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Precut Post–Laser In Situ Keratomileusis / Photorefractive Keratectomy Donor Corneas for Use in Endothelial Keratoplasty: Potential Impact of Postcut Morphology on Visual Outcomes

      Purpose

      To evaluate the accuracy, complication rates, cut quality, and degree of induced hyperopic shift of eye bank–prepared post–laser in situ keratomileusis (LASIK)/photorefractive keratectomy (PRK) donor corneas compared to those of non-post-LASIK/PRK donor corneas.

      Methods

      The cut accuracy and failure rates of all post-LASIK/PRK donor cornea tissue processed for use in Descemet stripping automated endothelial keratoplasty (DSAEK) from January 2012 through December 2016 were compared to control cornea donor tissue. Corneas were analyzed for regularity and morphology of cut using anterior segment optical coherence tomography images. Using a mathematical model, the hyperopic shifts induced by post-LASIK/PRK donor lenticules were compared to the control corneas.

      Results

      During the study period, 733 post-LASIK/PRK and 10 437 non-post-LASIK/PRK donor corneas were processed for DSAEK. Cut accuracy and quality were similar (P > .05), but there was an increased tissue wastage rate of 5.0% compared to 2.2% (P < .000001). For tissue < 100 μm in central thickness (P = .0001), and for tissue between 100 and 150 μm in central thickness (P = .0023), the difference between central and peripheral thickness when comparing the post-LASIK/PRK and control corneas was statistically significant. These differences resulted in a 1.96 diopter (D), 1.60 D, and 2.35 D hyperopic shift when using donor corneas 100 μm, 125 μm, and 150 μm thick, respectively, from post-LASIK/PRK donors compared to 1.11 D, 0.38 D, and 1.96 D from control donors.

      Conclusions

      Eye bank technicians and surgeons should be aware of the increased risk of tissue wastage when cutting post-LASIK/PRK corneas compared to non-post-LASIK/PRK donors. Surgeons should also be aware of the theoretical increase in hyperopic shift when using post-LASIK/PRK donor corneas compared to non-post-LASIK/PRK donors when cut to less than 150 μm.
      NOTE: Publication of this article is sponsored by the American Ophthalmological Society.
      Endothelial keratoplasty (EK), which includes both Descemet stripping endothelial keratoplasty (DSEK) and Descemet membrane endothelial keratoplasty (DMEK), is currently the surgical intervention of choice among corneal surgeons for the treatment of isolated corneal endothelial dysfunction.
      • Price F.W.
      • Price M.O.
      Evolution of endothelial keratoplasty.
      In 2016, EK was the most common keratoplasty procedure performed in the United States, outnumbering penetrating keratoplasty (PK) (28 327 EKs compared to 18 579 PKs).

      Eye Bank Association of America. 2016 Eye Banking Statistical Report. Available at: www.restoresight.org. Accessed 20 December 2017.

      Of the EK cases performed, 21 868 were DSEK and 6459 were DMEK.

      Eye Bank Association of America. 2016 Eye Banking Statistical Report. Available at: www.restoresight.org. Accessed 20 December 2017.

