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= Post-LASIK Ectasia<br> =
== Definition ==
Corneal ectasia is one of the most devastating complications after [[LASIK_for_Myopia_and_Astigmatism|Laser In situ Keratomileusis]] (LASIK). Post-LASIK ectasia is considered in patients who developed increasing myopia, with or without increasing astigmatism, loss of uncorrected visual acuity, often loss of best-corrected visual acuity, with keratometric steepening, with or without central and paracentral corneal thinning, and topographic evidence of asymmetric inferior corneal steepening after LASIK procedure.<sup>1 </sup>Ectatic changes can occur as early as 1 week<sup>2</sup> or can be delayed up to several years after LASIK.<sup>3,4 </sup>The actual incidence of ectasia is undetermined, although the incidence rate of 0.04%<sup>5</sup> to 0.2%<sup>6</sup> to 0.6%<sup>7</sup> has been reported.
== Risk factors ==
The Ectasia Risk Score System designed by Randleman and colleagues<sup>8</sup>, is a controversial screening tool carefully developed by an evidence-based review of a large series of LASIK ectasia cases. The Ectasia Risk Score System scale may help to identify high-risk patients preoperatively. It is controversial in its utility because diagnostic methods of screening for preoperative ectasia have changed dramatically over the past 10 years, and now include possibly more sensitive techniques of corneal 'tomography' (Pentacam, Orbscan, Gallei) which can measure posterior corneal curvature rather than placido-disc based 'topography' which only measure anterior corneal curvatures. In the Randleman et al score system, the most common risk factors, in order of significance include:
=== 1. Abnormal preoperative topography ===
Abnormal topography compromises of [[Keratoconus|keratoconus]], pellucid marginal corneal degeneration, or forme fruste keratoconus with an I-S value of 1.4 or more<sup>9</sup> and is the most significant factor with highest relative risk.
The axial map placido disc-based topography pattern classification using in this score system consists of:
==== 1. Normal/symmetrical ====
Includes round, oval, or symmetric bowtie patterns. <br>
==== 2. Suspicious ====
Includes the following asymmetric patterns:
===== a. Asymmetric bowtie =====
i. Asymmetric steepening in any direction less than 1.0 diopter (D) <br>ii. No skewed radial axis <br>
===== b. Inferior steep/skewed radial axis =====
i. Signiﬁcant skewed radial axis with or without inferior steepening<br>ii. One diopter or more of inferior steepening in some areas but an I-S value of less than 1.4.<sup>9,10</sup><br>
==== 3. Abnormal ====
Includes [[Keratoconus|keratoconus]], pellucid marginal corneal degeneration, or forme fruste keratoconus with an I-S value of 1.4 or more.<sup>9</sup> <br>
=== 2. Low residual stromal bed (RSB) thickness ===
RSB thickness is especially important after LASIK because both stress-strain analysis<sup>11</sup> and tensile strength analysis<sup>12</sup> indicate greater strength in the anterior 40% relative to posterior 60% of stroma and LASIK reduces anterior corneal structural integrity.<br>It is clear that cutoff of 250 microns does not absolutely discriminate development of ectasia, however the risk of ectasia increases reciprocally relative to RSB thickness. <br>
=== 3. Young age ===
Younger age may be a significant risk factor for ectasia in patients without other risk factors. One hypothesis is that some of these individuals would have developed delayed onset forme fruste or keratoconus even without LASIK procedure.
=== 4. Low preoperative corneal thickness ===
Corneal thickness, degree of myopia and RSB are related and RSB thickness is the most significant predictor of ectasia among them.
=== 5. High myopia ===
Despite the early reported cases of ectasia for extreme myopia (more than 12 D), post-LASIK ectasia has been reported in numerous patients with low myopia<sup>13</sup> and even hyperopia.<sup>14</sup>
'''The Ectasia Risk Score System''' is a cumulative score system. Risk categories based on points are:<br>0-2 points=low risk, 3 points=moderate risk, 4 points=high risk.
The score system may be summarized as<sup>8</sup>:<br>Abnormal topography, RSB <240 microns, corneal thickness less than 450 microns and Manifest refraction spherical equivalent (MRSE)> -14 D: each 4 points
Inferior steepening pattern or skewed radial axis in topography, RSB between 240 to 259 microns, age between 18 to 21 years, corneal thickness between 451 to 480 microns, MRSE between -12 to -14 D: each 3 points
RSB between 260 and 279 microns, age between 22 to 25 years, corneal thickness between 481 to 510 microns and MRSE between -10 to -12 D: each 2 points
Asymmetric bowtie pattern in topography, RSB between 280 to 290 microns, age between 26 to 29 years, MRSE between -8 to -10 D: each one point
Normal pattern or symmetric bowtie, RSB more than 300 microns, age more than 30 years, corneal thickness more than 510 microns, MRSE less than -8 D: each 0 point.
