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Management of chronic habits of abnormal eye rubbing. Cont Lens Anterior Eye 2008; 31:95-102. [PMID: 18356094 DOI: 10.1016/j.clae.2007.07.008] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2007] [Revised: 07/25/2007] [Accepted: 07/25/2007] [Indexed: 11/24/2022]
Abstract
A review of the provocations and the consequences of chronic habits of abnormal rubbing indicates a range of possible adverse responses. Gentle rubbing may double intraocular pressure. However, the combination of tight eye closure and forceful rubbing may raise intraocular pressure to more than 10 times normal levels. The possibility that, in susceptible individuals, chronic habits of abnormal rubbing may lead to the development or progression of keratoconus has been extended to the possibility of rubbing related adverse responses in other diseases and conditions. The adverse consequences of rubbing appear to be active processes, in contrast to the apparent passive nature of any recovery from those responses. Avoidance of the possibility of permanent adverse changes is clearly preferable. However, advice to avoid rubbing may not be successfully followed. Education and counseling appear to be the foundations for helping patients to control chronic habits of abnormal rubbing. An instrument has been developed as the basis for patient education and counseling for this purpose. It is intended as a take-home document which might have relevance to other family members. The widening of the application of this form of patient education to all members of a family, and a wider range of conditions, may produce beneficial synergy with advantage to patients who may have the most to gain from controlling chronic habits of abnormal rubbing.
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Biomechanical characteristics of the ectatic cornea. J Cataract Refract Surg 2008; 34:510-3. [PMID: 18299080 DOI: 10.1016/j.jcrs.2007.11.018] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2006] [Accepted: 11/28/2007] [Indexed: 11/23/2022]
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Kirwan C, O'Keefe M. Corneal hysteresis using the Reichert ocular response analyser: findings pre- and post-LASIK and LASEK. Acta Ophthalmol 2008; 86:215-8. [PMID: 17888086 DOI: 10.1111/j.1600-0420.2007.01023.x] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
PURPOSE To evaluate and compare corneal hysteresis in patients prior to and following laser in situ keratomileusis (LASIK) and laser-assisted subepithelial keratectomy (LASEK) using the Reichert ocular response analyser (ORA). METHODS Corneal hysteresis was recorded prior to and 3 months after corneal laser refractive surgery for myopia. Preoperative corneal hysteresis was correlated with age and preoperative central corneal thickness (CCT). Postoperative corneal hysteresis was correlated with postoperative CCT in both the LASIK and LASEK treatment groups. The correlations between postoperative change in hysteresis and stromal ablation depth, percentage of tissue ablated, optical zone and patient age were also examined. RESULTS A total of 84 eyes of 84 patients were involved in the study. LASIK was performed in 63 eyes and LASEK in 21. Mean preoperative corneal hysteresis of all eyes was 10.8 +/- 1.5 mmHg. Mean age, preoperative CCT, corneal hysteresis and ablation profile were similar in both groups. A statistically significant decrease in hysteresis occurred following LASIK (p < 0.01) and LASEK (p < 0.01) with similar decrements observed in both treatment groups. A moderate correlation was found between postoperative hysteresis and postoperative CCT in LASIK (r = 0.7) and LASEK (r = 0.7) treated eyes. A weak correlation was found between postoperative decrease in hysteresis and the parameters examined. CONCLUSION Corneal hysteresis decreased following LASIK and LASEK. Similar reductions occurred following both procedures, indicating that LASIK involving a thin 120-mum flap did not induce additional biomechanical change. Postoperative reduction in hysteresis did not correlate with the amount or percentage of corneal tissue removed, nor with optical zone or patient age.
