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Dr. Vedat Kaya (MAKALE)


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Doktor Vedat Kaya, Canan Aslı Utine, Sezen Harmancı Karakuş, Işılay Kavadarlı ve Ömer Faruk Yılmaz tarafından hazırlanmış olan bu makaleyi ilginize sunarız.

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Dr. Vedat Kaya (MAKALE)

  1. 1. ORIGINAL ARTICLERefractive and Visual Outcomes AfterIntacs vs Ferrara Intrastromal Corneal RingSegment Implantation for Keratoconus:A Comparative StudyVedat Kaya, MD; Canan Asli Utine, MD, MSc; Sezen Harmanci Karakus, MD; Isilay Kavadarli, MD;Ömer Faruk Yilmaz, MD ABSTRACTPURPOSE: To evaluate the refractive, topographic,optical, visual acuity, and quality outcomes of two types I ntrastromal corneal ring segments (ICRS) have been implanted to delay or prevent the need for penetrating keratoplasty and to achieve refractive correction with improvement in visual acuity and quality in corneal ectatic diseases.1-14 Intacs (Addition Technology Inc, Sunnyvale,of intrastromal corneal ring segment (ICRS) implanta-tions in keratoconus. California) and Ferrara ICRS (Ferrara Ophthalmics Ltda, Belo Horizonte, Brazil) aim to improve geometry of the corneal sur-METHODS: In this retrospective study, 16 eyes that had face and modulation of refractive effect with their unique de-been implanted with Intacs ICRS (Addition TechnologyInc) (Intacs group) and 17 eyes implanted with Ferrara signs, internal and external diameters, thicknesses, and arcICRS (Ferrara Ophthalmics Ltda) (Ferrara group) were lengths.2,12evaluated. Pre- and postoperative examinations includ- Topographic and refractive results of ICRS implantation withed uncorrected and corrected distance visual acuities different designs have been compared previously.15,16 Because(UDVA and CDVA, respectively), manifest refraction, the aim of ICRS implantation is visual rehabilitation, postop-slit-lamp examination, topography, and ocular wavefrontanalysis. Contrast sensitivity measurements under phot- erative visual quality is as important as topographic, refractive,opic, scotopic, and scotopic with glare conditions were and visual acuity outcomes. Improved lower and higher orderperformed 1 year postoperatively. aberrations and uncorrected and corrected distance visual acu- ities (UDVA and CDVA, respectively) after Intacs implantationRESULTS: One year postoperatively, a significant de- have been reported.13 In our study, a comparative evaluation ofcrease was noted in spherical equivalent refractive error Intacs and Ferrara ICRS implantations was performed in termsof 3.76Ϯ0.39 diopters (D) and 3.42Ϯ0.88 D andkeratometry of 3.43Ϯ0.24 D and 3.28Ϯ0.78 D in the of visual acuity, refraction, topography, objective ocular opti-Intacs and Ferrara groups, respectively; and increase cal quality (ie, wavefront aberrations), and subjective visualin mean UDVA and CDVA in Snellen lines of 0.18Ϯ0.04 quality (ie, contrast sensitivity function).and 0.21Ϯ0.05, respectively, in the Intacs group and0.21Ϯ0.09 and 0.26Ϯ0.08, respectively, in the Ferrara PATIENTS AND METHODSgroup (PϽ.01 for all). The postoperative increase inUDVA and CDVA and decrease in keratometry readings In this retrospective, comparative study, eyes implantedwere not significantly different between groups (PϾ.05 with Intacs ICRS (Intacs group) between January 2008 andfor all). Mean higher order aberrations decreased in the January 2009 and Ferrara ICRS (Ferrara group) between MayIntacs group and increased in the Ferrara group (PϾ.05for both). Postoperatively, a significant decrease wasnoted in scotopic contrast sensitivity when glare was in- From Beyoglu Eye Research and Training Hospital (Kaya, Karakus, Kavadarli,troduced in the Ferrara group, which was positively cor- Yilmaz); and Yeditepe University, Department of Ophthalmology (Utine),related with pupil diameter (r(15)=0.50, P=.04). Istanbul, Turkey. The authors have no financial or proprietary interest in the materials pre-CONCLUSIONS: Both ICRS types provided comparable sented herein.refractive, topographic, and optical quality outcomes.Eyes with Ferrara ICRS experienced greater decrease in This study was presented at the 44th Turkish Ophthalmology Society nationalscotopic contrast sensitivity under glare, which was sig- meeting, September 29 - October 3, 2010, Antalya, Turkey.nificantly correlated with pupil diameter. [J Refract Surg. Correspondence: Canan Asli Utine, MD, MSc, Yeditepe University, Dept of2011;xx(x):xxx-xxx.] doi:10.3928/1081597X-2011 Ophthalmology, Gazi Umur Pasa sok. No: 28, Besiktas Balmumcu 34345 Istanbul Turkey. Tel: 90 533 5587635; Fax: 90 212 2112500; E-mail: cananutine@gmail. com Received: February 8, 2011; Accepted: July 18, 2011 Posted online:Journal of Refractive Surgery • Vol. xx, No. x, 2011 1
  2. 2. Intacs vs Ferrara Intrastromal Corneal Ring Segments/Kaya et al2008 and December 2008 for visual rehabilitation of diameter of 8.10 mm, an internal diameter of 6.77 mm,keratoconus were included. In all patients, diagnosis and variable thickness of 0.25 to 0.45 mm in 0.05-mmof keratoconus was based on corneal topography and increments, which allows modulation of the refrac-slit-lamp observation (asymmetric bowtie pattern with tive effect.18or without skewed axes, keratometry у47.00 D, pres- Ferrara ICRS have a triangular cross-section thatence of stromal thinning, conical protrusion of the cor- theoretically induces a prismatic effect to reduce pho-neal apex, Fleischer ring, Vogt striae, or anterior stro- tic phenomena.9 Circumference arc lengths of 90, 120,mal scar). Nine eyes with grade 2 and 7 eyes with grade 160, and 210° are available. Each segment has an3 keratoconus comprised the Intacs group, and 11 eyes internal diameter of 4.40 mm, external diameter ofwith grade 2 and 6 eyes with grade 3 keratoconus com- 5.60 mm, and variable thickness of 0.15 to 0.35 mmprised the Ferrara group, which were classified by cri- in 0.05-mm increments.teria described by Krumeich et al.17 All surgeries were performed at Yeditepe Univer- SURGICAL TECHNIQUEsity, and 1-year postoperative examinations were per- All surgical procedures were performed under top-formed at Beyoglu Eye Research and Training Hospi- ical anesthesia, with the first Purkinje reflex markedtal, Istanbul, Turkey, by the same surgeon (V.K.). The as the corneal central point. A 60-kHz femtosecondstudy adhered to the tenets of the Declaration of Hel- laser (IntraLase; Abbott Medical Optics, Santa Ana,sinki and written informed consent was obtained from California) was used to create intrastromal channelsall participants before examination. for the intrastromal corneal ring with the following Pre- and 1-year postoperative examinations included settings: entry cut thickness 1 μm, ring energy 1.50UDVA, CDVA, manifest refraction, slit-lamp examina- to 2.50 μJ, and entry cut energy 1.50 μJ. In the Intacstion, corneal topography, and ocular wavefront analy- group, a 10/0 monofilament nylon suture was placedsis. At 1 year, contrast sensitivity measurements under at the incision site, which was removed 1 month post-photopic and scotopic with and without glare condi- operatively. Postoperative treatment included topicaltions were also performed. ofloxacin 0.3% (Exocin; Allergan, Mougins, France) All visual acuity measurements were completed and prednisolone acetate 1% (Predforte, Allergan) fourusing an Optec 