Intrastromal corneal ring segmentimplantation to correct astigmatismafter penetrating keratoplastySandro Coscarelli, MD, G...
astigmatism,7–9other authors report that laser in situkeratomileusis (LASIK)10,11or the implantation oftoric phakic intrao...
Statistical AnalysisData reported here are from the 12-month examinationafter ICRS implantation. Statistical analysis incl...
statistically significant (P!.0001) (Table 1). Vectorialanalysis showed that most eyes had a statisticallysignificant redu...
DISCUSSIONPost-PKP residual astigmatism and refractive error arefrequently observed,11,18and their management maybe a chal...
postoperatively, whereas 43 eyes (72.8%) improved atleast 1 line. The mean SE value decreased from À6.34G 3.40 D to À2.66 ...
central corneal wound healing, which could be unsat-isfactory in post-PKP corneas. This leaves the opticalcenter of the co...
22. Genvert GI, Cohen EJ, Arentsen JJ, Laibson PR. Fittinggas-permeable contact lenses after penetrating keratoplasty.Am J...
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FR and the astigmatism after penetrating keratoplasty

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FR and the astigmatism after penetrating keratoplasty

  1. 1. Intrastromal corneal ring segmentimplantation to correct astigmatismafter penetrating keratoplastySandro Coscarelli, MD, Guilherme Ferrara, MD, Jose F. Alfonso, MD, PhD, Paulo Ferrara, MD, PhD,Jesus Merayo-Lloves, MD, PhD, Luana P.N. Araujo, MD, Aydano P. Machado, PhD,Jo~ao Marcelo Lyra, MD, PhD, Leonardo Torquetti, MD, PhDPURPOSE: To evaluate the clinical outcomes of implantation of Ferrara intrastromal corneal ringsegments (ICRS) in patients with astigmatism after penetrating keratoplasty (PKP).SETTING: Private clinic, Belo Horizonte, Brazil.DESIGN: Retrospective consecutive case series.METHODS: Chart records of post-PKP patients who had ICRS implantation from May 2005 toSeptember 2009 were retrospectively reviewed. The following parameters were studied:corrected distance visual acuity (CDVA), keratometry (K) values, spherical equivalent (SE),spherical refractive error, corneal topographic astigmatism, minimum K, and maximum K.RESULTS: The study evaluated 59 eyes (54 patients). The mean CDVA (logMAR) improved from0.45 G 0.17 (SD) (range 0.18 to 1.00) to 0.30 G 0.17 (range 0.00 to 1.00). The mean SE wasÀ6.34 G 3.40 diopters (D) (range 0.37 to À16.50 D) preoperatively and À2.66 G 2.52 D (range0.87 to À10.50 D) postoperatively. The mean spherical refractive error decreased from À7.10 G3.07 D (range 2.15 to 16.68 D) preoperatively to À3.46 G 2.05 D (range 0.88 to 10.79 D) postop-eratively. No patient lost visual acuity. The mean corneal topographic astigmatism decreasedfrom 3.37 G 1.51 D preoperatively to 1.69 G 1.04 D postoperatively. The mean maximumK value decreased from 48.09 G 2.56 D to 44.17 G 2.67 D and the mean minimum K value,from 44.90 G 2.54 D to 42.46 G 2.63 D. All changes were statistically significant (P.0001).CONCLUSION: Intrastromal corneal ring segments effectively reduced corneal cylinder in patientswith astigmatism after PKP.Financial Disclosure: Drs. Ferrara and Merayo-Lloves have proprietary interest in the Ferrara ring.Drs. Coscarelli, Torquetti, and Alfonso have no financial or proprietary interest in any material ormethod mentioned.J Cataract Refract Surg 2012; 38:1006–1013 Q 2012 ASCRS and ESCRSThe postoperative astigmatism associated with pene-trating keratoplasty (PKP) is a common condition inclinical practice. The reason for this could be relatedto factors inherent to the receptor, such as previouscorneal trauma or keratoconus.1Additional contrib-uting factors may include the trephination technique,inadequate fixation of the eye during surgery withcompression or deformation of the ocular globe,the suture technique, and postoperative issues