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Corneal biomechanics evaluation with a high-speed Scheimpflug camera: the role of intraocular pressure

Poster Details

First Author: M.Ruão PORTUGAL

Co Author(s):    R. Almeida   P. Neves   I. Lopes-Cardoso   J. González-Méijome   J. Salgado-Borges  

Abstract Details



Purpose:

To measure the changes in intra-ocular pressure (IOP) and corneal biomechanics with a high-speed Scheimpflug camera, after cataract extraction. Also to determine the rule of IOP in the corneal biomechanics changes after cataract surgery.

Setting:

Ophthalmology Department, CHEDV, Sta. Maria da Feira, Portugal.

Methods:

Thirty-two eyes from 32 patients scheduled for cataract surgery (20 females, 12 males; mean age=73±7years) were included in the study. They undergone phacoemulsification followed by pseudophakic IOL implantation by the same experienced surgeon. Examinations were performed between 5 to 8 months after surgery. All patients were evaluated with high-speed Scheimpflug camera (Corvis ST, Oculus, Wetzlar, Germany). Measurements were performed in the morning between 9:00 and 11:00 AM before and after surgery (minimum of 2 hours after awaking) to avoid the impact of diurnal changes in IOP and biomechanical corneal properties. Statistical analysis was performed by paired sample T-Test and Pearson correlation coefficient using SPSS v.20.

Results:

The mean IOP after surgery was 1.5 mmHg lower than pre-surgery (p<0.001). Similarly, other biomechanical parameters have also shown statistically significant differences after cataract surgery, namely maximum corneal deformation amplitude (diff.=0.08±0.10 mm, p<0.001), time of the first applanation (diff.=-0.15±0.24 ms, p=0.001), the velocity of the corneal apex at the second applanation (diff.=-0.04±0.09 m/s, p=0.024), peak distance (diff.=0.16±0.25 mm, p=0.001), deflection length at the time of the highest concavity (diff.=0.17±0.33 mm, p=0.007), deflection amplitude of the highest concavity (diff.=0.07±0.10 mm, p=0.001) or highest concavity deflection area (diff.=0.37±0.53 mm2, p<0.001). So as to evaluate the potential influence of IOP's changes in the differences observed in the biomechanical parameters, changes in IOP and biomechanical parameters (post-surgical minus pre-surgical) have been correlated. While the differences in some biomechanical parameters are well explained by the changes in IOP (i.e. time of the first applanation r=0,973; p<0.001) others such as the applanation 2 velocity or nasal-temporal symmetry 1 and 2 times (r=0.551 and r=-0.574, respectively) were not.

Conclusions:

Cataract surgery affect the average IOP measured with Corvis in the medium term after surgery. This decrease in IOP is somewhat comparable too the one obtained in other studies using the gold standard for IOP measuring (Goldmann applanation tonometry). On the other hand, changes in biomechanical parameters obtained with Corvis after cataract surgery are generally well correlated with the changes in IOP, however some other parameters are not, and those might represent aspects of the biomechanical behavior of the cornea independent of the IOP. These modifications might be a reflection of the changes in the anterior chamber dynamics induced by the removal of the ageing crystalline lens and replacement by a thin intra-ocular lens rather than reflecting changes in the corneal tissue characteristics. FINANCIAL INTEREST: NONE

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