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Depth-dependent Cohesive Tensile Strength in Human Donor Corneas: Implications for Refractive Surgery. J Refract Surg 2008; 24:S85-9. [DOI: 10.3928/1081597x-20080101-15] [Citation(s) in RCA: 158] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Randleman JB, Woodward M, Lynn MJ, Stulting RD. Risk Assessment for Ectasia after Corneal Refractive Surgery. Ophthalmology 2008; 115:37-50. [PMID: 17624434 DOI: 10.1016/j.ophtha.2007.03.073] [Citation(s) in RCA: 468] [Impact Index Per Article: 29.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2006] [Revised: 03/30/2007] [Accepted: 03/30/2007] [Indexed: 11/18/2022] Open
Abstract
PURPOSE To analyze the epidemiologic features of ectasia after excimer laser corneal refractive surgery, to identify risk factors for its development, and to devise a screening strategy to minimize its occurrence. DESIGN Retrospective comparative and case-control study. PARTICIPANTS All cases of ectasia after excimer laser corneal refractive surgery published in the English language with adequate information available through December 2005, unpublished cases seeking treatment at the authors' institution from 1998 through 2005, and a contemporaneous control group who underwent uneventful LASIK and experienced a normal postoperative course. METHODS Evaluation of preoperative characteristics, including patient age, gender, spherical equivalent refraction, pachymetry, and topographic patterns; perioperative characteristics, including type of surgery performed, flap thickness, ablation depth, and residual stromal bed (RSB) thickness; and postoperative characteristics including time to onset of ectasia. MAIN OUTCOME MEASURES Development of postoperative corneal ectasia. RESULTS There were 171 ectasia cases, including 158 published cases and 13 unpublished cases evaluated at the authors' institution. Ectasia occurred after LASIK in 164 cases (95.9%) and after photorefractive keratectomy (PRK) in 7 cases (4.1%). Compared with controls, more ectasia cases had abnormal preoperative topographies (35.7% vs. 0%; P<1.0x10(-15)), were significantly younger (34.4 vs. 40.0 years; P<1.0x10(-7)), were more myopic (-8.53 vs. -5.09 diopters; P<1.0x10(-7)), had thinner corneas before surgery (521.0 vs. 546.5 microm; P<1.0x10(-7)), and had less RSB thickness (256.3 vs. 317.3 microm; P<1.0x10(-10)). Based on subgroup logistic regression analysis, abnormal topography was the most significant factor that discriminated cases from controls, followed by RSB thickness, age, and preoperative corneal thickness, in that order. A risk factor stratification scale was created, taking all recognized risk factors into account in a weighted fashion. This model had a specificity of 91% and a sensitivity of 96% in this series. CONCLUSIONS A quantitative method can be used to identify eyes at risk for developing ectasia after LASIK that, if validated, represents a significant improvement over current screening strategies.
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158
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Mearza AA, Koufaki FN, Aslanides IM. Airbag induced corneal ectasia. Cont Lens Anterior Eye 2007; 31:38-40. [PMID: 17964211 DOI: 10.1016/j.clae.2007.09.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2007] [Revised: 09/01/2007] [Accepted: 09/18/2007] [Indexed: 10/22/2022]
Abstract
PURPOSE To report a case of airbag induced corneal ectasia. METHODS Case report. RESULTS A patient 3 years post-LASIK developed bilateral corneal ectasia worse in the right eye following airbag deployment in a road traffic accident. At last follow up, best corrected vision was 20/40 with -4.00/-4.00 x 25 in the right eye and 20/25 with -1.25/-0.50 x 135 in the left eye. CONCLUSIONS This is a rare presentation of trauma induced ectasia in a patient post-LASIK. It is possible that reduction in biomechanical integrity of the cornea from prior refractive surgery contributed to this presentation.
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Affiliation(s)
- Ali A Mearza
- Charing Cross Hospital, Department of Ophthalmology, Fulham Palace Road, London W6 8RF, UK.
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Binder PS. Analysis of ectasia after laser in situ keratomileusis: Risk factors. J Cataract Refract Surg 2007; 33:1530-8. [PMID: 17720066 DOI: 10.1016/j.jcrs.2007.04.043] [Citation(s) in RCA: 188] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2007] [Accepted: 04/25/2007] [Indexed: 11/15/2022]
Abstract
PURPOSE To examine a database of laser in situ keratomileusis (LASIK) procedures for preoperative and operative factors assumed to increase the risk for developing post-LASIK ectasia. SETTING Private clinical practice. METHODS A computer database was queried for eyes that had LASIK for myopic refractive errors with the following characteristics: preoperative corneal thickness 500 microm or less, mean keratometry greater than 47.0 diopters (D), patient age 25 years or younger, attempted correction greater than -8.0 D, refractive astigmatism not with-the-rule and greater than 2.0 D, and residual stromal bed thickness (RST) 250 microm or less. Flap thickness and RST were measured using ultrasound pachymetry. All recorded information was exported to MS Excel and analyzed for eyes that had ectasia. RESULTS Of the 9700 eyes in the database, none with the above characteristics developed ectasia over mean follow-up periods exceeding 2 years. Seven eyes had multiple risk factors without ectasia. Three eyes with abnormal preoperative topography developed ectasia. CONCLUSIONS Individual preoperative and operative factors did not in and of themselves increase the risk for ectasia. Unmeasured and unknown factors that affect the individual cornea's biomechanical stability, in combination with some suspected risk factors as well as the current inability to identify corneas at risk for developing ectatic disorders, probably account for most eyes that develop ectasia today.
