Low vision 1 Flashcards
why is VA important? (part 1 of 2- 6 reasons)
- Allows early eye disease detection
- Understand how much Mag we might need
- Social legal purposes : SI/SSI certification
- Predicating every day tasks
- compare the norm values
6.Quantify patient’s subjective impression of visual performance
why is VA important? (part 2/2- 3 reasons)
- used to understand mag of required device can be
- Refraction procedures and decision
making- eg when to dispense spx - Predicting visual function for everyday tasks- eg LP- may struggle with daily activities vs px with 6/6
how do we note snellen notation?
VA = Test Distance/
Distance letter subtends 5 min of arc
which method of notation isnt used very much?
Keller A system
How is VA recorded?
Snellen and LogMAR
Example of converting:
6/60 - Snellen
60/6 - MAR
1 - log(MAR)
Keller A System 1 min arc MAR is A1 i.e. 6/6 is A1
what are the Most common distance VA charts?
- Snellen
- logMAR : bailt-lovie distance chart, ETDRS and keller A charts
- Thompson Test chart
Variables for an ideal chart?
- Portable
- Good Lighting
- High contrast
- Good range of sizes
What are the characteristics of Snellen chart?
It is cheap
However:
It is hard to control crowding (6/60 has no crowding)
Hard to score letter by letter
What are the characteristics of LogMAR ?
1.Equal number of letters on each line
2.Log progressive of letter size
3. Larger
4. More expensive
Each letter has a weight of 0.02
conversion factor of logMAR done at different distances?
-3m: Add 0.30
-1.5 m: Add 0.60
-0.75 m: Add 0.90
- 1m: Add 0.80
PRIYESH I DIDNT NUMBER SO NOONE GETS CONFUSED
Conversion factor for ETDRS test charts?
ETDRS similar but used at 4m, correction factor ½ distance- 2m-0,3, 1m= 0.6 0.5m= 0.9
what type of px do we used BRVT for?
Good for px HM, CF, where we can’t do letter VA- px with poor vision
how do we carry out BRVT - Berkeley Rudimentary vision test?
1.Tumbling E
2.Grating card pair : H or V. Used when Tumbling is not seen
3.Basic vision card :One area is white and one area is Black. Ask the px to point out which area is white and which is black
what is the Freiburg Visual acuity test and how does it compare with BRVT?
Similar to the BRVT but on the computer!
Landots C instead of tumbling E.
It does not have different ranges like BRVT does
How can we conduct home low vision testing and how do we do it?
1.)Home acuity Test
2.) Test carried out at 150cm/190cm (do 190cm if vision allows)- sent string of 150cm long- chart has 5 lines- ranges from 3/60 to 6/7.5 or if good va 190cmcm- 6/96 to 6/6
3.) Note correct answers
What is contrast threshold?
This is the smallest difference in luminance the px can detect.
We measure it using sine wave grating cards