角膜接触镜均适合于华人吗?
作者：Carly S.Y.Lam Hui HeangKoh Kah Ooi Tan
单位：
关键词：
眼视光学杂志/990308
摘要 目的：亚洲市场的隐形眼镜，绝大多数是西方国家设计和生产的。尽管华人和白人眼部参数的差异之处尚未完全明了，但是亚洲的一些验配师还是喜欢单纯以镜片配戴的“舒适度”作为验配标准。作者调查了华人配戴几种水凝胶软镜的临床表现，以确定科学的验配评判标准。方法：在香港理工大学和新加坡理工大学这两处研究中心，各挑选十名年轻隐形眼镜配戴者，每只眼睛分别配戴6种不同类型的镜片(Weicon38E、HydronZ6、Medalist、Acuvue、Focus和SeeQuence)，20分钟之后由5名视光师分别对其进行验配评价，并让配戴者对配戴的舒适程度作0～100分的主观评价。结果：两地各种镜片的配戴舒适程度主观评价差异无显著(P>0.05)，然两地各种镜片的配戴特征的差异具有显著性(P<0.05)。结论：亚洲之外设计的镜片，如根据个体差异进行适当选择再作验配，对于华人来说是比较适合的。没有哪种镜片能够适合所有华人的眼睛配戴的，某些镜片配戴的主观舒适度虽与其他种类镜片相同，但是检查时可发现其偏紧。因此，仅仅根据“舒适度”作为隐形眼镜验配评判依据，而不作必要的配戴评价，就容易导致配戴过紧。故对每位病人均作试戴评价，仍不失为选择适合于华人配戴的隐形眼镜的最佳方法。
, http://www.100md.com
Soft contact lenses for Chinese eyes?
Carly S.Y.Lam1,BSc(Hons),MSc,PhD,MBCO,FAAO
Hui Heang Koh2,BSc(Optom)
Kah Ooi Tan3,BOptom(Hons),MBA,PhD
Abstract Most contact lenses available in Asia are designed and manufactured in the Western countries.Althongh the ocular characteristics between the Chinese and Cancasian are not fully understood,some practitioners in Asia prefer to judge the fitting solely based on the `comfort' of the lens.This study investigates the clinical performance of some hydrogel on Chinese eyes.This study was conducted at two centres(The Hong Kong Polytechnic University and Singapore Polytechnic).Ten young soft contact lens wearers were recruited in each centre.Six different types of lenses(Weicon 38E,Hydron Z6,Medalist,Acuvue,Focus and SeeQuence)were fitted on one eye.The fittings were assessed 20 minutes later by 5 optometrists at each centre,and the comfort levels were graded subjectively on a 0 to 100 scale.The results show that comfort levels were not significantly different among the lenses tested in both centres(P>0.05).However,there were significant differences (P<0.05) in fitting characteristic in both certres.Fitting of most lenses were acceptable,however,Acuvue and SeeQuence lenses were found to be significantly tighter (P<0.05).As conclusion,lenses designed outside Asia are suitable for Chinese eyes provided that proper selection and fitting are performed to suit individual variation.There is no single lens that suits all Chinese eye.Some lenses are equally comfortable,however,the fitting could be tighter when compared to the others.Thus,judging fitting based on `comfort' without proper fitting assessment may result in prescribing a tight lens.Trial fitting assessment on every patient is still the best way to select the appropriate lenses for Chinese eyes.
, 百拇医药
Key words soft contact lens Chinese Comfort Fitting assessment
Hong Kong and Singaporean Chinese are more myopic than other racial groups[1～3].Contact lenses provide an alternative correction to refractive errors.Most contact lenses available in Asia are designed and manufactured in the Western countries.However,little has been done to evaluate the suitability of the currently available contact lenses for the Chinese eyes.
, http://www.100md.com
Variations in the anterior segment characteristics among different ethnic groups have been reported[4～9].The corneal curvatures of Japanese were found to be steeper than Caucasians[4].The corneal shape of the Chinese eye has been found to be different from Caucasians in their curvature,peripheral flattening and diameter[5,6].Such differences have important implications for contact lens manufacturers,contact lens practitioners and eye surgeons.Several studies given also shown that Chinese has a different tear characteristics that the tear break up time and tear volume were found to be shorter and lesser than Caucasians[7～9].
