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REFRACTIVE SURGERY

The effect of hinge location on corneal sensation and dry eye

after LASIK: a systematic review and meta-analysis

Yi-fan Feng & Ji-guo Yu & Dan-dan Wang & Jun-hua Li &

Jin-hai Huang & Jie-liang Shi & Ting Ye & Qin-mei Wang &

Yun-e Zhao

Received: 14 January 2012 /Revised: 18 May 2012 /Accepted: 24 May 2012 /Published online: 15 June 2012# Springer-Verlag 2012

Abstract

Background The aim of this meta-analysis is to investigatethe possible effect of hinge location on corneal sensation

and dry eye syndrome after laser-assisted in situ keratomi-

leusis (LASIK).

Methods A comprehensive literature search was conducted

in the PubMed, EMBASE, and Cochrane Controlled Trials

Register to identify potentially relevant randomized con-

tro lled tr ia ls (RCTs ) o f c o mp arin g th e e ffe cts o f

horizontal-hinge flaps and vertical-hinge flaps on corneal

sensation and dry eye after LASIK. Meta-analyses were

pe rf orme d fo r co rn ea l se ns atio n, te ar brea k-up ti me

(TBUT), Schirmer's I test and corneal fluorescein staining

(CFS) at 1 week, 1, 3, and 6 months postoperatively. Results Eight RCTs (657 eyes) investigating the effects of

hinge location on the corneal sensation and dry eye syn-

drome after LASIK were identified. The results showed that

the horizontal-hinge group causes less loss of sensation than

the vertical-hinge group, and the difference was significant

at 3-month postoperative ( p00.01). The TBUT value was

significantly larger and a lower percentage of patients with

CFS in the horizontal-hinge group than in the vertical-hinge

group at 1-month postoperative ( p00.007 and p00.01,

respectively) and 3-month ( p00.03 and p00.009, respec-

tively); Schirmer's I test values were also higher in thehorizontal-hinge group, but the difference did not reach

statistically significance at each postoperative period.

Conclusions According to the available data, we suggest

that hinge location may have some effect on corneal sensa-

tion and dry eye syndrome after LASIK at the early postop-

erative period. However, there was no significant difference

between the groups at 6 months after surgery. Further well-

organized, prospective, randomized studies involving more

patients are warranted.

Keywords Laser-assisted in situ keratomileusis . Hinge

position . Corneal sensation . Dry eye

Introduction

Dry eye syndrome is a frequent postoperative complication

of laser-assisted in situ keratomileusis (LASIK) [1]. Al-

though estimates of the incidence of dry eye syndrome vary

widely (from 3 – 59 % [1 – 3]), almost all patients will have

transient dry eye during the immediate postoperative period.

These symptoms, such as mild irritation, foreign-body sen-

sation to pain, photophobia, and fluctuating visual acuity

between blinks, are considered to be associated with sever-

ing of the corneal nerves in LASIK surgery [4]. Corneal flap

creation and ablation of the stroma during LASIK cause the

innervation damage to afferent sensory nerves, which can

produce a relative loss of corneal sensation. This loss of

sensation appears to be a significant contributing factor to

the reduction in tear secretion, tear film stability, blink rate,

and conjunctival goblet cell density [5, 6].

Because of the variability in corneal innervation patterns,

altering flap characteristics in LASIK may affect postoperative

Proprietary interest The authors have no proprietary or commercial

interests in any material discussed in this article. The authors have full

control of all primary data and agree to allow Graefes Archive for

Clinical and Experimental Ophthalmology to review data upon request.

ClinicalTrials.gov identifier NCT01507025

Y.-f. Feng : J.-g. Yu : D.-d. Wang : J.-h. Li : J.-h. Huang :

J.-l. Shi : T. Ye : Q.-m. Wang : Y.-e. Zhao (*)

The Affiliated Eye Hospital of Wenzhou Medical College, School

of Optometry and Ophthalmology, Wenzhou Medical College,

No. 270, Xueyuan Road,

Wenzhou, Zhejiang Province, China

e-mail: [email protected]

Graefes Arch Clin Exp Ophthalmol (2013) 251:357 – 366

DOI 10.1007/s00417-012-2078-5



corneal sensation and dry eye disease. Some studies have

reported that postoperative corneal sensation may be higher

and recovery faster in eyes with horizontal-hinge flaps (nasal-

or temporal) than in eyes with vertical-hinge flaps (superior) [7,

8]. However, some other studies were unable to confirm differ-

ences in the effect of hinge position on corneal sensation and

dry-eye symptoms [9, 10]. Currently, no systematic review of

this subject is available. This study reviewed the publishedliterature and performed a meta-analysis aimed to investigate

the effects of hinge location on corneal sensation and dry eye

symptoms after LASIK.

