research article corneal aberrations, contrast...

Research ArticleCorneal Aberrations Contrast Sensitivity and Light Distortionin Orthokeratology Patients 1-Year Results

Elena Santolaria-Sanz12 Alejandro Cervintildeo2 and Joseacute M Gonzaacutelez-Meacuteijome3

1Private Practice Onda Castellon Spain2Optometry Research Group Department of Optics amp Optometry amp Vision Sciences Universidad de Valencia Valencia Spain3CEORLab-Center of Physics (Optometry) Universidade do Minho Braga Portugal

Correspondence should be addressed to Jose M Gonzalez-Meijome jgmeijomefisicauminhopt

Received 3 May 2016 Revised 27 July 2016 Accepted 30 August 2016

Academic Editor Suphi Taneri

Copyright copy 2016 Elena Santolaria-Sanz et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Purpose To evaluate the corneal higher-order aberrations (HOA) contrast sensitivity function (CSF) and light distortion (LD)in patients undergoing orthokeratology (OK)Methods Twenty healthy subjects (mean age 2140 plusmn 8 years) with mean sphericalequivalent refractive error M = minus219 plusmn 097D were evaluated at 1 day 1 month and 1 year after starting OK treatment MonocularLD photopic monocular CSF and corneal HOA for 6mm pupil size were measured Results LD showed an increase after the firstnight (119901 lt 005) and recovery to baseline after 1 month remaining stable after 1 year (119901 gt 005) Spherical-like coma-like andsecondary astigmatism HOA RMS increased significantly (119901 le 0022) from baseline to 1-month visit remaining unchanged overthe follow-up Contrast sensitivity formedium frequencies (30 424 and 600 cpd) was significantly correlated with LD parametersat baseline (119903 le minus0529 119901 lt 0001) However after 1 year of treatment this correlation was only statistically significant for 12 cpdspatial frequency (119903 le minus0565119901 lt 0001) Spherical-like RMS for 6mmpupil size correlatedwith irregularity of the LD (119903 = minus0420119901 lt 005) at the 1-year visit Conclusion LD experienced by OK patients recovers after one month of treatment and remains stablein the long term while optical aberrations remain significantly higher than baseline

1 Introduction

Orthokeratology (OK) provides independence of conven-tional compensation by spectacles or contact lenses duringthe waking hours [1] For myopia correction central corneais flattened to achieve the desired reduction in the powerof the anterior corneal surface while the midperipheralcornea steepens [2 3] as a result of the epithelial thicknessredistribution from the center [4]This treatment deterioratesthe quality of vision [5ndash8] and it has been shown that suchchanges are dependent on pupil size [9] and strongly affectedby the amount of refractive error being corrected [10]

In clinical practice OK subjects usually complain of sub-jective perception of dysphotopic phenomena in the form ofhaloes ghosting or glare (here considered as light distortionphenomena or LD) Those are more intense at the beginningof treatment anddecrease over time [11 12]Wehave observedin a cross-sectional study that OK subjects report subjective

complaints that are transient during the first days or weeks oftreatment Common complaints include perception of haloesand starburst around light sources either in outdoor (iecar lights) or indoor conditions [13] In a different studywe have quantified the amount of LD over the period ofadaptation to OK treatment in a cohort of 29 subjects andobserved that LD phenomena increase at the first day butdecrease again towards baseline values after 30 days [14]However in that study we were not able to measure LDphenomena beyond the first month Thus we cannot ensurethat the adaptation period does not undergo further changesin the long term Other authors found a correlation betweencorneal irregularity and asymmetry parameters after 1 monthof OK treatment [15] what might suggest that the opticalquality of the front corneal surface during OK treatmentmight affect LD phenomena Considering that our previousstudy showed that LD improves from 1 day to 1 month oftreatment despite the increase in HOA up to 7 days after

Hindawi Publishing CorporationJournal of OphthalmologyVolume 2016 Article ID 8453462 8 pageshttpdxdoiorg10115520168453462

2 Journal of Ophthalmology

Table 1 Demographic refractive and keratometric data of subjects(mean plusmn SD) and range [minimum and maximum]

AGE 2140 plusmn 8 years [18 to 42]SAMPLE (malefemale ratio) 20 subjects (416)M (baseline) minus219 plusmn 097D [minus100 to minus475]J0 (baseline) minus004 plusmn 021 D [minus050 to 046]J45 (baseline) 001 plusmn 012D [minus029 to 036]Flattest keratometric radius 774 plusmn 029mm [720 to 864]Steepest keratometric radius 763 plusmn 030mm [706 to 863]Decimal VA (monocular) 118 plusmn 009 [100 to 150]

initiation of treatment becoming stable thereafter it has beenhypothesized that LD is not related to HOA themselves orthat there is an LD adaptation process even when the opticalquality of the anterior corneal surface remains significantlyaffected by spherical-like and coma-like HOA [2 3] Whileseveral studies have addressed the longitudinal changes inHOA and contrast sensitivity (CS) over a period of 1 yearto date no study has addressed the temporal changes in LDphenomena beyond 1 month of treatment

