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Distance Vertical Phoria by von Graefe Technique
PURPOSE To determine the relative vertical position of the visual axes of the eyes at distance when fusion has been broken．
EQUIPMENT
·Phoropter．
·A distance acuity chart that can isolate letters.
SET-UP
·The phoropter should contain the patient’s distance correction and be set for the patient’s distance PD．
·Display a single letter on the distance chart, one line larger than the patient’s best corrected visual acuity in the poorer eye．
·Place the Risley prisms before both eyes．Instruct the patient to close his eyes while you are adjusting the prisms．Set the prism before the left eye at 6Δ base and set the prism before the right eye at 12Δ base in．The 6Δ base prism serves as a measuring prism and the 12Δ base in prism serves as a dissociating prism tor the vertical phoria test(see Figure 4-3)．
Note：The distance lateral phoria test and the distance vertical phoria test are generally performed sequentially since the set for the two tests is the same．
STEP-BY-STEP PROCEDURE
1．Instruct the patient to open both eyes．Ask the patient how many targets he sees and where they are in relation to one another．The patient should see two targets；one and to the right, one down and to the left．If patient sees only one target, check to see if one eye is occluded or alternately occlude each eye to help the patient locate each of the images in space or change the amount of base in prism in front of the right eye．If the patient sees two targets，hut one is and to the left and the other is down and to the right, increase the amount of base in prism on the right eye until the targets are seen in the appropriate relationship．
2．Instruct the patient to look at the target to the right.
3．Instruct patient to look at the target to the right, but think about the other，or left one．Tell him that you will make the left target move．Ask him to tell you when the two images or targets are horizontally lined , one next to the other．Inform him that he should always see double and to continue to look at the target to the right．
4．At about 2Δ per second，reduce the base in prism until the patient reports horizontal alignment of the two targets．Note the amount of prism and the direction of the base of the prism when the patient reports that the two targets are aligned．
5．Continue changing the measuring prism in the same direction (ie，overshoot the point of horizontal alignment) until the patient sees the two targets as one and to the left，one down and to the right．
6．Bring the measuring prism back in the other direction until the patient again reports alignment of the two targets．Note the amount of prism and the direction of the base of the prism when the patient reports that the two targets are aligned(see Figure 4-4)．
7．The result is the average of values in steps 4 and 6, if they are within 2Δof each other．If the two values are not within 2Δof one another，repeat the measurement，emphasizing the instructions to the patient，and average the two closest values．
RECORDING
·Record the size of the deviation in prism diopters and the type of deviation observed．For vertical phorias，you must always identify the eye with the hyper deviation．
EXAMPLES
·DVP：ortho
·DVP：2Δ right hyper
·DVP：1Δ left hyper
EXPECTED FINDINGS
0rtho(no deviation)is the expected finding． |
