How do they adjust for testing in rooms less than 6m?
Why at 6m?- because its close enough to infinity i.e 0.16D
testing closer than 6m is further away from infinity so final Rx compensated accordingly
in a 3m room, 1/3=0.33D so remove +0.25D on R and L and leave px on green for duochrome
What is the law when issuing prescriptions?
immediately after carrying out an NHS or private sight test you ust issue:
a prescription
a statement indicationg that no prescription is necessary
What is the Fan and Block method
subjective technique for astig
for cross cyl= COLC on retina
for F&B= place posterior focal lines on retina + COLC and anterior focal line in front to retina
Fan= semi circle of lines to indicate different cyl axis. 180 at top and 90 at sides
The blocks and arrow rotate so the arow can be pointed to the clearest line on the fan
Fan and block procedure
arrow and block is pointed to clearest line ( this indicates cyl axis)
-ve cyl added at this axis (estimate power)
check if lines appear equally clear. If so, add more cyl. If not, decrease cyl
Ads and Disads with F&B
Ads:
works well with larger cyl
good fo identifying cyl axis
helps students understand astig
Disads:
my not be availble on more modern charts
not good with small cyls
needs VA of 6/18 or better
Last changed3 months ago
