准分子激光角膜切削术治疗近视和近视散光的临床研究
作者：张华 郭绒霞 孙乃学 王峰 张道过 王彤 孙健 杨振国 胡海涛 任惠民 刘勇
单位：
关键词：准分子激光角膜切削术；近视；近视散光
眼科新进展000102
摘 要：目的 评价准分子激光角膜切削术矫正近视的结果。方法 我院自1996年9月到1997年10月，应用SVS APEX型(Summit Technology Inc.USA)准分子激光治疗仪，对168例近视患者(316只眼)行PRK手术，对其中的150例(260只眼，占84%)患者随诊至少3mo以上，最长1a；男68例(116只眼，占40.1%)，女82例(144只眼，占59.9%)。150例(260只眼)近视患者术前等值球镜屈光度为-1.25～-10.00D(-4.67D±1.63D)，散光0～-2.00D(-0.33D±0.45D)；按屈光度分为两组：A组(-1.25～-5.90D)，B组(-6.00～-10.00D)。结果 A组术后第10天，有68.9%(132/220)裸眼视力达到矫正视力，1、3、6和12mo分别为90%、96%、95%和94%.B组术后第10天，有35.9%(13/40)裸眼视力达到矫正视力，1、3、6和12mo分别为83%、87%、86%和84%.全组仅3只眼(0.64%)除外，均为0.5～1.0级的角膜上皮下雾状混浊，其出现的百分比手术后10d和1、3、6、12mo分别为32.9%、84.2%、62.4%、9.0%和2.8%.结论 提示准分子激光角膜切削术治疗-10.00D以内的近视是一种安全有效、稳定性好、预测性强的方法，-6.00D以下效果更好。
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分类号：R776.62;R778.1+1 文献标识码：A
文章编号：1003-5141(2000)01-0005-05
Evaluation of excimer laser photorefractive keratectomy for treatment of myopia and myopic astigmatism
ZHANG Hua
(Assiduously studying for his Doctor degree in Xi'an Medical University)
GUO Rong-Xia,SUN Nai-Xue,WANG Feng,ZHANG Dao-Guo,WANG Tong,SUN Jian,YANG Zhen-Guo,HU Hai-Tao,REN Hui-Min,LIU Yong
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(Department of Ophthalmology,the First People's Hospital of Jining,Jining 272111,Shandong Province,China)
Abstract：Objective To evaluate the efficacy and accuracy of photorefractive keratectomy(PRK) for myopia and myopic astigmatism.Methods SVS APEX PLUS excimer laser with a wave length of 193nm(Summit Technology Inc.Waltham,Mass,USA) was applied.Three hundred and sixteen myopic eyes of 168 patients were treated with PRK from Suptember 1996 to October 1997,and 260 eyes(84%) of 150 patients were followed-up for more than three month,including male 68(116 eyes,40.1%) and female 82(144 eyes,59.9%).The preoperative spherical equivalent refractive errors ranged from -1.25D to -10.00D(mean -4.67D± 1.63D),and astigmatism ranged from 0 to -2.00D(mean -0.33D±0.45D). The patients were divided into two groups according to the refraction:group A(from -1.25D to -5.90D) and group B(from -6.00D to -10.00D).The number of eyes in the two groups were 220 and 40,respectively.Results In group A,After 10 days,68.9% had the uncorrected visual acuity(UCVA) equal to or one line better or lower than the preoperative best corrected visual acuity(BCVA).After 1 ,3,6 and 12 months,90%,96%,95% and 94% had the UCVA equal to or one line better or lower than the preoperative BCVA,respectively.In group B,after 10 days,1,3,6 and 12 months,UCVA equal to or one line better or lower than the preoperative BCVA occurred in 35.9%,83.0%,87.0%,86.0% and 84.0% of the patients respectively. Most of the haze showed 0.5～1 grades except 3 eyes with the haze of 2 grade at 3 or 6 months and it changed to l and 0.5 grade respectively at one year.after 10 days and 1,3,6,12 months postoperatively,the corneal haze was noted in 32.9%,84.8%,62.8%,9.0%and 2.8% of the treated eyes respectively.Conclusion We found that the 193nm excimer laser PRK is a predictable,safe,stable,and effective refractive surgery for correcting myopia up to-10.00D in Chinese patients,and the effect is better in myopia lower than -6.00D.
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Key words：excimer laser photorefractive keratectomy;myopia;myopic astigmatism▲
In 1983,Trokel,et al[1] first reported the laboratory reasearch about excimer laser.Clinical using of excimer laser photorefractive keratectomy were begun by Marshall,et al[2]in 1988. During the last dacade,a new corneal refractive surgery-excimer laser photorefractive keratectomy(PRK) has been developed rapidly[3-8].
, 百拇医药 The excimer laser produces high-energy UV radiation pulses with a 193nm wave length.The energy absorbed by the cornea with each pulse is sufficient to cause disruption of intramolecular bonds and ablation of corneal tissue with submicron accuracy and minimal effect on adjacent tissue[3].The argon fluoride exeimer laser has emerged as a powerful tool in the surgical treatment of myopia.PRK is a new refractive surgery that is gradually accepted by both surgeons and patients worldwide.This study presents the results of 260 visible eyes treated with PRK and followed up for more than three month to evaluate the predictability,stability and safety of PRK.
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PATIENTS AND METHODS
Selection of patients To be eligible for inclusion in this study,patients were required to be at least 18 years of age,have stable myopia of up to -10D at the corneal plane with or without stable astigmatism of up to -2D,and have best corrected visual acuity of 0.8 or better.
