Within recent years the early diagnosis of glaucoma has made considerable strides even though the management and social consequences of this disease remain as always a challenge to ophthalmology. The tonometer remains one of the most important tools in the early diagnosis of glaucoma, both as a means of measuring the intraocular pressure, as well as a means of carrying out tonography. In conjunction with scotometry, it gives the best indication of the success of medical control of conservative therapy.
It has been realized for some considerable time1 that all forms of impression tonometry with the Schiøtz, McLean, or Gradle tonometers are far from reliable guides of the intraocular pressure, even when accurately standardized, because the indentation is influenced by variations in the scleral rigidity of normal human eyes and to a lesser degree by differences in corneal curvature. It has also been appreciated that tonography is influenced by
DRANCE SM. The Coefficient of Scleral Rigidity in Normal and Glaucomatous Eyes. AMA Arch Ophthalmol. 1960;63(4):668-674. doi:10.1001/archopht.1960.00950020670008