      In addition, a growing number of surgeons prefer to use eye bank–prepared microkeratome-cut tissue for DSEK (preparation using a microkeratome thus making it Descemet stripping automated endothelial keratoplasty [DSAEK]), since an increasing body of literature has demonstrated that eye bank precut corneas have comparable endothelial cell loss, visual and refractive outcomes, and dislocation rates compared with surgeon-cut tissue using a microkeratome.
      • Price M.O.
      • Baig K.M.
      • Brubaker J.W.
      • Price Jr., F.W.
      Randomized, prospective comparison of precut vs surgeon-dissected grafts for descemet stripping automated endothelial keratoplasty.
      • Terry M.A.
      Endothelial keratoplasty: a comparison of complication rates and endothelial survival between precut tissue and surgeon-cut tissue by a single DESAEK surgeon.
      Because the shape of the posterior lenticule that is cut for DSAEK has thicker edges than central tissue, the posterior curvature of the host cornea increases post-DSAEK, causing a slight hyperopic shift, which has been reported to range from 0 to 2 diopters (D).
      • Koenig S.B.
      • Covert D.J.
      • Dupps Jr., W.J.
      • Meisler D.M.
      Visual acuity, refractive error, and endothelial cell density six months after Descemet stripping and automated endothelial keratoplasty (DSAEK).
      • Covert D.J.
      • Koenig S.B.
      New triple procedure: Descemet’s stripping and automated endothelial keratoplasty combined with phacoemulsification and intraocular lens implantation.
      • Jun B.
      • Kuo A.N.
      • Afshari N.A.
      • Carlson A.N.
      • Kim T.
      Refractive change after descemet stripping automated endothelial keratoplasty surgery and its correlation with graft thickness and diameter.
      • Laaser K.
      • Bachmann B.O.
      • Horn F.K.
      • Cursiefen C.
      • Kruse F.E.
      Descemet membrane endothelial keratoplasty combined with phacoemulsification and intraocular lens implantation: advanced triple procedure.
      • Bahar I.
      • Kaiserman I.
      • McAllum P.
      • Slomovic A.
      • Rootman D.
      Comparison of posterior lamellar keratoplasty techniques to penetrating keratoplasty.
      • Terry M.A.
      • Shamie N.
      • Chen E.S.
      • et al.
      Endothelial keratoplasty for Fuchs’ dystrophy with cataract: complications and clinical results with the new triple procedure.
      • Bahar I.
      • Kaiserman I.
      • Livny E.
      • Slomovic A.
      Changes in corneal curvatures and anterior segment parameters after descemet stripping automated endothelial keratoplasty.
      • Lombardo M.
      • Terry M.A.
      • Lombardo G.
      • Boozer D.D.
      • Serrao S.
      • Ducoli P.
      Analysis of posterior donor corneal parameters 1 year after Descemet stripping automated endothelial keratoplasty (DSAEK) triple procedure.
      • Esquenazi S.
      • Rand W.
      Effect of the shape of the endothelial graft on the refractive results after Descemet’s stripping with automated endothelial keratoplasty.
      • Holz H.A.
      • Meyer J.J.
      • Espandar L.
      • et al.
      Corneal profile analysis after Descemet stripping endothelial keratoplasty and its relationship to postoperative hyperopic shift.
      • Rao S.K.
      • Leung C.K.
      • Cheung C.Y.
      • et al.
      Descemet stripping endothelial keratoplasty: effect of the surgical procedure on corneal optics.
      • Yoo S.H.
      • Kymionis G.D.
      • Deobhakta A.A.
      • et al.
      One-year results and anterior segment optical coherence tomography findings of Descemet stripping automated endothelial keratoplasty combined with phacoemulsification.
      • Gorovoy M.S.
      Descemet-stripping automated endothelial keratoplasty.
      • Price Jr., F.W.
      • Price M.O.
      Descemet’s stripping with endothelial keratoplasty in 50 eyes: a refractive neutral corneal transplant.
      • Hwang R.Y.
      • Gauthier D.J.
      • Wallace D.
      • Afshari N.A.
      Refractive changes after Descemet stripping endothelial keratoplasty: a simplified mathematical model.
      • Price M.O.
      • Price Jr., F.W.
      Descemet’s stripping with endothelial keratoplasty: comparative outcomes with microkeratome-dissected and manually dissected donor tissue.
      • Lee W.B.
      • Jacobs D.S.
      • Musch D.C.
      • et al.
      Descemet’s stripping endothelial keratoplasty: safety and outcomes: a report by the American Academy of Ophthalmology.
      • Dupps Jr., W.J.
      • Qian Y.
      • Meisler D.M.
      Multivariate model of refractive shift in Descemet-stripping automated endothelial keratoplasty.
      • Scorcia V.
      • Matteoni S.
      • Scorcia G.B.
      • et al.
      Pentacam assessment of posterior lamellar grafts to explain hyperopization after Descemet’s stripping automated endothelial keratoplasty.
      • Di Pascuale M.A.
      • Prasher P.
      • Schlecte C.
      • et al.