Preoperatively,all the patients were asked to explain their refractive and spectacle histories.Wearers of soft contact lenses were assessed 2 weeks after lens removal.All the patients received a routine ophthalmic examination including dominant eyes,slit-lamp microscope and ophthalmoscopic examinations,intraocular pressure(IOP)measured by non contact tonometer(NCT),uncorrected visual acuity(UCVA)and the best corrected visual acuity(BCVA),corneal topography(corneal analysis system,EYESYS,USA)and skiascopy to detect spherical errors or spherical equivalent errors in patients with astigmatism.Then the plans were made to correcting spherical or spherical equivalent errors.Patients were excluded if they had a history of ocular trauma or surgery,keratoconus,ocular or significant systemic diseases,or if they were receiving therapy likely to interfere with corneal wound healing.For example,patients with dry eye syndrome,keratoconjunctivitis,uveitis,keratoconus,keratoglobus,glaucoma,autoimmune and diabetic disease,and these incapable of cooperating during the operation being excluded. Written informed consent was provided by each patient.
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Patients From September,1990 to October,1997,we treated 316 myopic eyes of 168 patients and 260 eyes(84%) of 150 patients were followed-up for more than three months,including male 62 cases(116 eyes,40.1%) and female 82 cases(144 eyes,59.9%).The preoperative spherical equivalent refractive errors ranged from -1.25D to -10.00D(mean -4.67D± 1.63D),and astigmatism ranged from 0 to -2.00D(mean -0.33D±0.45D).The patients' ages ranged from 18 to 50 years old (average 27 years old).We divided the patients into 2 groups according to refraction:groups A(from-1.25D to -5.90D) and group B(from -6.00D to -10.00D).The number of eyes in the two group were 220 and 40 respectively.
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Surgical techniques SVS APEX PLUS excimer laser with a wave length of 193nm(Summit Technology Inc.Waltham,Mass,USA) was applied.The pulse energy density was set at 180mJ/cm2,pulse frequency at 10Hz,maxmium ablation diameter 6.0mm,and ablation depth 0.25μm per pulse.From -1.25D to - 6.0D,the patients received a single-step procedure.From -6.00D to - 10.00D,the patients received a multi-zone procedure.5 minutes before operation,5g.L-1 dicaine were instilled to constrict pupil for determining optical center during ablation and act as topical anesthesia respectively.The patient was trained 1-2 times to fixate monocularly at the indicatory light well during the operation.Aiming He-Ne beams were focused by 3-dimensional space localization to insure that the ablation was at the optical center of cornea.A paton was used to remove the epithelium mechanically from the area demarcated by the marker with a diameter of 7.0mm.After the refractive parameters has been input,laser was delivered for ablation.The laser pulse frequency,energy density and diaphragm dilation were controlled by a computer.Postoperatively,the routine follow-up was made on day 1,3,and 10,and at month 1,3,6 and 12 to evaluate epithelium covering,corneal haze and the same routine examinations were made as preoperatively,5g.L-1 corticotetramycin ointment was applied to the treated eye three times a day before mechanically denuded cornea was covered by epithelium.Treatment with topital antibiotics was continued until epithelialization had been completed.Postoperatively,1g.L-1 Fluorometholone(FML Liguifilm)was used four times each day for the first month,three times a day for the second month,twice a day for the third month,and once each day during the fourth month,fifth mondth and sixth month.If obvious corneal haze or quick hyperopic shift was found,then high-dose topical steroid was instilled,if the hyperopic shift was slow,then low-dose topical steroid was used.
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Corneal haze Corneal haze was graded clinically according to a subjective scale[5]:grade 0.0,normal,clear cornea and without haze even under slit lamp;grade 0.5,barely detectable haze;grade 1,trace haze,not affecting refraction,faint corneal haze visible only by oblique illumination with slit lamp;grade 1.5 haze visible with slit beam,mild haze,mildly affecting refraction;grade 2,morderate haze,refraction possible but difficult; grade 3,opacity prevents refraction,partially obscures iris detail; grade 4,marked opacity,completely obscures iris detail;and grade 5,unable to visualize anterior chamber.
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Statistical methods Data were entered into a computer database and statistical analysis.Differences between refractive measurements within treatment groups were analyzed by using the paired t test.The two-sample t test was used to analyze differences between groups A and B in corneal clarity and spherical equivalents .Differences were considered statistically significant when P<0.05.Within the text,mean values are presented with +SD(
)
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RESULTS
Postoperative course All the patients complained of ocular pain,foreign body sensation,lacrimation and photophobia after surgery,and 8.9% of them felt severe pain and needed oral analgesic.The corneal epithelium regenerated and covered the ablated areas completely in 99.45% of the eyes within three days after PRK,and only two eyes(0.55%)had denuded areas less than 5% of the original ones,but they were all covered completely 7 days later.
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Visual acuity and refractive See the table 1,table 2 and table 3.
Table 1 The changes of uncorrected visual acuity at the different time in the two groups (x±s) Group
Per-Op PRK
Post-Op PRK
10 days
1month
3 months
6 months
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Group A
4.28±0.23
4.94±0.10
5.00±0.11
4.99±0.13
5.01±0.12
5.03±0.13
(n=220)
(220)
(220)
(218)
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(130)
(65)
(25)
Group B
4.16±0.24
4.88±0.13
4.95±0.14
4.94±0.15
4.94±0.14
4.97±0.12
(n=40)
(40)
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(38)
(37)
(28)
(16)
(10)
Total
4.20±0.25
4.88±0.13
4.96±0.11
4.96±0.14
4.97±0.13
4.99±0.11
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(260)
(258)
(255)
(158)
(81)
(35)
Table 2 Uncorrected visual acuity(UCVA)
distribution in 6 months after PRK UCVA
Group A
Group B
≥1.0
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37(46)
21(34)
≥0.8
70(88)
32(38)
≥0.5
220(220)
40(40)
≤0.1
0(0)
0(0)
Table 3 Spherical equivalents following
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PRK for group A and group B () Myopia MSE
Group A(n=220)
Group B(n=40)
Preoperative postoperative
-4.16±0.64(220)
-7.12±2.31(40)
10 days
1.08±0.57(218)
1.47±1.33(39)
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1 month
0.95±0.79(210)
1.06±1.11(37)
3 months
0.27±1.00(190)
0.32±1.34(31)
6 months
0.65±0.81(160)
0.04±1.27(26)
12 months
0.25±0.76(130)
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1.21±0.97(24)
The changes of visual acuity at different time in the two groups were showed by the table 1 and table 2.On the three day,the UCVA was markedly improved and at first month,it was closest to the pre-operative BCVA. In group A,on the 10th day,68.9% has the uncorrected visual acuity (UCVA) equal to or one line better or lower than the preoperative best corrected visual acuity(BCVA).At 1,3,6 and 12 months,90%,96%,95% and 94% had the UCVA equal to or one line better or lower than the preoperative BCVA,respectively.In group B,on the tenth day,1,3,6 and 12 months,UCVA equal to or one line better or lower than the preoperative BCVA occurred in 35.9%,83%,87%,86% and 84% of the patients respectively.
