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Y. Pang, H. Gabriel, F. Saeed, K. Frantz; A Prospective Study of Different Test Targets for the Nearpoint of Convergence. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5881.
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Nearpoint of convergence (NPC) is an important measurement in the assessment of convergence insufficiency (CI). The most common method used in clinic to measure NPC is with an accommodative target (AC); however, CI subjects may use extra accommodation to achieve the vergence demand when tested with an AC and this may result in falsely normal NPC values. The purpose of this study is to determine whether NPC measured with a transilluminator (TR) or transilluminator with a red lens (RL) will be a more sensitive method to identify CI subjects than using an AC.
Subjects were 32 optometry students from the Illinois College of Optometry, including 16 subjects with normal binocular vision (control group) and 16 subjects with CI. None of the subjects had accommodative insufficiency. The NPC was measured in three ways: AC, TR, and RL. Each test method was performed by a different examiner and the test sequence was randomized. Statistical analysis was performed using Student’s t-test and one-way analysis of variance.
NPC break value (means in cm) with RL was more receded than NPC with AC (RL: 13.46, AC, 10.30; difference: 3.16) in the CI group, verses not receded in the controls (RL: 4.01, AC, 4.26; difference: -0.25). The difference between those two methods was significant between the CI and control groups (P=0.0014). The same trend was found for the difference in NPC recovery value with RL and AC (P=0.0001, CI vs. control). The difference in NPC break with TL and AC showed no statistically significant difference between the CI and control group (P=0.052); however, the difference in NPC recovery with TL and AC was significant (P=0.004, CI vs. control).
NPC with red lens is more receded than NPC with accommodative target in the CI group, possibly due to extra accommodative vergence when tested with accommodative target. Additionally, there was no significant difference between those two test methods in normal subjects, which further indicates that NPC with red lens is a more sensitive test to identify CI subjects than NPC with accommodative target. Our results were different from previous reports.
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