title: Optic neuropathy and increased retinal glial fibrillary acidic protein due to microbead-induced ocular hypertension in the rabbit.
abstract: OBJECTIVE
  To characterize whether a glaucoma model with chronic elevation of the intraocular pressure (IOP) was able to be induced by anterior chamber injection of microbeads in rabbits.
  
  
  METHODS
  In order to screen the optimal dose of microbead injection, IOP was measured every 3d for 4wk using handheld applanation tonometer after a single intracameral injection of 10 µL, 25 µL, 50 µL or 100 µL microbeads (5×106beads/mL;n=6/group) in New Zealand White rabbits. To prolong IOP elevation, two intracameral injections of 50 µL microbeads or phosphate buffer saline (PBS) were made respectively at days 0 and 21 (n=24/group). The fellow eye was not treated. At 5wk after the second injection of microbeads or PBS, bright-field microscopy and transmission electron microscopy (TEM) were used to assess the changes in the retina. The expression of glial fibrillary acidic protein (GFAP) in the retina was evaluated by immunofluorescence, quantitative real-time polymerase chain reaction and Western blot at 5wk after the second injection of microbeads.
  
  
  RESULTS
  Following a single intracameral injection of 10 µL, 25 µL, 50 µL or 100 µL microbead, IOP levels showed a gradual increase and a later decrease over a 4wk period after a single injection of microbead into the anterior chamber of rabbits. A peak IOP was observed at day 15 after injection. No significant difference in peak value of IOP was found between 10 µL and 25 µL groups (17.13±1.25 mm Hgvs17.63±0.74 mm Hg;P=0.346). The peak value of IOP from 50 µL group (23.25±1.16 mm Hg) was significantly higher than 10 µL and 25 µL groups (allP<0.05). Administration of 100 µL microbead solution (23.00±0.93 mm Hg) did not lead to a significant increase in IOP compared to the 50 µL group (P=0.64). A prolonged elevated IOP duration up to 8wk was achieved by administering two injections of 50 µL microbeads (20.48±1.21 mm Hgvs13.60±0.90 mm Hg in PBS-injected group;P<0.05). The bright-field and TEM were used to assess the changes of retinal ganglion cells (RGCs). Compared with PBS-injected group, the extended IOP elevation was associated with the degeneration of optic nerve, the reduction of RGC axons (47.16%,P<0.05) and the increased GFAP expression in the retina (4.74±1.10vs1.00±0.46,P<0.05).
  
  
  CONCLUSIONS
  Two injections of microbeads into the ocular anterior chamber of rabbits lead to a prolonged IOP elevation which results in structural abnormality as well as loss in RGCs and their axons without observable ocular structural damage or inflammatory response. We have therefore established a novel and practical model of experimental glaucoma in rabbits.
authors.affiliation: School of Ophthalmology & Optometry Affiliated to Shenzhen University, Shenzhen 518040, Guangdong Province, China; Shenzhen Eye Hospital Affiliated to Jinan University, Shenzhen Key Laboratory of Ophthalmology, Shenzhen 518040, Guangdong Province, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Zhao
authors.affiliation: Shenzhen Eye Hospital Affiliated to Jinan University, Shenzhen Key Laboratory of Ophthalmology, Shenzhen 518040, Guangdong Province, China.
authors.forename: Tian-Hui
authors.initials: TH
authors.lastname: Zhu
authors.affiliation: Shenzhen Eye Hospital Affiliated to Jinan University, Shenzhen Key Laboratory of Ophthalmology, Shenzhen 518040, Guangdong Province, China.
authors.forename: Wen-Chieh
authors.initials: WC
authors.lastname: Chen
authors.affiliation: Shenzhen Eye Hospital Affiliated to Jinan University, Shenzhen Key Laboratory of Ophthalmology, Shenzhen 518040, Guangdong Province, China.
authors.forename: Shi-Ming
authors.initials: SM
authors.lastname: Peng
authors.affiliation: Shenzhen Eye Hospital Affiliated to Jinan University, Shenzhen Key Laboratory of Ophthalmology, Shenzhen 518040, Guangdong Province, China.
authors.forename: Xiao-Sheng
authors.initials: XS
authors.lastname: Huang
authors.affiliation: Department of Ophthalmology, Schepens Eye Research Institute, Massachusetts Eye and Ear, Harvard Medical School, Boston 02114, USA.
authors.forename: Kin-Sang
authors.initials: KS
authors.lastname: Cho
authors.affiliation: Department of Ophthalmology, Schepens Eye Research Institute, Massachusetts Eye and Ear, Harvard Medical School, Boston 02114, USA.
authors.forename: Dong Feng
authors.initials: DF
authors.lastname: Chen
authors.affiliation: Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, East Melbourne 3002, Australia; Ophthalmology, Department of Surgery, University of Melbourne, East Melbourne 3002, Australia.
authors.forename: Guei-Sheung
authors.initials: GS
authors.lastname: Liu
keywords: glial fibrillary acidic protein; microbead; ocular hypertension; optic neuropathy; rabbit