Materials and methods

This meta-analysis was performed according to a predeter-

mined protocol described in the following paragraphs [11, 12].

Search strategy

Two reviewers (Y.F.F. and J.G.Y.) independently searched

the following electronic databases: PUBMED, EMBASE,

and the Cochrane Controlled Trials Register, and the last

search was performed on November 15, 2011. The follow-

ing keywords were used: laser in situ keratomileusis,

LASIK, hinge position corneal sensation, and dry eye. There

was no language restriction on the publications. All relevant

studies were obtained and assessed to determine whether

they met standard quality criteria for inclusion in the study.

In addition, the reference lists of original reports and review

articles retrieved through the search were reviewed for ad-

ditional studies not yet included in the computerized

databases.

Trials selection

Studies fulfilling the following inclusion criteria were in-

cluded in the present meta-analysis: (1) each trial should be

a prospective randomized controlled clinical trial (RCT), (2)

the age of the patient population should be over 18 years, (3)

the patients were scheduled to undergo LASIK and assigned

to horizontal-hinge flap (HF) group or vertical-hinge flap

(VF) group, (4) at least one of following outcomes was

assessed: corneal sensation, tear break-up time (TBUT),

Schirmer's I test, and the proportion of patients with corneal

fluorescein staining (CFS). Exclusion criteria were as fol-

lows: (1) non-RCTs, (2) patients who had a previous oph-

thalmic surgery or ocular surface disorders, and (3) the raw

data were not completed. If more than one version of the

same study was retrieved, only the most recent was used.

Two reviewers (Y.F.F. and J.G.Y.) separately evaluated stud-

ies based on inclusion and exclusion criteria, and discrep-

ancies were resolved by discussion.

Data extraction

Data extraction was performed according to the customized

protocol by two reviewers (Y.F.F. and J.G.Y.) independently.

A customized form was used to record the following data:

the authors of the study, the year of publication, information

on study design (whether randomization, allocation conceal-

ment, intention-to-treat (ITT) analysis, double blind or sin-gle blind), location of trial, length of study, number of

subjects, patient age, sex, and the preoperative mean spher-

ical equivalent refraction (SE).

Qualitative assessment

The RCTs were analyzed for their quality based on the

Delphi list for quality assessment of randomized clinical

trials [13]. For each trial, a quality score was calculated,

where “yes” was scored as one point for a certain quality

item and “no” and “don’t know” were scored as zero points.

The quality of individual study was then determined bygiving a total additive score to each study. Based on these

assessments and the Cochrane Collaboration guidelines, the

two reviewers (Y.F.F. and J.G.Y.) independently evaluated

the studies, and disagreements were resolved by discussion.

Outcome measures

The outcome parameters for inclusion were corneal sensation,

TUBT, Schirmer's I test, and the proportion of patients with

CFS. Studies presented results at varying follow-up periods,

and we chose to analyze results at 1 week and 1, 3, and

6 months due to their common presence in most study reports.

In absence of continuous outcome values reported in a

table or text, the values were measured when presented in a

figure. Figures used to extract data were electronically

scanned and viewed at full screen size (1024×768 pixels)

and a digital ruler was used to measure. All figures were

read by the same researcher (Y.F.F.).

Statistical analysis

Original data were obtained from the articles as much as

possible; data that could not be obtained were to be calcu-

lated when necessary. When standard deviation (SD) was

not available, it was calculated using the sample sizes and

standard error. When neither an SD nor a standard error of

end point measurement was available, baseline SD was used

as an estimate of the SD of any time point postoperatively.

When only the p value for the difference between the two

groups was reported, the SD was calculated according to the

p value and the sample sizes.

Statistical analysis was performed using RevMan

software (version 5.0; Cochrane Collaboration, Oxford,

358 Graefes Arch Clin Exp Ophthalmol (2013) 251:357 – 366



United Kingdom). Summary estimates, including 95 %

confidence intervals (CIs), were calculated. For contin-

uous outcome, means and standard deviations were used

to calculate the weighted mean difference (WMD; e.g.,

corneal sensation, TBUT, Schirmer's I test). For dichot-

omous outcomes, the odds ratio (OR; e.g., proportions

of CFS) was calculated.