      Corneal deturgescence after Descemet stripping automated endothelial keratoplasty evaluated by Visante anterior segment optical coherence tomography.
      • Chen E.S.
      • Terry M.A.
      • Shamie N.
      • et al.
      Stability of hyperopic refractive shift following Descemet-stripping automated endothelial keratoplasty.
      Despite not increasing the posterior curvature of the cornea in the same manner, post-DMEK eyes also develop a hyperopic shift, but only on the order of 0.49 D,
      • Price M.O.
      • Giebel A.W.
      • Fairchild K.M.
      • Price F.W.
      Descemet’s membrane endothelial keratoplasty: prospective multicenter study of visual and refractive outcomes and endothelial survival.
      presumably owing to the deturgescence of the cornea post-transplant.
      • Ham L.
      • Dapena I.
      • Moutsouris K.
      • et al.
      Refractive change and stability after Descemet membrane endothelial keratoplasty: effect of corneal dehydration-induced hyperopic shift on intraocular lens power calculation.
      This hyperopic shift is important when counseling patients, especially when choosing intraocular lens powers when EK is combined with cataract extraction.
      • Bahar I.
      • Kaiserman I.
      • McAllum P.
      • Slomovic A.
      • Rootman D.
      Comparison of posterior lamellar keratoplasty techniques to penetrating keratoplasty.
      • Terry M.A.
      • Shamie N.
      • Chen E.S.
      • et al.
      Endothelial keratoplasty for Fuchs’ dystrophy with cataract: complications and clinical results with the new triple procedure.
      • Bahar I.
      • Kaiserman I.
      • Livny E.
      • Slomovic A.
      Changes in corneal curvatures and anterior segment parameters after descemet stripping automated endothelial keratoplasty.
      • Lombardo M.
      • Terry M.A.
      • Lombardo G.
      • Boozer D.D.
      • Serrao S.
      • Ducoli P.
      Analysis of posterior donor corneal parameters 1 year after Descemet stripping automated endothelial keratoplasty (DSAEK) triple procedure.
      • Esquenazi S.
      • Rand W.
      Effect of the shape of the endothelial graft on the refractive results after Descemet’s stripping with automated endothelial keratoplasty.
      • Holz H.A.
      • Meyer J.J.
      • Espandar L.
      • et al.
      Corneal profile analysis after Descemet stripping endothelial keratoplasty and its relationship to postoperative hyperopic shift.
      • Rao S.K.
      • Leung C.K.
      • Cheung C.Y.
      • et al.
      Descemet stripping endothelial keratoplasty: effect of the surgical procedure on corneal optics.
      • Yoo S.H.
      • Kymionis G.D.
      • Deobhakta A.A.
      • et al.
      One-year results and anterior segment optical coherence tomography findings of Descemet stripping automated endothelial keratoplasty combined with phacoemulsification.
      Previous analyses on the accuracy (achieving an actual thickness of the lenticule within 20 μm of the desired thickness) and cut failure rates (percentage of tissue that is rendered unusable owing to complications from cutting) of eye bank–cut corneas have mainly concentrated on corneas with no history of refractive procedures.
      • Katzman R.L.
      • Hoover C.K.
      • Kalifa Y.M.
      • Jeng B.H.
      Assessment of accuracy and cut-failure rates of eye bank-cut corneas for use in endothelial keratoplasty: a comparison of outcomes between 2010 and 2013.
      • Kelliher C.
      • Engler C.
      • Speck C.
      • et al.
      A comprehensive analysis of eye bank-prepared posterior lamellar corneal tissue for use in endothelial keratoplasty.
      However, in the last 20 years there has been an increase in the popularity of refractive procedures, such as laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK), and there has been anecdotal evidence, as well as some limited data, suggesting that post-LASIK corneas result in higher complication rates during precutting for DSAEK.
      • Ham L.
      • Dapena I.
      • Moutsouris K.
      • et al.
      Refractive change and stability after Descemet membrane endothelial keratoplasty: effect of corneal dehydration-induced hyperopic shift on intraocular lens power calculation.
      Despite successful processing, however, it is unknown whether or not the refractive predictability is as good with these tissues compared with normal corneas: the previous laser ablation may alter the central-to-peripheral thickness ratio of the endothelial keratoplasty lenticule, which may in turn result in unanticipated refractive changes.
      In this study, we sought to evaluate the accuracy and complication rates of eye bank–prepared post-LASIK/PRK precut donor corneas compared to those of non-post-LASIK/PRK donor corneas. We also evaluated the cut quality (regularity of cut morphologies) of post-LASIK/PRK donor corneas by using anterior segment optical coherence tomography (OCT) and determined, using a mathematical model, whether a larger hyperopic shift would be expected using post-LASIK/PRK corneas for DSAEK compared to non-post-LASIK/PRK corneas.

