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Horizontal Vergences at Near
PURPOSE To measure，through the application of prism，the patient’s ability to use horizontal vergence to maintain binocular vision．Prisms which induce retinal disparity are gradually increased in power，forcing the patient’s vergence system to compensate for the disparity．
Note：The following description presumes the reader has read the procedure for horizontal vergences at distance．As distance and near testing are quite similar，some information previously stated is omitted here．
EQUIPMENT
·Phoropter with near point rod．
·Nearpoint card with an isolated vertical line of letters．The lettering on these cards approximates 20/30．A card with a block of letters of comparable size is frequently used．
SET-UP
·The phoropter should contain the habitual or induced near correction and be adjusted for the patient’s near PD．
·Place the vergence target under good illumination on the nearpoint rod, 40 cm from the patient．
·The Risley prisms，set to 0，should be positioned before both eyes (see Figure 4-11)．
STEP-BY-STEP PROCEDURE
1．Instruct the patient to open both eyes and ask him what he sees．He should see one clear image．If the patient sees two targets, end the test and record “diplopia．”
2．Instruct the patient to look at the target and try to keep it clear．Ask that the patient report if：
a．the target blurs (blur point)．
b．the target becomes double (break point)．
c．the target moves either left or right (spression)．
3．Introduce base in prism before both eyes at a speed of approximately 1 prism diopters per second．
4．As prism is added, note the total amount of prism before the two eyes when the patient reports the letters have blurred (blur point) and when the line of letters has broken into two (break point)．
5．Overshoot the break point slightly by adding a little more prism in the same direction．
6．Instruct the patient to tell you when the target becomes single again．
7．Reduce prism until the patient reports the target is single (recovery point) and note the total amount of prism before both eyes．
8．Repeat steps 2 to 7 with base out prism before both eyes．
RECORDING
·Record the technique and the distance at which it was performed, distance or near．
·Record the orientation of the prisms (BI and BO) along with the corresponding results．
·Each result should contain three values, blur，break，and recovery, in prism diopters．
·If no blur point is observed, an (x)is entered．
·If recovery values are in the direction opposite to what you expect, record the value as a negative value．
EXAMPLES
·Near Horizontal Vergences
BI：8/14/8 B0：20/24/18
·Near Horizontal Vergences
BI：Spression OS B0：12/16/4
EXPECTED FINDINGS
·Morgan (adult, clinical population)
Near BI： 13/21/13 Standard deviation 4/4/5
Near B0： 17/21/11 Standard deviation 5/6/7
·Saladin and Sheedy (adult，nonclinical population)
Near BI： 14/19/13 Standard deviation 6/7/6
Near B0： 22/30/23 Standard deviation 8/12/11
·The numbers provided are population norms．These serve as a general indicator．Precise interpretation of the vergence findings require that they be viewed in relation to other functional testing． |
