Influence of target type and RAF rule on the measurement of near point of convergence
Article first published online: 11 JAN 2007
Ophthalmic and Physiological Optics
Volume 27, Issue 1, pages 22–30, January 2007
How to Cite
Adler, P. M., Cregg, M., Viollier, A.-J. and Margaret Woodhouse, J. (2007), Influence of target type and RAF rule on the measurement of near point of convergence. Ophthalmic and Physiological Optics, 27: 22–30. doi: 10.1111/j.1475-1313.2006.00418.x
- Issue published online: 11 JAN 2007
- Article first published online: 11 JAN 2007
- Received: 28 April 2005 Revised form: 4 December 2005, 24 February 2006 Accepted: 26 February 2006
- near point of convergence;
- RAF rule
Purpose: 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.