Impact of acute intraocular pressure elevation on the visual acuity of non-human primates

Glaucoma is the leading cause of irreversible blindness worldwide and elevated intraocular pressure (IOP) is an established risk factor. Visual acuity, the capacity for fine analysis of spatial frequency (SF) information, is relatively preserved in central vision until the later stages of chronic glaucoma. However, for acute glaucoma that is associated with sharp IOP elevation, how visual acuity is affected by acute IOP elevation remains unclear.

Using intrinsic-signal optical imaging of large areas of visual cortices V1 and V2 in seven rhesus macaques, visual acuity was directly examined during acute IOP elevation at 70 mmHg, a pressure often observed in acute angle-closure glaucoma. Acute IOP elevation was achieved by reversible monocular anterior chamber perfusions, and visual acuity was quantified by cortical population responses to various SFs ranging from 0.5-6 cycles/°.

Acute IOP elevation particularly depressed the ability of the visual cortex to register fine details (at high SFs referring to visual acuity), an effect that was progressively more severe toward the central visual field. These results completely contrast with long-term impairments present in chronic glaucoma.

Our results show that impairment of fine visual discrimination within the central visual field is the principal consequence of sharp IOP elevation, implicating relatively greater dysfunction in parvocellular pathways. This study provides direct cortical neural evidence for the immediate visual acuity impairment in acute glaucoma patients. FUND: National Natural Science Foundation of China, Chinese Academy of Sciences, Shanghai Committee of Science and Technology, and Shanghai Municipal Health Commission.