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Complication The central subepithelial corneal opacity(haze):Most of the haze showed 0.5-1 grades except 3 eyes with the haze of 2 grade at 3 or 6 months and it changed to l and 0.5 grade respectively after one year.On the 10th days and 1,3,6,12 months postoperatively,the corneal haze was noted in 32.9%,84.2%,62.4%,9 .0%and 2.8% of the treated eyes,respectively.The results in our study showed that no statistical correlations were found between the development of haze and either one of the following factors:refractive errors,age or sex(P>0.1),consistent with Seiler's results[6，8].
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Transient elevated intraocular pressures(IOP>3.2kPa) responding to steroid were observed in 20.4% of the eyes and IOP≥4.0kPa in 8.6% of them.The IOP resumed normal level by tapering or stopping the corticosteriod and by the use of betablockers or the inhibitor of carbonic anhydrase.The IOP of all the treated eyes were normal 6 months and one year postoperatively.
Complication was decentration of the ablation zone.With corneal topographical analysis,decentration of 0.5mm or over was found in 15 eyes(14.9%).
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The complaints of halo,glare or decreased vision at might or under dim light occurred in 36.8% of all the eyes especially marked between one to three months,but basically disappeared at one year after PRK .The other occular symptoms foreign body sensation,dry sensation and asthenopia in a few patients.No other serious complications occurred.
Intraocular pressure,IOP The change of IOP before and after PRK see the table 4.Table 4 The change of IOP before and after PRK (kPa)
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Per-Op PRK
Post-Op PRK
10 days
1month
3 months
6 months
12 months
Group A
1.78±0.40
0.66±0.32
1.10±0.51
1.23±0.45
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0.92±0.56
1.32±0.55
(n=220)
(220)
(211)
(189)
(150)
(123)
(110)
Group B
1.80±0.43
0.64±0.36
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1.12±0.49
1.12±0.50
0.96±0.61
1.28±0.51
(n=40)
(40)
(38)
(35)
(30)
(28)
(25)
Two hundred and sixty cases of myopia before and after PRK were studied with non-contact tonometer(NCT).IOP of 1、3、6 months after PRK were significantly lower than that before PRK.The study indicated that the change of the corneal shape after PRK was the major reason for reducing IOP.The methods of testing IOP needed to be advanced.
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DISCUSSION
The treatment of myopia by modification of the corneal curvature with the excimer laser would appear to be a realistic objective.Its role will be determined only by the accumulation of data from clinical studies that document the predictability and long-term stability of the refractive outcome along with an assessment of the risks of the procedure.This report describes 150 ptients(260 eyes)PRK procedures for myopia with or without astigmatism.
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Immediately after the excimer laser corneal ablation,patients may experience moderate to severe pain[9].It may become severe with in a few hours,and has been reported to peak 24 hours after the treatment. Topical preparations of diclofenac sodium[9-11],indomethacin sodium,and flurbiprofen sodium[11，12] have been successfully used to alleviate postoperative pain.In our study,the uses of topical nonsteroidal anti -infalmmatory drug were diclofenac sodium eyedrops.Of course,it will be important in future studies to determine the best way to manage the postoperative conditions of patients to minimize pain without comproulicing epithelial healing or ideal refractive outcome[13].
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Re-epithelialization.One aspect that people concern about PRK is the re-epithelialization of the corneal wound.Normally epithelial cells are firmly attached to the Bowman's membrane by an adherent complex consisting of basement membrane,hemidesmosome and anchoring fibrils[14].PRK did evoke a wound healing response in the corneal epithelium and stroma and the first phase of the healing response was the epithelial repair. Re-epithelialization of the corneal surface completed within 72 hours after surgery in most of our patients.Mechanical rather than laser removal of the epithelium was used to be a trend towards greater accuracy of final refraction[15].
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From the results of our clinical study,the predictability of 98.6% in group A was higher than that of 88.9% in group B(P=0.003).The pereentage of UCVA of 1.0 or better in group A(94%) was obviously higher than that in group B(84%)(P<0.001).This might be related to the poorer preoperative BCVA in group B.The preoperative BCVA was 1.0 or more only in 88.9% of the eyes in group B,but 98.9% in group A. Between 6 and 12 months after PRK,changes in refraction 0.50D or less occurred in 92.8% of the eyes,and of 1.00D or more only in 5 eyes (9.7%),showing that the refractive state was stable during the period. The difference between attempted and achieved correction within±1.00D was noted in 97.4% of all the eyes,showing good predictability which was similar to that reported by Wang,et al[6]or by Talley,et al[3]. Our study showed improved results that may be due to proper selection of operative indications,shorter operative time,utility of corneal topography,strict follow-up,longer use of topital corticosteroid and adjustment of the steroid dose.
