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Near Point of Convergence (NPC)
PURPOSE To determine the patient’s ability to converge the eyes while maintaining fusion．
EQUIPMENT
·Penlight or transilluminator．
·Red glass．
·Near accommodative target (reduced Snellen letter taped to a penlight or tongue depressor：four different sizes in the range of 20/25 to 20/200 are needed)．
·Overhead lamp．
Note：The penlight or transilluminator is used as a target for initial screening．The penlight with red glass and the accommodative target are used when the near point of convergence is greater than 7 cm/10 cm or when a complete binocular work is being done．
SET-UP
·The patient wears his habitual near correction．
·The overhead lamp is directed toward the target．
·The penlight(or other target)is held by the examiner at 40 cm．
STEP-BY-STEP PROCEDURE
1．Instruct the patient to look at the light(or other target)and to report how many targets he sees．If the target appears double，move it further from the patient until it appears single before proceeding with the test．
2．Move the target toward the patient，observing the patient’s eyes until the patient reports that the target appears double or until you see one eye lose fixation on the target．Note the distance from the patient’s eyes at which the patient reports that the target doubles or at which you note that the patient loses bifixation．This is the break point．
3．Move the target away from the patient’s eyes and note the distance at which the patient’s deviated eye regains fixation．The patient will report single vision at this distance if he reported diplopia in step 2．This is the recovery point．
4．If break and recovery are closer to the patient than 7 cm, record the results. If the NPC is greater than 7 cm record the results and then repeat the test using the penlight with a red glass placed over the patient’s right eye．Then repeat the NPC a third time using an accommodative target．
RECORDING
·Record NPC and sc or cc．
·Record the target used：
“Lite” for penlight
“RG” for penlight with red glass
“Accomm.” for accommodative target
·Record the linear distance(in cm，mm，in，or ft)at which the eye deviated or at which the patient reported diplopia(break)．
·Record the distance in cm，mm，in，or ft at which the eye regained fixation or at which the patient reported single vision(recovery)．
·Record which eye deviate and in which direction, if you were able to make this observation．
·Record diplopia if the patient reported seeing two targets．Record spression if the patient did not report seeing two targets but a break was observed．
·If the examiner was able to move the target to the bridge of the patient’s
nose without the patient’s losing fixation，record TTN(for “to the nose”)．
·Repeat this recording for each target used．
EXAMPLES
·NPC cc lite—TTN
·NPC sc lite 10 cm/12 cm OS out, spression
RG 15 cm/20 cm OS out，spression
accomm．8 cm/10 cm OS out，spression
EXPECTED FINDINGS
Break：3 cm±4 cm
Recovery：5 cm±5 cm
A break point of greater than 7 cm is considered abnormal．The recovery point is expected to be within 10 cm．These figures reflect the mean finding for a normative population plus one standard deviation．It is normal for the patient to report diplopia at the break point． |
