Optic Nerve Head Morphological Changes Over 12 Hours in Seated and Head-Down Tilt Postures

Area of Science:

• Ophthalmology
• Neuroscience
• Biomechanics

Background:

• Optic nerve head (ONH) morphology is crucial for visual function.
• Daily changes in ONH structure and their influencing factors are not fully understood.
• Understanding these changes is vital for diagnosing and managing optic neuropathies.

Purpose of the Study:

• To investigate diurnal changes in ONH morphology.
• To compare ONH changes in seated versus 6° head-down tilt (HDT) postures over 12 hours.

Main Methods:

• 30 healthy subjects underwent Optical Coherence Tomography (OCT) scans every 2 hours for 12 hours.
• Measurements included Bruch's membrane opening-minimum rim width (BMO-MRW), retinal thickness, and RNFL thickness.
• Intraocular pressure (IOP) and optic nerve sheath diameter (ONSD) were also monitored.

Main Results:

• A significant decrease in BMO-MRW (average 9.55 µm) was observed over 12 hours in the seated position, more pronounced in females.
• Retinal thickness and RNFL thickness also showed modest decreases.
• In HDT posture, IOP and ONSD increased, but BMO-MRW thinning was prevented.

Conclusions:

• Neuroretinal rim thinning occurs throughout the day in healthy individuals, unrelated to IOP or ONSD.
• Head-down tilt posture mitigates diurnal ONH thinning, suggesting translaminar pressure influences ONH structure.