6500P Vision Tester (Stereo Optical, times daily for 2 weeks; the latter was then taperedChicago, Illiniois), and results were recorded as total over 4 weeks. Preservative-free artificial tear substi-number of identified letters and corresponding visual tute (Refresh Plus; Allergan, Irvine, California) wasacuities in Snellen lines. Visual acuity testing was used as needed.performed at a standardized luminance level of 85 Thickness and degree of arc of ICRS were selectedand 3.0 cd/m2 (photopic and scotopic lighting, respec- and their location was planned according to cone loca-tively). Corneal topographies were performed using tion on axial topography for the specific nomogramsthe Orbscan II (Bausch & Lomb, Salt Lake City, Utah). of each ICRS. In the Intacs group, implantation wasOcular wavefront analysis measurements were per- performed according to the International Pre-Surgicalformed using the Ocular Wavefront Analyzer (COAS) Planning Guide and Comprehensive Nomogram for(SCHWIND eye-tech-solutions GmbH & Co.KG, Intacs, May 2008 (, Germany) under scotopic conditions. nomogramlar/Nomogram_2008_intl_053008.pdf.Total and higher order ocular aberrations (μm) were Accessed September 2, 2011). In the Ferrara group,recorded. Pupil diameters were measured under sco- implantation was performed according to the nomo-topic conditions, using a handheld infrared Colvard gram described previously.11 Both types of ICRS werepupillometer (Oasis Medical Inc, Glendora, Califor- implanted in intracorneal channels from the incisionnia), with the fellow eye occluded. Contrast sensitivity placed on the steepest meridian of the cornea. Formeasurements with and without glare conditions were implantation of Intacs, if the cone was located sym-performed with the Functional Acuity Contrast Test metrically, the incision site was placed on the posi-(FACT) in both photopic and scotopic conditions us- tive cylindrical axis of manifest refraction for the Optec 6500P. The average score in each spatial If the cone was located asymmetrically, the incisionfrequency test was recorded. site was verified by using the manifest refraction yield- ing CDVA, posterior float in Orbscan topography, andINTRACORNEAL RING SEGMENTS peripheral flattening and keratomety values. For im- Intacs ICRS consist of a pair of semicircular ring plantation of the Ferrara ICRS, the steepest meridian ofsegments of hexagonal transverse shape and circum- the anterior corneal surface was defined as the incisionference arc length of 150°. Each segment has an external site per the nomogram.2 Copyright © SLACK Incorporated
  3. 3. Intacs vs Ferrara Intrastromal Corneal Ring Segments/Kaya et al TABLE 1 TABLE 2 Preoperative Characteristics of Postoperative Characteristics of 22 Patients Implanted With Intacs 22 Patients Implanted With Intacs or Ferrara Intrastromal Corneal Ring or Ferrara Intrastromal Corneal Ring Segments Segments MeanϮStandard Deviation MeanϮStandard Deviation Intacs ICRS Ferrara ICRS P Value Intacs ICRS Ferrara ICRS P Value Spherical refractive Ϫ4.16Ϯ0.89 Ϫ3.95Ϯ1.41 .63 Spherical Ϫ2.18Ϯ1.11 Ϫ1.81Ϯ2.11 .53 error (D) refractive error (D) Cylindrical refractive Ϫ3.98Ϯ1.32 Ϫ3.54Ϯ1.26 .34 error (D) Cylindrical Ϫ2.61Ϯ0.93 Ϫ2.13Ϯ1.03 .17 refractive error (D) SEQ (D) Ϫ6.15Ϯ1.16 Ϫ5.39 Ϯ2.11 .21 SEQ (D) Ϫ2.39Ϯ0.77 Ϫ1.97Ϯ1.23 .24 Maximum K (D) 52.54Ϯ3.48 51.95Ϯ3.78 .64 Maximum K (D) 49.11Ϯ3.24 48.67Ϯ3.00 .70 UDVA (Snellen) 0.18Ϯ0.11 0.20Ϯ0.14 .72 UDVA (Snellen) 0.37Ϯ0.15 0.41Ϯ0.23 .53 CDVA (Snellen) 0.34Ϯ0.14 0.34Ϯ0.21 .97 CDVA (Snellen 0.55Ϯ0.19 0.60Ϯ0.29 .58 Total aberrations 6.11Ϯ1.40 5.99Ϯ1.80 .84 (µm) Total aberrations 4.33Ϯ1.42 4.46Ϯ2.04 .86 (µm) HOA (µm) 1.88Ϯ0.45 1.77Ϯ0.51 .49 HOA (µm) 1.55Ϯ0.55 