Dimensions of the Neural Canal at the Optic Nerve Head in Non-arteritic Ischemic Optic Neuropathy Compared to Normal Subjects

Abstract

 

Purpose:

 

To compare neural canal dimensions at the optic nerve head between patients with non-arteritic anterior ischemic optic neuropathy (NAION) and normal subjects using enhanced depth imaging optical coherence tomography (EDI OCT).

 

Methods:

 

Patients with NAION and normal subjects were prospectively recruited. Complete ophthalmologic examinations were performed including horizontal and vertical serial EDI OCT of the optic nerve head for the eye with NAION and for one randomly selected eye of normal subjects. Horizontal and vertical diameters of the optic disc, Bruch’s membrane opening (BMO), lamina cribrosa, and narrowest neural canal opening (NCO) were measured from EDI OCT cross-sectional images (Figure A and B) and compared between NAION patients and normal subjects. The narrowest NCO was determined by review of serial EDI OCT images.

 

Results:

 

Sixteen eyes from 16 patients with NAION (10 women; mean age, 61±13 yrs) and 43 eyes from 43 normal subjects (21 women; mean age, 44±15 yrs) were included. In the NAION group, corrected visual acuity ranged from counting fingers at 6 inches to 20/20, and 24-2 visual field mean deviation of 13 eyes was -16.3±11.1 dB (three eyes had Goldmann perimetry because of poor vision). All neural canal dimension measurements (horizontal and vertical diameters of the optic disc, BMO, lamina cribrosa and narrowest NCO) showed excellent measurement reproducibility (intraclass correlation coefficient: 0.921-0.972). Mean horizontal and vertical diameters of the optic disc, BMO, and narrowest NCO were smaller in NAION patients compared to those in normal subjects, but their differences did not reach statistical significance, both before and after controlling for age and gender (all P>0.1; Table). Mean horizontal and vertical diameters of the lamina cribrosa were significantly smaller in the NAION group compared to those in the normal group, both before and after controlling for age and gender (all P<0.001; Table).

 

Conclusions:

 

Crowding of the neural canal at the lamina cribrosa level may be a risk factor for NAION and play a role in its pathophysiology.  

 

Keywords: imaging/image analysis: clinical • neuro-ophthalmology: optic nerve • neuro-ophthalmology: diagnosis