Statistical heterogeneity was tested using the Chi-squareand I2 statistic. Fixed-effects models were used unless sig-

nificant evidence of statistical heterogeneity or clinical di-

versity was found. However, for results showing significant

heterogeneity (I2>50 %), a random-effects meta-analysis

was performed by DerSimonian-Laird method [14]. This

model can yield wider CI, which would reduce the hetero-

geneity. A p value less than 0.05 was considered statistically

significant. Potential publication bias was examined using a

funnel plot [15].

Results

Literature search

The combined search identified a total of 302 publications.

However, only 11 articles were considered potentially rele-

vant. Of the 11 publications, three finally were excluded for

non-randomized design [16], animal model [17], and no

measurable outcomes [18]. Thus, the remaining eight RCTs

published between 2003 and 2009 were included in this

meta-analysis [7 – 10, 19 – 22].

A total of 366 participants with 657 eyes in eight

included studies were enrolled in this meta-analysis; 328

eyes assigned to the VF group and 329 eyes to the HF

group. Sample sizes in these studies ranged from 20 to

106. The mean age was ranged between 26.5 and

40.8 years and the follow-up time was 6~ 12 months.

Of the eight RCTs, six studies reported random selec-

tion of VF in one eye and HF in the other eye in each

patient [8 – 10, 19, 21, 22]. Corneal flap was created by

mechanical microkeratome in six studies [7 – 9, 19, 20,

22] and by femtosecond laser in remaining two studies

[10, 21] (Table 1). The included trials are also assessed

on their quality (Table 2).

Corneal sensitivity

Five studies reported corneal sensitivity by using the

Cochet – Bonnet esthesiometer [7, 8, 10, 21, 22]. Because

statistically significant heterogeneity was evident for the

outcome of corneal sensitivity, a random-effects model

was used to combine the data. Analysis of these data

showed that the mean decrease in corneal sensation was

significantly greater in the VF group compared to the HF

group 3 months postoperatively (WMD −0.81; 95 % CI

−1.46 to −0.17; p00.01). There was no significant differ-

ence between the two groups at postoperative 1-week

(WMD −0.24; 95 % CI −0.57 to 0.08; p00.14), 1-month

(WMD −0.29; 95 % CI −0.59 to −0.01; p00.06) and 6-

month (WMD −0.20; 95 % CI −0.41 to 0.00; p00.06)

(Fig. 1).

Tear break-up time

Five studies reported data for the TUBT [8, 9, 19, 20, 22]. In

one study, the 2-month results were used as a proxy for 1-

month results [19]. Analysis of these data showed that the

mean decrease in TBUT was significantly greater in the VF

group compared to the HF group at 1 week (WMD −0.40;

95 % CI −0.66 to −0.14; p00.003), 1-month (WMD −0.44;

95 % CI −0.77 to −0.12; p00.007) and 3-month (WMD

−0.37; 95 % CI −0.71 to −0.03; p00.03) postoperative

visits. There was no significant difference between the two

groups at the 6-month visits (WMD −

0.28; 95 % CI−

0.62 to0.06; p00.11) (Fig. 2).

Schirmer's I test

Five studies reported data for the Schirmer ’s I score [8, 9,

19, 20, 22]. Analysis of these data showed that there was no

significant difference in the mean decrease in Schirmer ’s I

score between the VF group and the HF group at 1 week

(WMD −0.14; 95 % CI −0.78 to 0.50; p00.67), 1 month

(WMD −0.40; 95 % CI −1.13 to 0.33; p00.28), 3 months

(WMD −0.13; 95 % CI −0.74 to 0.47; p00.67), 6 months

(WMD0−

0.29, 95 % CI −

1.12 to 0.53, p00.49) postopera-

tively. (Fig. 3)

Corneal fluorescein staining

Three studies reported data for proportion of patients

with corneal fluorescein staining [8, 10, 22]. Analysis of

these data showed that the VF group showed a signif-

icantly greater percentage of patients with CFS com-

pared to the HF group at 1 month (OR 3.7; 95 % CI

1.37 to 10.03; p00.01) and 3 months (OR 9.69; 95 %

CI 1.75 to 53.70; p00.009) postoperatively. There was

no significant difference between the two groups at

pos toper ative 1 week (OR 1.7 4; 95 % CI 1.3 7 to

10.03; p00.01) and 6 months (OR 3.7; 95 % CI 1.37

to 10.03; p00.01) (Fig. 4).

