title: A comparison of applanation tonometry using conventional reusable goldmann prisms and disposable prisms.
abstract: OBJECTIVE
  To determine the agreement between intraocular pressure (IOP) measurements using conventional Goldmann applanation tonometry (GAT) and Tonosafe disposable prisms, and also to provide a comprehensive cost analysis of the use of both types of prisms
  
  
  METHODS
  : In this prospective observational study, 198 eyes of 100 glaucoma patients had their IOPs measured by 5 consultant ophthalmologists. Data were analyzed using the Bland-Altman method of differences, and correlation was measured using the Pearson coefficient. An analysis of the cost incurred using the 2 methods over a 6-month period was performed.
  
  
  RESULTS
  The majority were Chinese (82%), with a male preponderance (57%). The range of IOPs as measured by GAT was 4 to 34 mm Hg. Using the Bland-Altman method to compare GAT and disposable prisms, the bias was 0.2 mm Hg. Tonosafe overestimated the IOP by 0.2 mm Hg in the right eye and underestimated it by 0.2 mm Hg in the left eye. The Tonosafe IOP correlated well with GAT, with a Pearson coefficient of correlation(r) of 0.91 (P<0.0005) for the right eye and 0.92 (P<0.0005) for the left eye, respectively. For those with GAT IOP≥21 mm Hg (n=26), Tonosafe underestimated the IOP by 0.35 mm Hg. The cost incurred by Tonosafe prisms was approximately 8 times that of GAT, but the cost differential reverses when GAT had to be replaced after every 100 cycles of disinfection.
  
  
  CONCLUSIONS
  We found a good correlation between Tonosafe prisms and conventional GAT in measuring the IOP. Tonosafe prisms may be of use, especially if the risk of transmission of infection is high. However, cost may limit its more widespread use.
authors: *Singapore National Eye Centre †Department of Ophthalmology, National University of Singapore, Singapore.
authors: Andrew S H
authors: AS
authors: Tsai
authors: Alicia C
authors: AC
authors: How
authors: Daniel H W
authors: DH
authors: Su
authors: Kelvin Y
authors: KY
authors: Lee
authors: Tina T
authors: TT
authors: Wong
authors: Shamira A
authors: SA
authors: Perera
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004209:Disposable Equipment; D005260:Female; D005901:Glaucoma / Q000175:diagnosis* / Q000503:physiopathology; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012189:Retrospective Studies; D014065:Tonometry, Ocular / Q000295:instrumentation* / Q000379:methods; D055815:Young Adult