Influence of target type and RAF rule on the measurement of near point of convergence.
OBJECTIVE
This study was designed to investigate if the use of different target types or the RAF rule affected the measurement of near point of convergence (NPC).


METHODS
The subjects comprised three groups: (1) 20 children aged 6-9 years (2) 17 children aged 11-13 years (3) 14 adults aged 20-30 years. Five targets were used to measure the NPC: (1) pencil tip, (2) fingertip, (3) penlight, (4) N5 letter and (5) vertical line target on the RAF rule.


RESULTS
There was no significant difference in NPC measurements between the pencil tip, fingertip and N5 target in free space. The penlight resulted in significantly more remote NPC break and recovery points compared with the fingertip and pencil tip (p < 0.05). The RAF rule influences the NPC obtained (p < 0.001). The greatest difference in NPC measurements was observed when comparing the RAF line target and the finger in free space; the former resulted in NPC values of 1.9 times (95% CI 1.6-2.2 times) as much as those obtained with the finger.


CONCLUSIONS
Use of the penlight and RAF rule resulted in a more distant NPC break point compared with other targets. The effect of the RAF rule was more apparent for more receded NPC points.
Adler
Paul M
PM
paul.adler@eyezine.co.uk
Cregg
Mary
M
Viollier
Ann-Julie
AJ
Margaret Woodhouse
J
J
D000328:Adult; D000367:Age Factors; D002648:Child; D003290:Convergence, Ocular; D004867:Equipment Design; D006801:Humans; D012680:Sensitivity and Specificity; D014787:Vision Tests / Q000295:instrumentation* / Q000379:methods