Publication bias

Publication bias was assessed for all pooled WMDs and OR

with confidence intervals and shown as a funnel plot in

Fig. 5. No evidence of publication bias was found.

Graefes Arch Clin Exp Ophthalmol (2013) 251:357 – 366 359



T a b l e 1

C h a r a c t e r i s t i c s o

f r a n

d o m i

z e

d c o n t r o l l e d t r i a l s i n t h e m e t a - a n a

l y s i s

A u t h o r ( s )

Y e a r , l o c a t i o

n

N o . o f e y e s

F l a p c r e a t i o n

M e a n a g e

( y e a r s , r a n

g e )

G e n d e r ( M / F )

P r e o p . m e a n S E ( D , r a n g e )

F o l l o w - u p

( m o n t h s )

M a i n o u t c o m e

V F

H F

V F

H F

D o n n e n f e l d e t a l . [ 8 ]

2 0 0 3 , U S A

5 2

5 2

M K

4 0 . 1

2 5 / 2 7

N R ( − 4 . 7 0 ~ + 1 . 8 0 )

6

( 1 )

T B U T ; ( 2 ) S c h i r m e r 1 t e s t ;

( 3

) C F S ; ( 4 ) O S D I ; ( 5 ) C S

L e e e t a l . [ 1 9 ]

2 0 0 3 , K o r e a

2 5

2 5

M K

2 6 . 5 ( 2 2 – 2

9 )

9 / 2 1

− 9 . 4 8 ± 2 . 1 8

− 8 . 1 4 ± 2 . 1

6

( 1 )


( 3

) C S

M i a n e t a l . [ 1 0 ]

2 0 0 7 , U S A

3 3

3 3

F S

4 0 . 8 ( 2 8 – 6

5 )

1 5 / 1 8

− 3 . 7 5 ( − 0 . 3 8 ~ − 9 . 5 0 )

− 4 . 0 2 ( − 0 . 7 5 ~ − 9 . 5 0 )

1 2

( 1 )


( 3

) C F S ; ( 4 ) O S D I ; ( 5 ) C S

D e P a i v a e t a l . [ 2 0 ]

2 0 0 6 , U S A

1 7

1 8

M K

3 8 . 5 1

1 9 / 1 6

− 4 . 9 0 ± 2 . 3 7

− 3 . 0 3 ± 1 . 6 7

6

( 1 )


( 3

) C F S ; ( 4 ) C S

M i a n e t a l . [ 2 1 ]

2 0 0 9 , U S A

2 8

2 8

F S

3 8 . 9 ( 2 2 – 6

5 )

N R

− 4 . 2 ( − 0 . 7 5 ~ − 1 0 . 0 0 )

− 4 . 4 ( − 0 . 7 5 ~ − 9 . 7 5 )

1 2

( 1 )


( 3

) C F S ; ( 4 ) O S D I ; ( 5 ) C S

G h o r e i s h i e t a l . [ 9 ]

2 0 0 5 , I r a n

1 0 6

1 0 6

M K

2 7 . 5

3 0 / 7 6

− 4 . 7 0 ± 1 . 8 3

6

( 1 )


( 3

) O S D I ; ( 4 ) C S

V r o m a n e t a l . [ 2 2 ]

2 0 0 5 , U S A

4 7

4 7

M K

3 8 . 6 ( 2 2 – 5

5 )

N R

− 4 . 0 7 ± 1 . 7 7

− 4 . 1 9 ± 1 . 9 1

6

( 1 )


( 3

) C F S ; ( 4 ) O S D I ; ( 5 ) C S

N a s s a r a l l a e t a l . [ 7 ]

2 0 0 5 , B r a z i l

2 0

2 0

M K

2 6 . 2 ( 2 0 – 3

5 )

1 8 / 2 2

N R ( − 1 . 0 0 ~ − 2 . 5 0 )

8

( 1 )

