J CATARACT REFRACT SURG - VOL 32, OCTOBER 2006

Local corneal thickness changes

after small-incision cataract surgery

Matthias Bolz, MD, Stefan Sacu, MD, Wolfgang Drexler, PhD, Oliver Findl, MD

PURPOSE: To assess whether a temporal limbal–corneal incision approach for phacoemulsificationcataract surgery induces a gradient in corneal thickening along the horizontal meridian.

SETTING: Department of Ophthalmology, Medical University of Vienna, Vienna, Austria.

METHODS: Corneal thickness in 21 eyes of 21 patients was measured preoperatively as well as 1 day, 1week, and 1 and 3 months after phacoemulsification through a temporal limbal–corneal incision. Mea-surements were performed using partial coherence interferometry (PCI) with a commercial instrument,the ACMaster (Carl Zeiss Meditec, Jena). Measurements were taken along the horizontal meridian cen-trally along the visual axis at 1.5 mm, 3.0 mm, and 4.5 mm eccentricity.

RESULTS: Preoperatively, there were slight nasal–temporal differences in corneal thickness at alleccentricities. The mean thickness was 522 mm G 34 (SD) at 1.5 mm nasally and 513 G 36 mm at1.5 mm temporally (P<.01). On day 1, there was a significant mean increase in corneal thickness(38 G 43 mm) along all locations. The thickening was slightly more pronounced in the peripherythan in the center, a difference not reaching statistical significance. At 1 week, corneal thickness re-turned almost to baseline at all locations except for 3.0 mm temporally, where it was slightly, butnot significantly, thicker (mean 8 G 14 mm). At 1 month, corneal thickness at the 3.0 mm temporallocation returned to baseline.

CONCLUSIONS: A nasal–temporal difference in corneal thickness was found preoperatively in all pa-tients. Phacoemulsification through a temporal limbal–corneal incision caused an increase in cornealthickness along the horizontal meridian 1 day after surgery. The prolonged corneal thickening at3.0 mm eccentricity temporally could be a result of the proximity to the incision site.

J Cataract Refract Surg 2006; 32:1667–1671 Q 2006 ASCRS and ESCRS

Phacoemulsification through a temporal clear corneal or

limbal–corneal incision using topical anesthesia is widely

established in cataract surgery. Short recovery,1 low in-

duced astigmatism and good early visual acuity,2 low inci-

dence of surgical complications,2–4 and less postoperative

Accepted for publication May 17, 2006.

From the Department of Ophthalmology (Bolz, Sacu, Findl) andthe Zentrum fur Biomedizinische Technik und Physik (Drexler),Medical University of Vienna, Vienna, Austria.

Presented in part at the XXIInd Congress of the European Societyof Cataract & Refractive Surgeons, Paris, France, September 2004.

Dr. Drexler is a consultant to Carl Zeiss Meditec AG. No other au-thor has a proprietary or financial interest in any material ormethod mentioned.

Corresponding author: Oliver Findl, MD, Department of Ophthal-mology, Medical University of Vienna, Wahringer Gurtel 18-20,Vienna A-1090, Austria. E-mail: oliver.findl@meduniwien.ac.at.

Q 2006 ASCRS and ESCRS

Published by Elsevier Inc.

intraocular pressure elevation than with sclerocorneal inci-

sions5 have been reported.

However, phacoemulsification damages the corneal

endothelium. Several authors6–8 have measured endothe-

lial cell loss caused by irrigation and the heat generated

by phacoemulsification devices, which reduces corneal

metabolism postoperatively.9 The extent of postoperativeendothelial cell loss depends on intraoperative phacoemul-

sification time.7 In addition, shorter eyes have a signifi-

cantly higher incidence of endothelial cell loss,7 probably

because of a more shallow anterior segment.

Measuring corneal thickness changes after phacoemul-

sification has been used to assess surgically induced corneal

edema. Lundberg et al.10 report that the degree of perma-

nent corneal endothelial damage is related to the degreeof early postoperative corneal swelling. Thus, measuring

the differences in pachymetry postoperatively seems useful

in assessing the effects of phacoemulsification on corneal

integrity.10

0886-3350/06/$-see front matterdoi:10.1016/j.jcrs.2006.05.018

1667

CORNEAL THICKNESS CHANGES AFTER CATARACT SURGERY

Partial coherence interferometry (PCI)11–14 is an ap-

propriate technique for high-precision, noncontact corneal

thickness measurements.11 A prototype of the ACMaster

(Carl Zeiss Meditec, Jena) used in this study allows assess-

ment of corneal thickness at several eccentricities to the

corneal center. We used PCI to identify a possible gradientin corneal thickening induced by a temporal clear corneal

approach during cataract surgery. The aim was to evaluate

local postoperative corneal thickness changes over time

caused by phacoemulsification via a temporal clear limbal

approach.