2.06Ϯ1.29 .25 ICRS = intrastromal corneal ring segments, SEQ = spherical equivalent refraction, K = keratometry, UDVA = uncorrected distance visual acuity, Photopic CS 126.75Ϯ120.05 121.65Ϯ102.25 .90 CDVA = corrected distance visual acuity, HOA = higher order aberrations Scotopic CS 103.44Ϯ92.94 72.94Ϯ53.46 .25 Scotopic CS with 90.25Ϯ74.39 40.06Ϯ49.28 .03* glare Intracorneal channel depth was determined by ICRS = intrastromal corneal ring segments, SEQ = spherical equivalentthe pachymetric map on Orbscan topography in both refraction, K = keratometry, UDVA = uncorrected distance visual acuity, CDVA = corrected distance visual acuity, HOA = higher order aberrations, CS =groups as 70% of the thinnest pachymetric reading in contrast sensitivitythe 3.4-mm diameter zone in the Intacs group and the *Statistically significant. Note. Luminance level was 85 cd/m2 and 3.0 cd/m2 for photopic and scotopic2.4-mm diameter zone in the Ferrara group, with the lighting, respectively.origin as the fixation point. Inner and outer diametersof the intracorneal channels were 6.8 and 7.8 mm, re-spectively, in the Intacs group and 4.8 and 5.6 mm,respectively, in the Ferrara group. divided by mean preoperative CDVA. Correlations be- tween preoperative maximum keratometry and post-STATISTICAL ANALYSIS operative gain in UDVA and CDVA, and between pupil Statistical analysis was performed using the Statis- diameter and postoperative gain in contrast sensitivitytical Package for Social Sciences (SPSS Inc, Chicago, function at photopic and scotopic conditions with orIllinois), version 15.0. The Kolmogorov-Smirnov without glare were studied using Pearson’s correlationtest was used for normality of distribution of each coefficient (r) if variables were normally distributed. Aparameter. A Mann-Whitney U test was conducted to P value Ͻ.05 was considered statistically stages of keratoconus in both groups. If datawere normally distributed, paired-samples t test was RESULTSperformed to compare pre- and postoperative find- In the Intacs group, 16 eyes of 11 patients (4 men andings in each group. An independent-samples t test was 7 women) were implanted and 17 eyes of 11 patientsperformed to compare pre- and postoperative UDVA, (7 men and 4 women) were implanted in the FerraraCDVA, keratometry, spherical, cylindrical and spheri- group. Mean patient age was 23.0Ϯ2.7 and 24.2±3.9cal equivalent manifest refractive errors, pupil diam- years in the Intacs and Ferrara groups, respectively.eters, total and higher order wavefront aberrations, Mean preoperative pupil diameter was 5.99Ϯ0.39 andand postoperative contrast sensitivity scores in both 6.16Ϯ0.50 mm in the Intacs and Ferrara groups, respec-groups. Efficacy index was defined as mean postop- tively (P=.30). No significant difference in stages of kera-erative UDVA divided by mean preoperative CDVA. toconus was detected between groups (U=78.50, P=.23).Safety index was defined as mean postoperative CDVA All eyes in the Intacs group and all but three eyesJournal of Refractive Surgery • Vol. xx, No. x, 2011 3
  4. 4. Intacs vs Ferrara Intrastromal Corneal Ring Segments/Kaya et alin the Ferrara group were implanted with two ICRS; In both groups, correlation between preoperativethree eyes in the Ferrara group were implanted with maximum keratometry and gain in UDVA and CDVAa single segment. Patients were followed for 16.0Ϯ1.8 was not statistically significant (r(14)=Ϫ0.25, P=.34months in the Intacs group and 22.0Ϯ3.7 months in and r(14)=Ϫ0.14, P=.60, respectively, for the Intacsthe Ferrara group. group and r(15)=0.43, P=.08 and r(15)=0.39, P=.12, re- Pre- and postoperative characteristics in both groups spectively, for the Ferrara group).are