
Saccule: Senses vertical motion (e.g., moving up and down, like in an elevator
-rapid
vergence
-ergence is a type of eye movement that helps you focus on objects at different distances by moving your eyes inward or outward.
Key Features:
Convergence:
Eyes move inward (toward each other) to focus on a close object, like when reading a book.
Divergence:
Eyes move outward (away from each other) to focus on a faraway object, like looking at a distant mountain.
How It Works:
Vergence adjusts the angle between your eyes to ensure that the image of the object you’re looking at falls on corresponding spots on both retinas.
This is crucial for depth perception and maintaining a single, clear image instead of seeing double.
3D scleral search coil
-magnetic contact lens inserted into eye
-high spatial and temporal recordings of 3d eye movements
-invasive and uncomfortable techniques
3D video oculography
-uses infrared cameras
-uses a partially reflective mirror
-tracks pupils for horizontal and vertical movements
-lower temporal and spatial resolution compared to scleral search coil but non-invasive and comfortable