suchas the patient’s age and receptor corneal disease,time on topical corticosteroids, and early sutureremoval.2Previous studies2–4report several risk factors thatmay increase the incidence of post-PKP astigmatismand its management. Contact lenses are a better choicethan spectacles to correct astigmatism because theyprovide better quality of vision.5,6Moreover, thecorrected distance visual acuity (CDVA) with contactlenses is usually better than with spectacles in thistype of astigmatism. When optical methods fail toachieve satisfactory visual rehabilitation, surgicaltreatment may be necessary. Whereas some authorshave published that incisions and wedge resection ofthe cornea could be useful to correct theQ 2012 ASCRS and ESCRS 0886-3350/$ - see front matterPublished by Elsevier Inc. doi:10.1016/j.jcrs.2011.12.0371006ARTICLE
  2. 2. astigmatism,7–9other authors report that laser in situkeratomileusis (LASIK)10,11or the implantation oftoric phakic intraocular lenses (pIOLs) could achievebetter and more predictable results.12,13In the present study, we evaluated the use of intra-stromal corneal ring segments (ICRS) as an alternativesurgical option for the treatment of astigmatism inpatients who had PKP for keratoconus, bullous kerat-opathy, radial keratotomy (RK), post-LASIK ectasia,or stromal scarring. The outcome analysis comprisedthe CDVA, spherical equivalent (SE), refractive error,corneal topographic astigmatism, and minimum andmaximum keratometry (K) values. To our knowledge,this study has the largest sample of patients with ICRSimplantation to correct post-PKP astigmatism in theliterature.PATIENTS AND METHODSThis retrospective study included consecutive post-PKPpatients who had ICRS implantation (Ferrara ring, Ferrarae Hijos) from May 2005 to September 2009 to correct residualastigmatism. All patients were informed about the possibleintraoperative and postoperative complications and gavewritten informed consent in accordance with institutionalguidelines and the Declaration of Helsinki.Inclusion criteria were a clear and transparent cornealgraft, a minimum of 2.50 diopters (D) and a maximum of8.00 D of astigmatism, and contact lens intolerance. All pa-tients had at least 2 years of follow-up after PKP beforeICRS implantation. Patients who did not meet the inclusioncriteria were not evaluated in this study.Surgical TechniqueThe same surgeon (S.C.) performed all surgeries usinga manual technique as previously described.14The surgerywas performed using topical anesthesia after miosis wasachieved with pilocarpine 2.0%. The visual axis was markedby pressing a Sinskey hook on the central corneal epitheliumwhile asking the patient to fixate on the corneal light reflex ofthe microscope light. Using a marker tinted with gentianviolet, a 5.0 mm optical zone and incision site were alignedto the desired axis in which the incision would be made.This incision site was always at the steepest topographicaxis of the cornea given by the topographer.A square diamond blade was set at 80% of corneal thick-ness at the incision site, and this blade was used to makethe incision. A pocket was formed in each side of the incisionusing a stromal spreader. Two (clockwise and counterclock-wise) 270-degree semicircular dissecting spatulas wereconsecutively inserted through the incision and gentlypushed with quick rotary back-and-forth tunneling move-ments. After channel creation, the ring segments wereinserted using a modified McPherson forceps. The ringswere properly positioned with the aid of a Sinskey hook.Postoperative Regimen and AssessmentThe postoperative regimen consisted of tobramycin 0.3%and dexamethasone 0.1% eyedrops 4 times a day for1 week, after which the dose was tapered over 3 weeks. Inaddition, patients received topical lubricants 4 times a dayfor at least 3 months.Postoperative examinations