shown in Tables 1 and 2. Preoperative refractive,keratometry, visual acuity, optical, and visual quality OPTICAL QUALITY OUTCOMEScharacteristics were not significantly different in both Postoperative total aberration values decreased sig-groups (PϾ.05 for all). nificantly in each group (P=.03 for both). Mean higher order aberrations decreased in the Intacs group and in-REFRACTIVE AND KERATOMETRY OUTCOMES creased in the Ferrara group; however, postoperative One year postoperatively, spherical and cylindrical changes in higher order aberrations were not statisti-refractive errors and spherical equivalent refraction cally significant in either group (P=.68 in the Intacsdecreased significantly compared with preoperative group and P=.29 in the Ferrara group).values in each group (PϽ.01 for all). Postoperatively,one (6.3%) eye in the Intacs group and three (17.6%) VISUAL QUALITY OUTCOMESeyes in the Ferrara group were within Ϯ1.00 D of em- Scotopic contrast sensitivity score decreased undermetropia, in terms of spherical equivalent refraction. glare compared with no glare effect in both groupsPostoperative change in spherical and cylindrical (P=.07 in the Intacs group; PϽ.01 in the Ferrararefractive errors and spherical equivalent refraction group) at 1 year. Mean decrease was 13.19Ϯ26.61was not significantly different between groups (P=.93, in the Intacs group and 32.88Ϯ28.56 in the FerraraP=.81, and P=.39, respectively). group (P=.05). A positive significant correlation was One year postoperatively, maximum keratometry noted between mean decrease and pupil diameter indecreased significantly in each group compared with the Ferrara group (r(15)=0.50, P=.04), but not in thepreoperative readings (PϽ.01 for both groups). Kera- Intacs group (r(14)=0.11, P=.69). A significant negativetometry gains (ie, amount of decrease in keratometry correlation was seen between scotopic contrast sen-readings) were not significantly different between sitivity with glare and pupil diameter in the Ferr-groups (P=.65). ara group (r(15)=Ϫ0.52, P=.03), but not in the Intacs group (r(14)=Ϫ0.02, P=.95); however, no significantVISUAL ACUITY OUTCOMES correlations were present between pupil diameter One year postoperatively, mean UDVA and CDVA and photopic and scotopic contrast sensitivities with-improved significantly in each group (PϽ.01 for all). out glare in either group, (r(14)=Ϫ0.11, P=.68 andSafety index was 1.62 in the Intacs group and 1.76 in r(14)=0.02, P=.95, respectively, in the Intacs group,the Ferrara group. Efficacy index was 1.09 in the Intacs and r(15)=Ϫ0.15, P=.58 and r(15)=Ϫ0.21, P=.42,group and 1.21 in the Ferrara group. respectively, in the Ferrara group). In the Intacs group, UDVA increased at least 1 Snellenline in 14 (87.5%) eyes. In 10 (62.5%) eyes, this increase COMPLICATIONSwas у2 lines. In the Ferrara group, UDVA increased at No intra- or postoperative complications that wereleast 1 Snellen line in 15 (88.2%) eyes. In 10 (58.8%) visually significant or necessitated removal of ICRSeyes, this increase was у2 lines. In 2 (12.5%) eyes of occurred in any eye during follow-up. One eye in thethe Intacs group and 2 (11.8%) eyes in Ferrara group, Intacs group did not have the corneal incision sutureno increase in UDVA was noted. The gain in UDVA was removed postoperatively as the patient was lost tonot significantly different between groups (P=.48). follow-up. At 1-year, neovascularization was noted at In the Intacs group, CDVA increased at least 1 Snel- the stromal channel, which did not disturb integrity oflen line in 14 (87.5%) eyes. In 8 (50%) eyes, this in- corneal channel.crease was у2 lines. In 2 (12.5%) eyes, no increase inCDVA was seen. In the