Abnormal intraocular pressure Low intraocular pressure 2019-06-12T10:37:45Z An abnormal decrease of the pressure within the eye. Ocular hypotony Ocular hypotony is defined statistically as an intraocular pressure (IOP) of less than 6.5 mmHg, three standard deviations below the mean. Clinically significant hypotony is when the IOP is so low that there is resultant visual loss. Hypotony has also been described as low pressure in an individual eye, leading to functional changes and structural changes.