, 百拇医药
Although the ocular characteristics of the Chinese and Caucasian eyes are not fully understood,the different fitting behaviours of some practitioners in this region may further complicate the selection of contact lenses for the Chinese eyes.Asia is one of the fastest growing contact lens markets.Contact lens practitioners in Asia include optometrists,ophthalmologists,and opticians.Fitting attitude in Asia is somewhat different from that in other westen countries.
, http://www.100md.com Speed is very critical in current trend of practice in Asia as to cope with the demand of busy practice and the high patient turnover rate.Some practitioners prefer to judge the suitability of a lens based on the subjective comfort of the fitting,without proper assessments of the fitting of the lenses.Common concept is that "Comfortable" means "Good Fit"!
It is thus interesting to find out whether lenses designed and manufactured outside Asia are suitable for Chinese eyes and investigate the clinical performance of some hydrogel lenses on the Chinese eyes.And also to determine if the selection of lenses based on `comfort'has any clinical implications on the fitting characteristics of the lens and to evaluate the relationship between `comfort'and `fitting characteristics'of soft lenses on Chinese eyes.
, http://www.100md.com
1 Methods & Materials
This study was conducted at two different centres:The Optometry Clinic,The Department of Optometry and Radiography,The Hong Kong Polytechnic University and the Optometry Clinic,Singapore Polytechnic.10 soft contact lens wearers(age:16～33),were recruited in each centre.A preliminary examination was carried out on each subject.A clinical assessment included the suitability of the subject for soft contact lens wear.The subject chosen should have worn contact lenses for more than one year.His/her corneal astigmatism must be less than 1.25Dc.The subject should be free from any ocular diseases or pathology such as corneal ulcer or eye surgery,any previous allergic reaction to contact lens such as giant papillary conjunctivitis,any systemic diseases that will affect the ocular conditions such as diabetic mellitus or hypertension.
, 百拇医药
Six different types of lenses currently available in the market were tested,these include Weicon 38E,Hydron Z6,Medalist,Acuvue,Focus and SeeQuence.Table 1 lists the parameters and materials of these lenses.
Table 1 Types of lenses used in the study LENSES
MATERIAL &
MANUFACTURING
DIAMETER
BOZR
, 百拇医药
SeeQuence
Polymacon 38.6%
(Spin-cast)
14.0
(Only one BOZR
is available)
Focus
Wifilcon A 55%
(Molded)
14.0
8.6
8.9
, 百拇医药
-
Weicon 38E
Tefilcon 38%
13.8
Steep
(ST)
Flat
(FL)
-
Acuvue
Etafilcon A 58%
(Stabilized soft molding)
, 百拇医药
14.0
8.4
8.8
-
Hydron
Zero 6
Polymacon 38%
(Lathe-cut)
14.0
8.1
8.4
8.7
Medalist
, 百拇医药
Polymacon 38%
(Spin-cast front/lathed
back)
14.0
8.4
8.7
-
Prior to the assessment of fitting and comfort in the trial,subjects were fitted with the six different types of contact lenses to determine the optimum fit of each type of lenses.An optometrist who was not involved in the assessment part undertook the fitting.
, 百拇医药
On the assessment trial,the subject was first asked to evaluate the `comfort'of the lens after 20 minutes of lens insertion as illustrated in Appendix 1.The comfort levels were graded on a 0 to 100 scale,where 0 indicated `Totally can not tolerate the lens',and 100 indicates `Can not feel the lens at all'.Every subject was requested to adapt to the lenses for about 20 minutes before grading the comfort levels of each lens.
The fitting of the lenses for each subject were then assessed by 5 optometrists.The performance of each type of lens was determined according to the assessment criteria illustrated in Appendix 2.All the optometrists were graduates from different optometry schools(Australia,United Kingdom,Malaysia,and Hong Kong).The fitting assessment includes lens coverage,centration,lens movement,lag of movement,tightness.The fitting characterstics were graded as unacceptable fit,good/acceptable fit and optimum fit.
, 百拇医药
The sequence of lenses to be fitted to each subject was selected randomly.This was a double-masked study that the subjects and the examiners did not know the type of lenses during the assessment.An optometrist who wasnot know the type of lenses during the assessment.An optometrist who not involved in any fitting assessment carried out the fitting and removal of the lenses.
