Visual System Flashcards
3 layers of eye coat?
Sclera - hard and opaque
Choroid - pigmented and vascular
Retina - neurosensory tissue
Sclera?
White of eyes
Tough, opaque, protective outer coat
High water content
Uvea?
Vascular coat of eyeballs, most vascular part of eye
Between sclera and retina
Iris, ciliary body and choroid
Retina?
Thin layer of tissue, lines inner part of eye
Captures light (which is sent to brain via optic nerve)
Optic nerve?
Transmits electrical impulses from retina to brain
Connects to back of eye near macula
Visible portion called “optic disc”
Macula?
In centre of retina
Small and highly sensitive, responsible for detailed vision (e.g. reading)
Fovea = centre
Blind spot?
Where optic nerve meets retina - no light sensitive cells
Corresponding anatomical landmark for physiological blindspot?
Optic disc
Central vision?
Focus
Detail day vision, colour vision, reading, facial recognition
Fovea has highest conc. of cone photoreceptors
Central vision assessment?
Visual acuity assessment
Loss of fovea vision = poor visual acuity
Peripheral vision?
Motion
Shape, movement, night vision, navigation vision
Peripheral vision assessment?
Visual field assessment
Extensive loss of visual field = unable to navigate in environment, may need white stick
Retinal outer layer?
Photoreceptors - 1st order neuron
Detection of light
Retinal middle layer?
Bipolar cells (2nd order neuron)
Local signal processing to improve contrast sensitivity
Retinal inner layer?
Retinal ganglion cells (3rd order neuron)
Transmission of signal from eye to brain
Photoreceptor classes
Rods - more sensitive to light, slow response, night vision (scotopic vision)
Cones - less sensitive to light, faster response, day light fine vision and colour vision (photopic vision)
2 types of lenses?
Convex - brings light to a point
Concave - spreads light outwards
Emmetropia?
Adequate correlation between axial length and refractive power
Parallel light falls on retina
Ametropia?
Refractive error
Mismatch between axial length and refractive power
Parallel light rays don’t wall on retina
Myopia meaning?
Near-sightedness
Parallel rays converge at focal point anterior to ulna
Myopia causes?
Excessive long globe (axial myopia)
Excessive refractive power (refractive myopia)
Myopia symptoms?
Blurred distant vision
Squint
Headache
Hyperopia meaning?
Far-sightedness
Parallel rays converge at focal point posterior to retina
Hyperopia causes?
Excessive short globe (axial hyperopia)
Insufficient refractive power (refractive hyperopia)
Hyperopia symptoms?
Visual acuity at near tends to blur relatively early (more noticeable when tired)
Eye pain, headaches in frontal region, burning sensation in eyes
Near response triad?
Pupillary miosis
Convergence
Accommodation
adaptation for near vision