<br>Other risk factors include eye rubbing, family history of keratoconus, refractive instability, BCVA less than 20/20 preoperatively, and male gender and should be considered especially in borderline cases.<br>
One significant criticism of the Risk Score System is that any individual less than 22 years old is automatically classified as at least 'Moderate Risk', despite the low incidence of ectasia in this age group.
== Histopathology and Immunohistochemical characteristics ==
Light microscopy and hematoxylin-eosin staining of post-LASIK ectasia corneas demonstrated RSB thinning, hypocellular stromal scar, larger than normal artifacteous interlamellar cleft in RSB and fewer areas of Bowman’s layer disruption than keratoconus.<sup>15</sup><br>Transmission electon microscopy (TEM) showed thinning of the collagen lamellae and loss of lamellar number in the RSB and decreased interfibril distance.<sup>15</sup><br>Immunohistochemical evaluation of post-LASIK ectasia revealed abnormal epithelial basement membrane (EBM) structure similar to keratoconus and bullous keratopathy and increase in certain proteinases indicating lysis and remodeling of EBM.<sup>16</sup><br>Confocal microscopic analysis of post-LASIK ectasia showed unevenly distributed highly reflective collagen scars with reduced keratocyte density and background transparency at the anterior stroma compared to normal post-LASIK eyes.<sup>17</sup><br>
== Treatment<br> ==
=== 1. Contact lens ===
Various types of contact lenses such as rigid gas permeable (RGP), custom wavefront-guided soft contact lenses, hybrid lenses and tandem soft contact lens-rigid gas permeable lenses can be used for visual rehabilitation. If patient has intolerance to RGPs, then soft contact lenses in tandem use, hybrid contact lenses (SynergEyes, Synerg Eyes Inc., Carlsbad, CA, USA) and scleral lenses are the next options. Custom wavefront-guided soft contact lenses have been used in keratoconus with similar visual acuity compared to RGP and decreased aberrations.<sup>18,19</sup> <br>
=== 2. Intracorneal ring segments (ICRS) ===
[[Intrastromal_Corneal_Ring_Segments_(ICRS)|ICRSs]] including Intacs (Addition Technology Inc. Des Plaines, Illinois, USA) and KeraRings (Ferrara Ophthalmics, Belo Horizonte, Brazil) may improve visual function in ecstatic corneas. Intracorneal rings are placed symmetrically or asymmetrically on the steep meridian or about the cone.<sup>20,21</sup> Different wound location, size, symmetry and number of segments that are used depend on surgeon and patient.
=== 3. Corneal collagen cross-linking (CXL) ===
It has been recently documented that [[Corneal_Collagen_Cross-Linking|cross-linking]] may stop the progression of ectasia.<sup>22,23</sup> Most of the [[Corneal_Collagen_Cross-Linking|cross-linking]] effect occurs in the anterior 200 microns of cornea that is weakened by flap creation.<br>
=== 4. Combination treatments ===
Some surgeons consider off-label treatments combining [[Intrastromal Corneal Ring Segments (ICRS)|ICRSs]] with corneal [[Corneal Collagen Cross-Linking|crosslinking]], and others even consider perfoming additional customized excimer laser ablation.<sup>25,26</sup>
=== 5. Penetrating keratoplasty (PKP) ===
[[Penetrating_Keratoplasty|PK]] is the last resort for visual rehabilitation in patients with post-LASIK ectasia.<sup>27</sup>
== References ==
1. Binder PS, Lindstrom RL, Stulting RD, et al. Keratoconus and corneal ectasia after LASIK [letter]. J Cataract Refract Surg 2005; 31:2035–2038
2. Rao SN, Epstein RJ. Early onset keratectasia following laser in situ keratomileusis: case report and literature review. J Refract Surg 2002;18:177–184.
3. Geggel HS, Talley AR. Delayed onset keratectasia following in situ keratomileusis. J Cataract Refract Surg 1999;25:582–586.
4. Lifshitz T, Levy J, Klemperer I, Levinger S. Late bilateral keratectasia after LASIK in a low myopic patient. J Refract Surg 2005;2:494–496.
5. Randleman JB, Russell B, Ward MA, et al. Risk factors and prognosis for corneal ectasia after LASIK. Ophthalmology 2003; 110:267–275.
