title: Reflectance decreases before thickness changes in the retinal nerve fiber layer in glaucomatous retinas.
abstract: OBJECTIVE
  Glaucoma damages the retinal never fiber layer (RNFL). RNFL thickness, measured with optical coherence tomography (OCT), is often used in clinical assessment of the damage. In this study the relation between the RNFL reflectance and thickness at early stages of glaucoma was investigated.
  
  
  METHODS
  A rat model of glaucoma was used that involved laser photocoagulation of the trabecular meshwork. The reflectance of the RNFL in an isolated retina was measured, followed by immunohistochemical staining of the axonal cytoskeleton. RNFL thickness was measured by confocal fluorescence imaging. RNFL reflectance was calculated for bundle areas located at radii of 0.22, 0.33, and 0.44 mm from the optic nerve head (ONH) center. Linear regression was used to study the relation between reflectance and thickness. For glaucomatous eyes, only those bundles with no apparent structural damage were used.
  
  
  RESULTS
  Bundles in 11 control retinas and 10 treated retinas were examined. Bundle thickness of both groups at each radius was similar (P = 0.89). The reflectance of the bundles at radii of 0.33 and 0.44 mm was found to be similar in both control and treated retinas (P > 0.5). However, the reflectance of the bundles at the 0.22-mm radius decreased significantly in the treated group (P = 0.005).
  
  
  CONCLUSIONS
  Elevation of intraocular pressure causes decrease in RNFL reflectance for bundles near the ONH. Change in RNFL reflectance precedes thinning of the RNFL. The results suggest that a decrease in RNFL reflectance near the ONH is an early sign of glaucomatous damage.
authors: Bascom Palmer Eye Institute, University of Miami, Miami, Florida 33136, USA. xhuang3@med.miami.edu
authors: Xiang-Run
authors: XR
authors: Huang
authors: Ye
authors: Y
authors: Zhou
authors: Wei
authors: W
authors: Kong
authors: Robert W
authors: RW
authors: Knighton
mesh_terms: D000818:Animals; D001369:Axons / Q000473:pathology*; D003599:Cytoskeleton / Q000473:pathology; D018450:Disease Progression; D005260:Female; D005901:Glaucoma / Q000473:pathology*; D007429:Intraocular Pressure; D018613:Microscopy, Confocal / Q000379:methods; D051381:Rats; D017208:Rats, Wistar; D012165:Retinal Ganglion Cells / Q000473:pathology* / Q000648:ultrastructure; D041623:Tomography, Optical Coherence / Q000379:methods*; D014129:Trabecular Meshwork / Q000473:pathology