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Sub-epithelial corneal haze is a common complication after PRK.In most cases,the haze is mild and does not affect the vision.However,severe haze may reduce both visual acuity and contrast sensitivity.The nature and cause of haze are not yet clear.It is found to be associated with deposition of collagen type Ⅲ,mis-alignment of collagen fibers and changes in extra-cellular matrix.Wang,et al[7]found corticosteroid may significantly reduce the deposition of collagen Ⅲ ,which is closely related to the haze observed under slit lamp microscope. Corneal haze appeared in most of our patients after surgery,but 97.2% of the operative corneas had been cleared completely at one year,showing the important effect of corticosteroid to reduce or eliminate the haze.The mechanisms of producing haze may be related to corneal epithelial migration,formation of adhesion structures of the epithelium,and stromal remodeling.Although controversies exist[16],corticosteroid eye drops are given to the patients for a few month by most doctors after PRK.
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The mechanism of elvated IOP responding to steriod is still unknow. The percentage of elevated IOP in our study(20.4%) was similar to reported by Wang,et al[6].
The possible causes of decreased BCVA might be due to the corneal haze of grade 2 or more,decentration of the ablation site and irregular astigmatism.Small involuntary movements of the patient or the surgeon difficulty in the persistent fixation at the indicatory light by the patient especially in the one-step ablation in high myopia,pupillary movement or irregularity and difficulty in constricting the pupil preoperatively might all contribute to centering errors.Corneal topography is an important method to show the details of corneal surface after PRK,for example to verify that the ablation is centered or not.Part of the regression of effect after PRK was due to decentration of the ablation,so it is important to ablate at the center of the cornea to achieve and attempted corrective result.
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Halo and glare might be related to the corneal haze and pupil's size,and larger zone of ablation could help to ease them.Decreased vision at night or under dim light was related to the corneal haze,the dilated pupil larger than the ablated optical zone,steepness of the ablated margin and decreased contrast sensitivity.Foreign body or dry sensation seemed to be related to altered tear film properties due to prolonged corticosteroid eyedrops,and asthenopia was related to residual astigmatism,corneal haze and persistent hyperopic state,especially in the older patients.Corneal ulceration or perforation,keratoleukoma,endophthamitis and ablepsia occurred in none of the treated eyes in our study.
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From the results of our clinical study,we found that 193nm excimer laser PRK is a predictable,safe,stable,and effective refractive surgery for correcting myopia up to -10.00D in Chinese patients,and the effect was better in myopia lower than -6.00.Edited by LIU Xue-Li■
基金项目：Foundation item:Supported by the Public Health Bureau of Shandong Province.
作者简介：He was born on November 1965 in Jining,Shangdong Province,and worked in Department of Ophthalmology,Jining First Municipal Hospital.Now,he is assiduously studying for his Doctor degree in Xi'an Medical University.Fifty articles were published in medical journals,and 2 monographs were published by publishers.He have been mainly engaging in immunologic mechanism and therapy of simple herpetic keratitis.Tel:+86-29-5274735.
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References：
[1]Trokel SL,Srinivasan R,Braren B.Excimer laser surgery of the cornea[J]. Am J Ophthalmol 1983;96(6)∶710-716.
[2]Marshall J,Trokel SL,Rothery S.et al.Long-term healing of the central corneal after photorefractive keratectomy using an excimer laser[J].Ophthalmology 1988;85(12)∶1411-1420.
[3]Talley AR,Hardten DR,Sher NA,et al.Results one year after using the 193-nm excimer laser for photorefractive keratectomy in mild to moderate myopia.Am J Ophthalmol 1994;118(3)∶304-312.
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[4]Wu WCS,Stark WJ,Green WR.Corneal wound healing after 193-nm excimer laser keratectomy[J].Arch Ophthalmol 1991;109(11)∶1426-1432.
[5]Snibson GR,Carson CA,Aldred GF,et al. One-year evaluation of excimer laser photorefraction keratectomy for myopia and myopic astigmadtism[J]. Arch Ophthalmol 1995;113(8)∶994-1000.
[6]Wang Zaowen,Pang Guoxiang,Zheng Wei,et al.An analysis on follow-up results of photorefractive keratectomy for treatment of myopia[J].Chin J Ophthalmol.1995;31(3)∶126-180..
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[7]Wang Zheng，Li Shaozhen.Study of excimer laser ablated cornea and the effects of corticosteroid[J].Chin J Ophthalmol 1996;32(4)∶248-251.
[8]Seiler T,Wollensak J.Myopic photorefractive keratectomy with the excimer laser[J].Ophthalmology 1991;98∶1156-1163.
[9]Sher NA,Barak M,Daya S,et al.Excimer laser photorefractive keratectomy in high myopia[J].Arch Ophthalmol 1992;110(8)∶935-943.
[10]Sher NA,Frantz JM,Tallry A,et al.Topical diclofenac in the treatment of ocular pain after excimer photorefractive keratectomy[J].J Refract Corneal Surg 1993;9(5)∶425-436.
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[11]Arshinoff S,D'Addario D,Sadler C,et al.Use of topical nonsteroidal anti-inflammatory drugs in excimer laser photorefractive keratectomy[J]. J Cataract Refract Surg 1994;20(3)∶216-222.
[12]Cherry PMH,Tutton MK,Adhikary H,et al.The treatment of pain following photorefractive keratectomy[J].J Cataract Refract Surg 1994; 20(3)∶222-225.
[13]Vajpayee RB,McCarty CA,Taylor HR,et al.Overcorrection after excimer later treatment of myopia and myopic astigmatism[J].Arch Ophthalmol 1996；114(3)∶252-256.
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[14]Gipson IK.Adhesive mecthanisms of the corneal epithelium[J]. Arch Ophthalmol,1992;70(suppl)202-210.
[15]McDonald MB,Frantz JM,Klyce SD,et al.One-year refractive results of central photorefractive keratectomy for myopia in the nonhllman primate cornea[J].Arch Ophthalmol 1990;108(1)∶40-48.
