ARTICLE

Corneal biomechanical properties and intraocularpressure changes after phacoemulsification

and intraocular lens implantationRaciha Beril Kucumen, MD, Nursal Melda Yenerel, MD, Ebru Gorgun, MD, Destan Nil Kulacoglu, MD,

Banu Oncel, MD, Maryo Cenk Kohen, MD, Murat Levent Alimgil, MD

PURPOSE: To evaluate corneal viscoelastic and intraocular pressure (IOP) changes measured by anocular response analyzer (ORA) after phacoemulsification and intraocular lens (IOL) implantation.

SETTING: Yeditepe University Department of Ophthalmology, Istanbul, Turkey.

METHODS: Fifty-one eyes scheduled for cataract surgery were included in the study. Corneal hys-teresis (CH), corneal resistance factor (CRF), corneal-compensated intraocular pressure (IOPcc),and Goldmann-correlated IOP (IOPg) were measured by ORA preoperatively and 1 week and1 and 3 months postoperatively. Central corneal thickness (CCT) was measured using the ORA’sintegrated handheld ultrasonic pachymeter.

RESULTS: The mean preoperative CCT (537 mm G 46 [SD]) did not change significantly by the endof 1 month postoperatively. The mean preoperative IOPcc (17.2 G 3.0 mm Hg) decreased signif-icantly by 3 months postoperatively (15.2 G 3.7 mm Hg) (P Z .018). The mean CH decreased from10.36 G 1.48 mm Hg preoperatively to 9.64 G 1.26 mm Hg at 1 week (P Z .028); it increased topreoperative values at the end of 1 month (10.20 G 1.70) and 3 months (10.74 G 1.54) (P>.05).The mean CRF decreased from 10.94 G 2.54 mm Hg preoperatively to 9.99 G 1.77 at 1 week(P Z .026); it increased to preoperative values at 1 month (10.26 G 1.59) and 3 months (10.35G 1.46) (P>.05).

CONCLUSIONS: Although CH and the CRF decreased in the early postoperative period, the param-eters increased and reached preoperative values by 3 months postoperatively, showing that cornealbiomechanical properties are influenced by phacoemulsification and IOL implantation.

J Cataract Refract Surg 2008; 34:2096–2098 Q 2008 ASCRS and ESCRS

The ocular response analyzer (ORA, Reichert Ophthal-mic Instruments, Buffalo, NY)measures the biomechan-ical properties of the cornea in vivo. It provides severalmeasurements including corneal hysteresis (CH), thecorneal resistance factor (CRF), the corneal-compensatedintraocular pressure (IOPcc), and the Goldmann-

Accepted for publication August 15, 2008.

From the Department of Ophthalmology, Yeditepe University EyeHospital, Istanbul, Turkey.

No author has a financial or proprietary interest in any material ormethod mentioned.

Corresponding author: Raciha Beril Kucumen, MD, AssistantProfessor in Ophthalmology, Gokce Sokak Erenli Apt. 8/3 Caddebo-stan 34728, Istanbul, Turkey. E-mail: berilkucumen@hotmail.com.

Q 2008 ASCRS and ESCRS

Published by Elsevier Inc.

2096

correlated intraocular pressure (IOPg).1,2 Corneal hys-teresis is described as the viscous damping due tothe viscoelastic resistance of the cornea to a deforma-tion pulse by an air jet of the tonometer. WhereasCH may reflect corneal viscosity, the CRF may relateto the elastic properties of the cornea.3 Both parame-ters are measured by the ORA using a dynamic bidi-rectional process.1

The aim of this study was to evaluate the effect ofphacoemulsification and intraocular lens (IOL)implantation on CH and the CRF and to evaluate theIOPcc and IOPg values simultaneously recorded bythe ORA.

PATIENTS AND METHODS

This prospective study comprised 51 eyes of 51 consecutivepatients with senile cataract who had uneventful cataractsurgery from November 2007 through March 2008 at the

0886-3350/08/$dsee front matter

doi:10.1016/j.jcrs.2008.08.017

2097CORNEAL BIOMECHANICS AND IOP AFTER CATARACT SURGERY

Department of Ophthalmology, Yeditepe University EyeHospital. The study followed the tenets of the Declarationof Helsinki. The Ethics Committee of the Yeditepe UniversityMedical School approved the study protocol. All patientsprovided informed consent. Patients with anterior segmentpathology other than cataract and with previous ophthalmicsurgery or trauma were excluded from the study.

All patients had uneventful clear corneal cataract surgeryby the same surgeon (R.B.K.). The surgical technique con-sisted of microcoaxial phacoemulsification and foldableIOL implantation in the capsular bag through a 2.4 mm clearcorneal incision. The same ophthalmic viscosurgical device(sodium hyaluronate 3%–chondroitin sulfate 4% with so-dium hyaluronate 1% [DuoVisc]) and the same phaco ma-chine (Infinity Vision System, Alcon Laboratories Inc., Ft.Worth, TX) were used in all cases. An AcrySof SA60BMIOL or an AcrySof IQ SN60WF IOL (both Alcon) was im-planted, the latter using the Monarch II IOL delivery systemwith the Monarch C cartridge.

After a routine ophthalmic examination including visualacuity, slitlamp biomicroscopy, tonometry, and fundoscopy,the CH, CRF, IOPcc, and IOPg were measured by the ORApreoperatively and at the end of 1 week and 1 and 3 monthspostoperatively. Central corneal thickness (CCT) was mea-sured with the integrated handheld ultrasonic pachymeter(20 MHz) of the ORA through the end of the first postoper-ative month. The ORA examination was performed at least3 times. Disqualified scale values were deleted, repeat mea-surements taken, and the average values recorded.

