Week 9: Visual System Flashcards
Rods
Black and White –> Peripheral vision
Cones
Color –> Central vision
Pathway of Vision
Visual information from the eyes travels through the optic nerve to the optic chiasm, where some fibers cross over while others continue on the same side. These split fibers form the optic tracts, which relay information to the lateral geniculate nucleus (LGN) in the thalamus. From the LGN, signals are sent to the primary visual cortex located in the occipital lobe, where the brain processes and interprets the visual information. Beyond this primary area, the brain integrates these signals with other sensory inputs and higher cognitive functions to form our perception of the visual world.
Eye Lens accommodation
Adjusting the curvature of the lens
- Ciliary muscle flexion: ligaments loosen, curving the lens
- Ciliary muscle relaxation: ligaments tighten, making it flat
Lens flexibility decreases with age
- Cataracts surgery: artificial lens
- Curvature cannot be adjusted, leading to being far-sighted
Glaucoma
Impaired filtration of vitreous humor, causing pressure buildup on periphery (Tunnel vision) Peripheral vision is lost
Diabetic Retionathy
Prolonged high blood glucose damages small blood vessels
- Black dots
Lesions to visual system
Impairment to visual fields depends on where is occurs along the visual processing system
Cut after chiasm on right side (loss of all vision in right eye)
Cut on chiasm in middle (Right visual field on left eye and left visual field on right eye)
Cut before chiasm on right side (Right visual field on both sides)
Cut at the bottom right (only a corner taken out on left side)
Nystagmus
Repetitive, uncontrolled movements of the eye
- Caused by impairment to at least one of these
(Fixation, vestibulo-ocular reflex, and gaze-holding system (ability to hold gaze on an object)
Amblyopia
Also known as “lazy eye”
- Patched placed over the good eye to force use of the lazy eye
- If not done early in life it can become permanent due to neurodevelopment and neuroplasticity
Scotoma
Areas of blindness (One black spot at top corner)
Peripheral Field Loss
AKA tunnel vision
Glare Sensitivity
Inability to accommodate to change in lighting (can look blurry)
Visual Field Cut
Field cuts involve partial blindness where the patient cannot see on the affected side.
Optokinetic Reflex
Helps to hold images on the retina during stable and dynamic head movement (looking out the window of a moving vehicle)
Visual Acuity
The ability to see visual detail
Object Fixation
The ability to locate and focus on a stationary object or target (important for people with low levels of consciousness)
Visual Pursuit/Tracking
The ability to lock onto and maintain fixation on a moving target across the whole visual field (Assessed with the X and the H test)
Functional Acuity
The ability to see detail at both near and far distances
(i.e., does the person have visual deficits while performing functional tasks - reading a clock to tell time or finding clothes in a closet and then getting dressed)
Diplopia
Double vision. The symptom of an ocular muscle imbalance
Saccades
Quick precise eye movements made during visual scanning or a visual search (E.g., looking for a person in a crowded room)
Accommodation
Allows for changing focal length (looking near to far or far to near)
Includes
- Changing the thickness of the lens
- Convergence of the eyes
- Pupillary constriction
Examples
- Driving and looking at road and speedometer
Convergence
The ability of both eyes to move medially during a near task. Allows for reading.
Visual Field
The space one is able to see when looking straight ahead
- Normal field of vision is approximately 160 degrees with both eyes
Visual attention
The ability to visually direct attention within all visual fields
Contrast sensitivity
Contrast sensitivity (CS) is the ability to perceive sharp and clear outlines of very small objects. It is also defined as the ability to identify minute differences in the shadings and patterns.
Trochlear Nerve lesion
a unilateral trochlear nuclear lesion affects the contralateral nerve and superior oblique muscle, while a fascicular lesion affects the ipsilateral nerve and muscle
Abducens nerve lesion
On exam, there is inability to abduct the affected eye. Abducens nerve palsy causes an incomitant esotropia due to the unopposed action of the antagonistic medial rectus muscle. The affected eye turns in toward the nose and is unable to abduct properly.
Cone photoreceptors are responsible for _____ vision and are concentrated in the ____ portion of the retina
Color, Central
Where do the medial portions of the optic nerve cross the brain hempisphere
Optic chiasm
The ventral visual stream is responsible for _____ whereas the dorsal visual stream is responsible for _____
Perception (knowing); Action (doing)
While the ciliary muscle of the eye is relaxed, the lens ligaments tighten. Which shape of the eye is the lens in?
Flat
An inability to move the gaze of one eye medially suggest impairment to which cranial nerve
CN #3 Oculomotor
An OTR has 2 clients with visual impairments
Clients A and B both have difficulty seeing in their left visual field. Client A is aware of the deficit and will turn their head more to see. Client B is unware of the deficit and will for example leave their left shoe untied.
Client A most likely has ____ and Client B most likely has a ____
Visual field cut; visual attention deficit
An OTR is conducting an initial evaluation with diabetes. The outpatient complains of small black dots in their vision. The OTR refers the outpatient to an ophthalmologist for which of the following conditions?
Scotoma
An OTR conducts a chart review with a client in acute care. The OTR notes that the client had a stroke that is impacting the right optic tract. Which of the following visual field losses should the OTR anticipate
3 (both left halves of visual field are affected)
An OT student goes to fieldwork at a vision clinic. The OT student sees the OT administer an assessment where the client looks straight ahead at the therapists nose. The OT has a highlighter in their hand out of the clients field of view, and then moves the highlighter horizontally. The OT asks the client to let the OT know when they first see the highlighter come into view. Which of the following assessments is the OT most likely administering?
Visual Field Test
An OTR observes a client trying to find utensils during a cooking task. The OTR notes that as the client scans the drawers and cabinets are disorganized and tend to undershoot or overshoot the visual target. This most likely indicates an impairment to which of the following.
Saccades