PATIENTS AND METHODS

The study was conducted at the Department of Ophthalmol-ogy, Medical University of Vienna, Vienna, Austria. All researchand measurements followed the tenets of the Helsinki agreement,and all patients provided informed consent.

The study’s 21 patients (21 eyes) were recruited from a con-tinuous cohort. The inclusion criterion was age-related cataract.Exclusion criteria were a history of ocular disease or intraocularsurgery, laser treatment, diabetes requiring medical control, andglaucoma.

Cataract surgery was performed by the same surgeon (O.F.)using the same technique comprising phacoemulsification andtopical anesthesia of lidocaine 4% eyedrops. A temporal, single-plane, 3.2 mm limbal–corneal incision was created. A dispersiveophthalmic viscosurgical device (OVD), hydroxypropyl methyl-cellulose 2% (Medioclear), was injected and a capsulorhexisperformed. After thorough hydrodissection, the nucleus wasemulsified with an Orbit unit (Oertli Instrumente AG) using anab interno cracking technique, after which coaxial aspiration ofthe cortical remnants was done. After the anterior chamber wasexpanded with a cohesive OVD (Healon [sodium hyaluronate1%]), a foldable hydrophobic acrylic intraocular lens (IOL) wasimplanted in the capsular bag with an injector system. The OVDwas aspirated thoroughly from the retrolental space and the ante-rior chamber using an irrigation/aspiration tip. The main incisionand the paracenteses were hydrated with balanced saline solution(BSS) through a thin cannula.

Corneal thickness was measured preoperatively as well as1 day, 1 week, and 1 and 3 months after surgery by PCI using theACMaster. Measurements were performed along the horizontalmeridian centrally along the visual axis and at 1.5 mm, 3.0 mm,and 4.5 mm eccentricity. Mean values and standard deviationswere generated. The principles11–14 and the reproducibility of

J CATARACT REFRACT SURG1668

corneal thickness measurements15 of PCI have been reported indetail. Eccentric measurements were performed by having the ex-amined eye of the patient fixate on a target and eccentric LEDs in-corporated in the ACMaster.

To evaluate the influence of phacoemulsification on postop-erative corneal thickening, phacoemulsification time was corre-lated to the assessed relative changes in corneal thickness on thefirst postoperative day. Reproducibility was determined with re-peated measurements in 8 eyes taken at 10-minute intervals.

All other evaluation was done on a personal computer usingstandard software (MS Excel and SPSS; Sigmaplot 8.0, Systat Soft-ware Inc.). To compare changes in corneal thickness over time, thepaired t test was used. The Bonferroni adjustment was applied tomultiple t tests. A P value less than 0.05 was considered statisti-cally significant.

RESULTS

The mean age of the patients was 71.8 years G 10.8 (SD);

the median age was 73.5 years.

Preoperatively, there was a slight nasal–temporal dif-

ference in corneal thickness at all eccentricities (Table 1

and Figure 1). Corneas were slightly thicker in the nasalhalf along the horizontal meridian, reaching statistical sig-

nificance at the 1.5 mm eccentricity (P!.01). This signifi-

cant difference at 1.5 mm was found at all follow-up

measurements except the first day after surgery (P!.06)

(1 week, P!.01; 1 month, P!.05; 3 months, P!.01).

On the first postoperative day, the mean increase in

corneal thickness at all locations was 38 G 43 mm. The

thickening was more pronounced in the peripheral corneathan centrally; the mean was 31 G 42 mm centrally, 58 G55 mm 4.5 mm temporally, and 35 G 38 mm nasally. How-

ever, the differences in thickening between locations were

not statistically significant (4.5 mm temporal/central:

P Z.09; 4.5 mm nasal/central: P Z.24). At 1 week, corneal

thickness returned to baseline at all locations; the mean in-

crease at all locations compared to baseline was 7 G 53 mm.