were performed at 1 and7 days, after 1 and 6 months, and then every year. Measure-ment of CDVA, slitlamp evaluation, refraction, cornealtopography, fundoscopy, and tonometry were performedat each control visit. Visual acuity was determined ona Snellen chart and then converted to logMAR notation.The K values were obtained by corneal topography(CT4000 Corneal Topographer, Eyetech, Inc.).To evaluate the CDVA, refractive error, and corneal topo-graphic astigmatism, the nonparametric Mann-Whitney testwas used because at least 1 datum from the sample did nothave a Gaussian distribution. The SE was corrected by Welchtransformation because of significant difference between2 standard deviations (SDs).Analysis of AstigmatismThe astigmatism results were analyzed arithmetically(nonvector analysis) and with regard to the cylindrical axisusing vector analysis. Although empirical changes in cylin-ders are commonly reported, they do not accurately reflectthe true nature of the change in cylinder. Cylinders havea magnitude and an axis, which are related to the sphericalpower.15To take into account all 3 components, the data inthis study were transformed into Cartesian coordinates (ie,x and y coordinates) to allow mathematic analyses. The re-sult in the Cartesian coordinate form was then reconvertedinto polar coordinates (sphere, cylinder, axis). To distinguishthe mean value of the cylinder calculated in this manner, theterm centroid has been proposed.16Refractions before and 12 months after ICRS insertionwere assessed for astigmatism using the power vectormethod.17Any spherocylindrical refractive error was ex-pressed by 3 dioptric powers: M, J0, J45, with M being theaspheric lens equal to the SE of the given refractive errorand J0 and J45 being 2 Jackson cross-cylinders equivalentto the conventional cylinders. These numbers are the coordi-nates of a point in a 3-dimensional dioptric space, being thepower vector from the origin of this space to the point (M, J0,J45). Thus, the length of the vector is a measure of the overallblurring strength of the spherocylindrical refractive error.Changes in refractive error induced by the surgery werecomputed by the ordinary rules of vector extraction.The target astigmatism is the intended astigmatic correc-tion in each individual eye. The ideal target astigmatismwas zero (ie, intention to correct the full magnitude of thecylinder).Submitted: May 23, 2011.Final revision submitted: November 18, 2011.Accepted: December 5, 2011.From Ennio Coscarelli Eye Clinic (Coscarelli), Paulo Ferrara EyeClinic (G. Ferrara, P. Ferrara, Torquetti), Belo Horizonte andBrazilian Study Group of Artificial Intelligence and Cornea (Araujo,Machado, Lyra, Torquetti), Maceio, Brazil; Fernandez-Vega EyeInstitute (Alfonso, Merayo-Lloves), Oviedo, Spain.Corresponding author: Guilherme Ferrara, MD, Avenida Brasil,1312 – Santa Efigenia – Belo Horizonte, MG 30140-001, Brazil.E-mail: guilherme@ferrararing.com.br.1007ICRS FOR ASTIGMATISM CORRECTION AFTER PKPJ CATARACT REFRACT SURG - VOL 38, JUNE 2012
  3. 3. Statistical AnalysisData reported here are from the 12-month examinationafter ICRS implantation. Statistical analysis included theStudent t test, Welch transformation, and Mann-Whitneynonparametric test and was performed using Instat for Mac-intosh software (version 3.1a, Graphpad Software). Vectorialanalysis was performed using SigmaPlot software (SPSSInc.). Internet-Based Refractive Analysis software (ZubisoftGmbH) was used for clinical outcomes analysis.RESULTSThis study included 59 eyes of 54 patients. The meanage of the 28 women (51.85%) and 26 men (48.14%)was 36.01 years G 11.02 (SD) (range 19 to 72 years).The indications for PKP were keratoconus in 49 eyes,post-LASIK ectasia in 5 eyes, progressive hyperopiasecondary to RK in 2 eyes, stromal scarring in 2 eyes,and bullous keratopathy