[16]Gartry DS,Muir MG,Lohmann CP,et al.The effect of topical corticosteroids on refractive outcome and corneal corticosteroids on refractive outcome and corneal haze after photorefractive kerat etomy:prospective,randomized,double-blind trial[J].Arch Ophthalmol 1992; 110(8)∶994-1001.
Received date：Feb 6,1998, http://www.100md.com
单位：
关键词：准分子激光角膜切削术；近视；近视散光
眼科新进展000102
摘 要：目的 评价准分子激光角膜切削术矫正近视的结果。方法 我院自1996年9月到1997年10月，应用SVS APEX型(Summit Technology Inc.USA)准分子激光治疗仪，对168例近视患者(316只眼)行PRK手术，对其中的150例(260只眼，占84%)患者随诊至少3mo以上，最长1a；男68例(116只眼，占40.1%)，女82例(144只眼，占59.9%)。150例(260只眼)近视患者术前等值球镜屈光度为-1.25～-10.00D(-4.67D±1.63D)，散光0～-2.00D(-0.33D±0.45D)；按屈光度分为两组：A组(-1.25～-5.90D)，B组(-6.00～-10.00D)。结果 A组术后第10天，有68.9%(132/220)裸眼视力达到矫正视力，1、3、6和12mo分别为90%、96%、95%和94%.B组术后第10天，有35.9%(13/40)裸眼视力达到矫正视力，1、3、6和12mo分别为83%、87%、86%和84%.全组仅3只眼(0.64%)除外，均为0.5～1.0级的角膜上皮下雾状混浊，其出现的百分比手术后10d和1、3、6、12mo分别为32.9%、84.2%、62.4%、9.0%和2.8%.结论 提示准分子激光角膜切削术治疗-10.00D以内的近视是一种安全有效、稳定性好、预测性强的方法，-6.00D以下效果更好。
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分类号：R776.62;R778.1+1 文献标识码：A
文章编号：1003-5141(2000)01-0005-05
Evaluation of excimer laser photorefractive keratectomy for treatment of myopia and myopic astigmatism
ZHANG Hua
(Assiduously studying for his Doctor degree in Xi'an Medical University)
GUO Rong-Xia,SUN Nai-Xue,WANG Feng,ZHANG Dao-Guo,WANG Tong,SUN Jian,YANG Zhen-Guo,HU Hai-Tao,REN Hui-Min,LIU Yong
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(Department of Ophthalmology,the First People's Hospital of Jining,Jining 272111,Shandong Province,China)
Abstract：Objective To evaluate the efficacy and accuracy of photorefractive keratectomy(PRK) for myopia and myopic astigmatism.Methods SVS APEX PLUS excimer laser with a wave length of 193nm(Summit Technology Inc.Waltham,Mass,USA) was applied.Three hundred and sixteen myopic eyes of 168 patients were treated with PRK from Suptember 1996 to October 1997,and 260 eyes(84%) of 150 patients were followed-up for more than three month,including male 68(116 eyes,40.1%) and female 82(144 eyes,59.9%).The preoperative spherical equivalent refractive errors ranged from -1.25D to -10.00D(mean -4.67D± 1.63D),and astigmatism ranged from 0 to -2.00D(mean -0.33D±0.45D). The patients were divided into two groups according to the refraction:group A(from -1.25D to -5.90D) and group B(from -6.00D to -10.00D).The number of eyes in the two groups were 220 and 40,respectively.Results In group A,After 10 days,68.9% had the uncorrected visual acuity(UCVA) equal to or one line better or lower than the preoperative best corrected visual acuity(BCVA).After 1 ,3,6 and 12 months,90%,96%,95% and 94% had the UCVA equal to or one line better or lower than the preoperative BCVA,respectively.In group B,after 10 days,1,3,6 and 12 months,UCVA equal to or one line better or lower than the preoperative BCVA occurred in 35.9%,83.0%,87.0%,86.0% and 84.0% of the patients respectively. Most of the haze showed 0.5～1 grades except 3 eyes with the haze of 2 grade at 3 or 6 months and it changed to l and 0.5 grade respectively at one year.after 10 days and 1,3,6,12 months postoperatively,the corneal haze was noted in 32.9%,84.8%,62.8%,9.0%and 2.8% of the treated eyes respectively.Conclusion We found that the 193nm excimer laser PRK is a predictable,safe,stable,and effective refractive surgery for correcting myopia up to-10.00D in Chinese patients,and the effect is better in myopia lower than -6.00D.
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Key words：excimer laser photorefractive keratectomy;myopia;myopic astigmatism▲
In 1983,Trokel,et al[1] first reported the laboratory reasearch about excimer laser.Clinical using of excimer laser photorefractive keratectomy were begun by Marshall,et al[2]in 1988. During the last dacade,a new corneal refractive surgery-excimer laser photorefractive keratectomy(PRK) has been developed rapidly[3-8].
, 百拇医药 The excimer laser produces high-energy UV radiation pulses with a 193nm wave length.The energy absorbed by the cornea with each pulse is sufficient to cause disruption of intramolecular bonds and ablation of corneal tissue with submicron accuracy and minimal effect on adjacent tissue[3].The argon fluoride exeimer laser has emerged as a powerful tool in the surgical treatment of myopia.PRK is a new refractive surgery that is gradually accepted by both surgeons and patients worldwide.This study presents the results of 260 visible eyes treated with PRK and followed up for more than three month to evaluate the predictability,stability and safety of PRK.
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PATIENTS AND METHODS
Selection of patients To be eligible for inclusion in this study,patients were required to be at least 18 years of age,have stable myopia of up to -10D at the corneal plane with or without stable astigmatism of up to -2D,and have best corrected visual acuity of 0.8 or better.
