Unit 2 Flashcards
What to avoid before testing vision ?
Dilation
Instillation of eye drops
Physical contact
Purpose of taking VA
- Quantify vision
- Evaluate for improvement or digression of VA
- Establish acuity priors to procedures
- Establish acuity following injury, surgery or treatment
- In children to detect amblyopia
Visual acuity is based on three things
- Detection
-Ability to tell that something is there - Recognition
-Correctly indentifying familiar objects.optotypes of decreasing size by recognizing small details - Resolution
-Being able to identify smaller and smaller gaps or orientation in a single optotype or pattern
Which letters to use for children when determining VA
HOTVXU / Sheridan - Gardiner test
These letters are symmetrical and reversible and easy to recognize
Problems with the standard Snellen chart?
-20/100 line often has only two letters
-20/20 line has 5-8 letters
-Many snellen charts go directly from 20/400 to 20/200
-No standardization as to what font, which letters, or spacing between letters and rows is used
Sloan and ETDRS
The spacing between ototypes is the same
-Each line has the same number of ototypes
-ETDRS has become the preferred system when working w/ low vision pxs, as well as for research bc it is more repetable
ETDRS
Early treatment diabetic retinopathy study
What are some other types of recognition type tests other than letters
-Tumbling Es
-Landolt “C” , Landolt broken rings
-Pictures (Allen pictures / lea symbols)
-Numbers
-
Allen pictures
Uses objects that are almost unievrsally recognized, especially by children
-ex. hand, truck, horse etc..
-Prior to testing make sure the px can identify each pic
Distance acuity systems
-Standard 20 foot test distance must be maintained
-Some poster style wall charts are calibrated at 10 feet instead of 20
-Not all exam lanes are 20+ feet long so projectors with mirrors can be used to create an equivalent of 20 feet or we can use computer based systems
Near acuity testing systems
-most commonly done w a hand-held card showing opotypes in decreasing size
-Rosenbaum pocket screener
-Offers numbers, tumbling Es, Xs and Os
if the px is unable to read the 20/20 line what do we do ?
-Proceed VA with pinhole in place
-Pinhole can determine if a px is capable of seeing the 20/20 line
If the pinhole does not help the pxs VA what does that mean?
This could be due to some type of pathology
If a patients acuity does not improve with pinhole should we proceed with refraction?
No - because it is likely the have a cataract or some other disease
Bailey Lovie VA - what is it commonly used to measure
Contrast sensitivity
What is contrast sensitivity ?
the ability to tell the difference between two similar colors or shades of grey
-It is an important measure of quality of vision (glare with night driving)