2 Results
2.1 Coverage
, 百拇医药 All the six types of lenses were bigger than or equal to 13.8mm in total diameter.Majority of the lens completely covered the cornea except the Acuvue lenses,with which 20% and <5% of the fitting had the cornea partly exposed among the Hong Kong and Singaporean subjects respectively.
2.2 Centration
The lens centration was described either centred,decentred to nasal,temporal,superior or inferior side.The Weicon 38E,Focus and Hydron Zero 6 lenses provided well centration on the cornea in majority of the subjects Acuvue,Medalist and SeeQuence lenses provided less well centration among the six type of lenses.The decentration direction was mainly towards superior or temporal side.
, 百拇医药
2.3 Fitting Assessment
The fittng pattern of each type of the lenses were described by the examiners according to the following scale:
1=Unacceptable(steep or loose)
2=Good/Acceptable(steep or loose)
3=Optimal
The mean values from the five examiners were used in the analysis.Table 2 shows the ranking of the six types of lenses based on the overall fitting assessment of the lenses in the two centres.The lenses were ranked according to the absolute scores as well as to the statistical significance between the fitting assessment of the lens types.Non-parametric Kruskal-Wallis H test was used to analyse the data and the result showed that there were significant differences in the fitting assessment among the six types of lenses (Chisquare=30.1,P<0.001).Comparison between any two lenses shows that in the Singapore,Weicon 38E was more acceptable than the other lenses(P<0.05),followed by Medalist and Focus(P<0.05),Hydron Z6 and Acuvue(P<0.05),and SeeQuence,which was found to be significantly tighter than the other lenses(P<0.05).In Hong Kong,the fitting of four types of lenses(Hydron Z6,Weicon 38E,Focus and Medalist)were not significantly different from each other(P>0.05).This was followed by Acuvue and SeeQuence lenses,which were found to be significantly tighter in fitting (P<0.05).Figure 1 shows the average best fit scores with standard deviation of the six different lenses in both centres.
, 百拇医药
Table 2 Ranks according to fitting assessment RANK
ABSOLUTE SCORE
STATISTCIAL ANALYSIS
SINGAPORE
HONG KONG
SINGAPORE
HONG KONG
1
W38E
Hydron Z6
W38E
, 百拇医药
Hydron Z6
Focus
W38E
Medalist
2
Medalist
Focus
Medalist
Acuvue
Focus
SeeQuence
3
, 百拇医药 Focus
W38E
Hydron Z6
Acuvue
4
Hydron Z6
Medalist
SeeQuence
5
Acuvue
Acuvue
6
SeeQuence
, 百拇医药
SeeQuence
Figure 1 Fitting assessment
2.4 Comfort assessment
Table 3 shows the ranking of the six types of lenses based on the subjects' assessment of comfort.Based on absolute scores,Medalist was found to be the most comfortable lens while Hydron Z6 was found to be the least comfortable lens among the Singaporean subjects.For the Hong Kong subjects,Focus lens provided the best comfort whereas Acuvue lens was the least comfortable lens.However,Kruskal-Wallis one-way anova test shows that lens comfort difference among the lenses are not statistically
, 百拇医药
significant in both centres.Figure 2 shows the average comfort in percentage of the lens as expressed by the subjects in the two centres.
Table 3 Ranks according to comfort assessment RANK
ABSOLUTE SCORE
STATISTCIAL ANALYSIS
SINGAPORE
HONG KONG
SINGAPORE
, http://www.100md.com HONG KONG
1
Medalist
Focus
All the same
(No statistical
significance)
All the same
(No statistical
significance)
2
SeeQuence
, 百拇医药
W38E
-
-
3
W38E
SeeQuence
-
-
4
Focus
Medalist
-
-
, 百拇医药
5
Acuvue
Hydron Z6
-
-
6
Hydron Z6
Acuvue
-
-
Figure 2 Comfort assessment
, http://www.100md.com
2.5 Best lens
For each subject,the lens that obtained the highest score was classified as the best lens for him/her.Table 4 shows the best lens for each subject based on fitting assessment and comfort assessment.The results showed that different lenses performed differently on different subjects.Lenses such as Weicon 38E and Hydron Z6 are of better fit and comfort to Chinese eyes as compared to other lens types.However,individual variations do exist,not a single lens is suitable for ALL the subjects.