Preoperatively,all the patients were asked to explain their refractive and spectacle histories.Wearers of soft contact lenses were assessed 2 weeks after lens removal.All the patients received a routine ophthalmic examination including dominant eyes,slit-lamp microscope and ophthalmoscopic examinations,intraocular pressure(IOP)measured by non contact tonometer(NCT),uncorrected visual acuity(UCVA)and the best corrected visual acuity(BCVA),corneal topography(corneal analysis system,EYESYS,USA)and skiascopy to detect spherical errors or spherical equivalent errors in patients with astigmatism.Then the plans were made to correcting spherical or spherical equivalent errors.Patients were excluded if they had a history of ocular trauma or surgery,keratoconus,ocular or significant systemic diseases,or if they were receiving therapy likely to interfere with corneal wound healing.For example,patients with dry eye syndrome,keratoconjunctivitis,uveitis,keratoconus,keratoglobus,glaucoma,autoimmune and diabetic disease,and these incapable of cooperating during the operation being excluded. Written informed consent was provided by each patient.
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Patients From September,1990 to October,1997,we treated 316 myopic eyes of 168 patients and 260 eyes(84%) of 150 patients were followed-up for more than three months,including male 62 cases(116 eyes,40.1%) and female 82 cases(144 eyes,59.9%).The preoperative spherical equivalent refractive errors ranged from -1.25D to -10.00D(mean -4.67D± 1.63D),and astigmatism ranged from 0 to -2.00D(mean -0.33D±0.45D).The patients' ages ranged from 18 to 50 years old (average 27 years old).We divided the patients into 2 groups according to refraction:groups A(from-1.25D to -5.90D) and group B(from -6.00D to -10.00D).The number of eyes in the two group were 220 and 40 respectively.
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Surgical techniques SVS APEX PLUS excimer laser with a wave length of 193nm(Summit Technology Inc.Waltham,Mass,USA) was applied.The pulse energy density was set at 180mJ/cm2,pulse frequency at 10Hz,maxmium ablation diameter 6.0mm,and ablation depth 0.25μm per pulse.From -1.25D to - 6.0D,the patients received a single-step procedure.From -6.00D to - 10.00D,the patients received a multi-zone procedure.5 minutes before operation,5g.L-1 dicaine were instilled to constrict pupil for determining optical center during ablation and act as topical anesthesia respectively.The patient was trained 1-2 times to fixate monocularly at the indicatory light well during the operation.Aiming He-Ne beams were focused by 3-dimensional space localization to insure that the ablation was at the optical center of cornea.A paton was used to remove the epithelium mechanically from the area demarcated by the marker with a diameter of 7.0mm.After the refractive parameters has been input,laser was delivered for ablation.The laser pulse frequency,energy density and diaphragm dilation were controlled by a computer.Postoperatively,the routine follow-up was made on day 1,3,and 10,and at month 1,3,6 and 12 to evaluate epithelium covering,corneal haze and the same routine examinations were made as preoperatively,5g.L-1 corticotetramycin ointment was applied to the treated eye three times a day before mechanically denuded cornea was covered by epithelium.Treatment with topital antibiotics was continued until epithelialization had been completed.Postoperatively,1g.L-1 Fluorometholone(FML Liguifilm)was used four times each day for the first month,three times a day for the second month,twice a day for the third month,and once each day during the fourth month,fifth mondth and sixth month.If obvious corneal haze or quick hyperopic shift was found,then high-dose topical steroid was instilled,if the hyperopic shift was slow,then low-dose topical steroid was used.
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Corneal haze Corneal haze was graded clinically according to a subjective scale[5]:grade 0.0,normal,clear cornea and without haze even under slit lamp;grade 0.5,barely detectable haze;grade 1,trace haze,not affecting refraction,faint corneal haze visible only by oblique illumination with slit lamp;grade 1.5 haze visible with slit beam,mild haze,mildly affecting refraction;grade 2,morderate haze,refraction possible but difficult; grade 3,opacity prevents refraction,partially obscures iris detail; grade 4,marked opacity,completely obscures iris detail;and grade 5,unable to visualize anterior chamber.
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Statistical methods Data were entered into a computer database and statistical analysis.Differences between refractive measurements within treatment groups were analyzed by using the paired t test.The two-sample t test was used to analyze differences between groups A and B in corneal clarity and spherical equivalents .Differences were considered statistically significant when P<0.05.Within the text,mean values are presented with +SD(
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RESULTS
Postoperative course All the patients complained of ocular pain,foreign body sensation,lacrimation and photophobia after surgery,and 8.9% of them felt severe pain and needed oral analgesic.The corneal epithelium regenerated and covered the ablated areas completely in 99.45% of the eyes within three days after PRK,and only two eyes(0.55%)had denuded areas less than 5% of the original ones,but they were all covered completely 7 days later.
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Visual acuity and refractive See the table 1,table 2 and table 3.
Table 1 The changes of uncorrected visual acuity at the different time in the two groups (x±s) Group
Per-Op PRK
Post-Op PRK
10 days
1month
3 months
6 months
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Group A
4.28±0.23
4.94±0.10
5.00±0.11
4.99±0.13
5.01±0.12
5.03±0.13
(n=220)
(220)
(220)
(218)
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(130)
(65)
(25)
Group B
4.16±0.24
4.88±0.13
4.95±0.14
4.94±0.15
4.94±0.14
4.97±0.12
(n=40)
(40)
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(38)
(37)
(28)
(16)
(10)
Total
4.20±0.25
4.88±0.13
4.96±0.11
4.96±0.14
4.97±0.13
4.99±0.11
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(260)
(258)
(255)
(158)
(81)
(35)
Table 2 Uncorrected visual acuity(UCVA)
distribution in 6 months after PRK UCVA
Group A
Group B
≥1.0
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37(46)
21(34)
≥0.8
70(88)
32(38)
≥0.5
220(220)
40(40)
≤0.1
0(0)
0(0)
Table 3 Spherical equivalents following
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PRK for group A and group B (
) Myopia MSEGroup A(n=220)
Group B(n=40)
Preoperative postoperative
-4.16±0.64(220)
-7.12±2.31(40)
10 days
1.08±0.57(218)
1.47±1.33(39)
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1 month
0.95±0.79(210)
1.06±1.11(37)
3 months
0.27±1.00(190)
0.32±1.34(31)
6 months
0.65±0.81(160)
0.04±1.27(26)
12 months
0.25±0.76(130)
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1.21±0.97(24)
The changes of visual acuity at different time in the two groups were showed by the table 1 and table 2.On the three day,the UCVA was markedly improved and at first month,it was closest to the pre-operative BCVA. In group A,on the 10th day,68.9% has the uncorrected visual acuity (UCVA) equal to or one line better or lower than the preoperative best corrected visual acuity(BCVA).At 1,3,6 and 12 months,90%,96%,95% and 94% had the UCVA equal to or one line better or lower than the preoperative BCVA,respectively.In group B,on the tenth day,1,3,6 and 12 months,UCVA equal to or one line better or lower than the preoperative BCVA occurred in 35.9%,83%,87%,86% and 84% of the patients respectively.