Different devices are available for measuring the distur-bances surrounding bright spots against dark backgroundsome of them use software [16ndash20] others use custom-made[21] or commercially available ones [19] We use a physicaldisplay to present the stimuli as this allows us to have a widerdynamic range of luminance from the main glare source andthe detection peripheral stimuli [20] and this instrument hasbeen shown to be consistent with [17] and sensitive to changesin higher-order aberrations (HOA) artificially induced [18]

Thus the purpose of the present study was to evaluate thelong-term visual effects of corneal optical quality degradationin OK patients by measuring the LD phenomena and CSF

2 Methods

A total of 20 neophyte subjects were recruited and fitted withOK lenses for myopia correction Subjects were followed andwore their lenses successfully for at least 1 year Demographicand refractive data of subjects are presented in Table 1Inclusion criteria required that they were over 18 years of agehad less than 100 diopters (D) of refractive astigmatism werefree of ocular disease had not contraindication for overnightCL wear and presented a best corrected monocular visualacuity of 090 decimals (2025) or better

Subjects were informed of the purpose of the study andsigned a consent form after all of their questions had beenanswered Following the tenets of theDeclaration ofHelsinkithe protocol of the study has been reviewed and approvedby the IRB Subjects underwent a comprehensive optometricexamination

21 Outcome Measures In this study all measures have beenobtained monocularly in order to correlate aberration datawith clinical data obtained with the different methodologiesSubjective baseline refraction and refraction at the time ofdata collection were determined as the spherocylindrical

combination Endpoint criterion was the highest positive(or less negative) refraction that allowed the patient toachieve theirmaximumvisual acuity in agreementwith usualrefraction procedures to control for accommodation effects

LD was analyzed with an experimental prototype [20]at a distance of 20m in a darkened room It consists ofan array of 240 1mm wide LEDs distributed radially at 15∘intervals over 160mm with a linear separation of 10mmaround a central 5mm white LED that acts as glare sourceas previously described [17 18 20] The system is controlledby a custom-made software that interfaces with the patientto detect the peripheral stimuli seen and discriminate themfrom those hidden by the central glare source Characteristicsand examination procedures in the context of assessment ofOK patients have been previously described [14] In brief intotally darkened room the instrument presents the centralsource of glare at maximum intensity while the peripheralLEDs are randomly turned on and off The patient providesfeedback regarding the stimuli that can be seen by clickinga remote actuator The system reads and stores the feedbackinformation and within 45 to 75 seconds the instrumentprovides a drawing of the area where the peripheral stimulicannot be seen by the patient along with different quanti-tative metrics Metrics of distortion size included the LDIcalculated as the ratio of the area or points missed by thesubject and the total area explored and is expressed as apercentage () Best Fit Circle Radius (BFCRadius) is definedas the circle that best fits to the distortion area resultingfrom the linear binding of all points in each meridian of thedeviceThehigher values of LDI andBFCRadius are interpretedas a lower ability to discriminate small stimuli surroundingthe central source of light Irregularity of the distortion areais derived as the deviation of the actual polygonal shapeobtained from the BFC fit and is called the BFC Irregularity(BFCIrreg) The standard deviation of BFCIrreg called BFCSDmeasures how asymmetric is the departure of the actualdistortion limits from the perfect circular shape of the BFCTogether BFCIrreg and BFCSD can be interpreted as thedeviation of the actual distortion from a perfectly rotationalsymmetric shape The higher the value of this parameter thelarger the deviation from a circular shape expressed in mm

The corneal aberrations were derived from topographydata using the Oculus Easygraph (Oculus DutenhofenGermany) for a circular aperture of 60mm The root meansquares (RMS) for 4th- and 6th-order spherical aberration(spherical-like) third- and fifth-order horizontal and verticalcoma aberration (coma-like) and fourth- and sixth-ordersecondary astigmatism (secondary astigmatism) were calcu-lated

Decimal high-contrast visual acuity and CSF were mea-sured at distance of 5m under photopic conditions with theLCD screen 2210158401015840 LCD (Topcon CC-100XP Tokyo Japan)Frequencies tested were 150 212 300 424 600 849 12001697 and 2400 cycles per degree (cpd)

22 Statistical Analysis Statistical analysis was conductedusing SPSS software v150 (SPSS Inc Chicago IL) Descrip-tive statistics of the variables measured in the study were

Journal of Ophthalmology 3

0

5

10

15

20

25

Baseline 1 day 30 days 1 year

LDI (

)

Follow-up visit

(a)

5

10

15

20

25

30

Baseline 1 day 30 days 1 yearFollow-up visit

BFC R

adiu

s(m

m)

(b)

05

1

15

2

25

3


BFC I

rreg

(mm

)

(c)

Figure 1 Monocular LDI (a) BFCRadius (b) and BFCIrreg (c) parameters Error bars represent the standard error of the mean (SEM)

obtained Normality of data distribution was assessed withKolmogorov-Smirnov test Changes in different parame-ters from baseline to subsequent visits were comparedusing ANOVA test with Bonferroni correction Correlationsbetween different parameters were performed using Pearsoncorrelation Statistical significance criterion was establishedat 119901 lt 005

3 Results

All subjects included in the analysis showed a monocularvisual of 10 decimals or better at the 1-month and 1-year visits

