Flashcards in Quiz: Low Vision & Visual Perception Deck (39):
Definition of Low Vision
A visual impairment, not correctable by standard glasses, contact lenses, medicine, or surgery, that interferes with a person’s ability to perform everyday activities
In the US, what is legal blindness defined as?
- distance visual acuity of 20/200 or worse in the better seeing eye after best conventional correction\
- also defined as a visual field less than or equal to 20º at the widest point
What is accommodation?
the process of lens thickening and thinning
the flexibility of the lens fibers decreases and the lens becomes more rigid; accommodation becomes weaker; image falls in the back of the eyes; use a positive lens to fix it
What is the function of the vitreous chamber?
to support the retina
T or F: The surrounding retina is vital for central vision and defines a 180 degree half sphere of mainly rods.
False, vital for peripheral vision
Central Visual System
- involves macula-fovea, central optic nerve and central occipital lobe
- clear sight; color vision; reading and writing
- 30 degree visual field (5-10 is macula-fovea)
Peripheral Visual System
- involves peripheral retina, optic nerve and peripheral regions of the occipital lobe
- provides us with info that tells us where we are in space
- night vision; perception of motion, orientation and balance
- used when we walk, run, drive and maintain balance
What does CN III (three) do?
"the rest are three"
- eye elevation; eye depression; eye adduction; eye elevation and adduction
- opens eyelid
What does CN VI (six) do?
"six goes out"
- eye abduction
What does CN IV (four) do?
"four down and in"
- eye depression and adduction
What does CN V (five) do?
What does CN VII (seven) do?
"close your eyelid"
Age Related Macular Degeneration
- > 50 years old
- affects macula
- blurred vision, central scotomas, distorted vision, impairment of glare, color and contrast sensitivity
- slow recovery of visual function after exposure to bright light
- blind spot in that 30 degrees
- most common (75%)
- can develop to wet
- drusen or yellow spots on macular and geographic atrophy
- slight less severe and slower processing
- usually no treatment
- abnormal BV growth under macula
- 25% of all AMD
- more advanced, faster progression of vision loss
- medication: injection into the vitreous
Implantable Miniature Telescope (MIT)
- treatment for AMD
- take off lens and put magnifier inside to see better
- greater than or equal to 75 yo
- visual acuity: 20/160 to 20/800
- have evidence of visually significant cateract
- have adequate peripheral vision in the eye not scheduled for surgery
Diabetic Retinopathy (DR)
- after 10 - 15 years of diabetes; most will demonstrate
- reduced delivery of oxygen to the retina cells and eye tissues
- BV leak - hemorrhage
- vasogenic factors cause new BVs to form
- glasses prescription change frequently
- may cause glaucoma
- often leads to total blindness
What are the treatments of Diabetic Retinopathy?
- laser surgery; injection of corticosteroids, injection of anti-VEGF; vitrectomy
- group of genetic eye conditions: progressive retina dystrophy
- abnormality of photoreceptors or the retinal pigment epithelium
- night blindness (defective dark adaptation)
- reduction of visual field - tunnel vision
- loss of central vision late in the course
- pigment layer comes to the top of the retina --> then you can't see
- aqueous humour forms from ciliary body --> posterior chamber --> anterior chamber --> trabecular meshwork --> Schlemm's canal
- HTN inside the eye
- damages optic nerve
- reduced peripheral vision
- can cause total blindness
- open angle and close angle
- cause is not known/ there is not one cause
Open angle glaucoma
- 90% of glaucoma; gradually progressive visual field loss and optic nerve changes
- affects more asians and blacks
Close angle glaucoma
- 10%; sudden ocular pain; see halos around lights; red eye; very high intraocular pressure; sudden decreased vision and fixed, mid-dilated pupil
- opacity of the lens
- blurred vision
- sensitivity to glare
- treatable: leave back layer --> remove the front and replace it with an artificial layer
- measure of the eye's ability to distinguish object details and shape
- Snellen test; biVABA
- fovea is the region for maximum visual acuity --> primarily a function of cone receptors
- extent of space visible to the eye that is fixated straight ahead
- measured in degrees from fixation
- sensitive to color
- the ability to perceive and distinguish between colors
- results from stimulation of RGB cones
- problem is in the macula (AMD: difficulties with similar colors)
- process by which an eye adjusts to decreased illumination and becomes more sensitive to light
- accomplished by photo-activation of rods and light adaptation is achieved by cones
- ability to detect detail having subtle gradations in grayness between test target and background
- increasing contrast helps reading and other daily activity
inability to execute purposeful movement; cannot move eye to target
inability to visually guide limbs (mislocalization when reaching or pointing for objects)
inability to copy or build a simple design (3 blocks --> cannot build)
inability to judge depths and distances
inability to distinguish foreground with background
inability to judge variations in form, including visual form, visual closure, etc.
visual scanning/visual attention (2 levels)
1. an automatic/reflexive level (brain stem), like flash light
2. a voluntary level (cortex) - gathering purposeful information
inability to perceive the position of two or more objects in relation to self and to each other
unilateral space neglect
inability to attend to or respond to meaningful sensory stimuli presented in the affected hemisphere