Only at the 3.0 mm temporal location was corneal thick-ness slightly higher (mean 8 G 14 mm versus baseline),

although this did not reach statistical significance. At

1 month, corneal thickness at the 3.0 mm location returned

Table 1. Mean absolute corneal thickness at all temporal and nasal locations over time.

Mean Thickness (mm) G SD

Exam4.5 mm

Temporally3.0 mm

Temporally1.5 mm

Temporally Centrally1.5 mmNasally

3.0 mmNasally

4.5 mmNasally

Preop 529.11G 32.60 520.37 G 34.62 512.81 G 35.74 517.71 G 36.64 521.67 G 34.02 526.35 G 34.88 550.31 G 29.43Postop

Day 1 576.21 G 73.00 546.20 G 58.81 555.14 G 47.86 549.14 G 56.52 561.29 G 53.54 564.57 G 55.02 586.75 G 70.90Week 1 529.79 G 57.36 526.38 G 36.71 517.43 G 34.27 515.86 G 36.81 528.00 G 36.58 521.35 G 50.50 529.33 G 43.55Month 1 526.20 G 37.56 516.19 G 34.60 512.14 G 32.81 513.62 G 32.52 519.67 G 40.36 519.31 G 38.87 516.27 G 72.08Month 3 530.20 G 36.12 520.52 G 30.72 514.57 G 33.07 519.76 G 48.84 527.14 G 33.46 532.26 G 38.01 528.82 G 46.22

- VOL 32, OCTOBER 2006

CORNEAL THICKNESS CHANGES AFTER CATARACT SURGERY

to baseline. Relative local changes in corneal thickness(3.0 mm temporal, central, and 3.0 mm nasal) over time

are shown in Figure 2. The mean difference in corneal

thickness compared to baseline was 1 G 42 mm, at 1 month

and 6 G 41 mm at 3 months. Absolute corneal thickness

values at all eccentricities along the horizontal meridian

at day 0, day 1, and week 1 are shown in Figure 3.

At baseline and all follow-up examinations, it was not

possible to assess reliable corneal thickness values at

Figure 1. Differences in corneal thickness between corresponding tem-

poral and nasal eccentricities along the horizontal meridian at baseline,

before surgery. Box plots represent absolute values in millimeters at the

following eccentricities: 1.5 mm, 3.0 mm, and 4.5 mm. Dotted boxes rep-

resent temporal values; lined boxes represent nasal values.

J CATARACT REFRACT SURG -

4.5 mm eccentricity in 9 eyes and at 3.0 mm in 6 eyes,

mainly because of the presence of slight age-related corneal

opacities such as arcus senilis or postoperative corneal al-

terations. Thus, to avoid statistical bias, changes in corneal

thickness were assessed by case-wise deletion of missing

values. This is why the values of relative changes in cornealthickness reported above differ from the absolute values in

Table 1.

At the 3.0 mm and 1.5 mm eccentricities, corneal

thickness could be assessed precisely. There was a high

intraobserver reproducibility centrally (1.17 G 0.17 mm),

at 1.5 mm (temporally: 1.08 G 0.37 mm; nasally: 1.42 G0.59 mm) and at 3.0 mm (temporally: 0.58 G 0.73 mm; na-

sally: 1.7 G 0.77 mm). At 4.5 mm eccentricity, the repro-ducibility was lower (temporally: 6.25 G 0.09 mm;

nasally: 4.00 G 0.66 mm), which could have been caused,

in part, by the peripheral opacities.

The mean phacoemulsification time was 42.10 G24.70 seconds (median 35 seconds). No significant correla-

tions were found between the phacoemulsification time

and the relative change in corneal thickness at day 1

(r2 Z .06; data not shown).

DISCUSSION

Phacoemulsification surgery via a temporal clear lim-

bal approach caused an increase in corneal thickness at

all locations along the horizontal meridian 1 day after

surgery. One week after surgery, corneal thickness values

returned to baseline at nearly all eccentricities except3.0 mm temporally. Therefore, in normal uneventful cata-

ract surgery, corneal edema is initially diffuse across the en-

tire cornea, with similar increases in corneal thickness. The

ACMaster, which is based on the precise and reproduc-

ible15 PCI technique, was an appropriate tool to evaluate

Figure 2. Relative change in corneal thickness (mean G SD) in millimeters over time presented separately for the following eccentricities: 3.0 mm temporal,

central and 3.0 mm nasal. Measurements were performed 1 day postoperatively (d1) and after 1 week (w1), 1 month (m1), and 3 months (m3).

