Abstract
Purpose :
Primary open-angle glaucoma (POAG) with normal intraocular pressure (IOP) has been proposed to be caused by repetitive stress on the optic nerve (ON) when it becomes tethered during adduction, and is more common in East Asians than Caucasians. We hypothesized that variations in globe and orbital dimensions may influence stress concentration on the globe-optic nerve (ON) junction during adduction.
Methods :
Surface coil magnetic resonance imaging was employed to collect axial images of the orbits of 22 normal controls (Male: 8, Female:14, 59.2±13.4 yrs) and 23 POAG patients (Male: 7, Female:16, 63.7±10.4 yrs) with IOP never exceeding 21mmHg. Globe equatorial diameter, axial length (AL), and orbital length (OL) from globe center to orbital apex were measured to specify individualized mesh models of the globe and ON. FE simulations were repeated performed in each of 45 individual cases using 6° additional adduction from an initial 26° adducted configuration employing identical average human tissue material properties and boundary conditions.
Results :
The ratio of OL to AL ratio in subjects with POAG was 1.46±0.20 (±SD) was significantly less than in controls at 1.59±0.20 (P=0.005). FE simulations showed that stresses caused by adduction tethering were mostly concentrated at the temporal globe-ON junction near the retro-lamina region and peripapillary sclera encircling the optic disc. Subjects with POAG had 44.2±6.0 kPa mean stress in the entire finite element model, significantly higher at 40.7±5.2 kPa than normal subjects (P=0.022). Mean stress on the peripapillary ring was 34.0±4.9 kPa for POAG, significantly greater than 30.6±4.2 kPa for normal subjects (P=0.008). However, the mean stress on the optic disc was similar (P=0.4) for both POAG (15.3±1.4 kPa) and controls (15.3±1.7 kPa).
Conclusions :
Subjects with POAG at normal IOP tend to have shorter orbits relative to globe axial lengths than healthy subjects. These morphological characteristics are predicted to cause higher stress on the globe-ON junction when ON tethers during adduction.
This is a 2021 ARVO Annual Meeting abstract.