Purpose: To compare the optic nerve head appearance in glaucomatous eyes before and after marked reduction of intraocular pressure (IOP). Methods: The hospital-based observational case-series study included selected glaucoma patients for whom optic disc photographs taken before and 1week to 5months after surgical reduction of IOP were morphometrically examined. Results: The study included 23 eyes of 16 patients (mean age: 28.76.0years). Mean preoperative IOP was 31.6 +/- 7.7mmHg (22-52mmHg), and mean IOP drop was 21.5 +/- 8.4mmHg (11-45mmHg). The horizontal disc diameter decreased significantly (p<0.001) after surgery, while the vertical disc diameter did not change markedly (p=0.54). The width of the neuroretinal rim increased significantly in all disc quadrants (all p-values0.01), optic cup depth decreased (p<0.001), and reflectivity of the inner retinal surface increased significantly (p<0.001). Some eyes showed a pronounced reduction in beta zone of parapapillary atrophy parallel to an increase in horizontal disc diameter, and some eyes showed an enlargement of beta zone parallel to a reduction in horizontal disc diameter. Conclusions: After marked reduction of high IOP, some eyes of young adult patients with glaucoma can show a horizontal shrinkage of the optic nerve head, in addition to a partial restoration of the neuroretinal rim and a flattening of the optic cup. In addition, beta zone of parapapillary atrophy can decrease or increase, complementarily to changes in the horizontal disc diameter. These findings may be of interest for the biomechanics of the optic nerve head and the precision of imaging techniques.