The influence of the width of a full-thickness macular hole on preoperative visual acuity and its role for the intraoperative approach and closure rate were analysed in a prospective study. For 47 patients with a full thickness macular hole, a precise analysis of the central retina was performed with SD-OCT. An SF-gas-air mixture was used, with a lower concentration (15 %) for smaller holes ≤ 400 µm (group 1, n = 17) and a higher concentration (30 %) for larger holes > 400 µm (group 2, n = 30). Besides preoperative visual acuity, postoperative IOP fluctuations and closure rate were reviewed. The mean hole width with SD-OCT was 419 ± 155 µm, with a significant negative correlation with preoperative visual acuity (r = - 0.56, p = 0.002). In the first group, mean early postoperative IOP was 23 mmHg and in the second group 33 mmHg (p< 0.001). Thus, for small macular holes, early postoperative IOP decompensation from gas expansion in the eye could be minimised. The closure rate was 90 %, with no significant difference between the two groups (p > 0.05). Determining the width of a macular hole with SD-OCT is an important indicator for the necessary endotamponade. Using a lower gas concentration (15 %) for smaller holes (≤ 400 µm) to prevent postoperative IOP fluctuations does not negatively influence closure rates.