Morphological changes in the visual pathway induced by experimental glaucoma in Japanese monkeys

Area of Science:

• Ophthalmology
• Neuroscience

Background:

• Glaucoma is a leading cause of irreversible blindness worldwide.
• It involves damage to the optic nerve head (ONH) and visual pathways extending to the brain.
• The lateral geniculate nucleus (LGN) is a key secondary site of damage.

Purpose of the Study:

• To investigate time-dependent changes in the ONH, optic nerve (ON), and LGN following elevated intraocular pressure (IOP) in Japanese monkeys.
• To establish a primate model for studying glaucoma's progression.

Main Methods:

• Experimental glaucoma was induced by IOP elevation in the left eyes of nine Japanese monkeys.
• Ocular assessments including IOP measurement and fundus photography were performed weekly.
• Eyes and brains were enucleated at 2-48 weeks post-IOP elevation for histological evaluation of ONH, ON, and LGN.

Main Results:

• Elevated IOP was sustained throughout the study period.
• ONH cupping and rim thinning were observed from 2 weeks post-IOP elevation.
• Axon loss and decreased ON area were noted at 4 and 28 weeks, respectively.
• Neuronal loss in the LGN occurred early (2 weeks) in magnocellular layers and later (12 weeks) in parvocellular layers.
• Neuronal shrinkage in the LGN was observed in all layers starting at 2 weeks.

Conclusions:

• In Japanese monkeys, elevated IOP causes early, time-dependent damage to the ONH and LGN.
• Neuronal alterations in the LGN are detectable within the first few weeks of IOP elevation.
• This model provides insights into the early pathogenesis of glaucoma affecting both the optic nerve and central visual pathways.