IMPORTANCE Patients often report greater visual difficulties at home than expected from vision testing in the clinic. Such discordance may be owing to worse vision in the home than measured in clinic. OBJECTIVE To compare vision measured between the clinic and home and evaluate factors, including lighting, associated with these differences. DESIGN, SETTING, AND PARTICIPANTS This cross-sectional study conducted from 2005-2009 involved 126 patients with glaucoma and 49 without glaucoma recruited from the Glaucoma and Comprehensive Eye Clinics at Washington University, St Louis, Missouri. Patients underwent clinic and home visits, were aged 55 to 90 years, were consecutively recruited, and met inclusion criteria for this study. A total of 166 eligible patients refused participation. EXPOSURE Participants underwent clinic and home visits randomized to order of completion. At each visit, masked and certified examiners measured binocular distance visual acuity (DVA) with a nonbacklit chart, near visual acuity (NVA), contrast sensitivity (CS), CS with glare, and lighting. MAIN OUTCOMES AND MEASURES Differences in vision between the clinic and home. RESULTS The mean scores for all vision tests were significantly better in the clinic than home for participants with and without glaucoma (P < .05, matched-pair t tests). For DVA, 29% of participants with glaucoma read 2 or more lines better in the clinic than home and 39% with advanced glaucoma read 3 or more lines better. For the entire sample, 21% of participants read 2 or more lines better in the clinic than home for NVA and 49% read 2 or more triplets better in the clinic for CS with glare. Lighting was the most significant factor associated with differences in vision between the clinic and home for DVA, NVA, and CS with glare testing (P < .05, multiple regression model). Median home lighting was 4.3 times and 2.8 times lower than clinic lighting in areas tested for DVA and NVA, respectively. Home lighting was below that recommended in 85% or greater of participants. CONCLUSIONS AND RELEVANCE Vision measured in the clinic is generally better than vision measured at home, with differences mainly owing to poor home lighting. Knowledge that vision discrepancies between patient report and clinical testing may be owing to home lighting may initiate clinician-patient discussions to optimize home lighting and improve the vision of older adults in their homes.