Abstract
Purpose :
Neonatal retinal hemorrhage is a common finding in newborns that is observed in 2.6 - 50% of live births, but the underlying mechanism is not fully understood. This study utilized a computer simulation to evaluate the biomechanical events in the eye and orbit that occur during uterine contractions and passage of the head through the birth canal. Analysis of resultant stress and pressure may provide insight into the pathophysiology of neonatal retinal hemorrhage.
Methods :
A finite element computer model of the eye, optic nerve, bony orbit, and orbital fat was simulated and subjected to cyclic compressive forces that mimicked rises in intracranial pressure (ICP) associated with maternal contractions during normal vaginal delivery. Resulting changes in intraocular pressure (IOP), pressure in the optic nerve sheath, and stress within the sclera and retina were measured.
Results :
During contractions, increased ICP was transmitted into the orbit and exerted pressure on the globe and optic nerve sheath. IOP rose by 7.6 kPa near the posterior pole but only by 4.1 kPa and 4.0 kPa in vitreous at the center and periphery, respectively. Pressure in the center of the optic nerve sheath rose by 32.0 kPa and up to 134.0 kPa at its junction with the sclera. Stress in the retina was highest near the optic disk and reached 13.9 kPa in the preretinal layer and 13.0 in the intraretinal and subretinal layers. Stress in the sclera peaked at 298.7 kPa.
Conclusions :
Simulation results suggested that increased ICP and extracranial pressure increase risk of neonatal retinal hemorrhage through multiple factors. Increased intraorbital pressure distorts ocular anatomy and applies force to the retina; deformation and stress may cause rupture of retinal vasculature. Increased pressure within the optic nerve sheath may compress its contents and cause occlusion of the central retinal vein, resulting in venous outflow obstruction and ultimately rupture. Concentration of forces near the optic disk likely accounts for the tendency of neonatal retinal hemorrhage to occur posteriorly. The role of ICP in neonatal retinal hemorrhage is consistent with lower incidence in Cesarean section, in which ICP rises less, and higher incidence in forceps- or vacuum-assisted delivery, which may increase ICP further.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.