In vivo Assessment of Retinal Nerve Fiber Layer by CSLO, SLP, and OCT in Rhesus Monkeys With Idiopathic Bilateral Optic Atrophy

Abstract

 

Purpose:

 

Bilateral optic atrophy (BOA) in rhesus monkeys was reported recently and characterized by electrophysiological functional testing, clinical fundus examination, photography, and histopathology. The purpose of this study is to measure retinal nerve fiber layer thickness(RNFL) and optic disc parameters using confocal scanning laser ophthalmoscopy (CSLO), scanning laser polarimetry (SLP), and optical coherence tomography (OCT). These measures are used to test the hypothesis that retinal ganglion cell (RGC) axon loss is limited to the papillomacular bundle in this condition (versus being diffuse).

 

Methods:

 

RNFL and optic disc measurements were obtained, using a GDx–VCC, an OCT–Stratus, and an HRT1. Of 9 monkeys previously documented with BOA, SLP and OCT data were available for 4 and CSLO data for all nine. SLP and OCT data were compared with data from 4 controls, CSLO data against 57 controls. CSLO parameters evaluated included the cup disc area ratio (CDAR), rim volume (RV), and RNFL. RNFL was also measured by SLP and OCT, total retinal thickness (RT) by OCT. Data were pooled and compared by quadrant for temporal (T), superior (S), nasal (N), and inferior (I) using the Mann–Whitney U Test.

 

Results:

 

Each imaging device detected significant differences between BOA and control eyes. Table 1 shows that the T quadrant RNFL was most consistently affected, with less prevalent effects in S and I quadrants. There were no RNFL or total RT differences for the N quadrant. However, there were significant differences in the optic disc parameters RV and CDAR for the N quadrant.

 

Conclusions:

 

These results support previous findings in rhesus macaque monkeys with BOA by demonstrating loss of RGC axons manifest as decrease RNFL and loss of optic disc neural rim tissue. While the temporal quadrant was most severely and consistently affected, and normal RNFL and total RT were found in the nasal quadrant, there was loss in the optic disc neural rim tissue as measured using CSLO suggesting that some degree of diffuse loss may occur in this condition. This result awaits further analysis via histopathology and future structural imaging.  

 

Keywords: imaging/image analysis: clinical • nerve fiber layer • optic disc