Effect of Working Distance on Wesson Card Fixation Disparity and Its Clinical Predictors in Symptomatic Patients.

Abstract

Aim: Fixation disparity (FD) is a sensitive marker of binocular vision stress and is often assessed in patients with asthenopia. Working distance alters accommodative and vergence demands. However, its effect on FD under routine clinical settings is not well established.

Purpose: To investigate the effect of working distance on FD measured using the Wesson fixation disparity card (WFDC) at 25 cm and 40 cm in symptomatic young adults, and to explore associations with selected binocular vision and accommodative measures.

Methods: A cross-sectional study was conducted on 25 symptomatic participants aged 18-25 years. FD was measured at 25 cm and 40 cm using the WFDC under standard clinical conditions. Binocular vision and accommodative assessments included near phoria, near point of convergence (NPC), accommodative response (MEM), amplitude of accommodation, and stereoacuity. Paired t-tests were used to compare FD between distances. Agreement was assessed using Bland-Altman analysis and intraclass correlation coefficients (ICC), and associations were explored using correlation analysis.

Results: Mean FD was -3.76 ± 6.63 arcmin at 25 cm and -4.78 ± 7.20 arcmin at 40 cm, with no significant difference between distances (p = 0.20). A strong positive correlation (r = 0.84) and good agreement (ICC = 0.84) were observed, although the limits of agreement were relatively wide. No significant associations were found between FD and clinical measures.

Conclusion: FD is a sensitive indicator of binocular stress, often assessed in asthenopic patients. While working distance affects accommodation and vergence demands, its impact on FD in clinical practice remains unclear.