C S

V F v e r t i c a

l f l a p ; H F h o r i z o n t a l f l a p ; M M m e c

h a n

i c a

l m

i c r o

k e r a t o m e ; F S L f e m t o s e c o n

d l a s e r ; T B U T t e a r

b r e a

k - u p t i m e ; C F S c o r n e a

l f l u o r e s c e

i n s t a

i n i n g ; O S D I O c u

l a r

S u r f a c e

D i s e a s e

I n d e x ; N R

n o t r e p o r t e

d

T h e s t u

d y

b y

N a s s a r a

l l a e t a

l . [ 2 0 ] i n

c l u d i n g

f o u r g r o u p s a c c o r d

i n g t o t h e

h i n g e p o s i t i o n a n

d d e p t h p

l a t e ( D P ) — g r o u p

1 ,

n a s a

l h i n g e a n

d 1 3 0 μ m

D P ; g r o u p

2 ,

n a s a

l h i n g

e a n

d 1 6 0 μ m

D P ; g r o u p

3 ,

s u p e r i o r

h i n g e a n

d 1 6 0 μ m

D P ; g r o

u p

4 ,

s u p e r i o r

h i n g e a n

d 1 8 0 μ m

D P




Table 2 Quality assessment of randomized trials based on Delphi list for quality assessment of randomized clinical trials [13]

Study Randomization Allocation

concealment

Baseline

group

similarity

Eligibility

criteria

specified

Blinded

outcome

assessor

Care

provider

blinded

Patient

blinded

Point estimates

and measure of

variability presented

Intention

to treat

analysis

Total

score

Donnenfeld et al. [8] Yes Yes Yes Yes Yes Yes Yes Yes DNK 9

Lee et al. [19] Yes Yes Yes Yes No No No Yes Yes 6

Mian et al. [10] Yes Yes Yes Yes No No No Yes Yes 6De Paiva et al. [20] Yes Yes Yes Yes Yes Yes Yes Yes Yes 9

Mian et al. [21] Yes Yes Yes Yes No No No Yes DNK 5

Ghoreishi et al. [9] Yes Yes Yes Yes Yes Yes Yes Yes Yes 9

Vroman et al. [22] Yes Yes Yes Yes Yes Yes Yes Yes Yes 9

Nassaralla et al. [23] Yes Yes Yes Yes Yes No No Yes Yes 7

DNK do not know

Fig. 1 Forest plot of comparison showing corneal sensitivity in studies

comparing for LASIK with vertical flap versus horizontal flap at

postoperative 1 week, 1, 3, and 6 months (Chi2 Chi-square statistic,

CI confidence interval, df degrees of freedom, I 2 I-square heterogeneity

statistic, IV inverse variance, Z Z-statistic)




Discussion

Regarding the popularity of LASIK for the treatment of

refractive errors and the importance of ocular dryness com-

plaints after these procedures, we performed a meta-analysis

to compare different hinge positions of corneal flap making

for their effect on corneal sensation and dry eye. The present

study provided evidence that eyes with HF cause less loss of

sensation than VF and the difference reached significance at

postoperative 3 months; HF group had a significantly longer

TBUT and less percentage of patients with corneal staining

compared to VH group at postoperative 1 and 3 months;

Schirmer ’s I test values were also higher in the HF group,

although this difference was no statistically significant.

However, all the objective sings were not significantly dif-

ferent between the two groups at 6 months postoperatively.

Several mechanisms for dry eye symptoms after LASIK

have been proposed. These include damage to the goblet

cells by suction ring – induced pressure, decreased corneal

sensation and blink reflex, altered tear-film stability caused

by changes in corneal curvature, and medication-induced

effects [23]. Flap creation in LASIK severs all superficial

corneal nerves except at the hinge, which provides a route

for undisturbed innervation. Therefore, the location of the

hinge may be planned to afford the cornea the best sensory

advantage. Some previous studies found greater loss of

corneal sensation and increased dry eye signs and symptoms

in patients having surgery with VF than in those with HF [7,

8, 16]. These findings are supported by the traditional model

of corneal innervation that suggested that the long ciliary

nerves enter the cornea at the 3 o’clock and 9 o’clock

positions, with greater susceptibility to corneal nerve dam-

age with vertically hinged than with horizontally hinged [8].

Our meta-analysis of RCTs showed that compared to a

vertical-hinge location, a horizontal-hinge position lead to

less corneal sensory disturbance, which then resulted in

fewer dry eye complaints from patients. However, the true

distribution of corneal nerves is still controversial and is

Fig. 2 Forest plot of comparison showing tear break-up time in studies comparing LASIK with vertical flap versus horizontal flap at postoperative

1 week, 1, 3, and 6 months




being elucidated. Müller et al. [24] reported the opposite

finding that leashes extend across the corneal apex prefer-

entially in the 6 to 12 o’clock direction and other leashes

approach the apex in the 5 to 11, 7 to 1, 9 to 3, 2 to 8, and 4

to 10 o’clock directions. Further basic studies are needed to

clear up the subject.