, 百拇医药
Table 4 Best lens for the subjects SUBJECTS
BASED ON“F1TTING”
BASED ON“COMFORT”
SINGAPORE
HONG KONG
SINGAPORE
HONG KONG
1
W38E
Hydron Z6
Medalist
, 百拇医药
W38E
Hydron Z6
Focus
SeeQuence
2
W38E
W38E
Hydron Z6
Focus
Medalist
Acuvue
Acuvue
, 百拇医药 3
W38E
Hydron Z6
W38E
Medalist
Medalist
4
W38E
W38E
Medalist
Focus
W38E
Focus
, 百拇医药
5
W38E
Hydron Z6
W38E
W38E
Hydron Z6
Medalist
Focus
Acuvue
6
W38E
Medalist
W38E
, 百拇医药
W38E
Hydron Z6
Focus
Acuvue
7
W38E
Medalist
W38E
Hydron Z6
SeeQuence
8
W38E
Hydron Z6
, http://www.100md.com
Acuvue
W38E
Hydron Z6
Focus
Acuvue
9
Medalist
Hydron Z6
Focus
SeeQuence
Hydron Z6
10
, 百拇医药
W38E
Focus
W38E
Hydron Z6
Acuvue
SeeQucnce
3 Discussion and conclusion
When the optimum fit of each type of lens were compared for each subject,we found that some lens type tends to provide less optimal fitting.There was no significant difference in fitting perfomance among Weicon 38E,Focus,Hydron Zero 6 and Medalist lenses.SeeQuence and Acuvue lenses were found to perform differently and consistently provide more unacceptable steeper fittings than the others do.These could be attributed to the one-off base curve fitting of the SeeQuence lens or the design of the peripheral curves of these lenses.
, 百拇医药
Although the results from Hong Kong and Singapore are not exactly the same,it shares some similarities and trends.It seems that there is no specific type of lenses that suit every Chinese.Careful selection of patients and proper fitting and assessment are still the only and the best way to select appropriate lenses for the Chinese eyes.Some lenses are tighter in fitting when compared to the others,however,the comfort levels are not significantly different.Thus,judging fit based on `comfort'without proper fitting assessment may result in prescribing a tight lens.This should be of concern to those busy optical practices in Asia where some practitioners judge the suitability of a lens solely based on the `comfort'levels and without fitting assessment.Because of the individual variations in fitting behaviour,trial fitting assessment on every patient is still the best way to select the appropriate lenses for Chinese eyes.Fitting behaviour of a lens in one patient is not an adequate predictor of that lens' performance with other patients.
, 百拇医药
In conclusion,lenses designed outside Asia are suitable for Chinese eyes provided that proper selection and fitting are performed to suit individual variation.It was also found that the fitting assessment did not hold any relationship with the comfort grading.“Comfort"cannot be used as the only indicator for optimal lens fit.
4 Acknowledgement
The authors would like to acknowledge the contribution of Winnie Goh to make this study successful in Hong Kong.The work described in this paper was supported by the Hong Kong Polytechnic University Research Grants (Project No.0343 054).This project is sponsored by CTBA Vision(Atlanta).
, 百拇医药
From:1 Department of Optometry and Radiography,The Hong Kong Polytechnic University,Hong Kong.