31 Light Distortion Figure 1 shows the variations of size-related (LDI and BFCRadius) and irregularity-related(BFCIrreg) parameters of monocular LD over time BFCRadiusworsened after first night recovering normal values after1 month and 1 year (ANOVA with Bonferroni post hoccorrection 119901 lt 005) BFCIrreg followed a similar path withan increase after the first night and a reduction towards

Table 2 Statistically significant changes in parameters ofmonocularLD overtime (mean difference plusmn SEM)

Δ plusmn SEM SigLDI 1 day versus 1 month 069 plusmn 019 0007BFCRadius 1 day versus 1 month 180 plusmn 047 0005BFCIrreg 1 day versus 1 month 100 plusmn 025 0003

baseline values after 1 month (Table 2) and remaining stableafter 1 year of follow-up

While the size-related parameters of the LD recovered tobaseline values LD regularity parameters were lower after 1month compared to baseline

32 Corneal Aberrations Figure 2 shows the variations ofoptical quality of the anterior corneal surface over timeTable 3 summarizes the average differences and statisticalsignificance for those parameters where the RMS presenteda significant change between two visits as analyzed withANOVA with Bonferroni post hoc correction Spherical-like


SphericalComaSec astig


0

01

02

03

04

05

06

07

08

09

HO

A fo

r6m

m p

upil

size (

mic

rons

)

Figure 2 Optical quality of the corneal front surface for 6mmpupil size represented by the root mean square (RMS) of spherical-like aberrations coma-like aberrations and secondary astigmatismError bars represent the standard error of the mean (SEM)

Table 3 Changes in HOA between baseline and follow-up visits(mean difference plusmn SEM) for RMS values showing statisticallysignificant changes for 6mm pupil size

Δ plusmn SEM Sig

Spherical-like

Baseline versusDay 1 035 plusmn 005 lt0001

1 month 054 plusmn 005 lt00011 year 054 plusmn 005 lt0001

Day 1 versus 1 month 019 plusmn 005 0006Day 1 versus 1 year 019 plusmn 005 0008

Coma-like Baseline versus 1 month 029 plusmn 008 00091 year 030 plusmn 008 0006

Secondaryastigmatism Baseline versus 1 month 008 plusmn 002 0022

1 year 009 plusmn 002 0002

RMS underwent a statistically significant increase after thefirst night of treatment and worsened further up until the1-month visit compared to baseline (119901 lt 005) Coma-likeRMS as well as to a less extent secondary astigmatism RMSshowed a statistically significant increase up until the firstmonth visit remaining stable at the 1 year visit

33 Contrast Sensitivity Function Figure 3 shows the varia-tions in CSF between baseline and the 3 follow-up visits after1 day 1 month and 1 year of treatment Table 4 presents theaverage difference and the statistical significance for thosespatial frequencies showing statistically significant changesover the study period Bonferroni post hoc correction showedthat therewas only a significant decrease inCS for frequencies

15 212 3 424 6 849 12 1697 24Spatial frequency (cpd)

Baseline1 day

30 days1 year

1

12

14

16

18

2

22

24

Mon

ocul

ar C

SF (c

dg)

Figure 3 Monocular CSF Error bars represent the standard errorof the mean (SEM)

Table 4 Changes inCS between baseline and follow-up visits (meandifference plusmn SEM) for those frequencies showing significant changesbetween visits

Δ plusmn SEM Sig

LogCS 300 cpd Day 1 versus Baseline 004 plusmn 001 00061 year 005 plusmn 001 0044

LogCS 424 cpd Day 1 versus 1 month 007 plusmn 002 00421 year 008 plusmn 002 0022

LogCS 849 cpd Day 1 versus Baseline 009 plusmn 003 00171 month 013 plusmn 003 0001

LogCS 1697 cpd Day 1 versus 1 month 025 plusmn 006 0004

LogCS 2400 cpdBaseline versus 1 month 024 plusmn 007 0041

Day 1 versus 1 month 041 plusmn 008 00001 year 035 plusmn 009 0005

300 and 849 cpd from baseline on day 1 Furthermoresignificant changes from day 1 to 1 month were also observedfor 424 849 1697 and 2400 cpd spatial frequencies Finallyspatial frequencies of 300 424 and 2400 cpd presentedstatistically significant changes between 1 day and 1 year

34 Correlations We observed that there was a statisticallysignificant correlation between monocular CS for mediumfrequencies (30 424 and 600 cpd) and LD parameters atbaseline (119903 le minus0529 119901 lt 0001) However after 1 year of tre-atment this correlation was only statistically significant for12 cpd spatial frequency (119903 le minus0565 119901 lt 0001)

In general HOA were not significantly correlated withLD However after one year of treatment we observedthat there was a statistically significant correlation betweenspherical-like RMS for 6mmpupil size and irregularity of LD(119903 = minus0420 119901 lt 005)


Regarding correlations between monocular CS andHOA correlations were statistically significant between thespherical-like RMS for 6mm pupil size and frequencies424 (119903 = 0335119901 lt 005) and 1200 cpd (119903 = 0367119901 lt 005)at baseline After 1 year of treatment HOA were not sig-nificantly correlated with monocular CS values except forthe 424 cpd spatial frequency against coma-like RMS (119903 =minus0397 119901 lt 005) and secondary astigmatism RMS (119903 =minus0419 119901 lt 005)

