Exam #6: Vision Flashcards
What is accommodation? What are the physiologic events that give rise to accommodation?
1) Contraction of ciliary muscle
2) DECREASE in tension on suspensory ligaments
3) Lens RELAXES and become more spherical
*****This is used for NEAR vision
What is presbyopia?
Age related decline in near-vision due to an inability to accommodate
What is the blind spot?
Region of the optic disc WITHOUT photoreceptors
**Note that the optic disc is the head of the optic nerve in the retina
What is the fovea?
- Depression in the macula, which is the area of maximal focus of the light i.e. best vision
- Avascular zone
What is binocular disparity?
Difference in image location of an object seen by the left and right eyes, resulting from the eyes’ horizontal separation (parallax). The brain uses binocular disparity to extract depth information from the two-dimensional retinal images in stereopsis.
What is prosopagnosia?
Patients with problems visually identifying faces
What is object agnosia?
Patients with problems visually identifying objects
What is scotoma?
Visual field defect
Outline the position of the visual fields to the retina.
- Temporal visual field (monocular segment) projects nasally
- Nasal/ binocular segment projects to the temporal retina
Where does the retina project?
- Optic chiasm
- Right ends up in left hemisphere
- Left ends up in the right hemisphere
**Only the nasal crosses
What is the difference between the locations of rods and cones?
- Center of the fovea contains only cones that decrease laterally
- Lateral to the fovea, rods appear & increase in number
What are the functional differences between rod and cone vision?
Rods= black & white
- Peripheral vision
- Nighttime vision
Cones= color
Which receptor mediates scotopic vision? Photopic vision?
Scotopic= rods
- No color
- Poor acuity
Phototopic= cones
- High color
- High acuity
What are the electrophysiological changes that occur when a photoreceptor is stimulated by light?
Dark= entry of Na+ & Ca++ via channels held open by cGMP
- DEPOLARIZED in DARK
Light=
- Decrease cGMP & Na+ & Ca++ DECREASE
- K+ leaves
- Cell hyperpolarized
**Dependent on glutamate release
Define the term receptive field for visual neurons.
Area of the retina from which the neuron can be influenced
Which retinal cell type can produce action potential?
Ganglion cells
Which retinal cells are output cells?
Ganglion cells
Which retinal cells capture photons?
Photoreceptors–rods & cones
What is the function of retinal projections to the suprachiasmatic nuclei?
Hypothalamus: regulation of the circadian rhythms
What is the function of retinal projections to the pretectal nuclei?
Reflex control of pupil and lens
What is the function of retinal projections to the LGN?
This how we “actually see things”
What is the function of retinal projections to the superior colliculi?
Orienting movements of the head & eyes toward visual stimuli
What is the function of the dorsal visual stream to higher visual areas?
Motion and relative position of objects
What is the function of the ventral visual stream to higher visual areas?
High level form vision & object recognition
What is the clinical significance of having different pathways for different aspects of vision?
When the system breaks down, patients will have complex visual defects
What are the pigments associated with rods, cones, and ganglion cells?
Where are the genes located that code for cone pigments related to color blindness?
- Three cone pigments:
Red= x-chromosome
Green= x-chromosome
Blue= #7 - Rods= rhadopsin= #3
- Ganglion cells= melanopsin
Outline the mechanisms for depth perception. Which are monocular and which require vision in both eyes?
Depth perception requires only MONOCULAR ques
- Size of the object
- Motion parallax
For really good depth perception, need binocular vision for stereopsis
What is strabismus? Describe how strabismus can result in suppression of the visual image from one eye.
Strabismus refers to “squint” or cross-eyedness
- Causes one-eyed fixation
- Brain suppresses input from the other eye
Which type of vitamin deficiency can cause night blindness?
Vitamin A
Outline the pupillary light reflex. What is the different in function between the SNS & PNS?
PNS= contriction SNS= dilation
What is the result of a lesion to the optic nerve?
Ipsilateral monocular blindness
What is the result of a lesion to the optic chiasm?
Bitemporal hemianopsia
What is the result of a lesion to the optic tract?
Homonymous hemianopsia
What is the result of a lesion to Meyer’s Loop?
Superior quadrant anopsia
