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Vertical Vergences at Near
PURPOSE To measure the patient’s vertical fusional vergence abilities, through the uniocular application of base or base down prism．
The following description presumes the reader has read the procedure for vertical vergences at distance．As distance and near testing are quite similar, some information previously stated is omitted．
EQUIPMENT
·Phoropter with a nearpoint rod．
·A nearpoint card with an isolated line of horizontal 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 patient’s habitual or induced near correction and be set for the patient’s near PD．
·Place the near vergence target under good illumination on the nearpoint rod at 40 cm．
·The Risley prisms, set to 0, should be positioned before both eyes so that vertical prism may be introduced (see Figure 4-12)．
STEP-BY-STEP PROCEDURE
1．Ask the patient to open both eyes and report what he sees．He should see one clear image．
2．Instruct the patient to look at the line of letters and to tell you when it doubles．
3．At about 1 prism diopter per second introduce base prism before the right eye (right infravergence)．
4．Note the amount of base prism before the right eye at the break point．
5．Overshoot the break point slightly by adding a little more prism in same direction．
6．Instruct the patient to tell you when the target becomes single again．
7．Reduce the prism until the patient reports the target is single．This is the recovery point．Note the amount of base prism before the right eye．
8．Repeat steps 2 through 7 starting with base down prism over the right eye (right sravergence)．
RECORDING
·Record the technique and the distance at which it was performed (distance or near)．
·Record the eye over which the prism was introduced, the orientation of the prisms (BU and BD)，and the corresponding results．Each result should contain two values, break and recovery．
·If recovery values are in the direction opposite to what you expect, record the value as a negative value．
EXAMPLES
·Vertical vergences (near) OD：infra 4/2，sra 2/-1
·Vertical vergences (near) OD：BU 6/4，BD 3/1
EXPECTED FINDINGS
·Break： 3Δ to 4Δ
·Recovery: 1.5Δto 2Δ
·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 any vertical heterophoria that may exist． |
