[The relationship between central corneal thickness and Perkins applanation tonometry in rabbits]

Abstract

Objective: To investigate the relationship between central corneal thickness (CCT) and Perkins applanation tonometry and establish a mathematic model of correlation between true intraocular pressure (IOP), CCT and Perkins applanation tonometry.

Methods: The study included thirty-two new Zealand rabbits. One eye received excimer laser photorefractive keratectomy (PRK), the other eye was used as control. The eye selected randomly according to stochastic digital chart received PRK to thin the central cornea and to generate different central corneal thickness. The Perkins applanation tonometry, CCT, corneal curvature (CC) were measured by Perkins applanation tonometer, ultrasonic pachymetry and keratometer pre- and post-PRK. Direct intracameral IOP readings was measured by IOP transducer. Statistical analyses were performed with the Pearson correlation coefficient and stepwise regression analysis.

Results: There is no difference in the measurement of Perkins applanation tonometry, CCT and CC between experimental and controls. A significant correlation was found between IOP and CCT pre- and post-PRK (r = 0.761, P < 0.05; r = 0.829 P < 0.05). There is correlation between IOP and CC, (r = 0.098, P > 0.05; r = 0.260, P > 0.05). The slope of CCT was 0.066 mm Hg/micron pre-PRK and 0.053 mm Hg/micron post-PRK. However, the change of IOP correlated with CCT. Regression equation for direct intracameral IOP Y = 12.107 + 1.254X(1) - 0.033X(2) (X(1) = Perkins applanation tonometry, X(2) = CCT).

Conclusions: CCT is an important variable in the evaluation of applanation IOP and should be considered when the Perkins applanation tonometry was taken.