Abstract
Purpose :
Previous anatomic studies (e.g., Nork et al. Arch Ophthalmol 2000) suggested that EG and axotomy have similar inner but different outer retinal effects. To investigate if this difference could be measured in vivo, we compared the OCT retinal layer thickness values following hemiretinal endodiathermy axotomy (HEA) to EG in macaques.
Methods :
Three rhesus (Macaca mulatta, 2 male, 1 female; 5 and 4 yrs, respectively) monkeys and one cynomolgus (Macaca fascicularis, female, 11 yrs) monkey underwent HEA on the inferior retina in their right eyes as previously described (Dashek et al. IOVS 2013). Seven cynomolgus monkeys (7 male, 9-11 yrs) had laser trabecular meshwork destruction to induce EG in the right eye. Cross-sectional OCT retinal volume scans (Heidelberg Spectralis) at baseline and 12 weeks post HEA, and 5 to 7 months post intraocular pressure (IOP) elevation in the EG animals were compared. Retinal layer segmentation was adjusted manually (due to inaccuracies in automated segmentation) to delineate six retinal layers (nerve fiber, NF; ganglion cell, GC; inner plexiform, IP; inner nuclear, IN; outer plexiform, OP; and outer nuclear, ON). Statistical significance was determined using two-sided paired t tests.
Results :
Weekly IOP measures in EG monkeys had a mean of 52 mm Hg (SD=11) in the right eye with a minimum of 33 and a maximum of 63 mm Hg. Segmentation showed significant thickness decreases in inner retinal layers (NF, GC, IP) in inferior retinas following HEA (p < 0.0002) as well as in EG eyes (p < 0.0001). A moderate (not statistically significant) increase was found in the IN for both groups, which may be due to observed microcystoid macular degeneration. Although no significant difference was found in the thickness of outer retinal layers in the HEA eyes, there was an increase in these layers in EG eyes (p < 0.0008).
Conclusions :
Despite similar decreases in inner retinal layer thickness in both HEA and EG, only EG eyes show increased outer retinal layer thickening. These in vivo results agree with the Nork et al., 2000 histological study. The present study affirms that OCT is a sensitive tool for detecting changes in retinal thickness indicative of experimental glaucoma. However, the labor-intensive nature of manual correction of automated segmentation may limit OCT for monitoring human glaucoma.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.