Statistical analysis was by 1-way analysis of variance andPearson correlation analysis.

RESULTS

Twenty-two eyes received an AcrySof SA60BM IOLand 29 eyes, the AcrySof IQ SN60WF IOL. Therewere no statistically significant differences betweenthe 2 IOL groups; therefore, the patients were evalu-ated collectively in the comparison of preoperativeand postoperative measurements.

Table 1 and Figure 1 show the changes in ORAparameters and CCT from preoperatively to postoper-atively. The mean CCT did not change significantlyfrom preoperatively to the end of the first postopera-tivemonth; therefore, it was notmeasured at 3months.

J CATARACT REFRACT SURG

The change in the mean IOPcc from preoperativelywas not statistically significant at 1 week or 1 month.However, themean IOPccwas statistically significantlylower at 3 months than preoperatively (P Z .018).

The change in the mean IOPg was not statisticallysignificant between preoperatively and any postoper-ative time point (PO.05).

The mean CH decreased from before surgery to theend of the first week (P Z .028). At 1 and 3months, themean CH increased to preoperative values (PO.05).

The mean CRF decreased from before surgery to theend of the first week (P Z .026). At 1 and 3months, themean CRF increased to preoperative values.

DISCUSSION

Corneal biomechanical properties, characterized bythe CH and the CRF, have been studied recently incases with anterior segment pathology, keratoconus,and glaucoma and in surgical methods such as laser

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IOPcc IOPg CRF CH

Preop

1.week

1.month

3.month

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Figure 1. Comparison of the mean preoperative and postoperativeORA parameters (+ Z statistically significant value between preop-erative and postoperative measurements; CH Z corneal hysteresis;CRF Z corneal resistance factor; IOPcc Z corneal-compensatedintraocular pressure; IOPg Z Goldmann-correlated intraocularpressure).

Table 1. Changes in ORA parameters and CCT after cataract surgery.

Mean G SD

Postoperative

Parameter Preoperative 1 Week 1 Month 3 Months

IOPcc (mm Hg) 17.24 G 3.01 17.45 G 3.88 16.29 G 3.22 15.25 G 3.71IOPg (mm Hg) 16.55 G 3.45 16.25 G 4.39 15.55 G 2.84 14.83 G 3.67CRF (mm Hg) 10.64 G 2.54 9.99 G 1.77 10.26 G 1.59 10.35 G 1.46CH (mm Hg) 10.36 G 1.49 9.65 G 1.26 10.20 G 1.70 10.74 G 1.54CCT (mm) 537 G 46 546 G 46 539 G 44 d

CCT Z central corneal thickness; CH Z corneal hysteresis; CRF Z corneal resistance factor; IOPcc Z corneal-compensated intraocular pressure; IOPg Z Gold-mann-correlated intraocular pressure

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in situ keratomileusis and laser-assisted subepithelialkeratectomy.2,4–7 These biomechanical properties arealways evaluated in conjunction with the CCT; how-ever, the CCT on IOP measurement has been shownto differ according to the level of corneal elasticity orstiffness.8 It is important to recognize that 2 corneaswith the same CCT may have very different biome-chanics.9 Falkenberg et al.10 found that the CCT in-creased after clear cataract surgery. In our series, wedid not find a significant increase because our earliestpostoperative measurement was after 1 week.

Hager et al.11 report that on the first day aftercataract surgery, CH decreased and CCT increasedsignificantly. We assessed these parameters for a lon-ger period after surgery because the findings on thefirst postoperative day may change as a result ofmany factors. On the first day, patients may havedifficulty opening their eyes, and there is still a risk,although small, for contamination from the CCT mea-surement. In addition, microleakage from fresh cor-neal wounds cannot be ruled out during the first 24hours. The condition of the endothelium may be an-other factor affecting measurements taken at an earlypoint. Finally, our study focused on the results of op-erations performed by the same experienced surgeon.

The elasticity and rigidity of the cornea are thoughtto maintain the corneal shape, to which several bio-physical factors contribute. As mentioned, it hasbeen shown that CH decreases the first day after cata-ract surgery and that the CCT increases.11 Thesechanges have been attributed to corneal edema, whichlowers the damping capacity of the cornea. Althoughthe CH and CRF relate to the biomechanical propertiesof the cornea, we believe that CCT and corneal edemaare not the only factors that affect these properties. Webelieve that the globe reacts as a whole and intraocularchanges can also indirectly affect these parameters. Asenile cataract is situated just posterior to the cor-neoscleral rim and is often hard as a result of age-related changes, even cases of low-grade cataract.Removal of the senile cataract and implantation ofa thinner, smaller IOL likely changes the biophysicalbehavior of the entire eye, thus affecting the biophysi-cal properties of the cornea. We think that this arearequires further investigation, perhaps in groups ofcataracts based on grade classification or thickness,which can be measured by anterior segment opticalcoherence tomography. The assessment of axial lengthand confocal biomicroscopy may be other areas ofinterest in relation to ORA measurements after cata-ract surgery.

J CATARACT REFRACT SURG

In conclusion, cataract surgery using modern tech-nology changed the biomechanical properties of thecornea. Corneal hysteresis and the CRF basicallyreturned to normal preoperative values a short timeafter phacoemulsification with IOL implantation,probably due to corneal healing and/or capsularfibrotic changes that were not significant.

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First author:Raciha Beril Kucumen, MD

Department of Ophthalmology, YeditepeUniversity Eye Hospital, Istanbul, Turkey

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