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Affiliation(s)
- Perry S Binder
- Private Clinical Practice, San Diego, California 92122, USA.
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Salz JJ, Binder PS. Is there a "magic number" to reduce the risk of ectasia after laser in situ keratomileusis and photorefractive keratectomy? Am J Ophthalmol 2007; 144:284-5. [PMID: 17659956 DOI: 10.1016/j.ajo.2007.05.022] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2007] [Revised: 05/10/2007] [Accepted: 05/15/2007] [Indexed: 10/23/2022]
Affiliation(s)
- James J Salz
- Laser Vision Medical Associates Inc, Beverly Hills, CA 90211, USA.
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Bibliography. Current world literature. Curr Opin Ophthalmol 2007; 18:342-50. [PMID: 17568213 DOI: 10.1097/icu.0b013e3282887e1e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Tuli SS, Iyer S. Delayed Ectasia Following LASIK With No Risk Factors: Is a 300-µm Stromal Bed Enough? J Refract Surg 2007; 23:620-2. [PMID: 17598583 DOI: 10.3928/1081-597x-20070601-14] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE To report a case of ectasia occurring > 4 years following LASIK with no risk factors and a residual stromal bed > 300 microm. METHODS A 33-year-old woman presented 4 years after LASIK with mild blurring in the left eye. Uncorrected visual acuity (UCVA) had been 20/20 in both eyes previously. RESULTS Uncorrected visual acuity was 20/20 and 20/40 in the right and left eyes, respectively. Best spectacle-corrected visual acuity (BSCVA) was 20/20 with -0.75 +2.25 x 70 degrees refraction in the left eye, which matched topography. Preoperative corneal thickness was 595 microm, and topography showed no risk factors preoperatively or immediately postoperatively. Calculated residual stromal bed was 342 microm and measured 400 microm with ultrasound microscopy. One year postoperatively, UCVA decreased to 20/400, and BSCVA decreased to 20/60 with refraction of -4.50 +5.00 x 90 degrees. The patient was intolerant of contact lens wear and is considering collagen cross-linking, Intacs, or corneal transplantation. CONCLUSIONS Ectasia can occur more than 4 years after LASIK. Its etiology is unknown and management is challenging.
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Affiliation(s)
- Sonal S Tuli
- Department of Ophthalmology, University of Florida, Gainesville, Fla, USA.
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Rosen ES. Ectasia. J Cataract Refract Surg 2007; 33:931-2. [PMID: 17531667 DOI: 10.1016/j.jcrs.2007.04.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Abstract
PURPOSE To report three patients (four eyes) with hyperopic keratoconus. METHODS Patients were evaluated with corneal curvature topography, ultrasonic pachymetry, and rotating Scheimpflug camera. RESULTS One patient, without other risk factors, developed unilateral ectasia after LASIK following primary hyperopic ablation in an eye suspicious for keratoconus. Two additional hyperopic patients (three eyes) had curvature and elevation findings compatible with keratoconus. CONCLUSIONS Although rare, keratoconus could present in hyperopia. If keratoconus is suspected, we suggest avoidance of LASIK and its potential for development of corneal ectasia.
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Abad JC, Rubinfeld RS, Del Valle M, Belin MW, Kurstin JM. Vertical D. Ophthalmology 2007; 114:1020-6. [PMID: 17292474 DOI: 10.1016/j.ophtha.2006.10.022] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2005] [Revised: 10/09/2006] [Accepted: 10/10/2006] [Indexed: 10/23/2022] Open
Abstract
PURPOSE To describe a novel topographic curvature pattern, vertical D, which was present in some keratoconus suspects. This pattern was detected retrospectively in 2 patients who developed post-LASIK ectasia and prospectively in 4 patients who had other corneal abnormalities suggestive of keratoconus. DESIGN Retrospective interventional case series and prospective cross-sectional study. PARTICIPANTS After vertical D topographic curvature patterns were noted in 2 patients (3 eyes) who developed post-LASIK ectasia, 1168 consecutive potential refractive surgical candidates (2336 eyes) evaluated at a refractive center were screened to detect this vertical D pattern. METHODS Placido disc-based curvature topography, ultrasound pachymetry, and elevation-based Scheimpflug topography were performed on these patients. MAIN OUTCOME MEASURES Corneal curvature topographic patterns, central keratometry, inferior-superior and nasal-temporal ratios, skewed radial axis value, Humphrey Atlas PathFinder corneal analysis, corneal thickness, and corneal anterior and posterior elevation. RESULTS Four additional patients (7 eyes) with vertical D patterns were found (prevalence, 0.34%). In addition to this vertical D pattern, these patients had central corneal thickness < 500 microm and/or posterior corneal protrusion > 20 microm or positive results on keratoconus detection analyses. The 10 eyes with the vertical D pattern had more horizontal (nasal-temporal ratio) than vertical (inferior-superior ratio) curvature asymmetry: 0.98+/-0.04 diopters versus 0.44+/-0.2 diopters (paired t test, P<0.001). CONCLUSIONS We propose that vertical D is a novel corneal curvature pattern reflecting horizontal asymmetry that was present in keratoconus suspect patients even if standard keratoconus analyses' results were negative.