Ferrara group, CDVA increased DISCUSSIONat least one Snellen line in all (100%) eyes. In 13 The aim of ICRS implantation in patients with ectatic(76.5%) eyes, this increase was у2 lines. No eyes lost corneal pathologies is to provide refractive correctionany lines of CDVA during the follow-up period. The and improvement in UDVA and CDVA, allow patientsgain in CDVA was not significantly different between to wear contact lenses or spectacles, and delay or pre-groups (P=.33). vent the need for corneal transplantation.5,6 Because4 Copyright © SLACK Incorporated
  5. 5. Intacs vs Ferrara Intrastromal Corneal Ring Segments/Kaya et alcorneal cross-linking surgery has been increasingly signs. Additionally, the small sample size may be theperformed in eyes with keratoconus, the need for pen- cause of the statistical insignificance. In both groups,etrating keratoplasty may decrease and subsequently, refractive error was generally undercorrected. Postop-the importance of visual rehabilitation in these eyes erative spherical equivalent refraction of Ϯ1.00 D washas increased. Refractive predictability is particularly achieved in only 6.3% and 17.6% of eyes in the Intacsimportant when surgery is performed monocularly, to and Ferrara groups, respectively. All other eyes hadtarget a tolerable amount of anisometropia. To achieve myopic spherical equivalent refraction ϾϪ1.00 D. Thehigh-quality vision postoperatively, preoperative low relationship between uncorrected and corrected visualUDVA and CDVA should be improved, combined with gain and preoperative maximum keratometry readingsa decrease in or minimal induction of wavefront ab- yielded a mild negative correlation in the Intacs grouperrations and avoidance of postoperative visual com- and moderate positive correlation in the Ferrara group,plaints (eg, halo and glare). which was not statistically significant. Significant improvement in UDVA and CDVA after To the best of our knowledge, Intacs and FerraraICRS implantation has been reported, accompanied ICRS have not been compared in terms of wavefrontby decrease in spherical refraction in all studies1,2,7,8,19 aberrations and contrast sensitivity in photopic andand decrease in cylindrical refraction in some stud- scotopic environments and under glare effect. Wave-ies,1,7,8,10,19 but not in others after Intacs implanta- front aberrations affect ocular optical quality thattion.2,4,16 This has been explained by a greater segment may not be accurately evaluated by visual acuity anddiameter of Intacs ICRS, which induces only mini- conventional refractive error measurements alone.20mal central corneal flattening.16 However, the closer Contrast sensitivity is a measure of threshold contrastthe locations of segments from the pupil margins, the for seeing the target, impairment of which is closelygreater the likelihood of light scattering by ICRS, in- linked to visual–task performance problems, includingducing blur and glare sensation and reduction in con- difficulties in mobility, driving, reading, face recogni-trast sensitivity.16 tion, and an assortment of everyday tasks such as using To date, few comparative studies exist between the tools and finding objects.21 In our study, visual qual-two types of ICRS.15,16 Although good outcomes have ity of patients implanted with these two types of ICRSbeen reported for Intacs, Ferrara, and KeraRing (Medi- was evaluated in terms of wavefront aberrations andphacos Ltda, Minas Gerais, Brazil) ICRS,1-14 in compar- contrast sensitivity function. Implanted ICRS were notative studies, implantation of KeraRings, with virtu- selected according to patients’ preoperative character-ally the same characteristics as Ferrara ICRS, has been