title: Evaluation of retinal nerve fiber layer thickness parameters in myopic population using scanning laser polarimetry (GDxVCC).
abstract: BACKGROUND
  Myopia presents a significant challenge to the ophthalmologist as myopic discs are often large, tilted, with deep cups and have a thinner neuroretinal rim all of which may mimic glaucomatous optic nerve head changes causing an error in diagnosis.
  
  
  OBJECTIVE
  To evaluate the retinal fiber layer (RNFL) thickness in low, moderate and high myopia using scanning laser polarimetry with variable corneal compensation (GDxVCC).
  
  
  METHODS
  One hundred eyes of 100 emmetropes, 30 eyes of low myopes (0 to - 4 D spherical equivalent(SE), 45 eyes with moderate myopia (- 4 to - 8D SE), and 30 eyes with high myopia (- 8 to - 15D SE) were subjected to retinal nerve fiber layer assessment using the scanning laser polarimetry (GDxVCC) in all subjects using the standard protocol. Subjects with IOP > 21 mm Hg, optic nerve head or visual field changes suggestive of glaucoma were excluded from the study. The major outcome parameters were temporal-superior-nasal-inferiortemporal (TSNIT) average, the superior and inferior average and the nerve fibre indicator (NFI).
  
  
  RESULTS
  The TSNIT average (p = 0.009), superior (p = 0.001) and inferior average (p = 0.008) were significantly lower; the NFI was higher (P less than 0.001) in moderate myopes as compared to that in emmetropes. In high myopia the RNFL showed supranormal values; the TSNIT average, superior and inferior average was significantly higher(p less than 0.001) as compared to that in emmetropes.
  
  
  CONCLUSIONS
  The RNFL measurements on scanning laser polarimetry are affected by the myopic refractive error. Moderate myopes show a significant thinning of the RNFL. In high myopia due to peripapillary chorioretinal atrophy and contribution of scleral birefringence, the RNFL values are abnormally high. These findings need to be taken into account while assessing and monitoring glaucoma damage in moderate to high myopes on GDxVCC.
authors.affiliation: Glaucoma Facility, Dr. Rajendra Prasad Centre for Ophthalmic Sciences All India Institute of Medical Sciences, New Delhi 110029, India.
authors.forename: Tanuj
authors.initials: T
authors.lastname: Dada
authors.forename: A
authors.initials: A
authors.lastname: Aggarwal
authors.forename: S J
authors.initials: SJ
authors.lastname: Bali
authors.forename: A
authors.initials: A
authors.lastname: Sharma
authors.forename: B M
authors.initials: BM
authors.lastname: Shah
authors.forename: D
authors.initials: D
authors.lastname: Angmo
authors.forename: A
authors.initials: A
authors.lastname: Panda
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008403:Mass Screening / Q000379:methods*; D009216:Myopia / Q000175:diagnosis* / Q000453:epidemiology; D009412:Nerve Fibers / Q000473:pathology*; D015203:Reproducibility of Results; D012165:Retinal Ganglion Cells / Q000473:pathology*; D012189:Retrospective Studies; D057109:Scanning Laser Polarimetry / Q000379:methods*; D055815:Young Adult