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Aims: To characterise changes in ocular dimensions after combined cataract operation and trabeculectomy with mitomycin C using separate incisions (combined operation). Methods: 24 consecutive eyes that had combined operation and 16 eyes that had cataract operation alone were enrolled. The axial lengths before and after operations were determined with non-contact optical coherence biometry. The intraocular pressures (IOP), axial lengths, corneal curvatures, and the expected and observed refractive errors before and after operations were compared. Results: After a combined operation, mean IOP was significantly reduced from 16.6 (SD 5.8) mmHg to 10.9 (4.1) mmHg (p,0.00001), and mean axial length was significantly shortened from 24.10 (0.98) mm to 23.98 (0.96) mm (p,0.00001). The mean axial length reduction after combined operation (117 (57) mm) was significantly larger than the reduction after cataract operation alone (75 (38) mm, p,0.02), and correlated significantly with the postoperative IOP (p,0.002). There was a mean with the rule surgically induced corneal astigmatism of 0.44 (0.83) dioptre by vector analysis, and a significant increase of mean keratometry reading of 0.23 (0.46) dioptre after a combined operation. However, there was no significant difference between the expected and observed refractive errors. Conclusions: Despite an alteration of the axial length and corneal curvature, the refractive outcome after