2 Optometry Section,Singapore Polytechnic,Singapore.
3 CIBA Vision Group Management,Inc,Atlanta.
5 References
[1] Lam CSY,Goh WSH.The incidence of refractive errors among school children in Hong Kong and its relationship with the optical components.Clin Exp Optom,1991,74∶97～103
, 百拇医药
[2] Goh WSH,Lam CSY.Changes in refractive trends and optical components of Hong Kong Chinese aged 19～39 years.Ophthal Physiol Opt,1994,14∶378～382
[3] Chew SJ,Chia SC,Lee LKH.The pattern of myopia in young Singaporean men.Sing Med J,1988,29∶201～211
[4] Amano J,Tanaka K.Examination of patients after wear of contact lenses.Contacto,1968,12∶3～8
[5] Loran DFC,Lam CSY,French CN.An ethnic comparison of anterior segment characteristics:a preliminary report,J Brit Cont Lens Assoc,1984,7∶158～162
, 百拇医药
[6] Lam CSY,Loran DFC.Designing contact lenses for Oriental eyes.J Brit Cont Lens Assoc,1991,14∶109～114
[7] Cho P,Brown B.Review of the TBUT technique and a closer look at the TBUT of Hong Kong Chinese.Optom Vis Sci,1993,70∶30～38
[8] Cho P,Kwong YM.A pilot study of the comparative performance of two cotton thread tests for tear volume.J Br Contact Lens Assoc,1996,19∶77～82
[9] Cho P,Yap M.Schirmer Test.II.A clinical study of its repeatability.Optom Vis Sci,1993,70∶157～159
(收稿：1999-08-05), http://www.100md.com
单位：
关键词：
眼视光学杂志/990308
摘要 目的：亚洲市场的隐形眼镜，绝大多数是西方国家设计和生产的。尽管华人和白人眼部参数的差异之处尚未完全明了，但是亚洲的一些验配师还是喜欢单纯以镜片配戴的“舒适度”作为验配标准。作者调查了华人配戴几种水凝胶软镜的临床表现，以确定科学的验配评判标准。方法：在香港理工大学和新加坡理工大学这两处研究中心，各挑选十名年轻隐形眼镜配戴者，每只眼睛分别配戴6种不同类型的镜片(Weicon38E、HydronZ6、Medalist、Acuvue、Focus和SeeQuence)，20分钟之后由5名视光师分别对其进行验配评价，并让配戴者对配戴的舒适程度作0～100分的主观评价。结果：两地各种镜片的配戴舒适程度主观评价差异无显著(P>0.05)，然两地各种镜片的配戴特征的差异具有显著性(P<0.05)。结论：亚洲之外设计的镜片，如根据个体差异进行适当选择再作验配，对于华人来说是比较适合的。没有哪种镜片能够适合所有华人的眼睛配戴的，某些镜片配戴的主观舒适度虽与其他种类镜片相同，但是检查时可发现其偏紧。因此，仅仅根据“舒适度”作为隐形眼镜验配评判依据，而不作必要的配戴评价，就容易导致配戴过紧。故对每位病人均作试戴评价，仍不失为选择适合于华人配戴的隐形眼镜的最佳方法。
, http://www.100md.com
Soft contact lenses for Chinese eyes?
Carly S.Y.Lam1,BSc(Hons),MSc,PhD,MBCO,FAAO
Hui Heang Koh2,BSc(Optom)
Kah Ooi Tan3,BOptom(Hons),MBA,PhD
Abstract Most contact lenses available in Asia are designed and manufactured in the Western countries.Althongh the ocular characteristics between the Chinese and Cancasian are not fully understood,some practitioners in Asia prefer to judge the fitting solely based on the `comfort' of the lens.This study investigates the clinical performance of some hydrogel on Chinese eyes.This study was conducted at two centres(The Hong Kong Polytechnic University and Singapore Polytechnic).Ten young soft contact lens wearers were recruited in each centre.Six different types of lenses(Weicon 38E,Hydron Z6,Medalist,Acuvue,Focus and SeeQuence)were fitted on one eye.The fittings were assessed 20 minutes later by 5 optometrists at each centre,and the comfort levels were graded subjectively on a 0 to 100 scale.The results show that comfort levels were not significantly different among the lenses tested in both centres(P>0.05).However,there were significant differences (P<0.05) in fitting characteristic in both certres.Fitting of most lenses were acceptable,however,Acuvue and SeeQuence lenses were found to be significantly tighter (P<0.05).As conclusion,lenses designed outside Asia are suitable for Chinese eyes provided that proper selection and fitting are performed to suit individual variation.There is no single lens that suits all Chinese eye.Some lenses are equally comfortable,however,the fitting could be tighter when compared to the others.Thus,judging fitting based on `comfort' without proper fitting assessment may result in prescribing a tight lens.Trial fitting assessment on every patient is still the best way to select the appropriate lenses for Chinese eyes.
, 百拇医药
Key words soft contact lens Chinese Comfort Fitting assessment
Hong Kong and Singaporean Chinese are more myopic than other racial groups[1～3].Contact lenses provide an alternative correction to refractive errors.Most contact lenses available in Asia are designed and manufactured in the Western countries.However,little has been done to evaluate the suitability of the currently available contact lenses for the Chinese eyes.
