Von Grafe technique

I think finally I understand how roatory Risley prism is working  with using Von Grafe technique for measurement phoria .

 For lateral (horizental) phoria , we should use vertical prim to dissociate  and use horizental prism to measure .  The arrow of Risely shows the base .  Therfore for a typical set up :

OD : 12 prism diopter base in (BI)   (Measurement prism)

OS : 6prism diopter base up(BU) ( dissociated prism) fixed

Move OD prism until patient sees target lin up like buttons on a shirt, and patient should instructed to watch upper , non moving image( which belongs to right eye)

and for neutralize  Base out for esophoria and Base In for exophoria .

  The same procedure for vertical phoria , use horizental for dissociate & vertical for measurement .

OD: 12 BI & OS : 6 BUp  and move OS until patient sees target lin up ,

Base up for hypophoria and base down for hyperphoria .

This video clip is useful .

I have a confusion everytime , I used Risly prism , It looks I nearly forgot all of my optometry knowledge , but for teaching to students,  I should learn and remember all the basic and essential things . It's strange I'm  teaching  this module for the third year now , but anybody didn't ask me about rotary prim and I didn't feel I need to do the test.Some tests like Fan & Block or Von Grafe  don't have much application in the real professional clinics , but they 're essential for students to learn them .

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