      Methods

      Data were collected in a prospective manner from a single large eye-banking institution (Sightlife, Inc, Seattle, Washington, USA), as a part of their standard operating procedures. All human donor corneas that were processed for DSAEK from January 1, 2012 through December 31, 2016 were included in this study. All corneas were processed by trained technicians using a standard procedure. The cornea was mounted on an artificial anterior chamber (AAC; Moria, Inc, Doylestown, Pennsylvania, USA) on a bed of Optisol-GS corneal storage medium (Chiron Ophthalmics, Irvine, California, USA). Single-pass cutting was performed with a Moria CB microkeratome (AAC; Moria, Inc) using 1 of 3 head sizes (250 μm, 300 μm, 350 μm). Head selection was based on initial corneal thickness, desired final thickness as requested by the surgeon (if specified), and the technician's individual cutting nomogram. Pachymetry of the uncut cornea, postcut posterior cornea, and postcut cap (epithelium and anterior stroma) was performed using the RTVue AS-OCT (Optovue, Inc, Fremont, California, USA) or the Corneo-Gage Plus (Sonogage, Cleveland, Ohio, USA). The anterior cap was replaced after processing, and the entire cornea stored in Optisol-GS at 4 C. Pre- and post-processing specular microscopy of the donor tissue was performed using an EB-3000xyz specular microscope (HAI Laboratories, Lexington, Massachusetts, USA) by variable frame method: a single sample was processed, with a minimum sample size of 50 000 μm2 and an average of 150 cells counted.
      Collected data included pre- and postcut endothelial cell counts; target graft thickness (if specified) and achieved graft thickness; whether the tissue was previously scarred (any central anterior stromal scar not involving the posterior 150 μm of tissue, including previous keratorefractive surgery) or healthy; and whether the tissue was suitable for transplantation after processing was complete. Any tissue that was deemed unsuitable had the reason(s) clearly indicated: unacceptable graft thickness or unevenness, endothelial problems (an endothelial cell count near or below 2000 cells/mm2, cell dropout greater than 25% based on the specular reflection observed by slit-lamp examination, or endothelium that did not reflect light appropriately, making individual cells poorly discernable) identified either before or after cutting, and perforations.
      The cut failure rates of all post-LASIK/PRK donor cornea tissue processed for use in DSAEK were compared to all non-post-LASIK/PRK cornea donor tissue during the study interval. In addition, the cut quality of 222 post-LASIK/PRK donor corneas (stratified by central donor lenticule thickness: <100 μm, 100-150 μm, and >150 μm) were analyzed for regularity and morphology of cut using the anterior segment OCT images. The central and peripheral thicknesses of each lenticule that were not measured by the OCT were measured using ImageJ software (www.imagej.nih.gov). These data were compared to those from 201 control non-post-LASIK/PRK corneas (using the same stratification scheme). Statistical analysis was performed using a 2-sample t test, χ2 test, and 1-way analysis of variance. Using a published mathematical model to predict the refractive change post-DSAEK based on the ratio of central-to-peripheral donor lenticule thickness,
      • Hwang R.Y.
      • Gauthier D.J.
      • Wallace D.
      • Afshari N.A.
      Refractive changes after Descemet stripping endothelial keratoplasty: a simplified mathematical model.
      post-LASIK/PRK donor lenticules were compared to non-post-LASIK/PRK corneas at the different thickness stratifications to determine if a difference in hyperopic shift would be expected.