, http://www.100md.com
Variations in the anterior segment characteristics among different ethnic groups have been reported[4～9].The corneal curvatures of Japanese were found to be steeper than Caucasians[4].The corneal shape of the Chinese eye has been found to be different from Caucasians in their curvature,peripheral flattening and diameter[5,6].Such differences have important implications for contact lens manufacturers,contact lens practitioners and eye surgeons.Several studies given also shown that Chinese has a different tear characteristics that the tear break up time and tear volume were found to be shorter and lesser than Caucasians[7～9].
, 百拇医药
Although the ocular characteristics of the Chinese and Caucasian eyes are not fully understood,the different fitting behaviours of some practitioners in this region may further complicate the selection of contact lenses for the Chinese eyes.Asia is one of the fastest growing contact lens markets.Contact lens practitioners in Asia include optometrists,ophthalmologists,and opticians.Fitting attitude in Asia is somewhat different from that in other westen countries.
, http://www.100md.com Speed is very critical in current trend of practice in Asia as to cope with the demand of busy practice and the high patient turnover rate.Some practitioners prefer to judge the suitability of a lens based on the subjective comfort of the fitting,without proper assessments of the fitting of the lenses.Common concept is that "Comfortable" means "Good Fit"!
It is thus interesting to find out whether lenses designed and manufactured outside Asia are suitable for Chinese eyes and investigate the clinical performance of some hydrogel lenses on the Chinese eyes.And also to determine if the selection of lenses based on `comfort'has any clinical implications on the fitting characteristics of the lens and to evaluate the relationship between `comfort'and `fitting characteristics'of soft lenses on Chinese eyes.
, http://www.100md.com
1 Methods & Materials
This study was conducted at two different centres:The Optometry Clinic,The Department of Optometry and Radiography,The Hong Kong Polytechnic University and the Optometry Clinic,Singapore Polytechnic.10 soft contact lens wearers(age:16～33),were recruited in each centre.A preliminary examination was carried out on each subject.A clinical assessment included the suitability of the subject for soft contact lens wear.The subject chosen should have worn contact lenses for more than one year.His/her corneal astigmatism must be less than 1.25Dc.The subject should be free from any ocular diseases or pathology such as corneal ulcer or eye surgery,any previous allergic reaction to contact lens such as giant papillary conjunctivitis,any systemic diseases that will affect the ocular conditions such as diabetic mellitus or hypertension.
, 百拇医药
Six different types of lenses currently available in the market were tested,these include Weicon 38E,Hydron Z6,Medalist,Acuvue,Focus and SeeQuence.Table 1 lists the parameters and materials of these lenses.
Table 1 Types of lenses used in the study LENSES
MATERIAL &
MANUFACTURING
DIAMETER
BOZR
, 百拇医药
SeeQuence
Polymacon 38.6%
(Spin-cast)
14.0
(Only one BOZR
is available)
Focus
Wifilcon A 55%
(Molded)
14.0
8.6
8.9
, 百拇医药
-
Weicon 38E
Tefilcon 38%
13.8
Steep
(ST)
Flat
(FL)
-
Acuvue
Etafilcon A 58%
(Stabilized soft molding)
, 百拇医药
14.0
8.4
8.8
-
Hydron
Zero 6
Polymacon 38%
(Lathe-cut)
14.0
8.1
8.4
8.7
Medalist
, 百拇医药
Polymacon 38%
(Spin-cast front/lathed
back)
14.0
8.4
8.7
-
Prior to the assessment of fitting and comfort in the trial,subjects were fitted with the six different types of contact lenses to determine the optimum fit of each type of lenses.An optometrist who was not involved in the assessment part undertook the fitting.
, 百拇医药
On the assessment trial,the subject was first asked to evaluate the `comfort'of the lens after 20 minutes of lens insertion as illustrated in Appendix 1.The comfort levels were graded on a 0 to 100 scale,where 0 indicated `Totally can not tolerate the lens',and 100 indicates `Can not feel the lens at all'.Every subject was requested to adapt to the lenses for about 20 minutes before grading the comfort levels of each lens.
The fitting of the lenses for each subject were then assessed by 5 optometrists.The performance of each type of lens was determined according to the assessment criteria illustrated in Appendix 2.All the optometrists were graduates from different optometry schools(Australia,United Kingdom,Malaysia,and Hong Kong).The fitting assessment includes lens coverage,centration,lens movement,lag of movement,tightness.The fitting characterstics were graded as unacceptable fit,good/acceptable fit and optimum fit.
