Abstract

P 158

Comparison of Tonopen and applanation tonometry to intraocular needle tonometry in eyes with abnormal corneas

Neuburger J., Böhringer D., Birnbaum F., Reinhard T.
University Eye Hospital Freiburg

Objective: Tonometry in eyes with abnormal corneas is most likely not reliably due to measuring principles. The aim of this study is to compare Perkins applanation tonometry and Tonopen to intraocular needle tonometry in eyes with diseased corneas, respectively. A further aim is to declare the variance of any sampling errors from Perkins and Tonopen with corneal thickness or corneal diagnosis.
Methods: A total of 36 eyes were included prior to penetrating keratoplasty [Fuchs endothelial dystrophie (10), Graft failure following penetrating keratoplasty (6), Stromal corneal scars (5), Keratoconus (5), Bullous endothelial degeneration (4) and Other corneal diseases (6)]. Prior to surgery, sonographic central pachymetry (Pachette) as well as Perkins and Tonopen tonometry were applied in supine position. Subsequently, needle tonometry (Geuder) was performed under sterile conditions. Perkins and Tonopen results were correlated to needle tonometry, respectively using Pearson's correlation. Furthermore, sampling errors were entered into a multifactorial linear model including corneal diagnosis and corneal thickness
Results: Median sampling errors of Perkins and Tonopen were -3.3 (-24 bis 19) mmHg and -1.1 (-15 bis 19) mmHg, respectively. No statistically significant correlation to intraocular pressure was observable for Perkins tonometry (coefficient: 0.3; p=0.13). Tonopen, however, was statistically significantly correlated to intraocular pressure from Geuder tonometry (coefficient: 0.6; p<0.01). Samping errors of Perkins and Tonopen were neither significantly related to corneal thickness nor to corneal diagnosis.
Conclusions: Tonopen seems better suited for eye with diseased corneas than Perkins. However, discepancies up to 19 mmHg necessitate invasive needle tonometry in all cases of doupt.

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