      Results

      During the study period, 733 post-LASIK/PRK and 10 437 non-post-LASIK/PRK (control) donor corneas were processed for DSAEK. The average ages, pre- and postcut endothelial cell count, and difference in pre- to postcutting endothelial cell counts were not statistically significantly different (Table 1). Of these tissues, 37 (5.0%) post-LASIK/PRK donors were determined to be not suitable for transplantation because of a processing issue, compared to 230 (2.2%) in the control group (P < .000001). Of the 733 post-LASIK/PRK corneas that were processed, 364 were cut based on surgeon specification for tissue thickness; of these, 276 (75.8%) were cut within ±20 μm of the desired thickness. Of 364 age-matched controls, 280 (76.9%) were cut within ±20 μm of the desired thickness (P > .05).
      Table 1Comparison of Post-LASIK/PRK Donor Cornea Characteristics to Those of Non-post-LASIK/PRK Donors
      Post-LASIK/PRK CorneasNon-post-LASIK/PRK CorneasP Value
      Mean (SD) donor age, y56.2 (10.2)58.5 (12.6)>.99
      Mean (SD) precut ECC, mm22777 (324)2865 (329)>.99
      Mean (SD) postcut ECC, mm22812 (306)2864 (316)>.99
      Mean (SD) ECC difference, mm225 (193)-1 (204)>.99
      ECC = endothelial cell count; LASIK = laser in situ keratomileusis; PRK = photorefractive keratectomy; SD = standard deviation.
      Statistical testing done with 1-way analysis of variance.
      Of 222 post-LASIK/PRK lenticules that had postcut OCT images (Figure 1), 57 were <100 μm, 108 were between 100 and 150 μm, and 61 were >150 μm in central thickness. Of 201 age-matched non-post-LASIK/PRK lenticules with postcut OCT images, 48 were <100 μm, 131 were between 100 and 150 μm, and 22 were >150 μm in central thickness. In comparing the difference in thicknesses at the 2 peripheral edges of each image as a measure of cut quality, there was no significant difference in cut quality between the 2 groups stratified by postcut thicknesses (all P > .05; Table 2).
      Figure thumbnail gr1
      Figure 1Sample OCT image of donor cornea post-cut for DSAEK demonstrating measurements made in periphery and central cornea: epithelial thickness (top set of numbers), total thickness (middle set of numbers), and posterior lenticule thickness (bottom set of numbers).
      Table 2Mean Difference in Thicknesses at the 2 Peripheral Edges of Each Image as a Measure of Cut Quality When Stratified By Postcut Thicknesses
      Central ThicknessMean (SD) Difference (in μm) in Post-LASIK/PRK CorneasMean (SD) Difference (in μm) in Non-post-LASIK/PRK CorneasP Value
      <100 μm21.9 (19.1)26.5 (18.6).22
      100-150 μm24.4 (19.8)26.4 (22.1).47
      >150 μm23.9 (20.1)23.1 (18.7).86
      LASIK = laser in situ keratomileusis; PRK = photorefractive keratectomy; SD = standard deviation.
      Statistical testing done with paired t test.
      The mean central thickness measured in 222 post-LASIK/PRK donor corneas was 130.5 μm (standard deviation [SD] = 43.6 μm) compared to 118.7 μm (SD = 29.1 μm) in 201 non-post-LASIK/PRK donor corneas (P = .0013). The mean peripheral thickness (determined by averaging the peripheral thickness of both sides of the image in anterior segment OCT) measured in 222 post-LASIK/PRK donor corneas was 180.5 μm (SD = 44.4 μm) compared to 156.1 μm (SD = 40.1 μm) in non-post-LASIK/PRK donor corneas (P < .00001). For tissue < 100 μm in central thickness, and for tissue between 100 and 150 μm in central thickness, there was a statistically significant difference in the difference between central and peripheral thicknesses between the post-LASIK/PRK and non-post-LASIK/PRK eyes. This difference was not seen in the >150 μm group (Table 3, Figure 2).
      Table 3Mean Difference Between the Central and Peripheral Thicknesses Between the Groups Stratified by Central Thicknesses
      Central ThicknessMean (SD) Difference (in μm) in Post-LASIK/PRK CorneasMean (SD) Difference (in μm) in Non-post-LASIK/PRK CorneasP Value
      <100 μm69.8 (34.9)42.1 (28.4)<.0001
      100-150 μm48.5 (28.8)40.8 (25.4).0023
      >150 μm41.9 (27.0)32.9 (27.0).052
      LASIK = laser in situ keratomileusis; PRK = photorefractive keratectomy; SD = standard deviation.
      Statistical testing done with paired t test.
      Figure thumbnail gr2
      Figure 2The difference between the central and peripheral thicknesses between the groups stratified by central thicknesses.
      Using the formulas as modeled by Hwang and associates,
      • Hwang R.Y.
      • Gauthier D.J.
      • Wallace D.
      • Afshari N.A.
      Refractive changes after Descemet stripping endothelial keratoplasty: a simplified mathematical model.
      CPratio=(ttransplant)(2)peripheralthicknesses
      (1)


      rpc=11rpcttransplant+(2)(ttransplant)(1CP1)(h)2
      (2)


      Fpc+DSEK=n3n2rpc
      (3)


      Fcornea+DSEK=Fac+Fpc+DSEK(t+ttransplantn2)(Fac)(Fpc+DSEK)
      (4)


      d=d1[1n3(t+ttransplant)Fac(n2)(Fcornea+DSEK)+(t+ttransplant)]
      (5)


      Feye+DSEK=Fcornea+DSEK+Flens(dn3)(Fcornea+DSEK)(Flens)
      (6)


      Refractivechange=Feye+DSEKFeyewithoutDSEK
      (7)