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Randleman JB, Loft ES, Banning CS, Lynn MJ, Stulting RD. Outcomes of Wavefront-Optimized Surface Ablation. Ophthalmology 2007; 114:983-8. [PMID: 17337064 DOI: 10.1016/j.ophtha.2006.10.048] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2006] [Revised: 10/14/2006] [Accepted: 10/15/2006] [Indexed: 11/29/2022] Open
Abstract
PURPOSE To compare early visual outcomes after wavefront-optimized advanced surface ablation (ASA) with those after wavefront-optimized LASIK. DESIGN Retrospective comparative series. PARTICIPANTS One hundred thirty-six eyes undergoing ASA and 136 preoperative refraction-matched eyes undergoing LASIK from June 2004 through October 2005. METHODS Database review of preoperative characteristics, including patient age, gender, refraction, and central corneal pachymetry; perioperative information, including type of surgery, flap thickness (for LASIK cases), ablation depth, and residual stromal bed thickness; and postoperative information, including uncorrected visual acuity (UCVA) at 1 day, 1 week, 2 weeks, and 3 months, refraction at 3 months, and complications. All ASA patients had topical mitomycin C applied intraoperatively. MAIN OUTCOMES MEASURES Postoperative UCVA, best spectacle-corrected visual acuity (BSCVA), spherical equivalent (SE) refraction, speed of visual recovery, and postoperative complications. RESULTS Surface ablation patients were younger (35.4 years vs. 39.8 years, P = 0.0002) and had thinner corneas (514 microm vs. 549 microm, P<0.0001) preoperatively. Average UCVA was significantly better after LASIK at 1 day (20/26.8 vs. 20/50.4, P<0.0001) and 2 weeks (20/24.4 vs. 20/33.3, P = 0.0002) postoperatively. However, by 3 months postoperatively, UCVA was better after ASA (20/20.8 vs. 20/22.7, P = 0.05), and 81.5% of patients achieved 20/20 or better UCVA after ASA, compared with 70.5% after LASIK (P = 0.05). More ASA eyes had postoperative UCVA that achieved or surpassed preoperative BSCVA than LASIK eyes (66% vs. 41.6%, P<0.0001). There were 53 patients who underwent bilateral simultaneous ASA. By 1 week, 87.5% had 20/40 or better UCVA in at least one eye and 62.5% had 20/40 or better UCVA in both eyes. By 2 weeks, 86.8% had 20/40 or better UCVA in one eye and 82.6% had 20/40 or better UCVA in both eyes. CONCLUSION Initial visual recovery is more rapid after LASIK; however, by 3 months postoperatively UCVA and SE refractions were better after ASA. Advanced surface ablation is an effective alternative to LASIK, and based on early visual recovery, bilateral simultaneous surface ablation is a reasonable alternative to sequential surgery for the majority of patients.