4 Discussion

With the present study we found that despite a significantand stable deterioration of visual quality as observed in theaberrometric structure of the anterior corneal surface visualquality measured through CSF returns to baseline valueswithin the first month of treatment Similarly LD perceptionmeasured with an experimental device also returned tobaseline over the first month of treatment and remainedstable up to 1 year of follow-up In OK practice subjectsoccasionally report visual disturbances even though theirhigh-contrast visual acuity is excellent [22]

Although optical quality of the eye and quality of visionafter OK have been investigated [5 22 23] in the presentstudy we evaluated HOA CS and adaptation to LD simul-taneously in subjects undergoing OK for myopia during thefirst year of treatment

Measurement of CS can provide useful information aboutvisual function that may not be revealed by standard visualacuity testing [24 25] Previous studies have reported signifi-cant visual quality changes after OK with significant increaseof HOA and reduction in CS depending on the amount ofmyopic correction [22] In that study the authors observedthat BCVA was maintained at baseline over the follow-upperiod Ocular HOA significantly increased 1 month afterthe procedure and remained stable thereafter Regarding CSthere was an initial loss during overnight OK and the losspersisted during the 1-year follow-up Our present results donot agree with the persistent reduction in CS Instead wefound that CS recovered to baseline values after 1 month oftreatment

Similar to the findings previously reported by us in theshorter term [14] monocular CSF experienced a significantdecrease of 300 to 849 frequencies from baseline to day 1In the present study there was a correlation between CSF andHOA at baseline and this correlation was lost after treatmentonset and during the year of follow-upOn the other hand LDparameters and HOA were not correlated during the studyperiod except for spherical-like RMS for 6mmpupil size andBFCIrreg after one year of treatment In a previous work Villaet al reported a significant correlation between spherical-like RMS and LD [26] Although LD and CS are recoveredwith respect to baseline point there was a lack of correlationbetween them in the present study This might reflect thatLD itself does not in fact impair CS under the conditionsof examination It might be expected that performing CSanalysis under glare conditions might result in a significantcorrelation between LDI and CS but not for the conditions

under which we evaluated CS in the present study It has beensurprising to find an improvement in the higher frequenciesfor the CSF measurement improving from baseline to 1 yearafter an initial decrease This improvement over the bestcorrected CSF before treatment might be related in part tosome learning effects after repetitive application of the testHowever this is less likely because the tests were applied fora long period of time apart from each other

Several studies have shown thatCS significantly correlateswith some abilities associated with the patientrsquos quality oflife such as reading speed [27] or driving performance [28]However CS analysis is not sufficient to understand certaincomplaints reported by patients This is well recognized insubjects who have undergone corneal refractive surgery andreport frequent symptoms of night vision disturbances [2629 30] even when high-contrast visual acuity is excellent [31ndash35]

In order to evaluate other aspects of the visual quality ofthe patient in this longitudinal study we investigated changesin perception of LD changes in ocular HOA and CSF as rep-resentative parameters of vision quality in eyes undergoingovernightOKduring one year LD analysis showed a transientincrease followed by a reduction to baseline levels over thefirst month of treatment Changes observed in the long-termfrom 1month to 1 year are not significantThis is in agreementwith the clinical observation of adaptation to the distortioneffect In a recent work we have observed that subjectivereports of light distortions increasewhen treatment starts anddecreases over the period of treatment [13]

With the present study we can conclude that adaptationphenomena observed previously in the shorter-term [14] isnot expected to change in the longer term Our observationswith this experimental device are also in agreement withthe time course of night vision disturbances after refractivesurgery Though OK and corneal refractive surgery aredifferent procedures similar time course changes are foundwith HOA remaining high after the procedure while thecomplaints and subjective perceptions of the patients seemto improve faster after the procedure [36] Pop and Payette[30] showed a reduction in patients reporting night visiondisturbances from 25 at 1-month visit to 47 at the 12-month visit Our results however show that this reductionin night vision complaints might be faster recovering tobaseline after 1 month This might be explained because themeasurement device such as our LD analyzer is sensitiveto more severe forms of LD phenomena that do not allowto see objects around the bright source of light Even whenthe patient has recovered to a point where this kind ofdistortion is no longer present or is attenuated the patientmight still subjectively report it to some degree McAlindenet al evaluated the time course changes in the responses to theQuality of Vision (QoV) questionnaire in patients undergo-ing myopic and hyperopic LASEK corneal surgery [36] Thisinstrument accounts for frequency severity and bothersomeof visual symptoms including haloes and starburst and weinclude these kinds of phenomena below the umbrella of LDphenomena They also observed a rapid decline in the QoVscore after PRK surgery with the QoV scores returning tobaseline after 1 month following the treatment At present


there is no objective (and available) method tomeasure thosephotic phenomena isolated Instruments such as subjectivequestionnaires do not capture these features specifically Theone that approaches such measures in a somewhat specificway is the Quality of Vision questionnaire [36] Howeverthis includes other aspects of subjective visual complaints andthus cannot be directly compared

