Abstract
Objective: To assess the frequency and pattern of color vision defects in tuberculosis patients receiving ethambutol therapy and to evaluate the effectiveness of commonly used color vision tests.
Methodology: This cross-sectional study was conducted at the Tuberculosis unit of the University of Lahore Teaching Hospital over eight months. A total of 296 newly diagnosed tuberculosis patients aged 20-75 years with normal baseline visual acuity were enrolled. Color vision was assessed using Ishihara plates and Farsworth Munsell D-15 test at baseline and during follow-up visits. Follow-up examinations were conducted at 3rd and 6th months (first and second follow-ups, respectively) after the initiation of ethambutol therapy
Results: Color vision abnormalities were observed in 22(7.4%) patients, with deuteranopic defects being the most common (68.2%), followed by protanopia (22.7%) and tritanopia defects (9.1%). Most defects developed within the first three months of therapy and were generally mild and symmetrical. No significant association was found with age or gender (p>0.05). At follow-up, an increasing trend in color vision impairment was noted, although no significant loss of visual acuity or structural optic nerve changes were observed.
Conclusion: Ethambutol therapy is associated with early, predominantly red-green color vision defects, which may serve as sensitive indicators optic nerve toxicity. Routine color vision screening, particularly with more sensitive tests like Farnsworth D-15, is recommended for early detection and prevention of irreversible visual damage.

Key words: Color vision defects, tuberculosis, optic nerve.