Goldmann applanation tonometry - not as good as gold.

A thesis that linear mechanics does not apply to the analysis of cornea load during Goldmann applanation tonometry measurement and that the concept of surface tension in the lacrimal fluid is an ineffective attempt at circumventing the associated problems is put forward. The fundamental problem emerging during numerically simulated measurement of pressure on the eyeball, whose dimensions are considered to be calibrated, stems from the fact that the flattening of the cornea at the nominal intraocular pressure leads to a critical state in which the shell loses stability. The consequences are far-reaching. The Goldmann tonometer performs well at low intraocular pressure, but above the nominal pressure its readings are always understated. The cause of the error is not the tonometer itself (its readings can be even very accurate). It is shell "solution" called Imbert-Fick law which is faulty.