in 1 eye. Forty-nine patientshad a single eye treatment, whereas 5 patients hadboth eyes treated.All patients completed at least 1 year of follow-up.The mean follow-up was 14 months.Table 1 shows the preoperative and last follow-upexamination data. The preoperative corneal astigma-tism ranged from 3.00 to 5.00 D. Figures 1 and 2show the preoperative and postoperative CDVA. Nopatient lost visual acuity. Of the patients, 28 (47.4%)gained 2 or more lines of CDVA (Figure 3). Theimprovements in CDVA, SE, and refractive errorwere statistically significant (P!.0001).Intended CorrectionRegarding the predictability of the postoperative SE,43 eyes (72.8%) presented with undercorrection and9 (15.2%) with overcorrection. There was concordancebetween the attempted refraction and achieved refrac-tion in 7 eyes (13.0%) (Figure 4).The decrease in the mean corneal topographicastigmatism at 3.0 mm from preoperatively to post-operatively was statistically significant (P!.0001).Most eyes had more than 3.0 D of refractive astigma-tism preoperatively (Figure 5). Approximately halfthe eyes remained with more than 3.00 D of ref-ractive astigmatism postoperatively; the rest hadless than 3.00 D (Figure 6). The decrease in K valuesfrom preoperatively to postoperatively wasTable 1. Preoperative and last follow-up examination data.Parameter Preoperative PostoperativePValueEyes (n) 59 d dPatients (n) 54 d dSex (n)Male 26 d dFemale 28 d dMean age (y) 36.01 G 11.02 d dMean follow-up (mo) 14 d dCDVA (logMAR) .001Mean G SD 0.45 G 0.17 0.30 G 0.17Range 0.18, 1.00 0.00, 1.00SE (D) .001Mean G SD À6.34 G 3.40 À2.66 G 2.52Range 0.37, À16.50 0.87, À10.50Spherical refractiveerror (D).001Mean G SD À7.10 G 3.07 À3.46 G 2.05Range 2.15 to 16.68 0.88 to 10.79Mean TA at 3.0 mm (D) 3.37 G 1.51 1.69 G 1.04 .001Mean maximum K (D) 48.09 G 2.56 44.17 G 2.67 .001Mean minimum K (D) 44.90 G 2.54 42.46 G 2.63 .001CDVA Z corrected distance visual acuity; K Z keratometry; SE Z spher-ical equivalent; TA Z topographic astigmatismFigure 1. The CDVA (logMAR) before and after the ICRS implanta-tion (unpaired t test) (CDVA Z corrected distance visual acuity).Figure 2. Preoperative and postoperative CDVA (logMAR) (CDVAZ corrected distance visual acuity).1008 ICRS FOR ASTIGMATISM CORRECTION AFTER PKPJ CATARACT REFRACT SURG - VOL 38, JUNE 2012
  4. 4. statistically significant (P!.0001) (Table 1). Vectorialanalysis showed that most eyes had a statisticallysignificant reduction in spherocylinder refractiveerror (Figure 7).Double-Angle PlotFigure 8 shows the double-angle plots of the indi-vidual cylinders, providing an overview of the cylin-der magnitude (diopter) and axis (degree) of eachdata point. The radius from the center of the plot toeach individual point represents the magnitude ofthe cylinder. After ICRS implantation, the refractiveastigmatism centroid was 1.00 D closer to zero andthe SD of the astigmatism was reduced by a factor of1.66 (3.83 D/2.31 D). The relocation of the centroidcloser to the origin and the contraction of the ellipseon the doubled-angle plots show the amount ofimprovement.Figure 9 shows the doubled-angle plot of the preop-erative and postoperative keratometric astigmatism.Although there was a reduction in the mean kerato-metric astigmatism, it was considerably less than thereduction in refractive astigmatism.There were no vision-threatening complications.The ICRS were deeply implanted in all eyes(Figure 10). In 3 eyes (5%), the surgical procedurewas interrupted due to dehiscence of the inner layersof corneal transplantation, even 2 years aftertransplantation.Figure 3. Lines of CDVA lost and gained. Figure 4. Predictability of SE correction. The blue dots representundercorrection, the green dots represent full correction, and thered dots represent overcorrection (Cor. Z correlation; Coeff. Z coef-ficient; Lin. Z linear; SE Z spherical equivalent; Res. Var. Z re-sponse variable).Figure 5. Preoperative refractive astigmatism. Figure 6. Postoperative refractive astigmatism.1009ICRS FOR ASTIGMATISM CORRECTION AFTER PKPJ CATARACT REFRACT SURG - VOL 38, JUNE 2012
