The effect of posture on the intraocular pressure and pulsatile ocular blood flow in patients with non-arteritic anterior ischaemic optic neuropathy

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Abstract
Intraocular pressure (IOP) and pulsatile ocular bloodflow (POBF) have been recorded in 15 patients with unilateral non-arteritic anterior ischaemic optic neuropathy (na-AION) and in 28 healthy subjects of comparable age. Measurements were obtained in both the upright and lying postures with a pneumotonometer linked to a Langham ocular bloodflow system. By comparison with the healthy subjects, patients with na-AION were found to have a significantly greater postural pressure change in IOP (3.9 ± 0.4 mmHg in the affected eye and 3.6 ± 0.6 mmHg in the unaffected eye of the patients with na-AION compared to 2.2 ± 0.4 mmHg in the right eye of the healthy subjects P<0.01 and <0.05 respectively). There was no significant difference between the IOP in the affected and unaffected eyes of patients with na-AION nor between this group and the healthy subjects in either posture. Pulsatile ocular bloodflow measurements were similar in both groups and in both eyes of the patients with na-AION. In both groups POBF fell significantly on lying down (healthy right eyes −84 ± 16 ul/min p<0.01, na-AION affected eye −84 ± 24 ul/min p<0.01, unaffected eye −83 ± 26 ul/min p<0.001). These figures represent decrements of 19% in all groups. These findings suggest that assumption of the supine posture may be associated with a reduction in the pulsatile component of ocular perfusion. The importance of this in the pathogenesis of na-AION is discussed.