IOPcc IOPg GAT

P among three IOP

measurements

Preop. 14.31±2.42 14.19±2.54 13.43±2.19 0.205

Postop. 13.64±2.09 10.27±2.26 10.83±2.83 0.000

Percentage

change (%)

-2.98±17.50 -26.69±14.35 -18.11±19.80 0.000

P between preop. and

postop. 0.02 0.000 0.000

To compare the preoperative and postoperative measurement of

corneal biomechanical properties and intraocular pressure (IOP) using

Goldmann applanation tonometry (GAT) and the ocular response

analyzer (ORA; Reichert Ophthalmic Instruments, Buffalo, NY, USA)

in eyes undergoing myopic laser in situ keratomileusis (LASIK) using

IntraLase femtosecond laser for flap creation and Schwind ESIRIS

excimer laser ablation.

Materials and Methods

Fourty eyes of 20 patients who underwent corneal wavefront-guided

LASIK for the treatment of myopia using IntraLase femtosecond laser

for flap creation and Schwind ESIRIS excimer laser ablation were

enrolled in this study.

The IOP and corneal biomechanical markers were prospectively

measured preoperatively and 1 month following LASIK.

Manifest refraction spherical equivalent (MRSE), central corneal

thickness (CCT), ablation depth (AD), mean corneal curvature (K

reading) were also recorded.

IOP was measured preoperatively and 1 month following LASIK by

ORA and GAT.

ORA was used to measure corneal hysteresis (CH), corneal resistant

factor (CRF), Goldmann-correlated intraocular pressure (IOPg), and

corneal-compensated intraocular pressure (IOPcc) preoperatively and 1

month following LASIK.

The same technician performed all of the measurements with three

consecutive readings, including only good-quality measurements with

two distinct peaks. CCT was measured by ultrasonic pachymetry.

All statistical analyses were performed with SPSS ver 18.0 (SPSS

Inc., Chicago, IL, USA).

The paired-t test was used to compare preoperative and postoperative

IOP levels measured by GAT and ORA.

The statistical significance of preoperative IOP levels among the GAT,

IOPg and IOPcc was evaluated using analysis of variance (ANOVA)

for multiple comparison. Postoperative IOP measurements and

differences between preoperative and postoperative measurements

among three IOP measurements were also evaluated using ANOVA.

The Pearson correlation analysis was used to verify correlations

between preoperative IOP and possible influencing variables, including

patient age, sex, preoperative CCT, SE, K, CH, CRF. Postoperative

IOP and difference between preoperative and postoperative IOP were

evaluated for correlations with the same parameters.

Stepwise multiple regression analysis was used to analyze possible

parameters affecting IOP levels measured by GAT and ORA.

A P-value less than 0.05 was considered statistically significant.

Table 3. Changes in intraocular pressure measurements

after LASIK

Conclusion

Changes in biomechanical properties of the cornea and intraocular pressure following

corneal wavefornt-guided laser in situ keratomileusis using IntraLase femtosecond laser for

flap creation and Schwind ESIRIS excimer laser ablation Eun Ah Kim1, Soo Jeong Park2, Tae Won Kim2, Seong Jae Kim3, Ji Woong Lee4

1Department of Ophthalmology, Fatima Hospital, Daegu,Korea, 2Crystal Eye Hospital, Busan, Korea 3Department of Ophthalmology, Gyeongsang National University School of Medicine, Jinju, Korea

4Department of Ophthalmology, Pusan National University Hospital, Busan, Korea

Purpose

Table 4. Results of multiple regression analysis of preoperative IOPcc,

IOPg, and GAT when age, gender, preoperative CCT, MRSE, K, CH,

CRF were modeled.

Table 2. Preoperative and postoperative findings in corneal

biomechanical parameters

*by stepwise method

Table 1. Patient demographics (n=40 eyes)

*by stepwise method

Corneal wavefront-guided LASIK using IntraLase femtosecond

laser and Schwind ESIRIS laser produced marked decline in CH and

CRF, which may reflect changes in the viscous and elastic qualities of

the cornea. However, IOPcc showed statistically lower variation in

IOP measurement than IOPg and GAT.

Results

Characteristics Value

Age (y) 26.25±7.23 (18-42)

M/F 4/16

Ablation depth (µm) 98.95±13.50 (74-123)

Preop. Postop.

P-value

between preop.

and postop.

CCT (µm) 548.63±27.17 493.63±30.84 0.000

MRSE (diopter) -4.37±0.76 -0.14±0.80 0.000

Mean K (diopter) 43.67±0.77 40.49±1.2 0.000

CH (mmHg) 10.89±1.50 8.41±1.19 0.000

CRF (mmHg) 10.47±1.64 7.16±1.33 0.000

After LASIK, there was a reduction in IOP measurement.

ORA-corneal compensated (CC) (∆=-0.67±2.07mmHg;p=0.02)

ORA-Goldmann (G) (∆=-3.92±2.19mmHg;p=0.000)

GAT (∆=-2.6±2.51mmHg;p=0.000)

Although a significant difference was found between the preoperative and

postoperative IOPcc, IOPg and GAT (P=0.02, P=0.000 and P=0.000 respectively),

the percentage change in IOPg (-26.69±14.35) and GAT (-18.11±19.80) were

much greater than in the IOPcc (-2.98±17.50).

In addition, although there was no statistically significant difference among the

preoperative IOPcc, IOPg and GAT (P=0.205), the difference among

postoperative IOPcc, IOPg and GAT was statistically significant ( P=0.000).

IOPcc IOPg GAT

Coefficient S.E. P* Coefficient S.E. p* Coefficient S.E. P*

CH -3.205 0.208 0.000 3.039 0.185 0.000 2.417 0.252 0.000

CRF 2.556 0.191 0.000 -2.537 0.201 0.000 -2.216 0.275 0.000

Table 5. Results of multiple regression analysis of postoperative IOPcc,

IOPg, and GAT when age, gender, postoperative CCT, MRSE, K, CH,

CRF were modeled.

IOPcc IOPg GAT

Coefficient S.E. P* Coefficient S.E. p* Coefficient S.E. P*

CH -3.484 0.035 0.000 -2.797 0.034 0.000 -1.721 0.440 0.000

CRF 2.859 0.031 0.000 3.319 0.030 0.000 2.357 0.393 0.000

Table 6. Results of multiple regression analysis of ∆IOPcc, ∆IOPg, and

∆GAT when age, gender, AD, ∆CCT, ∆MRSE, ∆K, ∆CH, ∆CRF were

modeled.

∆IOPcc ∆IOPg ∆GAT

Coefficient S.E. P* Coefficient S.E. p* Coefficient S.E. P*

∆

CH

-3.135 0.313 0.000 -2.075 0.179 0.000 -2.348 0.503 0.000

∆

CRF

2.256 0.261 0.000 2.320 0.149 0.000 2.340 0.420 0.000

Table 7. Results of multiple regression analysis of postoperative IOPcc,

IOPg, and GAT when age, gender, preoperative CCT, MRSE, K, CH,

CRF were modeled.

IOPcc IOPg GAT

Coefficient S.E. P* Coefficient S.E. P** Coefficient S.E. P**

SE 1.105 0.341 0.003 1.023 0.393 0.013 1.116 0.433 0.014

CH -1.583 0.367 0.000 -1.051 0.423 0.018

CRF 1.416 0.337 0.000 1.444 0.388 0.001

CCT 0.040 0.012 0.002

* by backward method, **by stepwise method