  5. 5. DISCUSSIONPost-PKP residual astigmatism and refractive error arefrequently observed,11,18and their management maybe a challenge for anterior segment surgeons. In thisretrospective study, we evaluated 59 eyes of 49 pa-tients who had ICRS implantation to correct irregularastigmatism after previous PKP. Despite properwound healing and good anatomic results, highand/or irregular astigmatism can preclude satisfac-tory vision in these patients.Many factors inherent to the patient, host cornea,surgical technique, and postoperative managementmay influence the astigmatism.2Peripheral disorders,such as keratoconus,1can persist on the corneal hostand cause irregular astigmatism. This cause possiblyexplains the high prevalence of keratoconus patientsin our study. Although contact lenses and excimer la-ser refractive surgery are viable options in this groupof eyes,19–21contact lens–related problems, such asdry eye, neovascularization, and rejection of donorcornea, must be considered,22as well as contraindica-tions to PRK or LASIK because of high ametropia, lowbaseline corneal thickness, and young age that makethese patients unsuitable for corneal laser refractivesurgery.23The visual outcomes in our study were satisfactory.The CDVA was unchanged in 16 eyes (27.2%)Figure 7. Astigmatic vectors (J0 and J45) before and 12 months afterICRS implantation. The more central location (0,0) of postoperativedata represents the reduction of preoperative astigmatism by the im-plantation of the ICRS.Figure 8. Double-angle plot of refractive astigmatism. Individualcylinders demonstrate the cylinder magnitude (D) and axis (de-grees). The radius from the center of the plot to each individual pointrepresents the magnitude of the cylinder.Figure 9. Double-angle plot of keratometric astigmatism. Figure 10. Anterior segment optical coherence tomography showsthe ICRS deeply implanted in the cornea stroma and graft–host inter-face (yellow arrow).1010 ICRS FOR ASTIGMATISM CORRECTION AFTER PKPJ CATARACT REFRACT SURG - VOL 38, JUNE 2012
  6. 6. postoperatively, whereas 43 eyes (72.8%) improved atleast 1 line. The mean SE value decreased from À6.34G 3.40 D to À2.66 G 2.52 D, and the K values alsodecreased, improving the corneal irregularity.Alfonso et al.24and Morshirfar et al.12evaluated theresults of pIOL implantation in young patients for thecorrection of refractive errors after PKP and foundsafe, predictable, and stable visual and refractiveoutcomes. Alfonso et al.24describe the efficacy, pre-dictability, and safety of Implantable Collamer Lensposterior chamber pIOL implantation for the correc-tion of post-PKP refractive error in 15 eyes of 15 pa-tients; there was a large reduction in the refractiveerror and CDVA improvement. The postoperativeCDVA was 20/40 or better in 12 eyes (80%) and20/25 in 6 eyes (40%). No eye lost more than 1 lineof acuity, 2 eyes gained 1 line, and 5 eyes gainedmore than 2 lines; 8 eyes were unchanged. Morshirfaret al.12evaluated the Artisan iris-supported pIOL totreat high myopia after PKP in 2 patients; there wasimprovement in uncorrected distance visual acuityand CDVA and no significant endothelial cell densityloss 6 months postoperatively.Our findings are in agreement with results in otherstudies.25–27In a case report, Coskunseven et al.25advocate the use of ICRS, a minimally invasive proce-dure, to correct high astigmatism after PKP. Accordingto Coskunseven et al., eyes with thin corneal grafts andrecurrent keratoconus are unsuitable for laser refrac-tive corrections because of the possibility of postoper-ative complications. In