Test charts & Refraction Flashcards
Snellen acuity of 6/36 what do figures in the fraction represent?
6/36 = Testing distance/Just
legible letter which
subtends eye at 5’
Decimal acuity
6/36 = 0.1667 (divide top by bottom)
Notations for visual acuity
*HM @ 1M = Hand movement at
1M
*CF @ 50cm = Count fingers at
50cm
*NLP = No light perception
What does visual acuity recorded as logMAR value mean?
The logarithm of the minimum angle of resolution
What is logMAR of 0.0 in Snellen acuity?
logMAR 0.0 is Snellen acuity of 6/6
Advantages of Bailey-Lovie chart over Snellen chart
*Even progression of letter sizes
*Equal amount of letters on
each line
*There is no crowding as the
space between the letters is
even
*More precise for partial acuity
of a line
Relative Spectacle Magnification
RSM = height of corrected retinal
image size/height of
retinal image size in the
standard reduced
emmetropic eye
RSM = K/Fsp X Ke’/K’
Subjective Refraction
A method of refraction which DOES require a response from the patient
Objective Refraction
A method of refraction which does NOT require a response from the patient
Examples of techniques or instruments used in subjective refraction
*Cross cylinder
*Duochrome
*Fan & Block
Disadvantages of using traditional Snellen chart to assess VA of a low vision patient
*Fewer larger letters
*Smaller letters are crowded
*More letters on smaller lines
*Unequal number of letters on
each line
*High contrast letters
On the duochrome test if px reports that the targets appear equal on red & green
Px is corrected when he red & green appear equal
On the duochrome if the target seen is said to be darker & clearer on green
More plus is required (less minus is required)