, 百拇医药
The sequence of lenses to be fitted to each subject was selected randomly.This was a double-masked study that the subjects and the examiners did not know the type of lenses during the assessment.An optometrist who wasnot know the type of lenses during the assessment.An optometrist who not involved in any fitting assessment carried out the fitting and removal of the lenses.
2 Results
2.1 Coverage
, 百拇医药 All the six types of lenses were bigger than or equal to 13.8mm in total diameter.Majority of the lens completely covered the cornea except the Acuvue lenses,with which 20% and <5% of the fitting had the cornea partly exposed among the Hong Kong and Singaporean subjects respectively.
2.2 Centration
The lens centration was described either centred,decentred to nasal,temporal,superior or inferior side.The Weicon 38E,Focus and Hydron Zero 6 lenses provided well centration on the cornea in majority of the subjects Acuvue,Medalist and SeeQuence lenses provided less well centration among the six type of lenses.The decentration direction was mainly towards superior or temporal side.
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2.3 Fitting Assessment
The fittng pattern of each type of the lenses were described by the examiners according to the following scale:
1=Unacceptable(steep or loose)
2=Good/Acceptable(steep or loose)
3=Optimal
The mean values from the five examiners were used in the analysis.Table 2 shows the ranking of the six types of lenses based on the overall fitting assessment of the lenses in the two centres.The lenses were ranked according to the absolute scores as well as to the statistical significance between the fitting assessment of the lens types.Non-parametric Kruskal-Wallis H test was used to analyse the data and the result showed that there were significant differences in the fitting assessment among the six types of lenses (Chisquare=30.1,P<0.001).Comparison between any two lenses shows that in the Singapore,Weicon 38E was more acceptable than the other lenses(P<0.05),followed by Medalist and Focus(P<0.05),Hydron Z6 and Acuvue(P<0.05),and SeeQuence,which was found to be significantly tighter than the other lenses(P<0.05).In Hong Kong,the fitting of four types of lenses(Hydron Z6,Weicon 38E,Focus and Medalist)were not significantly different from each other(P>0.05).This was followed by Acuvue and SeeQuence lenses,which were found to be significantly tighter in fitting (P<0.05).Figure 1 shows the average best fit scores with standard deviation of the six different lenses in both centres.
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Table 2 Ranks according to fitting assessment RANK
ABSOLUTE SCORE
STATISTCIAL ANALYSIS
SINGAPORE
HONG KONG
SINGAPORE
HONG KONG
1
W38E
Hydron Z6
W38E
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Hydron Z6
Focus
W38E
Medalist
2
Medalist
Focus
Medalist
Acuvue
Focus
SeeQuence
3
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W38E
Hydron Z6
Acuvue
4
Hydron Z6
Medalist
SeeQuence
5
Acuvue
Acuvue
6
SeeQuence
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SeeQuence
Figure 1 Fitting assessment
2.4 Comfort assessment
Table 3 shows the ranking of the six types of lenses based on the subjects' assessment of comfort.Based on absolute scores,Medalist was found to be the most comfortable lens while Hydron Z6 was found to be the least comfortable lens among the Singaporean subjects.For the Hong Kong subjects,Focus lens provided the best comfort whereas Acuvue lens was the least comfortable lens.However,Kruskal-Wallis one-way anova test shows that lens comfort difference among the lenses are not statistically
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significant in both centres.Figure 2 shows the average comfort in percentage of the lens as expressed by the subjects in the two centres.
Table 3 Ranks according to comfort assessment RANK
ABSOLUTE SCORE
STATISTCIAL ANALYSIS
SINGAPORE
HONG KONG
SINGAPORE
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1
Medalist
Focus
All the same
(No statistical
significance)
All the same
(No statistical
significance)
2
SeeQuence
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W38E
-
-
3
W38E
SeeQuence
-
-
4
Focus
Medalist
-
-
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5
Acuvue
Hydron Z6
-
-
6
Hydron Z6
Acuvue
-
-
Figure 2 Comfort assessment
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2.5 Best lens
For each subject,the lens that obtained the highest score was classified as the best lens for him/her.Table 4 shows the best lens for each subject based on fitting assessment and comfort assessment.The results showed that different lenses performed differently on different subjects.Lenses such as Weicon 38E and Hydron Z6 are of better fit and comfort to Chinese eyes as compared to other lens types.However,individual variations do exist,not a single lens is suitable for ALL the subjects.