addition, Arriola-Villaloboset al.,5in a series of 9 patients, found that ICRS implan-tation improved the CDVA in all eyes and decreasedthe topographic mean, minimum, and maximumK values. They conclude that ICRS implantation mightbe a good surgical choice to correct high astigmatismafter PKP and yields good visual, refractive, andtopographic outcomes.Chang and Hardten27recommend that ICRS im-plantation after PKP not be performed until at least1 year after transplantation and at least 3 months aftersuture removal. We proceeded as Arriola-Villaloboset al.5suggest; that is, we waited at least 2 years aftercorneal transplantation and a minimum of 6 monthsafter suture removal to avoid damaging the interfaceby the traction generated by the dissectors used duringsurgery in the manual technique.The use of Ferrara ICRS with a 5.0 mm optical zonehas 2 advantages over the use of larger optical zoneICRS. First, the central cornea flattening is theoreticallygreater because the refractive outcome is inverselyproportional to the diameter of the segment.28Thesecond benefit is that a small diameter ensures greaterdistance between the rings and the graft–host junction.This reduces the risk for interface dehiscence orvascularization of the stromal channel by vessels ex-tending from the limbus and host cornea. Thus, in pa-tients with a corneal transplant with a diameter of7.5 mm or smaller, the ICRS with larger optical zones(6.0 or 7.0 mm) should not be used because the seg-ments would be very close to the graft–host junction.Potential disadvantages of ICRS with a small opticalzone are halos and glare. Some patients, especiallythose with large pupil diameters in dim-light condi-tions, occasionally report halos and glare.All patients had PKP performed by the samesurgeon (S.C.), who always used a discrepancy of0.50 mm in trephination between the donor graft(8.0 mm) and the host (7.5 mm). Because the FerraraICRS is placed at a 5.0 mm optical zone, it is alwayslocated far from the graft–host junction, which makesthe procedure safer for small-optical-zone ICRS. How-ever, in cases of small trephinations or decenteredgrafts, care must be taken to avoid excessive torque,which could open the previous keratoplasty wound,thus requiring sutures and postponing ICRS im-plantation. In our study, ICRS implantation had tobe postponed in 5% of cases (3/59 eyes) becausewound dehiscence occurred during dissection. Allpatients had at least 2 years of follow-up after PKP,which indicates that in some cases the graft–host inter-face strength can be permanently reduced. This maybe related to the depth (too shallow or too deep) ofthe passage of the 10-0 needle during the keratoplastyand early removal of sutures. Tunnel creation usingthe femtosecond laser in these cases could not onlyfacilitate the surgical procedure but also prevent thistype of complication.26,29Implantation of ICRS after PKP may yield resultsdifferent than those when the technique is used forkeratoconus treatment. Keratoconic corneas are thin-ner and more elastic than healthy corneas, whereascorneas that had PKP are more rigid, with normalthickness and elasticity. Theoretically, this couldexplain why 73% of eyes presented with undercorrec-tion and there was a low concordance between theattempted refraction and the achieved refraction. Thenomogram of the Ferrara ICRS is designed for kerato-conus treatment; thus, the ring thickness should beadjusted when using ICRS for post-keratoplasty cases.This means that thicker segments should be implantedin post-PKP patients given the same K values as inkeratoconus patients. The main purpose of ICRSimplantation is to regularize the corneal surface andimprove visual acuity; the refraction reduction afterthe surgery could be considered a secondary goal.There are several potential advantages of ICRSimplantation over other surgical techniques in eyeswith high astigmatism after PKP. First, ICRS implanta-tion avoids excimer laser treatment, eliminating1011ICRS FOR ASTIGMATISM CORRECTION AFTER PKPJ CATARACT REFRACT SURG - VOL 38, JUNE 2012