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Complication The central subepithelial corneal opacity(haze):Most of the haze showed 0.5-1 grades except 3 eyes with the haze of 2 grade at 3 or 6 months and it changed to l and 0.5 grade respectively after one year.On the 10th days and 1,3,6,12 months postoperatively,the corneal haze was noted in 32.9%,84.2%,62.4%,9 .0%and 2.8% of the treated eyes,respectively.The results in our study showed that no statistical correlations were found between the development of haze and either one of the following factors:refractive errors,age or sex(P>0.1),consistent with Seiler's results[6，8].
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Transient elevated intraocular pressures(IOP>3.2kPa) responding to steroid were observed in 20.4% of the eyes and IOP≥4.0kPa in 8.6% of them.The IOP resumed normal level by tapering or stopping the corticosteriod and by the use of betablockers or the inhibitor of carbonic anhydrase.The IOP of all the treated eyes were normal 6 months and one year postoperatively.
Complication was decentration of the ablation zone.With corneal topographical analysis,decentration of 0.5mm or over was found in 15 eyes(14.9%).
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The complaints of halo,glare or decreased vision at might or under dim light occurred in 36.8% of all the eyes especially marked between one to three months,but basically disappeared at one year after PRK .The other occular symptoms foreign body sensation,dry sensation and asthenopia in a few patients.No other serious complications occurred.
Intraocular pressure,IOP The change of IOP before and after PRK see the table 4.Table 4 The change of IOP before and after PRK (kPa)
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Per-Op PRK
Post-Op PRK
10 days
1month
3 months
6 months
12 months
Group A
1.78±0.40
0.66±0.32
1.10±0.51
1.23±0.45
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0.92±0.56
1.32±0.55
(n=220)
(220)
(211)
(189)
(150)
(123)
(110)
Group B
1.80±0.43
0.64±0.36
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1.12±0.49
1.12±0.50
0.96±0.61
1.28±0.51
(n=40)
(40)
(38)
(35)
(30)
(28)
(25)
Two hundred and sixty cases of myopia before and after PRK were studied with non-contact tonometer(NCT).IOP of 1、3、6 months after PRK were significantly lower than that before PRK.The study indicated that the change of the corneal shape after PRK was the major reason for reducing IOP.The methods of testing IOP needed to be advanced.
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DISCUSSION
The treatment of myopia by modification of the corneal curvature with the excimer laser would appear to be a realistic objective.Its role will be determined only by the accumulation of data from clinical studies that document the predictability and long-term stability of the refractive outcome along with an assessment of the risks of the procedure.This report describes 150 ptients(260 eyes)PRK procedures for myopia with or without astigmatism.
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Immediately after the excimer laser corneal ablation,patients may experience moderate to severe pain[9].It may become severe with in a few hours,and has been reported to peak 24 hours after the treatment. Topical preparations of diclofenac sodium[9-11],indomethacin sodium,and flurbiprofen sodium[11，12] have been successfully used to alleviate postoperative pain.In our study,the uses of topical nonsteroidal anti -infalmmatory drug were diclofenac sodium eyedrops.Of course,it will be important in future studies to determine the best way to manage the postoperative conditions of patients to minimize pain without comproulicing epithelial healing or ideal refractive outcome[13].
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Re-epithelialization.One aspect that people concern about PRK is the re-epithelialization of the corneal wound.Normally epithelial cells are firmly attached to the Bowman's membrane by an adherent complex consisting of basement membrane,hemidesmosome and anchoring fibrils[14].PRK did evoke a wound healing response in the corneal epithelium and stroma and the first phase of the healing response was the epithelial repair. Re-epithelialization of the corneal surface completed within 72 hours after surgery in most of our patients.Mechanical rather than laser removal of the epithelium was used to be a trend towards greater accuracy of final refraction[15].
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From the results of our clinical study,the predictability of 98.6% in group A was higher than that of 88.9% in group B(P=0.003).The pereentage of UCVA of 1.0 or better in group A(94%) was obviously higher than that in group B(84%)(P<0.001).This might be related to the poorer preoperative BCVA in group B.The preoperative BCVA was 1.0 or more only in 88.9% of the eyes in group B,but 98.9% in group A. Between 6 and 12 months after PRK,changes in refraction 0.50D or less occurred in 92.8% of the eyes,and of 1.00D or more only in 5 eyes (9.7%),showing that the refractive state was stable during the period. The difference between attempted and achieved correction within±1.00D was noted in 97.4% of all the eyes,showing good predictability which was similar to that reported by Wang,et al[6]or by Talley,et al[3]. Our study showed improved results that may be due to proper selection of operative indications,shorter operative time,utility of corneal topography,strict follow-up,longer use of topital corticosteroid and adjustment of the steroid dose.