Indeed HOA of the anterior corneal surface changedsignificantly in our study in agreement with previous work[8] In a recent paper conducted by our group where we haveevaluated HOA during the first month of OK treatment forone month and the present results demonstrate the stabilityin the longer term from 1 month to 1 year of treatment [14]The time course changes in HOA observed in the presentstudy are in agreement with values reported by other authors[5 22] with spherical-like and coma-like aberrations beingthe main contributors to the degradation of the image quality[7] This might be justified by the fact that 3rd- (coma-like)and 4th-order (spherical-like) aberrations are more directlyrelated to the creation and consolidation of the treatmentzone while secondary astigmatism affects more peripheralareas of the cornea presumably more subjected to day-to-day variations as a consequence of slight decentrations orpressure changes at the edge of the transition zone of the lens

The present study has several limitations We have notmeasured whole-eye HOA that could correlate better withthe visual functions that we aim to evaluate However themain changes in aberrations in our study are induced inthe front corneal surface and it is expected that the wholeeye aberrations would suffer similar changes We cannotensure that the LD parameter reflects specifically the haloesghost images starburst and glare reported subjectively bythe patient However we have reported in a recent studythat the system is sensitive to the photic phenomena inducedwhen we artificially incorporate different amounts and signof HOA [18] Although we cannot quantify each one of thephotic phenomena we consider that such effects are wellreflected in the short-term measurements in this study andthat adaptation takes place to reduce the size of the LDovertime in the middle [14] and longer term (present study)in agreement with transient subjective complaints expressedby the patient in the clinical setting [13] On the other side thelack of correlation between LDandCS valuesmight be relatedto the fact that we did not use a glare source while measuringthe CSF Compared to our previous study [14] we did notmeasure binocular functions of LD and CS in the presentstudy This does not reflect the actual viewing conditionsof the patients but we aimed to maximize the potentialchanges to be observed andwe know that they would bemorelikely detected under monocular conditions as binocularsummation will tend to improve the results of LD [14 37] andCS [38] We also aimed to explore the correlations with HOAspecific to each eye which forced us to do follow amonocularanalysis in this part of the studyOther factors thatmight limitthe correlation between optical quality (HOA) and visualquality (LD and CS) parameters include the fact that wecannot ensure that the pupil area in each condition is exactlythe same Furthermore neural adaptationmechanismsmightplay a significant role in adaptation to a deteriorated optical

quality while preserving a good visual function This abilityto adaptation has been reported previously in the presence ofHOA in human eyes [13 39ndash41]

In summary we have observed that the previouslyreported adaptation phenomena to increase HOA are main-tained in the longer term at least as far as it concernsthe LD and CSF To our knowledge this is the first studyaddressing the long-term changes in the optical quality ofthe anterior corneal surface with orthokeratology treatmentand the potential impact on visual quality measured throughmonocular CSF and LD measurement

Competing Interests

J M Gonzalez-Meijome has a proprietary interest in thedevice used in the present study to measure the light distor-tion The other authors do not have any financial interest inthe materials and instruments used in this study

Acknowledgments

This research was supported in part by Projects PTDCSAU-BEB0983912008FCOMP-01-0124-FEDER-010897 PTDCSAU-BEB0983922008 and Strategic Funding UIDFIS046502013

References

[1] L Sorbara D Fonn T Simpson F Lu and R Kort ldquoReductionof myopia from corneal refractive therapyrdquo Optometry andVision Science vol 82 no 6 pp 512ndash518 2005

[2] F Lu T Simpson L Sorbara and D Fonn ldquoCorneal refractivetherapy with different lens materials part 2 effect of oxygentransmissibility on corneal shape and optical characteristicsrdquoOptometry and Vision Science vol 84 no 4 pp 349ndash356 2007

[3] A Queiros J M Gonzalez-Meijome J Jorge C Villa-Collarand A R Gutierrez ldquoPeripheral refraction in myopic patientsafter orthokeratologyrdquoOptometry andVision Science vol 87 no5 pp 323ndash329 2010

[4] S Haque D Fonn T Simpson and L Jones ldquoCorneal andepithelial thickness changes after 4 weeks of overnight cornealrefractive therapy lens wear measured with optical coherencetomographyrdquo Eye and Contact Lens vol 30 no 4 pp 189ndash2062004

[5] T Hiraoka Y Matsumoto F Okamoto et al ldquoCorneal higher-order aberrations induced by overnight orthokeratologyrdquoAmerican Journal of Ophthalmology vol 139 no 3 pp 429ndash4362005

[6] R G Anera C Villa J R Jimenez and R Gutierrez ldquoEffectof LASIK and contact lens corneal refractive therapy on higherorder aberrations and contrast sensitivity functionrdquo Journal ofRefractive Surgery vol 25 no 3 pp 277ndash284 2009

[7] F Lu T Simpson L Sorbara and D Fonn ldquoThe relationshipbetween the treatment zone diameter and visual optical andsubjective performance in Corneal Refractive Therapy lenswearersrdquoOphthalmic and Physiological Optics vol 27 no 6 pp568ndash578 2007

[8] T Hiraoka C Okamoto Y Ishii T Kakita F Okamoto and TOshika ldquoTime course of changes in ocular higher-order aber-rations and contrast sensitivity after overnight orthokeratologyrdquo


Investigative Ophthalmology amp Visual Science vol 49 no 10 pp4314ndash4320 2008

[9] Y Wang K Zhao Y Jin Y Niu and T Zuo ldquoChanges of higherorder aberration with various pupil sizes in the myopic eyerdquoJournal of Refractive Surgery vol 19 no 2 pp S270ndashS274 2003

