Corneal biomechanical parameters and intraocular pressure: the effect of topical anesthesia

Abstract

Background: The intraocular pressures and biomechanical parameters measured by the ocular response analyzer make the analyzer a useful tool for the diagnosis and management of anterior segment disease. This observational study was designed to investigate the effect of topical anesthesia on the parameters measured by the ocular response analyzer: corneal hysteresis, corneal resistance factor, Goldmann-correlated intraocular pressure (IOPg), and corneal-compensated intraocular pressure (IOPcc).

Methods: Two sets of measurements were made for 78 eyes of 39 subjects, approximately 1 week apart. In session 1, each eye of each subject was randomized into one of three groups: polyvinyl alcohol (0.5%), tetracaine hydrochloride (0.5%), or oxybuprocaine hydrochloride (0.4%). In session 2, eyes that were in the polyvinyl alcohol group in session 1 were assigned to the tetracaine group, those in the tetracaine group in session 1 were assigned to oxybuprocaine group, and those in the oxybuprocaine group in session 1 were assigned to the polyvinyl alcohol group. For both sessions, each subject first had his or her central corneal thickness assessed with a specular microscope, followed by measurements of intraocular pressure and corneal biomechanical parameters with the Ocular Response Analyzer. All measurements were repeated for 2 minutes and 5 minutes following the instillation of either polyvinyl alcohol, tetracaine, or oxybuprocaine. The level of statistical significance was 0.05.

Results: Polyvinyl alcohol, tetracaine hydrochloride, and oxybuprocaine hydrochloride had no statistically significant (P > 0.05) effect on any of the biomechanical parameters of the cornea. There was no statistically significant effect on either IOPg (P > 0.05) or IOPcc (P > 0.05) 2 minutes after the eye drops were instilled in either session. Five minutes after the eye drops were instilled, polyvinyl alcohol showed no statistically significant effect on either IOPg (P > 0.05) or IOPcc (P > 0.05) in either session. Oxybuprocaine and tetracaine caused statistically significant (P < 0.05) reductions in IOPg in session 1, but only tetracaine had a significant (P < 0.05) effect in session 2. Tetracaine also caused a statistically significant (P < 0.05) reduction in IOPcc in session 1.

Conclusion: The statistically significant effect of topical anesthesia on IOPg varies with the anesthetic used, and while this effect was statistically significant in this study, the small effect is probably not clinically relevant. There was no effect on any of the biomechanical parameters of the cornea.

Keywords: corneal biomechanical parameters; corneal hysteresis; corneal resistance factor; intraocular pressure; ocular response analyzer; topical anesthesia.

Figure 1

Average corneal thickness values for session one before, 2 minutes after, and 5 minutes after the instillations of polyvinyl alcohol (0.5%), tetracaine hydrochloride (0.5%), and oxybuprocaine hydrochloride (0.4%). Note: The P values are the results of repeated-measures ANOVA comparisons for each eye drop. Abbreviation: ANOVA, analysis of variance.

Figure 2

Average corneal hysteresis values for session one before, 2 minutes after, and 5 minutes after the instillations of polyvinyl alcohol (0.5%), tetracaine hydrochloride (0.5%), and oxybuprocaine hydrochloride (0.4%). Note: The P values are the results of repeated-measures ANOVA comparisons for each eye drop. Abbreviation: ANOVA, analysis of variance.

Figure 3

Average corneal resistance factor values for session one before, 2 minutes after, and 5 minutes after the instillations of polyvinyl alcohol (0.5%), tetracaine hydrochloride (0.5%), and oxybuprocaine hydrochloride (0.4%). Note: The P values are the results of repeated-measures ANOVA comparisons for each eye drop. Abbreviation: ANOVA, analysis of variance.

Figure 4

Average Goldmann-correlated IOP values for session one before, 2 minutes after, and 5 minutes after the instillations of polyvinyl alcohol (0.5%), tetracaine hydrochloride (0.5%), and oxybuprocaine hydrochloride (0.4%). Note: The P values are the results of repeated-measures ANOVA comparisons for each eye drop. Abbreviations: ANOVA, analysis of variance; IOP, intraocular pressure.

Figure 5

Average corneal-compensated IOP values for session one before, 2 minutes after, and 5 minutes after the instillations of polyvinyl alcohol (0.5%), tetracaine hydrochloride (0.5%), and oxybuprocaine hydrochloride (0.4%). Note: The P values are the results of repeated-measures ANOVA comparisons for each eye drop. Abbreviations: ANOVA, analysis of variance; IOP, intraocular pressure.

Figure 6

Limits of repeatability for the Goldmann-correlated IOP before (solid black lines with arrow heads), 2 minutes post-instillation (dotted gray lines with diamond heads), and 5 minutes post instillation (dotted lines with round heads) of tetracaine hydrochloride (0.5%) in session 1. Abbreviation: IOP, intraocular pressure.

Figure 7

Limits of repeatability for the Goldmann-correlated IOP before (solid black lines with arrow heads), 2 minutes post instillation (dotted gray lines with diamond heads), and 5 minutes post instillation (dotted lines with round heads) of tetracaine hydrochloride (0.5%) in session 2. Abbreviation: IOP, intraocular pressure.