      and based on calculated values from formulas derived by Hwang and associates,
      • Hwang R.Y.
      • Gauthier D.J.
      • Wallace D.
      • Afshari N.A.
      Refractive changes after Descemet stripping endothelial keratoplasty: a simplified mathematical model.
      where:CP ratio = the central-to-peripheral ratio of the corneal graftd = the distance between the second principal place of the cornea and the first principal place of the lens.Fcornea + DSEK = power of the cornea post DSEKFeye+DSEK = power of the eye post DSEKFpc+DSEK = power of the posterior cornea post DSEKrpc′′ = the post DSEK posterior radius of curvature with nonuniform-width corneal graft and given the assumptions of:
      • Hwang R.Y.
      • Gauthier D.J.
      • Wallace D.
      • Afshari N.A.
      Refractive changes after Descemet stripping endothelial keratoplasty: a simplified mathematical model.
      Fac = power of the anterior cornea = +48.8 DFeye without DSEK = power of the eye before DSEK = +57.9 DFlens = power of the lens = +19.0 Dh′ = the chord length at which the CP ratio was measured = 0.0015 mn1 = air index of refraction = 1.00n2 = corneal index of refraction = 1.376n3 = aqueous index of refraction = 1.336d1 = first principal plan of the cornea = 0.005678rpc = recipient corneal posterior radius of curvature = 0.0068 mt = recipient corneal thickness = 500 umttransplant = corneal graft thickness = 100, 125, 150 umthen below would be an example of a calculation for a donor graft from a non-LASIK/PRK DSAEK lenticule with a 100 μm central thickness:
      CPratio=(0.0001)(2)0.000255=0.784
      (1)


      rpc=110.005950.0001+(2)(0.0001)(10.7841)(0.0015)2=0.00512
      (2)


      Fpc+DSEK=1.3361.3760.00512=7.81D
      (3)


      Fcornea+DSEK=48.8+(7.81)(0.0005+0.00011.376)(48.8)(7.81)=41.16D
      (4)


      d=0.005678[11.336(0.0005+0.0001)48.8(1.376)(41.16)+(0.0005+0.0001)]=0.00577
      (5)


      Feye+DSEK=41.16+19(0.005771.336)(41.16)(19)=56.78D
      (6)


      Refractivechange=56.7857.9=1.11D=1.11Dhyperopicshift
      (7)


      The differences in predicted hyperopic shifts at different central thicknesses of DSAEK lenticules from post-LASIK/PRK corneas and non-post-LASIK/PRK corneas are given in Table 4. At all 3 central thicknesses of 100 μm, 125 μm, and 150 μm, a larger than anticipated hyperopic shift is predicted.
      Table 4Predicted Hyperopic Shifts Using Corneas of Various Central Graft Thicknesses With Post-LASIK/PRK Donors Compared to Controls
      Central Graft Thickness (μm)Post-LASIK/PRK DonorsControls
      Peripheral Graft Thickness (Sum of Both Peripheral Edges) (μm)CP RatioPredicted Hyperopic Shift (Diopters)Peripheral Graft Thickness (Sum of Both Peripheral Edges) (μm)CP RatioPredicted Hyperopic Shift (Diopters)
      1003080.6491.962550.7841.11
      1253340.7491.603190.7840.38
      1504280.7012.354050.7411.96
      LASIK = laser in situ keratomileusis; PRK = photorefractive keratectomy.
      CP ratio (the central-to-peripheral ratio of the corneal graft) is calculated from formulas.
      • Hwang R.Y.
      • Gauthier D.J.
      • Wallace D.
      • Afshari N.A.
      Refractive changes after Descemet stripping endothelial keratoplasty: a simplified mathematical model.

      Discussion

      Corneal refractive surgery continues to be very popular, with approximately 800 000 LASIK or PRK procedures performed in 2010 in the United States alone (http://www.ophthalmologymanagement.com/printarticle.aspx?article=104645). Although there has been a decrease in the number of corneal refractive surgery cases being done since that time, by 2020 this number is expected to rebound to nearly the same level as in 2010 (https://www.statista.com/statistics/271478/number-of-lasik-surgeires-in-the-us/). As the patients who have had such procedures performed enter the corneal donor pool, a continued rise in the proportion of eyes having undergone these procedures will likely be seen. Currently, such a rise is already occurring: in 2016, of the 34 126 corneas intended for transplantation but not released, 508 corneas (1.5%) were owing to having undergone prior refractive surgery, compared to 298 (1.0%) of 30 185 corneas in 2012.

      Eye Bank Association of America. 2016 Eye Banking Statistical Report. Available at: www.restoresight.org. Accessed 20 December 2017.

      Eye Bank Association of America. 2012 Eye Banking Statistical Report. Available at: www.restoresight.org. Accessed 20 December 2017.