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Condon PI, O'Keefe M, Binder PS. Long-term results of laser in situ keratomileusis for high myopia: Risk for ectasia. J Cataract Refract Surg 2007; 33:583-90. [PMID: 17397729 DOI: 10.1016/j.jcrs.2006.12.015] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2006] [Accepted: 12/21/2006] [Indexed: 10/23/2022]
Abstract
PURPOSE To ascertain the long-term stability of laser in situ keratomileusis (LASIK) in highly myopic eyes. SETTING Clinical practice office-based surgery. METHOD Charts of eyes with high myopia who had LASIK surgery by the same surgeon between 1994 and 2000 were reviewed in 2003, and patients were given an appointment for follow-up examinations. In these highly myopic eyes, surgery was originally performed to create undercorrections with or without decreasing the ablation diameters to maximally conserve the residual stromal bed thickness. RESULTS Of the 107 eyes with myopia between -10.00 diopters (D) and -35.00 D reviewed and operated on in a 3-year period between 1994 and 1998, 35 eyes of 31 patients had a single enhancement procedure. One case of ectasia as a result of excessive tissue removal occurred in a patient with a preoperative refraction of -28.00 D. Of the 107 eyes reviewed, 78 (73%) were examined after 5 years, 68 (63%) after 7 years, and 15 (14%) between 9 years and 11 years. CONCLUSIONS Operating on eyes with highly myopic refractive errors and removing substantial tissue thickness did not produce ectasia in this series. Although high myopia has been considered a risk factor for post-LASIK ectasia, adherence to proper screening and intraoperative pachymetry appears to decrease the risk.
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169
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Klein SR, Epstein RJ. Ectasia after photorefractive keratectomy. Ophthalmology 2007; 114:395-6; author reply 396-7. [PMID: 17270693 DOI: 10.1016/j.ophtha.2006.10.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2006] [Accepted: 10/03/2006] [Indexed: 10/23/2022] Open
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Asbell P. Is conductive keratoplasty the treatment of choice for presbyopia? EXPERT REVIEW OF OPHTHALMOLOGY 2007. [DOI: 10.1586/17469899.2.1.121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Abstract
PURPOSE To report two cases of corneal ectasia, which developed after hyperopic LASIK. METHODS Preoperative pellucid marginal corneal degeneration was observed in patient 1. Patient 2 had no preoperative risk factors. RESULTS Patient 1, a 47-year-old man, developed corneal ectasia in his right eye 6 months after unilateral hyperopic LASIK. Preoperative manifest refraction was +2.00 +1.50 x 178 in the right eye and +1.00 sphere in the left eye. Corneal thickness was 585 microm and 575 microm (right and left eye, respectively). Preoperative topography of the right eye demonstrated inferior steepening in the far periphery, suggestive of early pellucid marginal corneal degeneration. Patient 2, a 35-year-old man, developed corneal ectasia in his right eye > 3 years after bilateral LASIK. Preoperative manifest refraction was +2.50 sphere and +3.25 sphere (right and left eye, respectively), and corneal thickness was 556 microm in both eyes. Preoperative topography was normal in both eyes with no evidence of asymmetry, steepening, or irregularity. CONCLUSIONS Corneal ectasia can occur after hyperopic LASIK in patients with or without recognized preoperative risk factors. Although uncommon, patients with pellucid marginal corneal degeneration can have hyperopic refractions and are at high risk for developing corneal ectasia after LASIK.
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Affiliation(s)
- J Bradley Randleman
- Department of Ophthalmology, Emory University and Emory Vision, Atlanta, Ga, USA.
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172
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Belin MW, Khachikian SS. New devices and clinical implications for measuring corneal thickness. Clin Exp Ophthalmol 2006; 34:729-31. [PMID: 17073893 DOI: 10.1111/j.1442-9071.2006.01395.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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173
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Reinstein DZ, Srivannaboon S, Archer TJ, Silverman RH, Sutton H, Coleman DJ. Probability Model of the Inaccuracy of Residual Stromal Thickness Prediction to Reduce the Risk of Ectasia After LASIK Part II: Quantifying Population Risk. J Refract Surg 2006; 22:861-70. [PMID: 17124880 DOI: 10.3928/1081-597x-20061101-05] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE To derive a statistical model to estimate the rate of excessive keratectomy depth below a selected cut-off residual stromal thickness (RST) given a minimum target RST and specific Clinical Protocol; apply the model to estimate the RST below which ectasia appears likely to occur and back-calculate the safe minimum target RST that should be used given a specific Clinical Protocol. METHODS Myopia and corneal thickness distribution were modeled for a population of 5212 eyes that underwent LASIK. The probability distribution of predicted target RST error (Part I) was used to calculate the rate of excessive keratectomy depth for this series. All treatments were performed using the same Clinical Protocol; one surgeon, Moria LSK-One microkeratome, NIDEK EC-5000 excimer laser, Orbscan pachymetry, and a minimum target RST of 250 microm--the Vancouver Clinical Protocol. The model estimated the RST below which ectasia appears likely to occur and back-calculated the safe minimum target RST. These values were recalculated for a series of microkeratomes using published flap thickness statistics as well as for the Clinical Protocol of one of the authors-the London Clinical Protocol. RESULTS In the series of 5212 eyes, 6 (0.12%) cases of ectasia occurred. The model predicted an RST of 191 microm for ectasia to occur and that a minimum target RST of 329 microm would have reduced the -rate of ectasia to 1: 1,000,000 for the Vancouver Clinical Protocol. The model predicted that the choice of microkeratome varied the rate of ectasia between 0.01 and 11,623 eyes per million and the safe minimum target RST between 220 and 361 microm. The model predicted the rate of ectasia would have been 0.000003: 1,000,000 had the London Clinical Protocol been used for the Vancouver case series. CONCLUSIONS There appears to be no universally safe minimum target RST to assess suitability for LASIK largely due to the disparity in accuracy and reproducibility of microkeratome flap thickness. This model may be used as a tool to evaluate the risk of ectasia due to excessive keratectomy depth and help determine the minimum target RST given a particular Clinical Protocol.
