AIM: To observe morphological optic disc characteristics in patients with preclinical diabetic retinopathy (DR) associated with chronic angle-closure glaucoma (CACG). METHODS: Twenty-two cases (43 eyes) of preclinical DR associated with CACG were enrolled in group A; 24 preclinical DR cases (46 eyes) were enrolled in group B; 26 CACG cases (51 eyes) were enrolled in group C; and 49 normal controls (49 eyes) were enrolled in group D. All underwent optical coherence tomography to measure the horizontal C/D ratio (HCDR), C/D area ratio (CDaR), vertical C/D ratio (VCDR), rim area (RA), cup volume (CV), disc area (DA) and average retinal nerve fiber layer (RNFL) thickness. RESULTS: The ages of groups A, B, C, and D were 67.60±3.36, 66.78±3.33, 65.98±3.83, and 67.54±3.17y, respectively. The HCDR values in groups A, B, and C were distinct relative to those in group D (P<0.0001, P<0.01, and P<0.05, respectively). The HCDR values in group A were higher compared with those in groups B (P<0.0001) and D (P<0.0001); while these values were virtually identical statistically between groups A and C (P>0.05). The CDaR values in group A were higher in comparison to those in groups B and D (P<0.0001 in both groups); while these values were virtually identical statistically between groups A and C (P>0.05). The RA values in group A were smaller relative to those in groups B and D (P<0.0001 in both groups); while groups A and C were not distinct statistically (P>0.05). The CV values in group A were greater in comparison to those in groups B and D (P<0.0001 in both groups); while groups A and C were not distinct statistically (P>0.05). DA was not distinct for comparisons of two groups among the four groups (P>0.05). HCDR value correlated with mean nasal RNFL thickness (r=-0.909, P<0.0001), mean superior RNFL thickness (r=-0.866, P<0.0001), mean inferior RNFL thickness (r=-0.650, P<0.001) and mean temporal RNFL thickness (r=-0.562, P<0.01) in group A. CONCLUSION: The HCDR was a sensitive morphological parameter in detecting structural visual disc changes in preclinical DR associated with CACG, which can reflect optic nerve damage caused jointly by CACG and diabetes. A higher HCDR may predict optic nerve atrophy.