A prospective study of different test targets for the near point of convergence

To determine whether different test targets including an accommodative target (AT), a transilluminator (TR), and a transilluminator with a red lens (RL), affect the near point of convergence (NPC) value; and to determine which test target is most sensitive to identify convergence insufficiency (CI) in young adults.

Subjects were 36 optometry students from the Illinois College of Optometry, including 18 subjects with normal binocular vision (control group) and 18 subjects with CI. None of the subjects had accommodative insufficiency. The NPC break and recovery were measured by three methods: AT, TR, and RL. Each test method was administered by a different examiner and the test sequence was randomized.

The mean NPC break values for AT, TR, and RL in the control group were 4.31, 3.76, and 4.08 cm respectively, compared to 10.05, 11.37 and 13.04 cm in the CI group. The mean recovery values were 6.23, 5.56, and 5.95 cm for AT, TR, and RL respectively in the control group, vs 12.21, 14.37, 16.40 cm in the CI group. Significant differences in NPC break and recovery values were detected in the CI group between RL and AT, but not between AT and TR, or TR and RL. There was no significant difference in NPC values using the three targets in the control group. For an NPC cut point of 6 cm (break) and 9 cm (recovery), RL had higher sensitivity (100%) and specificity (88.9%) as well as lower false positive (10%) and false negative (0%) values compared to AT.

NPC with RL is a more sensitive method to identify abnormal findings and assist in diagnosing CI compared to using AT or TR. We recommend that NPC with RL be routinely used to evaluate patients suspected of having CI.