istics or demands; but patients implanted with two dif-found to be superior to Intacs implantation in terms of ferent types of ICRS at different times were examined 1refractive correction and visual outcome.15,16 year postoperatively in this respect. In a comparative study, Kubaloglu et al15 found In the current study, total ocular aberrations werethat patients implanted with KeraRing had greater im- measured and compared, unlike previous studies,16,20provement in CDVA and greater decrease in maximum to outline the effect of ICRS implantation on ocularkeratometry compared with Intacs at 6 months and 1 aberration profiles. Significant improvement in totalyear postoperative. In that study, the nomogram used wavefront aberrations was noted in both groups post-for Intacs implantation was not clearly indicated; but operatively, which accompanied significant improve-in the current study, nomograms recommended by ments in spherical and cylindrical refractive errors.manufacturers for each ICRS type were used. Piñero Mean higher order aberrations decreased in the Intacset al16 also compared the short-term refractive and ab- group and increased in the Ferrara group postop-errometric performance of Intacs and Ferrara ICRS in eratively, although not statistically significantly. Theectatic corneas. In that study, although spherical error smaller inner diameter of the Ferrara ring may causeand spherical equivalent refraction were significantly greater effect on higher order aberrations, should anyreduced in both groups, cylindrical error decreased small amount of tilt or decentraton with respect tosignificantly in the Ferrara group but not in the Intacs pupil occur in ICRS, indicating that Intacs have limited effect in cor- In both groups, postoperative scotopic contrast sen-recting astigmatism. sitivity decreased significantly when glare effect was In the current study, refractive and visual outcomes introduced. Interestingly, this decrease in contrastwere better in the Ferrara group, but the difference sensitivity in eyes implanted with the Ferrara ICRS wasbetween groups did not reach statistical significance. greater compared with Intacs-implanted eyes and wasBoth types of ICRS rely on a similar mechanism of ac- significantly negatively correlated with pupil diameter.tion, although with different optical diameters and de- These results suggest that smaller inner diameter, asJournal of Refractive Surgery • Vol. xx, No. x, 2011 5
  6. 6. Intacs vs Ferrara Intrastromal Corneal Ring Segments/Kaya et alwell as the design of the Ferrara ICRS may cause light 7. Alió JL, Shabayek MH, Belda JI, Correas P, Diez Feijoo ED. Analysis of results related to good and bad outcomes of Intacsscatter and loss of contrast sensitivity, particularly in implantation for keratoconus correction. J Cataract Refractconditions such as driving at night. Surg. 2006;32(5):756-761. Our study has limitations in that the sample size 8. Kanellopoulos AJ, Pe LH, Perry HD, Donnenfeld ED. Modifiedwas small and represents results of a single center intracorneal ring segment implantations (INTACS) for the man- agement of moderate to advanced keratoconus: efficacy andonly. Additionally, preoperative contrast sensitivity complications. Cornea. 2006;25(1):29-33.measurements were not available for further analysis. 9. Siganos D, Ferrara P, Chatzinikolas K, Bessis N, Papastergiou G. This study showed that although slightly better refrac- Ferrara intrastromal corneal rings for the correction of keratoco-tive and keratometry correction can be achieved with nus. J Cataract Refract Surg. 2002;28(11):1947-1951.Ferrara ICRS compared to Intacs, implantation of Ferrara 10. Colin J, Cochener B, Savary G, Malet F, Holmes-Higgin D.ICRS may lead to decreased scotopic contrast sensitivity INTACS inserts for treating keratoconus: one-year results. Ophthalmology. 