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Sub-epithelial corneal haze is a common complication after PRK.In most cases,the haze is mild and does not affect the vision.However,severe haze may reduce both visual acuity and contrast sensitivity.The nature and cause of haze are not yet clear.It is found to be associated with deposition of collagen type Ⅲ,mis-alignment of collagen fibers and changes in extra-cellular matrix.Wang,et al[7]found corticosteroid may significantly reduce the deposition of collagen Ⅲ ,which is closely related to the haze observed under slit lamp microscope. Corneal haze appeared in most of our patients after surgery,but 97.2% of the operative corneas had been cleared completely at one year,showing the important effect of corticosteroid to reduce or eliminate the haze.The mechanisms of producing haze may be related to corneal epithelial migration,formation of adhesion structures of the epithelium,and stromal remodeling.Although controversies exist[16],corticosteroid eye drops are given to the patients for a few month by most doctors after PRK.
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The mechanism of elvated IOP responding to steriod is still unknow. The percentage of elevated IOP in our study(20.4%) was similar to reported by Wang,et al[6].
The possible causes of decreased BCVA might be due to the corneal haze of grade 2 or more,decentration of the ablation site and irregular astigmatism.Small involuntary movements of the patient or the surgeon difficulty in the persistent fixation at the indicatory light by the patient especially in the one-step ablation in high myopia,pupillary movement or irregularity and difficulty in constricting the pupil preoperatively might all contribute to centering errors.Corneal topography is an important method to show the details of corneal surface after PRK,for example to verify that the ablation is centered or not.Part of the regression of effect after PRK was due to decentration of the ablation,so it is important to ablate at the center of the cornea to achieve and attempted corrective result.
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Halo and glare might be related to the corneal haze and pupil's size,and larger zone of ablation could help to ease them.Decreased vision at night or under dim light was related to the corneal haze,the dilated pupil larger than the ablated optical zone,steepness of the ablated margin and decreased contrast sensitivity.Foreign body or dry sensation seemed to be related to altered tear film properties due to prolonged corticosteroid eyedrops,and asthenopia was related to residual astigmatism,corneal haze and persistent hyperopic state,especially in the older patients.Corneal ulceration or perforation,keratoleukoma,endophthamitis and ablepsia occurred in none of the treated eyes in our study.
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From the results of our clinical study,we found that 193nm excimer laser PRK is a predictable,safe,stable,and effective refractive surgery for correcting myopia up to -10.00D in Chinese patients,and the effect was better in myopia lower than -6.00.Edited by LIU Xue-Li■
基金项目：Foundation item:Supported by the Public Health Bureau of Shandong Province.
作者简介：He was born on November 1965 in Jining,Shangdong Province,and worked in Department of Ophthalmology,Jining First Municipal Hospital.Now,he is assiduously studying for his Doctor degree in Xi'an Medical University.Fifty articles were published in medical journals,and 2 monographs were published by publishers.He have been mainly engaging in immunologic mechanism and therapy of simple herpetic keratitis.Tel:+86-29-5274735.
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[2]Marshall J,Trokel SL,Rothery S.et al.Long-term healing of the central corneal after photorefractive keratectomy using an excimer laser[J].Ophthalmology 1988;85(12)∶1411-1420.
[3]Talley AR,Hardten DR,Sher NA,et al.Results one year after using the 193-nm excimer laser for photorefractive keratectomy in mild to moderate myopia.Am J Ophthalmol 1994;118(3)∶304-312.
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[4]Wu WCS,Stark WJ,Green WR.Corneal wound healing after 193-nm excimer laser keratectomy[J].Arch Ophthalmol 1991;109(11)∶1426-1432.
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[6]Wang Zaowen,Pang Guoxiang,Zheng Wei,et al.An analysis on follow-up results of photorefractive keratectomy for treatment of myopia[J].Chin J Ophthalmol.1995;31(3)∶126-180..
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[7]Wang Zheng，Li Shaozhen.Study of excimer laser ablated cornea and the effects of corticosteroid[J].Chin J Ophthalmol 1996;32(4)∶248-251.
[8]Seiler T,Wollensak J.Myopic photorefractive keratectomy with the excimer laser[J].Ophthalmology 1991;98∶1156-1163.
[9]Sher NA,Barak M,Daya S,et al.Excimer laser photorefractive keratectomy in high myopia[J].Arch Ophthalmol 1992;110(8)∶935-943.
[10]Sher NA,Frantz JM,Tallry A,et al.Topical diclofenac in the treatment of ocular pain after excimer photorefractive keratectomy[J].J Refract Corneal Surg 1993;9(5)∶425-436.
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[11]Arshinoff S,D'Addario D,Sadler C,et al.Use of topical nonsteroidal anti-inflammatory drugs in excimer laser photorefractive keratectomy[J]. J Cataract Refract Surg 1994;20(3)∶216-222.
[12]Cherry PMH,Tutton MK,Adhikary H,et al.The treatment of pain following photorefractive keratectomy[J].J Cataract Refract Surg 1994; 20(3)∶222-225.
[13]Vajpayee RB,McCarty CA,Taylor HR,et al.Overcorrection after excimer later treatment of myopia and myopic astigmatism[J].Arch Ophthalmol 1996；114(3)∶252-256.
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[14]Gipson IK.Adhesive mecthanisms of the corneal epithelium[J]. Arch Ophthalmol,1992;70(suppl)202-210.
[15]McDonald MB,Frantz JM,Klyce SD,et al.One-year refractive results of central photorefractive keratectomy for myopia in the nonhllman primate cornea[J].Arch Ophthalmol 1990;108(1)∶40-48.
[16]Gartry DS,Muir MG,Lohmann CP,et al.The effect of topical corticosteroids on refractive outcome and corneal corticosteroids on refractive outcome and corneal haze after photorefractive kerat etomy:prospective,randomized,double-blind trial[J].Arch Ophthalmol 1992; 110(8)∶994-1001.
Received date：Feb 6,1998, http://www.100md.com