The pressure difference between eye and brain changes with posture

pressure,eye ,brain, posture
Ann Neurol. 2016 Jun 28. doi: 10.1002/ana.24713. [Epub ahead of print]

The pressure difference between eye and brain changes with posture.

Abstract

OBJECTIVE:

The discovery of a posture-dependent effect on the difference between intraocular pressure (IOP) and intracranial pressure (ICP) at the level of lamina cribrosa could have important implications for understanding glaucoma and idiopathic intracranial hypertension and could help explain visual impairments in astronauts exposed to microgravity. The aim of this study was to determine the postural influence on the difference between simultaneously measured ICP and IOP.

METHODS:

Eleven healthy adult volunteers (age 46±10 years) were investigated with simultaneous ICP, assessed through lumbar puncture, and IOP measurements when supine, sitting, and in 9° head down tilt (HDT). The trans-lamina cribrosa pressure difference (TLCPD) was calculated as the difference between the IOP and ICP. To estimate the pressures at the lamina cribrosa, geometrical distances were estimated from MRI and were used to adjust for hydrostatic effects.

RESULTS:

The TLCPD (mm Hg) between IOP and ICP was 12.3±2.2 for supine, 19.8±4.6 for sitting and 6.6±2.5 for HDT. The expected 24-hour average TLCPD on earth- assuming 8 h supine and 16 h upright-was estimated to be 17.3 mm Hg. By removing the hydrostatic effects on pressure, a corresponding 24 h-average TLCPD in microgravity environment was simulated to be 6.7 mmHg.

INTERPRETATION:

We provide a possible physiological explanation for how microgravity can cause symptoms similar to those seen in patients with elevated ICP. The observed posture dependency of TLCPD also implies that assessment of the difference between IOP and ICP in upright may offer new understanding of the pathophysiology of idiopathic intracranial hypertension and glaucoma.

INTERPRETATION:

We provide a possible physiological explanation for how microgravity can cause symptoms similar to those seen in patients with elevated ICP. The observed posture dependency of TLCPD also implies that assessment of the difference between IOP and ICP in upright may offer new understanding of the pathophysiology of idiopathic intracranial hypertension and glaucoma.

Optical Coherence Tomographic Analysis of Retina in Retinitis Pigmentosa Patients

OCT, Retina, retinitis pigmentosa, optical coherence tomography
Ophthalmic Res. 2016 Jun 29. [Epub ahead of print]

Optical Coherence Tomographic Analysis of Retina in Retinitis Pigmentosa Patients.

Abstract

Retinitis pigmentosa (RP) is a progressive inherited retinal disease characterized by nyctalopia, visual field constriction, and reduced full-field electroretinograms. The progressive loss of photoreceptors leads to vision loss at the end stage of RP. The prevalence of RP is approximately 1/4,000. Since it is one of the major causes of visual impairment worldwide, morphological and functional assessments are useful for estimating the retinal structure and function in RP. Optical coherence tomography (OCT) is a well-established method of examining retinal structure in situ, and the obtained images by OCT help to analyze morphological abnormalities. Changes revealed by OCT have provided insights into the pathology of RP as well as for predicting the prognosis of RP. In this review, we present the typical morphological changes in RP and their relationships with visual function in eyes with RP.

Abstract

Retinitis pigmentosa (RP) is a progressive inherited retinal disease characterized by nyctalopia, visual field constriction, and reduced full-field electroretinograms. The progressive loss of photoreceptors leads to vision loss at the end stage of RP. The prevalence of RP is approximately 1/4,000. Since it is one of the major causes of visual impairment worldwide, morphological and functional assessments are useful for estimating the retinal structure and function in RP. Optical coherence tomography (OCT) is a well-established method of examining retinal structure in situ, and the obtained images by OCT help to analyze morphological abnormalities. Changes revealed by OCT have provided insights into the pathology of RP as well as for predicting the prognosis of RP. In this review, we present the typical morphological changes in RP and their relationships with visual function in eyes with RP.