2001;108(8):1409-1414.when glare effect is introduced in eyes with a large pupil 11. Torquetti L, Berbel RF, Ferrara P. Long-term follow-up of in-diameter. Implantation of ICRS with greater inner diam- trastromal corneal ring segments in keratoconus. J Cataract Re-eter that are placed farther away from the pupil margin fract Surg. 2009;35(10):1768-1773.may lead to better visual quality in these eyes. 12. Torquetti L, Ferrara P. Intrastromal corneal ring segment im- plantation for ectasia after refractive surgery. J Cataract Refract Surg. 2010;36(6):986-990. AUTHOR CONTRIBUTIONS Study concept and design (V.K., C.A.U.); data collection (V.K., 13. Sansanayudh W, Bahar I, Kumar NL, et al. Intrastromal corneal ring segment SK implantation for moderate to severe keratoco-S.H.K., I.K.); analysis and interpretation of data (V.K., C.A.U., nus. J Cataract Refract Surg. 2010;36(1):110-113.O.F.Y.); drafting of the manuscript (C.A.U.); critical revision of the 14. Hamdi IM. Optical and topographic changes in keratoconus af-manuscript (V.K., S.H.K., I.K., O.F.Y.); statistical expertise (C.A.U.); ter implantation of Ferrara intracorneal ring segments. J Refractsupervision (V.K., O.F.Y.) Surg. 2010;26(11):871-880. 15. Kubaloglu A, Cinar Y, Sari ES, Koytak A, Ozdemir B, Ozertürk Y. Comparison of 2 intrastromal corneal ring segment models REFERENCES in the management of keratoconus. J Cataract Refract Surg. 1. Shetty R, Kurian M, Anand D, Mhaske P, Narayana KM, Shetty 2010;36(6):978-985. BK. Intacs in advanced keratoconus. Cornea. 2008;27(9):1022- 1029. 16. Piñero DP, Alió JL, El Kady B, Pascual I. Corneal aberrometric and refractive performance of 2 intrastromal corneal ring seg- 2. Ertan A, Kamburoglu G. Intacs implantation using femtosecond ment models in early and moderate ectatic disease. J Cataract laser for management of keratoconus: comparison of 306 cases Refract Surg. 2010;36(1):102-109. in different stages. J Cataract Refract Surg. 2008;34(9):1521- 1526. 17. Krumeich JH, Daniel J, Knulle A. Live-epikeratophakia for kera- toconus. J Cataract Refract Surg. 1998;24(4):456-463. 3. Shabayek MH, Alió JL. Intrastromal corneal ring segment im- plantation by femtosecond laser for keratoconus correction. 18. Ertan A, Colin J. Intracorneal rings for keratoconus and kera- Ophthalmology. 2007;114(9):1643-1652. tectectasia. J Cataract Refract Surg. 2007;33(7):1303-1314. 4. Zare MA, Hashemi H, Salari MR. Intracorneal ring segment im- 19. Kwitko S, Severo NS. Ferrara intracorneal ring segments for plantation for the management of keratoconus: safety and ef- keratoconus. J Cataract Refract Surg. 2004;30(4):812-820. ficacy. J Cataract Refract Surg. 2007;33(11):1886-1891. 20. Chalita MR, Krueger RR. Wavefront aberrations associated 5. Kymionis GD, Siganos CS, Tsiklis NS, et al. Long-term follow- with the Ferrara intrastromal corneal ring in a keratoconic up of Intacs in keratoconus. Am J Ophthalmol. 2007;143(2):236- eye. J Refract Surg. 2004;20(6):823-830. 244. 21. West SK, Rubin GS, Broman AT, Muñoz B, Bandeen-Roche K, 6. Alió JL, Shabayek MH, Artola A. Intracorneal ring segments for Turano K. How does visual impairment affect performance on keratoconus correction: long-term follow-up. J Cataract Refract tasks of everyday life? The SEE Project. Salisbury Eye Evalua- Surg. 2006;32(6):978-985. tion. Arch Ophthalmol. 2002;120(6):774-780. AUTHOR QUERIES Page 4, right column: The format of correlation coefficient is not familiar. Please advise meaning of number inparentheses following the r.6 Copyright © SLACK Incorporated