The effect of Perkins, Tono-Pen, and Schiötz tonometry on intraocular pressure

We studied the intraocular pressure changes produced in five eye bank eyes by Perkins, Tono-Pen, and Schiötz tonometry performed by experienced and inexperienced personnel. When all users were considered together, Perkins tonometry produced a mean intraocular pressure increase of 0.7 mm Hg, significantly less than the mean increase of 12.1 mm Hg produced by Tono-Pen tonometry (P less than .05) or the mean increase of 16.5 mm Hg produced by Schiötz tonometry (P less than .01). There was no statistically significant difference between the intraocular pressure increase produced by Tono-Pen or Schiötz tonometry. Tonometry performed by inexperienced Tono-Pen users and experienced or inexperienced Schiötz users produced a significantly greater increase in intraocular pressure than that performed by experienced Tono-Pen users (P less than .05), and an extremely significant increase compared to tonometry performed by experienced or inexperienced Perkins users (P less than .01). The marked increase in intraocular pressure produced by Tono-Pen tonometry suggests that hand-held electronic applanation tonometers should be used with caution in eyes with a weakened cornea or sclera.