  7. 7. central corneal wound healing, which could be unsat-isfactory in post-PKP corneas. This leaves the opticalcenter of the cornea untouched, enhancing refractiveoutcomes. Second, the technique is reversible in casesof unsatisfactory refractive or clinical outcomes. Third,adjustment can be performed using thinner or thickerrings. In cases of unexpected corneal shape changes,1 segment can be removed or exchanged. Fourth, itavoids the complications of intraocular surgery.The results in our study suggested that ICRSimplantation is a promising treatment for post-PKPastigmatism, especially in eyes with thin and irregularcorneas. Long-term randomized comparative prospec-tive studies are needed to better evaluate this tech-nique as a treatment for irregular astigmatism inpost-PKP patients.WHAT WAS KNOWN Surgical treatments such as wedge resection of thecornea, LASIK, and pIOL implantation are often necessaryto manage high astigmatism after PKP when nonsurgicalmethods fail to achieve satisfactory visual acuity. Intrastromal corneal ring segment implantation for thetreatment of post-PKP astigmatism has been describedin a case report and a 9-patient case series.WHAT THIS PAPER ADDS In a larger clinical series, ICRS implantation improvedCDVA in 73% of eyes and produced significant reductionin topographic astigmatism. Dehiscence of the graft–host junction with mechanical dissection occurred in 5%of eyes.REFERENCES1. Lim L, Pesudovs K, Goggin M, Coster DJ. Late onset post-keratoplasty astigmatism in patients with keratoconus. BrJ Ophthalmol 2004; 88:371–376. Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1772053/pdf/bjo08800371.pdf.Accessed January 28, 20122. Barraquer RI, Alvarez de Toledo JP, Alvarez Fisher M, MartınezGrau G. Prevencion y tratamiento del astigmatismo en querato-plastia penetrante. Ann Oftalmol 2002; 10:69–80. Available at:http://www.nexusediciones.com/pdf/ao2002_2/of-10-2-003.pdf.Accessed January 28, 20123. Landau D, Siganos CS, Mechoulam H, Solomon A, Frucht-Pery J. Astigmatism after mersilene and nylon suture use forpenetrating keratoplasty. Cornea 2006; 25:691–6944. Alvarez de Toledo J, de la Paz MF, Barraquer RI, Barraquer J.Long-term progression of astigmatism after penetratingkeratoplasty for keratoconus; evidence of late recurrence.Cornea 2003; 22:317–3235. Arriola-Villalobos P, Dıas-Valle D, G€uel JL, Iradier-Urrutia MT,Jimenez-Alfaro I, Cui~na-Sardi~na R, Benıtez-del-Castillo JM.Intrastromal corneal ring segment implantation for high astigma-tism after penetrating keratoplasty. 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Accessed January 28, 201210. Aguilar-Montes G, Perez-Balbuena L, Naranjo-Tackman R.Manejo quirurgico con tecnica de lasik en la correccion delastigmatismo miopico secundario a transplante corneal [Lasiktechnique for myopic astigmatism correction after cornealtransplantation]. Rev Mex Oftalmol 2000; 74:221–23611. Campos M, Hertzog L, Garbus J, Lee M, McDonnell PJ. Photo-refractive keratectomy for severe postkeratoplasty astigmatism.Am J Ophthalmol 1992; 114:429–43612. Moshirfar M, Barsam CA, Parker JW. Implantation of an Artisanphakic intraocular lens for the correction of high myopia afterpenetrating keratoplasty. J Cataract Refract Surg 2004;30:1578–158113. Moshirfar M, Gregoire FJ, Mirzaian G, Whitehead GF,Kang PC. Use of Verisyse iris-supported phakic intraocularlens for myopia in keratoconic patients. J Cataract RefractSurg 2006; 32:1227–123214. Torquetti L, Berbel RF, Ferrara P. Long-term follow-up of intra-stromal corneal ring segments in keratoconus. 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