A novel approach using a polarized nonius test to evaluate the near point of convergence

Purpose

This study aims to evaluate the efficacy of a new method for measuring the near point of convergence (NPC) using a Nonius polarized target stimulus, comparing its sensitivity in detecting convergence ability to that of traditional approaches.

Methods

In this prospective study, 65 participants underwent near point of convergence (NPC) measurements using three methods: an accommodative target (NPC1), a penlight with a red filter (NPC2), and a Nonius polarized target (NPC3). Participants also completed the Convergence Insufficiency Symptom Survey (CISS). Statistical analyses, including repeated-measures ANOVA and Spearman’s correlation, were conducted to assess differences among the methods.

Results

The Nonius method demonstrated a median break point of 8.37 cm, significantly higher than the other methods, NPC1: 6.63 cm, and NPC2: 7.17 cm. Sensitivity for detecting CI symptoms was 92.6 % for the NPC3, which outperformed NPC1 (77.8 %) and NPC2 (74.1 %). NPC3 exhibited low specificity (7.4 %). Correlations between NPC measurements and CISS scores were weak and nonsignificant, though the strongest correlation was observed for NPC3

Conclusion

The Nonius polarized target method shows benefits compared to traditional methods in measuring NPC. This study provides a more sensitive method to measure convergence ability, reducing variability across clinical settings, and enhancing the reliability of assessments in both research and practice.