Abstract
Purpose :
An association between diffusion tensor imaging (DTI)-derived fractional anisotrophy (FA) and retinal nerve fiber layer (RNFL) thickness has been documented and may be used to suggest clinical severity of glaucoma. However, the time progression of these parameters is poorly understood. The current study tracked the progression of RNFL thinning and optic nerve degeneration in an experimental macaque model of glaucoma and tested 0.1% brimonidine (BR) in this model.
Methods :
Elevated intraocular pressure (IOP) was induced in one eye by laser photocoagulation in 12 macaques. Ophthalmic tests (IOP, OCT and MRI-DTI) were performed between 1-8 weeks following photocoagulation. Animals received either artificial tears (AT) or BR twice a day for 7 weeks after photocoagulation.
Results :
In the AT-treated group, beginning 1 week following photocoagulation, the mean (±SEM) IOP in the glaucomatous eye was elevated (54.0±7.2 mmHg), compared to the normal, contralateral eye (16.9±0.9 mmHg), and was significantly increased for the duration of the study. By contrast, 2 hr. after administration, BR transiently lowered IOP of the glaucomatous eye, with a maxmum decrease of 16.3 mmHg.
In AT-treated macaques, RNFL thickness in the glaucomatous eye was significantly decreased compared to the contralateral eye beginning three weeks after photocoagulation. RNFL thickness of glaucomatous eye decreased compared to the contralateral eye (area under the curve (AUC)) by 27.3%. Brimonidine treatment reduced RNFL thinning in the glautomatous eye—RNFL thickness was 12.8%.
Significantly decreased FA was observed beginning two weeks following photocoagulation, prior to significant changes in RNFL thickness. FA of the glaucomatous eye with BR treatment was not significantly decrease compared to the contralateral eye during the study period. Decreases in FA in the glaucomatous eye during treatment with AT and BR was 22.2% and 10.5%, respectively.
Conclusions :
Long-term ocular hypertension causes retinal degeneration--RNFL thinning in particular. Mesurable changes in FA occurred well before changes in RNFL thickness, suggesting that DTI could be used for early detection of disease progression of clinical glaucoma. Brimonidine appeared to show neuroprotective activity in macaques with experimentally induced glaucoma.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.