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

J Optom. 2025 Jul-Sep;18(3):100563. doi: 10.1016/j.optom.2025.100563. Epub 2025 Jun 13.

ABSTRACT

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.

PMID:40516220 | PMC:PMC12205783 | DOI:10.1016/j.optom.2025.100563