Subjective symptoms are important in the diagnosis and

management of dry eye. Seven studies, including our meta-

analysis, have compared the subjective dry eye symptoms

by a questionnaire method [8 – 10, 19 – 22]. The results were

generally consistent and showed that dry eye symptoms

were increased over preoperative values, but there was no

significant difference between the VF and HF groups at any

time point. However, we did not analyze the subjective

symptoms because not enough studies reported consistently

on the rates or extent in each group to perform a statistical

analysis. There is a limited consensus on how to define dry-

eye disease because symptoms often do not correlate with

clinical signs. Currently, an approach recommended by

Delphi for severity evaluation of dry eye was that combine

objective tests such as central corneal sensation, Schirmer

test with anesthesia, TBUT, corneal fluorescein staining,

and conjunctival lissamine green staining in conjunction

with subjective symptom assessment using the Ocular Sur-

face Disease Index (OSDI) questionnaire [25].

Using the femtosecond laser allows creation of horizon-

tally or vertically oriented flaps with the same keratome.

Two articles included in this study reported that when

performing LASIK with the IntraLase laser and using the

same keratome, hinge position had no effect on corneal

sensation and dry-eye disease parameters [10, 21]. Never-

theless, the femtosecond laser may generate more consistent

and predictable flap diameters and thicknesses than micro-

keratomes [26]. There may also be fewer flap-related com-

plications, including reduced epithelial injury and faster

recovery of corneal sensation with use of femtosecond lasers

[27, 28]. One recent study found that eyes with femtosecond

flaps had a lower incidence of LASIK-associated dry eye

Fig. 3 Forest plot of comparison showing Schirmer's I test in studies comparing LASIK with vertical flap versus horizontal flap at postoperative1 week,1, 3, and 6 months




and required less treatment for the disorder [29]. A deeper

lamellar dissection is expected to create a larger volume of

tissue through which nerves must regenerate, thus delaying

the return of corneal sensation. [22] Thus, the lower

Fig. 4 Forest plot of comparison showing corneal fluorescein staining in studies comparing for LASIK with vertical flap versus horizontal flap at

postoperative 1 week, 1, 3, and 6 months ( M-H Mantel-Haenszel)

Fig. 5 A funnel plot to explore

publication bias. The standard

error of mean difference of each

trial was plotted against the

mean difference for tear break-

up time. No skewed distribution

was observed, suggesting no

publication bias (the funnel plot

for other primary outcomes was

not represented here)




incidence of dry-eye signs and symptoms with the femto-

second lasers may be attributed to the creation of thinner

flaps, resulting in greater residual stromal beds and de-

creased corneal denervation. [10, 29]

The present study has limitations that result from the

quality of the individual trials and the methods of the

meta-analysis itself. First, our research was restricted to

studies published in indexed journals or in certain trialregisters and conference proceedings. We did not search

for unpublished studies or original data. Second, the studies

included were heterogeneous in terms of study location,

population, number of patients from different studies, and

basal condition. We must acknowledge that the preoperative

incidence of dry-eye signs and symptoms was low, which

may predispose to a lower postoperative incidence of dry-

eye disease as preexisting dry eye is a risk factor for severe

postoperative dry-eye disease. Third, other factors such as

the degree of preoperative myopia, depth of laser treatment,

and flap thickness may also play a role for developing a dry

eye [7, 20]. This review unfortunately did not comprise a sufficient number of studies to perform subgroup meta-

analyses for these risk factors.

In summary, the present study suggests that hinge loca-

tion of corneal flap dose have some effects on corneal

sensation and the dry eye syndromes after LASIK. Compar-

ing with a vertical hinge flap, a horizontal hinge flap would

lead to less corneal sensory disturbance and dry eye syn-

dromes at early postoperative period, although there was no

significant difference between the groups at 6 months after

surgery. However, due to the fact that multiple factors may

contribute to the disorder, further elucidation of corneal

nerve organization and regrowth patterns may help us un-

derstand how to minimize dry eye after LASIK.

Acknowledgments This research was partly supported by the Fi-

nancing Project of Science and Technology Innovation Plan for Col-

lege Students of Zhejiang Province, China (2011R413047).

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