PC - Fan and Block - Week 1 Flashcards
What happens to the two axis foci when an astigmatic eye is blurred intentionally for the fan and block method?
All axes move anteriorly, and the posterior axis is closest to the retina.
The limbs of the fan along which axis will appear clearest after fogging?
Along the axis of the posterior focal line.
What is the purpose of the fan and block method in the context of moving the anterior/posterior focal lines?
It is to move both focal lines anteriorly in front of the retina, then move the posterior line onto the retina, then use cylindrical lens to move the anterior line onto the retina.
By how much should one fog if the astigmatism is predicted to be < -1.00DC? What about > -1.00DC?
< -1.00DC - fog VA by 2 lines, +0.50DS
> -1.00DC - need +0.50DS plus half the estimated astigmatism
What are the instructions for the fan and block technique?
Do any of the lines on the fan chart appear blacker and clearer?
If a patient is asked about the clearness of the fan chart, and they report a single line is clearer, what does this mean? What about if multiple lines appear equally clear?
Single - indicates the meridian of the posterior line
Mutiple - the meridian of the posterior line likely falls in the middle of the clear lines
After asking a patient on the clearness of the fan chart, what is done next?
Align the point of the V wheel with the meridian of the clear line, and ask the patient whether one of the limbs of the V are clearer, or the same.
Suppose you’ve finished aligning the V wheel with the meridian. What would the patient report if it is on axis vs off axis?
On axis - both limbs are equally blurred
Off axis - one limb is clearer than the other
Consider a situation where the patient reports one limb is clearer than the other. In which direction should the V wheel be moved?
In the direction of the blurrier limb.
Consider you have finished aligning the V wheel, and the patient reports the limbs are equally blurry. What should you do next?
Direct them to the two block charts next to the V wheel. The lines aligned in the direction of the V point should appear clearer than the orthogonal. Ask them which block appears clearer to confirm.
Once a patient confirms which block chart appears clearer, what should you do?
They should report the block aligned with the direction of the V point to be clearer, the orthogonal should be blurrier.
Add minus cyl power until the patient reports the two block charts are equally blurry.
Consider a situatio where you need to add additional minus cyl power. What must you always do when you add minus cyl power?
For every -0.50DC, you must add +0.25DS to the spherical component to maintain the fog.
Consider having finished the fan and block technique, how can you refine your result?
Reduce DC by 0.25D, and expect reversal.
Can also return to the V chevron and andfirm/refine the axis.
Once the axis/DC power has been refined, what should be done next?
The fog should be reduced in 0.25DS steps until best vision is achieved.
What endpoint checks can be applied after fan and blocking?
The same as in BVS
+1.00 blur check
Duochrome
