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The relationship between clinical measures of visual function and their impact on patients' perception of their visual functioning is not fully understood. Gothwal and co-workers evaluated the impact of glaucoma on visual functioning in a South-Indian population using the Glaucoma Quality of Life-15 (GQL-15) questionnaire. Through Rasch analysis, the GQL-15 was pared down to a valid and reliable ten-item questionnaire that captures a single underlying construct in this population: vision-related activity limitation. This was named the Glaucoma Activity Limitation-10 (GAL-10) questionnaire and was correlated with measures of visual functioning in patients with mild, moderate and severe visual field loss. Rasch analysis allows for such correlations through the transformation of questionnaire outcomes from ordinal to interval scale. Multivariate models showed that income and visual field severity were significantly associated with glaucoma-specific visual functioning. Patients in the lower income group and those with severe visual field loss had poorer visual functioning compared with patient in the higher income group and those with mild visual field loss, respectively. Patients with mild visual field loss, however, did report functioning difficulties on the GAL-10 questionnaire. This challenges the common assumption that glaucoma patients are unaware of vision-related symptoms in the early stages of the disease. It is unclear whether the mild reductions in visual field extent are responsible for the functioning difficulties on the GAL-10, or whether these difficulties are due to deficits in other visual functions such as contrast sensitivity. Indeed, visual functioning difficulties on the GAL-10 were significantly correlated with deficits in visual acuity and contrast sensitivity. The significant scatter observed in each of these relationships complicates the interpretation of the results. Finally, the results of this study are consistent with others obtained from studies conducted in the Western world, and show increasingly worse visual functioning with increases in visual field loss.