Evaluation of corneal biomechanics with a highspeed Scheimpflug camera before and after cataract surgery: the role of intraocular pressure

PURPOSE: To measure changes in intraocular pressure (IOP) and corneal biomechanical parameters (BMP) with a high-speed Scheimpflug camera after cataract extraction, and to determine the role of IOP in the corneal biomechanical changes detected after cataract surgery. SETTING: Department of Ophthalmology, CHEDV, Santa Maria da Feira, Portugal. METHODS: Prospective, longitudinal cohort study conducted between October 2012 and October 2013. Thirty-three eyes from 33 patients (20 females, 13 males; mean age = 73 ± 7 years) were included in the study, and underwent phacoemulsification followed by pseudophakic intraocular lens (IOL) implantation. All patients were evaluated with a high-speed Scheimpflug camera (Corvis ST, Oculus, Wetzlar, Germany) before, and 5 to 8 months after surgery. Statistical analysis was performed by paired sample t-test and Pearson correlation coefficient using SPSS v.20. RESULTS: The mean IOP was 1.47 mmHg lower after surgery (p < 0.001). Other BMP also showed statistically significant differences after cataract surgery, namely corneal deformation amplitude (p < 0.001), time of the first applanation (p = 0.001), velocity of the corneal apex at the second applanation (p = 0.024),and peak distance (p = 0.001). In the correlation between changes in IOP and changes in BMP (post-surgical minus pre-surgical), only some changes in BMP are well explained by the changes in IOP (i.e. time of the first applanation r = 0.973; p < 0.001). CONCLUSION: Changes in some BMP obtained with Corvis after cataract surgery are generally well correlated with changes in IOP; others, however, are not, and may represent aspects of corneal biomechanical behaviour independent of the IOP.