6. Rad AS, Jabbarvand M, Saiﬁ N. Progressive keratectasia after laser in situ keratomileusis. J Refract Surg 2004; 20:S718–S722.
7. Pallikaris IG,Kymionis GD,Astyrakakis NI. Corneal ectasia induced by laser in situ keratomileusis. J Cataract Refract Surg2001; 27:1796–1802. <br>8. Randleman JB, Woodward M, Lynn MJ, Stulting RD. Risk assessment for ectasia after corneal refractive surgery. Ophthalmology 2008;115:37–50.
9. Rabinowitz YS, McDonnell PJ. Computer-assisted corneal topography in keratoconus. Refract Corneal Surg 1989;5: 400 – 8.
10. Rabinowitz YS. Videokeratographic indices to aid in screening for keratoconus. J Refract Surg 1995;11:371–9.
11. Kohlhaas M, Spoerl E, Schilde T, Unger G, Wittig C, Pillunat LE. Biomechanical evidence of the distribution of cross-links in corneas treated with riboﬂavin and ultraviolet A light. J Cataract Refract Surg 2006;32:279 –283.
12. Randleman JB, Dawson DG, Grossniklaus HE, McCarey BE, Edelhauser HF. Analysis of quantitative cohesive tensile strength in normal human corneas: implications for refractive surgery. J Refract Surg 2008;24:S85–S89
13. Amoils SP, Deist MB, Gous P, Amoils PM. Iatrogenic keratectasia after laser in situ keratomileusis for less than -4.0 to -7.0 diopters of myopia. J Cataract Refract Surg 2000;26: 967–77.
14. Randleman JB, Banning CS, Stulting RD. Corneal ectasia after hyperopic LASIK. J Refract Surg. 2007 Jan;2:98-102.
15. Dawson DG, Randleman JB, Grossniklaus HE, et al. Corneal ectasia after excimer laser keratorefractive surgery: histopathology, ultrastructure, and pathophysiology. Ophthalmology. 2008 Dec;115:2181-2191.e1
16. Maguen E, Maguen B, Regev L, Ljubimov AV. Immunohistochemical evaluation of two corneal buttons with post-LASIK keratectasia. Cornea. 2007 Sep;26:983-91.
17. Kymionis GD, Diakonis VF, Kalyvianaki M, et al. One-year follow-up of corneal confocal microscopy after corneal cross-linking in patients with post laser in situ keratosmileusis ectasia and keratoconus. Am J Ophthalmol. 2009;147:774-8, 778.e1
18. Marsack JD, Parker KE, Niu Y,etal. On-eye performance of custom wavefront guided soft contact lenses in a habitual soft lens-wearing keratoconic patient. J Refract Surg2007; 23:960–964.
19. Marsack JD, Parker KE, Applegate RA. Performance of wavefront-guided soft lenses in three keratoconus subjects. Optom Vision Sci 2008; 85:E1172– E1178.
20. Pinero DP, Alio JL, Uceda-Montanes A, et al. Intracorneal ring segment implantation in corneas with post laser in situ keratomileusis keratectasia. Ophthalmology 2009; 116:1665–1674.<br>21. Ferrara P, Torquetti L. Clinical outcomes after implantation of a new intrastromal corneal ring with a 210-degree arc length. J Cataract Refract Surg 2009; 35:1604–1608
22. Kamburoglu G, Ertan A. Intacs implantation with sequential collagen cross-linking treatment in post operative LASIK ectasia. J Refract Surg2008; 24:S726–S729.
23. Vincigeurra P,Camesasca FI,Albe E,Trazza S.Corneal collagen cross-linking for ectasia after excimer laser refractive surgery:1-year results. J Refract Surg 2009; 22:1–12.
24. Chan CC, Sharma M, Wachler BS. Effect of inferior-segment Intacs with and without C3-R on keratoconus. J Cataract Refract Surg2007; 33:75–80
25. Kymionis GD, Kontadakis GA, Kounis GA, et al. Simultaneous topography- guided PRK followed by corneal collagen cross-linking for keratoconus. J Refract Surg2009; 25:S807–S811.
26. Kanellopoulos AJ. Comparison of sequential vs same-day simultaneous collagen cross-linking and topography-guided PRK for treatment of keratoconus. J Refract Surg2009; 25:S8112–S8818.
27. Bromley JG, Randleman JB. Treatment strategies for corneal ectasia. Curr Opin Ophthalmol. 2010;21:255-8<br>
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