Low Vision Flashcards
What is low vision?
Uncorrectable reduced vision meaning vision cannot be improved by glasses/contacts
A person with low vision may still be able to use the visual system for reading but the standard size, contrast, or spacing are inadequate.
How does the PALS Survey define low vision?
Difficulty seeing someone from 12 feet or in reading a newspaper despite corrective lenses
What is blindness?
Very significant vision loss requiring alternative sensory pathway enhancements (auditory, tactile)
For a blind person, the visual system does not provide a useful input channel for reading or mobility. For individuals who are blind, alternative sensory pathways of either audition (hearing) or touch (feeling) must be used to provide input.
How is visual acuity measured?
Measured by determining the refractive index of the eye, typically using the Snellen Chart
How is the Snellen Chart scored?
Fraction measured in feet- You/Normal seeing person
Ex: 20/20 normal vision
20/10 better than normal
20/40 worse than normal
What is visual accommodation?
The process by which the ciliary muscles change the curvature of the lens and hence the focal point of the eye
What is normal visual accommodation?
For a person less than 20 years of age with normal visual accommodation, the eye can accommodate for an object located at about 4 inches.
Ability to accommodate decreases as an individual ages.
- At 50, the eye cannot accommodate to objects closer than 12 inche.
Give an example of accommodative insufficiency.
For example, if a person is using a keyboard device with a visual display, the separation of these two system components may require constant accommodation as visual gaze is directed at the keyboard and then at the display and back to the keyboard. Appropriate placement of the keyboard and visual display can reduce the amount of accommodation that is required and can result in significantly improved overall system performance.
What is accommodative insuffieciency?
Many types of disabilities affect accommodation; limitations in accommodation are referred to as accommodative insufficiency, which can be a significant factor when ATs are used.
What is the normal range of peripheral vision?
With the head and eyes fixed on a central point, normal range of peripheral vision in the right eye is 70º to the left and 104º to the right.
If eyes allowed to rotate with head remaining fixed, it is 166º to each side of central point.
What diseases/injuries affect visual field?
CP, TBI, diseases affecting eye and visual system
KNOW FIELD CUTS
Unilateral is also called anopia
What causes congenital blindness?
Optical nerve lesions main cause in high income countries
In low-income countries additional causes include corneal scarring from measles, vitamin A deficiency, the use of harmful traditional eye remedies, and ophthalmia neonatorum.
Retinopathy of prematurity is an important cause in middle-income countries.
Cataract, congenital abnormalities, and hereditary retinal dystrophies are significant causes in all countries.
What is age related macular degeneration?
Most common cause of blindness in seniors
It occurs most frequently in individuals over 65, beginning in one eye and progressing gradually to both eyes.
ARMD primarily affects the central vision with the peripheral vision being preserved. As it progresses, the size of the impaired central field gradually increases.
What are the types of ARMD?
There are two types of ARMD: dry, or atrophic, and wet, or endovascular.
- The dry form is much more common, but the wet form accounts for 80% to 90% of the cases of ARMD- related blindness.
What is Dynavision therapy?
Ortho for ROM
Neuro - CVA, TBI, midline, visual scanning
Attention deficit disorders
Visual field therapy
Keep head still and click lit up buttons
Central field loss and eccentric viewing (EV)
Train patients to move their eyes in a consistent way to look around their blind spot