[10] L Llorente S Barbero D Cano C Dorronsoro and S MarcosldquoMyopic versus hyperopic eyes axial length corneal shape andoptical aberrationsrdquo Journal of Vision vol 4 no 4 pp 288ndash2982004

[11] N Yamane K Miyata T Samejima et al ldquoOcular higher-order aberrations and contrast sensitivity after conventionallaser in situ keratomileusisrdquo Investigative Ophthalmology andVisual Science vol 45 no 11 pp 3986ndash3990 2004

[12] Z Wang J Chen and B Yang ldquoComparison of laser insitu keratomileusis and photorefractive keratectomy to correctmyopia from -125 to -600 dioptersrdquo Journal of RefractiveSurgery vol 13 pp 528ndash534 1997

[13] E Santolaria A Cervino A Queiros R Brautaset and JM Gonzalez-Meijome ldquoSubjective satisfaction in long-termorthokeratology patientsrdquo Eye and Contact Lens vol 39 no 6pp 388ndash393 2013

[14] E Santolaria Sanz A Cervino A Queiros C Villa-CollarD Lopes-Ferreira and J M Gonzalez-Meijome ldquoShort-termchanges in light distortion in orthokeratology subjectsrdquo BioMedResearch International vol 2015 Article ID 278425 7 pages2015

[15] T Kojima A Hasegawa S Hara et al ldquoQuantitative evaluationof night vision and correlation of refractive and topographicalparameters with glare after orthokeratologyrdquoGraefersquos Archive forClinical and Experimental Ophthalmology vol 249 no 10 pp1519ndash1526 2011

[16] J J Castro J R Jimenez C Ortiz A Alarcn and R G AneraldquoNew testing software for quantifying discrimination capacityin subjects with ocular pathologiesrdquo Journal of BiomedicalOptics vol 16 no 1 Article ID 015001 2011

[17] H Ferreira-Neves R Macedo-de-Araujo L Rico-del-Viejo AC da-Silva A Queiros and J M Gonzalez-Meijome ldquoVali-dation of a method to measure light distortion surroundinga source of glarerdquo Journal of Biomedical Optics vol 20 no 7Article ID 75002 2015

[18] R Macedo-de-Araujo H Ferreira-Neves L Rico-del-ViejoS C Peixoto-de-Matos and J M Gonzalez-Meijome ldquoLightdistortion and spherical aberration for the accommodating andnonaccommodating eyerdquo Journal of Biomedical Optics vol 21no 7 Article ID 075003 2016

[19] M C Puell M J Perez-Carrasco A Barrio B Antona and CPalomo-Alvarez ldquoNormal values for the size of a halo producedby a glare sourcerdquo Journal of Refractive Surgery vol 29 no 9pp 618ndash622 2013

[20] J M M Linhares H Neves D Lopes-Ferreira M Faria-Ribeiro S C Peixoto-de-Matos and J M Gonzalez-MeijomeldquoRadiometric characterization of a novel LED array system forvisual assessmentrdquo Journal of Modern Optics vol 60 no 14 pp1136ndash1144 2013

[21] A L Sheppard S Shah U Bhatt G Bhogal and J SWolffsohnldquoVisual outcomes and subjective experience after bilateralimplantation of a new diffractive trifocal intraocular lensrdquoJournal of Cataract andRefractive Surgery vol 39 no 3 pp 343ndash349 2013

[22] THiraoka COkamoto Y Ishii T Kakita andTOshika ldquoCon-trast sensitivity function and ocular higher-order aberrations

following overnight orthokeratologyrdquo Investigative Ophthalmol-ogy amp Visual Science vol 48 no 2 pp 550ndash556 2007

[23] D A Berntsen J T Barr and G L Mitchell ldquoThe effectof overnight contact lens corneal reshaping on higher-orderaberrations and best-corrected visual acuityrdquo Optometry andVision Science vol 82 no 6 pp 490ndash497 2005

[24] J J Perez-Santonja H F Sakla and J L Alio ldquoContrastsensitivity after laser in situ keratomileusisrdquo Journal of Cataractand Refractive Surgery vol 24 no 2 pp 183ndash189 1998

[25] W Verdon M Bullimore and R K Maloney ldquoVisual perfor-mance after photorefractive keratectomy a prospective studyrdquoArchives of Ophthalmology vol 114 no 12 pp 1465ndash1472 1996

[26] C Villa R Gutierrez J R Jimenez and J M Gonzalez-Meijome ldquoNight vision disturbances after successful LASIKsurgeryrdquo British Journal of Ophthalmology vol 91 no 8 pp1031ndash1037 2007

[27] S G Whittaker and J Lovie-Kitchin ldquoVisual requirements forreadingrdquoOptometry and Vision Science vol 70 no 1 pp 54ndash651993

[28] C Owsley K Ball G McGwin Jr et al ldquoVisual processingimpairment and risk of motor vehicle crash among olderadultsrdquo The Journal of the American Medical Association vol279 no 14 pp 1083ndash1088 1998