      While this impact on the donor pool is currently minor, a larger impact is to be expected in the future.
      • Edmonds J.
      • McEntire W.
      • Mifflin M.
      Descemet’s stripping automated endothelial keratoplasty using donor tissue from donors with a history of laser in situ keratomileusis or photorefractive keratectomy.
      This impact on the donor pool would not necessarily affect the need in the United States, but because the United States is one of the largest exporting countries for corneas, this decrease in donor pool would affect other countries in need of tissue.
      The Medical Standards of the Eye Bank Association of America state that the use of eyes having undergone corneal refractive surgery is contraindicated for penetrating keratoplasty. For endothelial keratoplasty (both DSAEK and DMEK), it is stipulated that “tissue with non-infectious anterior pathology that does not affect the posterior stroma and endothelium is acceptable.”
      • Medical Standards
      Eye Bank Association of America.
      However, because some radial keratotomy (RK) incisions can actually extend deep into the posterior stroma (and even perforate the Descemet membrane), it has been suggested that caution be exercised when considering post-RK corneas for EK.
      • Khalifa Y.M.
      • Davis D.
      • Mamalis N.
      • Moshirfar M.
      Donor corneas tissue with prior radial keratotomy: is it suitable for Descemet stripping automated endothelial keratoplasty?.
      For both DSAEK and DMEK, however, numerous groups have demonstrated excellent outcomes when using tissues that have previously undergone LASIK or PRK.
      • Philips P.M.
      • Terry M.A.
      • Shamie N.
      • et al.
      Descemet’s stripping automated endothelial keratoplasty (DSAEK) using corneal donor tissue not acceptable for use in penetrating keratoplasty as a result of anterior stromal scars, pterygia, and previous corneal refractive surgical procedures.
      • Armour R.L.
      • Ousley P.J.
      • Wall J.
      • et al.
      Endothelial keratoplasty using donor tissue not suitable for full-thickness penetrating keratoplasty.
      • Moshirfar M.
      • Khalifa Y.M.
      • Davis D.
      • et al.
      Descemet’s stripping automated endothelial keratoplasty (DSAEK) using donor corneas with previous laser in situ keratomilieus or photorefractive keratectomy: a case series and donor cap histopathology.
      • Fargione R.A.
      • Channa P.
      Cornea donors who have had prior refractive surgery: data from the Eye Bank Association of America.
      Although surgical complications and best-corrected visual acuities are commonly used as outcome measures for DSAEK, using post-LASIK/PRK donor corneas may offer other notable issues, including potentially increased tissue wastage rates from cut failures as well as increased postoperative hyperopic shift. In a previous study using data from 1501 corneas cut at SightLife, Inc, in 2013, the tissue wastage rate was 4.5% in corneas with anterior scars (including post–refractive surgery) compared to 1.36% in healthy corneas devoid of pathology.
      • Katzman R.L.
      • Hoover C.K.
      • Kalifa Y.M.
      • Jeng B.H.
      Assessment of accuracy and cut-failure rates of eye bank-cut corneas for use in endothelial keratoplasty: a comparison of outcomes between 2010 and 2013.
      In the current study using data from the same eye bank, but including over 10 000 corneas encompassing the years 2012-2016 (higher failure rates earlier on), the tissue wastage rates were similar: 5.0% in the post-LASIK/PRK group compared to 2.2% in the control group. Similar analyses have been performed using smaller datasets: 4.4% (5 failures in 113 attempts on post–refractive surgery donor tissue) compared to 1.6% (72 failures in 4519 attempts on non-post–refractive surgery corneas) at the Lions Vision Gift Eye Bank (Portland, Oregon, USA) from 2009 to 2012; and 1.5% (1 failure in 66 attempts on post–refractive surgery donor tissue) compared to 2.8% (17 failures in 600 attempts on non-post–refractive surgery corneas) at the John A. Moran Eye Center (surgeon cut).
      • Edmonds J.
      • McEntire W.
      • Mifflin M.
      Descemet’s stripping automated endothelial keratoplasty using donor tissue from donors with a history of laser in situ keratomileusis or photorefractive keratectomy.
      As such, although the increased tissue wastage rate is overall very small, technicians and surgeons who cut tissue should still be aware of this possibility.
      Postoperative hyperopic shifts after EK are a recognized entity, and the decreased posterior corneal curvature after insertion of the DSAEK lenticule, which has a thicker periphery than central corneal thickness, has been found to be the biggest contributor to this phenomenon. Another contributing factor in this hyperopic shift is the donor diameter, with increasing diameter of the graft leading to higher hyperopic shift.
      • Jun B.
      • Kuo A.N.
      • Afshari N.A.
      • Carlson A.N.
      • Kim T.
      Refractive change after descemet stripping automated endothelial keratoplasty surgery and its correlation with graft thickness and diameter.
