May 2008
Volume 49, Issue 13
Free
ARVO Annual Meeting Abstract  |   May 2008
Can Intraocular Pressure Measurements Neglect the Compliance of the Retropulsive Structures?
Author Affiliations & Notes
  • G. A. Thomas
    Physics, New Jersey Institute of Technology, Newark, New Jersey
  • I. A. Nwosuh
    Physics, New Jersey Institute of Technology, Newark, New Jersey
  • A. Khouri
    Ophthamology, University of Medicine and Dentistry of NJ, New Brunswick, New Jersey
  • R. D. Fechtner
    Ophthamology, University of Medicine and Dentistry of NJ, Newark, New Jersey
  • N. A. Ciampa
    Physics, New Jersey Institute of Technology, Newark, New Jersey
  • Footnotes
    Commercial Relationships  G.A. Thomas, None; I.A. Nwosuh, None; A. Khouri, None; R.D. Fechtner, None; N.A. Ciampa, None.
  • Footnotes
    Support  Hoffman Foundation
Investigative Ophthalmology & Visual Science May 2008, Vol.49, 695. doi:
  • Views
  • Share
  • Tools
    • Alerts
      ×
      This feature is available to authenticated users only.
      Sign In or Create an Account ×
    • Get Citation

      G. A. Thomas, I. A. Nwosuh, A. Khouri, R. D. Fechtner, N. A. Ciampa; Can Intraocular Pressure Measurements Neglect the Compliance of the Retropulsive Structures?. Invest. Ophthalmol. Vis. Sci. 2008;49(13):695.

      Download citation file:


      © ARVO (1962-2015); The Authors (2016-present)

      ×
  • Supplements
Abstract
 
Purpose:
 

Investigate the assumption that measurements of the intraocular pressure (IOP)can neglect the compliance of the retropulsive structures (RPS) holding the eye.

 
Methods:
 

In measuring the RPS using a tonometer, we test and confirm that the RPS are linear elastic materials. The force, F, is then related to the distance, x, by F=kx, where k is the force constant and its reciprocal is the compliance X.To determine this parameter, a rigid corneal shield is placed over the cornea and sclera. The tonometer probe is touched to the center of the shield and pushes on the shield and RPS, while F and x are recorded in the range of F and x comparable to a Goldmann tonometer. Using the calibration of our tonometer, we difine X for the RPS by this measurement.

 
Results:
 

In the standard interpretation of IOP, the RPS are assumed to be rigid, or that their compliance is zero. If this assumption is not true, a corneal measurement (such as Goldmann) gives X(cornea)+X and X should be subtracted before diagnosis. Our measurements, Figure 1, show that a typical normal subject shows linearity in F vs. x with {X, standard deviation, coeff. regression} = {0.035mm/gm, 0.08,0.997}, for small F in the range 0-3gm (pressures in the range 0-30mmHg). A low-order, non-linear fit is not statistically preferable. The range of values of X is 0.035 to 0.045mm/gm

 
Conclusions:
 

Our measurements show that X is not zero. In the small sample of normal patients measured thus far, average X is only about 5 times smaller than the values we observe for X(cornea), so the error in neglecting X appears to be significant in normal subjects that we have measured (and it is not constant). The linearity is significant because it means that the size of the correction applies at any IOP. Further studies are required to determine the extent to which X can be ignored in diagnosis for a wider class of patients. We suggest that patients with normal pressure glaucoma warrant particular study because X may be unusually large and reduce the apparent IOP.  

 
Keywords: cornea: clinical science • intraocular pressure 
×
×

This PDF is available to Subscribers Only

Sign in or purchase a subscription to access this content. ×

You must be signed into an individual account to use this feature.

×