[29] N I Fan-Paul J Li J S Miller and G J Florakis ldquoNightvision disturbances after corneal refractive surgeryrdquo Survey ofOphthalmology vol 47 no 6 pp 533ndash546 2002

[30] M Pop and Y Payette ldquoRisk factors for night vision complaintsafter LASIK formyopiardquoOphthalmology vol 111 no 1 pp 3ndash102004

[31] H Hamberg-Nystrom B Tengroth P Fagerholm D Epsteinand E M Van der Kwast - ldquoPatient satisfaction followingphotorefractive keratectomy for myopiardquo Journal of RefractiveSurgery vol 11 no 3 pp S335ndashS336 1995

[32] B L Halliday ldquoRefractive and visual results and patient sat-isfaction after excimer laser photorefractive keratectomy formyopiardquo British Journal of Ophthalmology vol 79 no 10 pp881ndash887 1995

[33] M Piovella F I Camesasca and C Fattori ldquoExcimer laser pho-torefractive keratectomy for high myopia four-year experiencewith amultiple zone techniquerdquoOphthalmology vol 104 no 10pp 1554ndash1565 1997

[34] I Brunette J Gresset J-F Boivin et al ldquoFunctional outcomeand satisfaction after photorefractive keratectomy Part 2 sur-vey of 690 patientsrdquo Ophthalmology vol 107 no 9 pp 1790ndash1796 2000

[35] C N J McGhee J P Craig N Sachdev K H Weed and A DBrown ldquoFunctional psychological and satisfaction outcomesof laser in situ keratomileusis for high myopiardquo Journal ofCataract and Refractive Surgery vol 26 no 4 pp 497ndash5092000

[36] C McAlinden E Skiadaresi K Pesudovs and J E MooreldquoQuality of vision after myopic and hyperopic laser-assistedsubepithelial keratectomyrdquo Journal of Cataract and RefractiveSurgery vol 37 no 6 pp 1097ndash1100 2011

[37] P Brito J Salgado-Borges H Neves J Gonzalez-Meijome andM Monteiro ldquoLight-distortion analysis as a possible indicatorof visual quality after refractive lens exchange with diffractivemultifocal intraocular lensesrdquo Journal of Cataract and RefractiveSurgery vol 41 no 3 pp 613ndash622 2015

[38] J R Jimenez C Villa R Gonzalez Anera R Gutierrez and LJimenez del Barco ldquoBinocular visual performance after LASIKrdquoJournal of Refractive Surgery vol 22 no 7 pp 679ndash688 2006


[39] P Artal L Chen E J Fernandez B Singer S Manzaneraand D R Williams ldquoNeural compensation for the eyersquos opticalaberrationsrdquo Journal of Vision vol 4 no 4 pp 281ndash287 2004

[40] D A Atchison and G Smith Optics of the Human Eye RetinalImage Quality Butterworth-Heinemann Woburn Ma USA2000

[41] M A Webster M A Georgeson and S M Webster ldquoNeuraladjustments to image blurrdquo Nature Neuroscience vol 5 no 9pp 839ndash840 2002

Submit your manuscripts athttpwwwhindawicom

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014


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Table 1 Demographic refractive and keratometric data of subjects(mean plusmn SD) and range [minimum and maximum]

AGE 2140 plusmn 8 years [18 to 42]SAMPLE (malefemale ratio) 20 subjects (416)M (baseline) minus219 plusmn 097D [minus100 to minus475]J0 (baseline) minus004 plusmn 021 D [minus050 to 046]J45 (baseline) 001 plusmn 012D [minus029 to 036]Flattest keratometric radius 774 plusmn 029mm [720 to 864]Steepest keratometric radius 763 plusmn 030mm [706 to 863]Decimal VA (monocular) 118 plusmn 009 [100 to 150]

initiation of treatment becoming stable thereafter it has beenhypothesized that LD is not related to HOA themselves orthat there is an LD adaptation process even when the opticalquality of the anterior corneal surface remains significantlyaffected by spherical-like and coma-like HOA [2 3] Whileseveral studies have addressed the longitudinal changes inHOA and contrast sensitivity (CS) over a period of 1 yearto date no study has addressed the temporal changes in LDphenomena beyond 1 month of treatment

Different devices are available for measuring the distur-bances surrounding bright spots against dark backgroundsome of them use software [16ndash20] others use custom-made[21] or commercially available ones [19] We use a physicaldisplay to present the stimuli as this allows us to have a widerdynamic range of luminance from the main glare source andthe detection peripheral stimuli [20] and this instrument hasbeen shown to be consistent with [17] and sensitive to changesin higher-order aberrations (HOA) artificially induced [18]

Thus the purpose of the present study was to evaluate thelong-term visual effects of corneal optical quality degradationin OK patients by measuring the LD phenomena and CSF

2 Methods

A total of 20 neophyte subjects were recruited and fitted withOK lenses for myopia correction Subjects were followed andwore their lenses successfully for at least 1 year Demographicand refractive data of subjects are presented in Table 1Inclusion criteria required that they were over 18 years of agehad less than 100 diopters (D) of refractive astigmatism werefree of ocular disease had not contraindication for overnightCL wear and presented a best corrected monocular visualacuity of 090 decimals (2025) or better

