title: In vivo measurement of regional variation in anterior scleral resistance to Schiotz indentation.
abstract: OBJECTIVE
  Recent studies indicate that ocular and scleral rigidity is pertinent to our understanding of glaucoma, age related macular degeneration and the development and pathogenesis of myopia. The principal method of measuring ocular rigidity is by extrapolation of data from corneal indentation tonometry (K(o) ) using Friedenwald's transformation algorithms. Using scleral indentation (Schiotz tonometry) we assess whether regional variations in resistance to indentation occur in vivo across the human anterior globe directly, with reference to the deflection of Schiotz scale readings.
  
  
  METHODS
  Data were collected from both eyes of 26 normal young adult subjects with a range of refractive error (mean spherical equivalent ± S.D. of -1.77 D ± 3.28 D, range -10.56 to +4.38 D). Schiotz tonometry (5.5 g & 7.5 g) was performed on the cornea and four scleral quadrants; supero-temporal (ST) and -nasal (SN), infero-temporal (IT) and -nasal (IN) approximately 8 mm posterior to the limbus.
  
  
  RESULTS
  Values of K(o) (mm(3) )(-1) were consistent with those previously reported (mean 0.0101 ± 0.0082, range 0.0019-0.0304). In regards to the sclera, significant differences (p < 0.001) were found across quadrants with indentation readings for both loads between means for the cornea and ST; ST and SN; ST and IT, ST and IN. Mean (±S.D.) scale readings for 5.5 g were: cornea 5.93 ± 1.14, ST 8.05 ± 1.58, IT 7.03 ± 1.86, SN 6.25 ± 1.10, IN 6.02 ± 1.49; and 7.5 g: cornea 9.26 ± 1.27, ST 11.56 ± 1.65, IT 10.31 ± 1.74, SN 9.91 ± 1.20, IN 9.50 ± 1.56.
  
  
  CONCLUSIONS
  Significant regional variation was found in the resistance of the anterior sclera to indentation produced by the Schiotz tonometer.
authors.affiliation: Ophthalmic Research Group, School of Life & Health Sciences, Aston University, Birmingham, UK. h.d.patel1@aston.ac.uk
authors.forename: Hetal
authors.initials: H
authors.lastname: Patel
authors.forename: Bernard
authors.initials: B
authors.lastname: Gilmartin
authors.forename: Robert P
authors.initials: RP
authors.lastname: Cubbidge
authors.forename: Nicola S
authors.initials: NS
authors.lastname: Logan
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D003315:Cornea / Q000473:pathology*; D005260:Female; D006801:Humans; D007429:Intraocular Pressure; D008268:Macular Degeneration / Q000473:pathology*; D008297:Male; D009216:Myopia / Q000473:pathology*; D012016:Reference Values; D012590:Sclera / Q000473:pathology*; D014065:Tonometry, Ocular / Q000379:methods*; D055815:Young Adult