VOL 32, OCTOBER 2006 1669

CORNEAL THICKNESS CHANGES AFTER CATARACT SURGERY

this corneal stress after cataract surgery. In addition, the

technique showed statistically significant nasal–temporaldifferences in corneal thickness preoperatively.

The postoperative corneal edema in our study could

have been the result of several factors that cause mechani-

cal stress such as turbulent irrigation fluids and nuclear

fragments during phacoemulsification or heat transfer

from the phaco tip. In addition, the intraocular irrigation

fluid, which has a slightly different pH, osmolarity, and

ion constitution than aqueous, could have caused cellularstress in the cornea. The prolonged thickening near the in-

cision site at 3.0 mm eccentricity (temporal) may be a result

of the mechanical stress exerted from the incision through

Descemet’s membrane, the proximity to the hot phaco tip,

or the higher mechanical stress caused by turbulence due to

inflow and outflow near the incision. This could also be

caused by edema from the injection of BSS in the corneal

stroma at the end of cataract surgery.The corneal edema caused by these factors was mea-

sured with the ACMaster. This device was appropriate for

investigating postoperative corneal thickness changes in el-

derly patients preoperatively and immediately postopera-

tively in a clinical setting. It allowed measurement of

several preset eccentricities by moving a visual target on

which the patient was asked to fixate. This technical feature

led to the observation of a slight nasal–temporal gradient incorneal thickness along the horizontal meridian. This gra-

dient was also detected before surgery.

Several studies describe local (preoperative) differences

in corneal thickness using several techniques such as

ultrasound,16–20 laser pachymetry,16 scanning slit-beam

Figure 3. Absolute corneal thickness values in millimeters at the following

temporal and nasal eccentricities: 4.5 mm, 3.0 mm, 1.5 mm, and centrally

(center). The dotted line represents preoperative values. The broken line

represents values at day 1. The continuous line represents values 1 week

after surgery. Mean values and standard error of the mean are depicted.

J CATARACT REFRACT SURG -1670

(Orbscan),18,21–23 confocal microscopy,20 PCI,15 or

Scheimpflug photography.18 Remon et al.17 report the cor-

nea is significantly thinner in the superior area in newborns.

In studies by Liu and Pflugfelder22 and Liu et al.,23 however,

the superior corneal area was found to be the thickest. Thus,

results in studies of corneal thickness and its changes overtime are highly variable, with some studies finding contra-

dicting results. This could, in part, be due to the difficulty

of taking into account all influencing factors such as physi-

ologic diurnal thickness fluctuations,21 corneal astigma-

tism, effects of a dry-eye syndrome22 or, more important,

the measurement technique.

Using PCI, a well-established technique for corneal pa-

chymetry, we showed that measuring different corneal loca-tions is feasible in elderly patients in the perioperative

setting. Slight corneal opacities, such as arcus senilis or cor-

neal edema in or close to the temporal incision area, atten-

uated the measurements and resulted in failures at the

4.5 mm eccentricity as a result of a low signal-to-noise ra-

tio. The PCI technique also has better interexaminer and

intraexaminer reproducibility than most other methods.

Several authors6,9 report that corneal thickeningcaused by phacoemulsification is reversible. Grupcheva

et al.24 found that postoperative corneal thickness in

the meridian closest to the incision measured with Orbs-

can technique was significantly higher than the mean

value of 12 meridians. This agrees with our results show-

ing mild edema at the 3.0 mm eccentricity 1 week after

surgery.

Apart from corneal thickening at the incision site,Lundberg et al.10 found strong correlations between total

postoperative endothelial cell loss and corneal swelling.

The degrees of permanent corneal endothelial damage

were reported to be reflected in the degree of early postop-

erative corneal thickening. Hence, investigating the

changes in corneal thickness seems appropriate when eval-

uating corneal stress during phacoemulsification surgery in

clinical trials in which OVDs or surgical techniques arecompared.

In conclusion, our study showed PCI to be appropriate

for assessing a preoperative nasal–temporal difference in

corneal thickness along the horizontal meridian as well as

postoperative changes in corneal edema precisely and re-

producibly. In all eyes, phacoemulsification seemed to

cause a significant alteration of the corneal layers that led

to edema. Nevertheless, these pachymetric changes werereversible, almost reaching baseline values 1 week after

surgery.

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