      Furthermore, with deturgescence of the central corneal edema after EK, there is some relative hyperopic shift of approximately 0.5 diopters, as also seen in DMEK.
      • Price M.O.
      • Giebel A.W.
      • Fairchild K.M.
      • Price F.W.
      Descemet’s membrane endothelial keratoplasty: prospective multicenter study of visual and refractive outcomes and endothelial survival.
      Interestingly, based on the thick lens formula,
      • Tunnacliffe A.H.
      • Hirst J.G.
      Optics.
      the addition of additional tissue to the existing stroma should induce a myopic shift. However, the effect of this minor myopic shift is counteracted by the reasons for the hyperopic shift discussed above, with the decreased radius of curvature of the posterior surface of the cornea being thought to be the greatest contributor.
      As the ratio of the central-to-peripheral graft thickness is thought to correlate with hyperopic shift because it decreases the radius of curvature of the posterior cornea,
      • Yoo S.H.
      • Kymionis G.D.
      • Deobhakta A.A.
      • et al.
      One-year results and anterior segment optical coherence tomography findings of Descemet stripping automated endothelial keratoplasty combined with phacoemulsification.
      theoretically then, with thinner tissue, the disparity between the peripheral and central corneal thickness should be less, therefore lowering the amount of increased posterior corneal curvature, and thus leading to less hyperopic shift. However, in a small retrospective study, Daoud and associates found that there was no significant difference in the amount of hyperopic shift from DSEK depending on the thickness of the graft (<100 μm vs 100-150 μm vs >150 μm).
      • Daoud Y.J.
      • Munro A.D.
      • Delmonte D.D.
      • et al.
      Effect of cornea donor graft thickness on the outcome of Descemet Stripping Automated Endothelial Keratoplasty Surgery.
      Hwang and associates have devised a formula to predict the hyperopic shift after DSAEK focusing on the reduced posterior corneal curvature.
      • Hwang R.Y.
      • Gauthier D.J.
      • Wallace D.
      • Afshari N.A.
      Refractive changes after Descemet stripping endothelial keratoplasty: a simplified mathematical model.
      Microkeratome preparation of DSAEK lenticules from post-LASIK/PRK corneas may also impact visual outcomes by accentuating the hyperopic shift seen after DSAEK where a nonuniform lenticule thickness with a low ratio of central-to-peripheral cut thicknesses creates a decreased posterior corneal curvature and therefore induces a hyperopic shift.
      • Holz H.A.
      • Meyer J.J.
      • Espandar L.
      • et al.
      Corneal profile analysis after Descemet stripping endothelial keratoplasty and its relationship to postoperative hyperopic shift.
      • Dupps Jr., W.J.
      • Qian Y.
      • Meisler D.M.
      Multivariate model of refractive shift in Descemet-stripping automated endothelial keratoplasty.
      • Dapena I.
      • Ham L.
      • Melles G.R.
      Endothelial keratoplasty: DSAEK/DSAEK or DMEK – the thinner the better?.
      In our current study, we have found that post-LASIK/PRK donor corneas that are used for DSAEK have a greater difference in central to peripheral thicknesses compared with non-post-LASIK/PRK corneas. This is especially true for thinner tissue (<100 μm as well as 100-150 μm central thickness). The CP ratio is lower in these post-LASIK/PRK corneas than in the controls, and based on the mathematical model from Hwang and associates,
      • Hwang R.Y.
      • Gauthier D.J.
      • Wallace D.
      • Afshari N.A.
      Refractive changes after Descemet stripping endothelial keratoplasty: a simplified mathematical model.
      an even greater hyperopic shift would be expected to be seen after use of thinner tissue from post-LASIK/PRK donors.
      This finding would suggest that post-LASIK/PRK donor corneas may not be ideal for use in DSAEK, as their use may induce an unpredictable hyperopic surprise, in addition to be being unsuitable for PK. However, there does not appear to be any contraindication for their use in DMEK. Although the cumulative number of cornea donors who have had LASIK or PRK is expected to increase, the popularity of DMEK is also increasing, with more DMEK being performed each year. As such, limiting post-LASIK/PRK donor corneas to use in DMEK would not greatly decrease our donor pool at this time. Nonetheless, surgeons should be aware of the possibility of increased hyperopic shift if they choose to use DSAEK tissue from post-LASIK/PRK donors. Future studies are warranted to determine if these predicted hyperopic shifts are indeed seen in patients, and if these shifts lessen over time, as they do in non-post–refractive surgery lenticules.
      Funding/Support: No funding or grant support. Financial Disclosures: Bennie H. Jeng is an unpaid associate medical director at SightLife, Inc. Patrick Conrick is an employee of SightLife, Inc. The following authors have no financial disclosures: Sheila Pabon and Saujanya Vadoothker. All authors attest that they meet the current ICMJE criteria for authorship.

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