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…
