PURPOSE. To investigate the characteristics of the prelamina and lamina cribrosa (LC) of both eyes in glaucoma patients with unilateral visual field (VF) defect. METHODS. Forty-one subjects diagnosed with primary open-angle glaucoma with unilateral VF loss and 41 age-matched healthy control subjects were scanned by swept-source optical coherence tomography (SS-OCT). All eyes were divided into three groups: VF-affected glaucomatous eyes (group A, n = 41), perimetrically unaffected fellow eyes (group B, n = 41), and healthy control eyes (group C, n = 41). The anterior prelaminar depth (APLD) and LC depth (LCD) were measured at the center of the reference line (the Bruch's membrane opening plane). The prelaminar tissue thickness (PTT) was obtained by subtracting the APLD from the LCD. The APLD, LCD, and PTT were compared among these groups. RESULTS. The APLD and LCD were significantly greater in group A than in the other groups (group B, P < 0.001; group C, P < 0.001). The prelaminar tissue was significantly thinner in group A than in the other groups (group B, P = 0.007; group C, P < 0.001). Also, the prelaminar tissue was significantly thinner in group B than in group C (P = 0.003). Multivariate analysis demonstrated a significant association between PTT and initial IOP among the overall study population (P < 0.05). CONCLUSIONS. In the fellow eyes with unilateral glaucoma patients, APLD was significantly greater, and the prelaminar tissue was significantly thinner, than in the healthy control eyes. Our findings suggest that subclinical or preperimetric changes of the LC and/or prelaminar tissue are already present in the fellow eyes with unilateral glaucoma.