Subjects were informed of the purpose of the study andsigned a consent form after all of their questions had beenanswered Following the tenets of theDeclaration ofHelsinkithe protocol of the study has been reviewed and approvedby the IRB Subjects underwent a comprehensive optometricexamination

21 Outcome Measures In this study all measures have beenobtained monocularly in order to correlate aberration datawith clinical data obtained with the different methodologiesSubjective baseline refraction and refraction at the time ofdata collection were determined as the spherocylindrical

combination Endpoint criterion was the highest positive(or less negative) refraction that allowed the patient toachieve theirmaximumvisual acuity in agreementwith usualrefraction procedures to control for accommodation effects

LD was analyzed with an experimental prototype [20]at a distance of 20m in a darkened room It consists ofan array of 240 1mm wide LEDs distributed radially at 15∘intervals over 160mm with a linear separation of 10mmaround a central 5mm white LED that acts as glare sourceas previously described [17 18 20] The system is controlledby a custom-made software that interfaces with the patientto detect the peripheral stimuli seen and discriminate themfrom those hidden by the central glare source Characteristicsand examination procedures in the context of assessment ofOK patients have been previously described [14] In brief intotally darkened room the instrument presents the centralsource of glare at maximum intensity while the peripheralLEDs are randomly turned on and off The patient providesfeedback regarding the stimuli that can be seen by clickinga remote actuator The system reads and stores the feedbackinformation and within 45 to 75 seconds the instrumentprovides a drawing of the area where the peripheral stimulicannot be seen by the patient along with different quanti-tative metrics Metrics of distortion size included the LDIcalculated as the ratio of the area or points missed by thesubject and the total area explored and is expressed as apercentage () Best Fit Circle Radius (BFCRadius) is definedas the circle that best fits to the distortion area resultingfrom the linear binding of all points in each meridian of thedeviceThehigher values of LDI andBFCRadius are interpretedas a lower ability to discriminate small stimuli surroundingthe central source of light Irregularity of the distortion areais derived as the deviation of the actual polygonal shapeobtained from the BFC fit and is called the BFC Irregularity(BFCIrreg) The standard deviation of BFCIrreg called BFCSDmeasures how asymmetric is the departure of the actualdistortion limits from the perfect circular shape of the BFCTogether BFCIrreg and BFCSD can be interpreted as thedeviation of the actual distortion from a perfectly rotationalsymmetric shape The higher the value of this parameter thelarger the deviation from a circular shape expressed in mm

The corneal aberrations were derived from topographydata using the Oculus Easygraph (Oculus DutenhofenGermany) for a circular aperture of 60mm The root meansquares (RMS) for 4th- and 6th-order spherical aberration(spherical-like) third- and fifth-order horizontal and verticalcoma aberration (coma-like) and fourth- and sixth-ordersecondary astigmatism (secondary astigmatism) were calcu-lated

Decimal high-contrast visual acuity and CSF were mea-sured at distance of 5m under photopic conditions with theLCD screen 2210158401015840 LCD (Topcon CC-100XP Tokyo Japan)Frequencies tested were 150 212 300 424 600 849 12001697 and 2400 cycles per degree (cpd)

22 Statistical Analysis Statistical analysis was conductedusing SPSS software v150 (SPSS Inc Chicago IL) Descrip-tive statistics of the variables measured in the study were


0

5

10

15

20

25


LDI (

)

Follow-up visit

(a)

5

10

15

20

25

30


BFC R

adiu

s(m

m)

(b)

05

1

15

2

25

3


BFC I

rreg

(mm

)

(c)



3 Results











0

01

02

03

04

05

06

07

08

09

HO

A fo

r6m

m p

upil

size (

mic

rons

)



Δ plusmn SEM Sig

Spherical-like






1 year 009 plusmn 002 0002




Baseline1 day

30 days1 year

1

12

14

16

18

2

22

24

Mon

ocul

ar C

SF (c

dg)



Δ plusmn SEM Sig












4 Discussion















Competing Interests


Acknowledgments


References



















































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of

















0

5

10

15

20

25


LDI (

)

Follow-up visit

(a)

5

10

15

20

25

30


BFC R

adiu

s(m

m)

(b)

05

1

15

2

25

3


BFC I

rreg

(mm

)

(c)



3 Results











0

01

02

03

04

05

06

07

08

09

HO

A fo

r6m

m p

upil

size (

mic

rons

)



Δ plusmn SEM Sig

Spherical-like






1 year 009 plusmn 002 0002




Baseline1 day

30 days1 year

1

12

14

16

18

2

22

24

Mon

ocul

ar C

SF (c

dg)



Δ plusmn SEM Sig












4 Discussion















Competing Interests


Acknowledgments


References



















































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of



















0

01

02

03

04

05

06

07

08

09

HO

A fo

r6m

m p

upil

size (

mic

rons

)



Δ plusmn SEM Sig

Spherical-like






1 year 009 plusmn 002 0002




Baseline1 day

30 days1 year

1

12

14

16

18

2

22

24

Mon

ocul

ar C

SF (c

dg)



Δ plusmn SEM Sig












4 Discussion















Competing Interests


Acknowledgments


References



















































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of


















4 Discussion















Competing Interests


Acknowledgments


References



















































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of






















Competing Interests


Acknowledgments


References



















































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of


























































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of
















research article corneal aberrations, contrast...

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