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Table 4 Best lens for the subjects SUBJECTS
BASED ON“F1TTING”
BASED ON“COMFORT”
SINGAPORE
HONG KONG
SINGAPORE
HONG KONG
1
W38E
Hydron Z6
Medalist
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W38E
Hydron Z6
Focus
SeeQuence
2
W38E
W38E
Hydron Z6
Focus
Medalist
Acuvue
Acuvue
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W38E
Hydron Z6
W38E
Medalist
Medalist
4
W38E
W38E
Medalist
Focus
W38E
Focus
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5
W38E
Hydron Z6
W38E
W38E
Hydron Z6
Medalist
Focus
Acuvue
6
W38E
Medalist
W38E
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W38E
Hydron Z6
Focus
Acuvue
7
W38E
Medalist
W38E
Hydron Z6
SeeQuence
8
W38E
Hydron Z6
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Acuvue
W38E
Hydron Z6
Focus
Acuvue
9
Medalist
Hydron Z6
Focus
SeeQuence
Hydron Z6
10
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W38E
Focus
W38E
Hydron Z6
Acuvue
SeeQucnce
3 Discussion and conclusion
When the optimum fit of each type of lens were compared for each subject,we found that some lens type tends to provide less optimal fitting.There was no significant difference in fitting perfomance among Weicon 38E,Focus,Hydron Zero 6 and Medalist lenses.SeeQuence and Acuvue lenses were found to perform differently and consistently provide more unacceptable steeper fittings than the others do.These could be attributed to the one-off base curve fitting of the SeeQuence lens or the design of the peripheral curves of these lenses.
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Although the results from Hong Kong and Singapore are not exactly the same,it shares some similarities and trends.It seems that there is no specific type of lenses that suit every Chinese.Careful selection of patients and proper fitting and assessment are still the only and the best way to select appropriate lenses for the Chinese eyes.Some lenses are tighter in fitting when compared to the others,however,the comfort levels are not significantly different.Thus,judging fit based on `comfort'without proper fitting assessment may result in prescribing a tight lens.This should be of concern to those busy optical practices in Asia where some practitioners judge the suitability of a lens solely based on the `comfort'levels and without fitting assessment.Because of the individual variations in fitting behaviour,trial fitting assessment on every patient is still the best way to select the appropriate lenses for Chinese eyes.Fitting behaviour of a lens in one patient is not an adequate predictor of that lens' performance with other patients.
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In conclusion,lenses designed outside Asia are suitable for Chinese eyes provided that proper selection and fitting are performed to suit individual variation.It was also found that the fitting assessment did not hold any relationship with the comfort grading.“Comfort"cannot be used as the only indicator for optimal lens fit.
4 Acknowledgement
The authors would like to acknowledge the contribution of Winnie Goh to make this study successful in Hong Kong.The work described in this paper was supported by the Hong Kong Polytechnic University Research Grants (Project No.0343 054).This project is sponsored by CTBA Vision(Atlanta).
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From:1 Department of Optometry and Radiography,The Hong Kong Polytechnic University,Hong Kong.
2 Optometry Section,Singapore Polytechnic,Singapore.
3 CIBA Vision Group Management,Inc,Atlanta.
5 References
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[2] Goh WSH,Lam CSY.Changes in refractive trends and optical components of Hong Kong Chinese aged 19～39 years.Ophthal Physiol Opt,1994,14∶378～382
[3] Chew SJ,Chia SC,Lee LKH.The pattern of myopia in young Singaporean men.Sing Med J,1988,29∶201～211
[4] Amano J,Tanaka K.Examination of patients after wear of contact lenses.Contacto,1968,12∶3～8
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[6] Lam CSY,Loran DFC.Designing contact lenses for Oriental eyes.J Brit Cont Lens Assoc,1991,14∶109～114
[7] Cho P,Brown B.Review of the TBUT technique and a closer look at the TBUT of Hong Kong Chinese.Optom Vis Sci,1993,70∶30～38
[8] Cho P,Kwong YM.A pilot study of the comparative performance of two cotton thread tests for tear volume.J Br Contact Lens Assoc,1996,19∶77～82
[9] Cho P,Yap M.Schirmer Test.II.A clinical study of its repeatability.Optom Vis Sci,1993,70∶157～159
(收稿：1999-08-05), http://www.100md.com