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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
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 signiﬁcant.compare 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
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 implantation.group, 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