Effect of corneal thickness on the accuracy of intraocular pressure measurement in rabbits after excimer laser photoablation

Abstract

Purpose To determine whether intraocular pressure (IOP) measurements using pneumotonometry and Tono-Pen tonometry are accurate after excimer laser photoablation of the central cornea in rabbits. Setting Department of Ophthalmology, Scott & White Hospital, Texas A & M University College of Medicine, Temple, Texas, USA. Methods Ten rabbits had excimer laser phototherapeutic keratectomy (PTK) in the right eye to thin the central corneal thickness (CCT) by approximately 20%. The left eye served as the control. The diameter of each PTK was 6.0 mm. Four weeks later, the rabbits were examined under general anesthesia. The eyes were cannulated, and IOP was maintained at 10, 20, and 30 mm Hg and measured using an IOP transducer, Tono-Pen, and pneumotonometer at each pressure level. The readings were compared. Results One rabbit was excluded from the study because of recurrent erosions and corneal edema. There was no statistically significant difference in measurement error between the operated eye and control eye for the Tono-Pen ( P = .12) or pneumotonometer ( P = .35). There were significant differences in measurement error as pressure increased for the Tono-Pen ( P < .01) and pneumotonometer ( P < .01). The increase in measurement error with the increase in pressure was similar in the 2 eyes: Tono-Pen ( P = .96) and pneumotonometer ( P = .55). A paired t test showed the observed CCT was comparable ( P = .79) in the pre-laser right eyes (mean 400.56 μm ± 11.29 [SD]) and control eyes (mean 401.78 ± 19.78 μm). Conclusion Photoablation of approximately 20% of the CCT in rabbits by excimer laser PTK did not significantly alter the accuracy of IOP measurements by the Tono-Pen or pneumotonometer.