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Affiliation(s)
- Dan Z Reinstein
- London Vision Clinic, 8 Devonshire Place, London W1G 6HP, United Kingdom.
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174
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Laser literature watch. Photomed Laser Surg 2006; 24:537-71. [PMID: 16942439 DOI: 10.1089/pho.2006.24.537] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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175
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Bibliography. Current world literature. Corneal and external disorders. Curr Opin Ophthalmol 2006; 17:413-8. [PMID: 16900037 DOI: 10.1097/01.icu.0000233964.03757.bd] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Randleman JB, Caster AI, Banning CS, Stulting RD. Corneal ectasia after photorefractive keratectomy. J Cataract Refract Surg 2006; 32:1395-8. [PMID: 16863983 DOI: 10.1016/j.jcrs.2006.02.078] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2006] [Accepted: 02/13/2006] [Indexed: 11/23/2022]
Abstract
Two patients developed corneal ectasia after photorefractive keratectomy (PRK). Case 1 had evidence of early keratoconus preoperatively, with manifest refractions of -4.00 +2.50 x 160 (20/20) in the right eye and -7.00 +3.00 x 180 (20/30) in the left eye; thin corneas (472 microm and 441 microm, respectively); and inferior paracentral steepening in the right eye and central steepening in the left eye on topography. Case 2 had manifest refractions of -8.50 +3.75 x 123 (20/20(-2)) in the right eye and -9.25 +4.00 x 077 (20/20(-1)) in the left eye; corneal thickness of 509 microm and 508 microm, respectively; and symmetric bow-tie patterns in both eyes on topography. Case 2 had a family history suspicious for keratoconus, with a sibling who had bilateral corneal transplantation at a young age. Both patients developed bilateral corneal ectasia after PRK.
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Affiliation(s)
- J Bradley Randleman
- Emory University Department of Ophthalmology and Emory Vision, Atlanta, Georgia 30322, USA.
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Abstract
PURPOSE OF REVIEW The aim of this article is to review the causes, risk factors, management, and future research directions for corneal ectasia after laser in situ keratomileusis. RECENT FINDINGS Complex corneal biomechanical processes influence the integrity of the normal and postoperative cornea, and developing an understanding of these processes facilitates recognition of risk factors for ectasia after laser in-situ keratomileusis. Currently identified risk factors include keratoconus, high myopia, low residual stromal bed thickness from excessive ablation or thick flap creation, and defined topographic abnormalities such as forme fruste keratoconus and pellucid marginal corneal degeneration. Ectasia can also rarely occur in patients without currently identifiable risk factors, and future identification of at-risk patients may be facilitated by corneal interferometry and corneal hysteresis measurements. Utilization of intraoperative pachymetry measurements at the time of surgery and confocal microscopy prior to enhancement to measure residual stromal bed thickness should avoid unanticipated low residual stromal bed thickness. Management options for ectasia after laser in situ keratomileusis include intraocular pressure reduction, rigid gas permeable contact lenses, and intracorneal ring segments, in addition to corneal transplantation. In the future, collagen cross-linking may reduce corneal steepening and improve refractive error. SUMMARY When ectasia develops, early recognition and proper management are essential to prevent progression, to promote visual rehabilitation, and to reduce the need for corneal transplantation for these patients.
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Affiliation(s)
- J Bradley Randleman
- Emory University Department of Ophthalmology and Emory Vision, Atlanta, Georgia 30322, USA.
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