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Update and Review of Diagnosis and Management of Post-Refractive Surgery Ectasia. J Cataract Refract Surg 2021; 48:487-499. [PMID: 34486581 DOI: 10.1097/j.jcrs.0000000000000808] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2021] [Accepted: 08/18/2021] [Indexed: 11/25/2022]
Abstract
ABSTRACT Post-Refractive Surgery Ectasia is a serious, sight-threatening, and highly - avoided complication seen after the following procedures: Laser in situ Keratomileusis, Photorefractive Keratectomy, Small Incision Lenticule Extraction, Radial and/or Arcuate Keratotomy. Specific risk factors may include age, corneal thickness, degree of refractive error, corneal topographic changes including irregular astigmatism, percent tissue ablation, and residual stromal bed. Biomarkers may be a new option to help indicate who is at greatest risk for ectasia. Visual aids including glasses or contacts lenses are often required to achieve optimal vision. Collagen crosslinking is the only treatment thought to stop progression of ectasia and prevent keratoplasty. Other surgical options may include topography-guided phototherapeutic keratectomy and intrastromal corneal ring segments. Ultimately an "ounce of prevention is a pound of cure" so careful preoperative screening and ultimately offering the safest and most effective treatments for patients is arguably the most important job of the refractive surgeon.
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Martin R, Rachidi H. Stability of posterior corneal elevation one year after myopic laser in situ keratomileusis. Clin Exp Optom 2021; 95:177-86. [DOI: 10.1111/j.1444-0938.2011.00665.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Affiliation(s)
- Raul Martin
- IOBA‐Eye Institute and Department of Physics TAO, University of Valladolid, Valladolid, Spain. E‐mail:
| | - Houda Rachidi
- IOBA‐Eye Institute and Department of Physics TAO, University of Valladolid, Valladolid, Spain. E‐mail:
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Seven-year observation of posterior corneal elevation after small incision lenticule extraction (SMILE) in patients with moderate and high myopia. J Cataract Refract Surg 2021; 47:1398-1402. [PMID: 33770391 DOI: 10.1097/j.jcrs.0000000000000639] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2020] [Accepted: 03/03/2021] [Indexed: 11/26/2022]
Abstract
Purpose To investigate the long-term changes in posterior corneal elevation in moderate and high myopia after small incision lenticule extraction (SMILE). Setting Eye & ENT Hospital, Fudan University. Design Prospective case series. Methods Thirty-three eyes of 20 patients (30.1+/-9.5 years, 7 male and 13 female, spherical equivalent [SE] range -4.00 to -8.75 D, average SE -6.25+/-1.29 D) who underwent SMILE were included. Changes in the posterior corneal elevation at central points (PCE), the thinnest point (PTE), the maximal point (PME), and an additional 20 points within the 4-mm area of the best-fit sphere were evaluated with a Pentacam (Oculus Optikgerate GmbH, Wetzlar, Germany) during a 7-year follow-up period. Mixed linear models were used to evaluate changes with P-values <0.05. Correlations of elevation changes and residual bed thickness (RBT) were also evaluated. Results No ectasia was observed among the 33 eyes. The safety index was 1.08, and the efficacy index was 1.03. The mean change in PCE at 1, 3, 5, and 7 years was -1.42+/-0.95, -2.67+/-0.98, -2.44+/-1.06, and -1.91+/-0.92 [micro]m, respectively. Significant differences were found at 3, 5, and 7 years (P=0.007, 0.023, and 0.040, respectively). PTE was significantly reduced at each time point compared to baseline. The mean change was -2.82+/-1.19, -3.55+/-1.22, -3.47+/-1.32, and -2.39+/-1.15 [micro]m, respectively (P=0.019, 0.004, 0.010, and 0.039, respectively). PME changed 2.45+/-1.02 [micro]m at 7 years compared to baseline (P=0.017). The changes in PCE and PME negatively correlated with the RBT. Conclusions Long-term posterior corneal elevation was stable in moderate and high myopia after SMILE.
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Nie Y, Gross H, Zhong Y, Duerr F. Freeform optical design for a nonscanning corneal imaging system with a convexly curved image. APPLIED OPTICS 2017; 56:5630-5638. [PMID: 29047704 DOI: 10.1364/ao.56.005630] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2017] [Accepted: 06/09/2017] [Indexed: 05/28/2023]
Abstract
Most existing techniques that are typically used by specialists to image the cornea are based on point, slit, or annular scanning due to a narrow field of view. The difficulty in achieving a larger field of view comes from the convex shape of the human eyeball. Field curvature for a refractive imaging system with positive power is typically negative and thus a concave image surface. In order to view the full cornea and sclera with snapshot imaging, we calculate qualified two- and three-mirror solutions from Seidel aberration theory. A three-mirror solution is further optimized as a high-resolution off-axis imaging system using freeform surfaces, which can obtain a full-field tailored image shell without scanning. The lateral resolution on the cornea is about 10 μm with good modulation transfer function (MTF) and spot performance. To ease the assembly, a monolithic design is achieved with slightly lower resolution, leading to a potential mass production solution.
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Abstract
Purpose: To compare changes in the corneal thickness profile before and 6 months after femtosecond laser in situ keratomileusis (LASIK) for hyperopia. Methods: In a prospective noncomparative case series study, 24 eyes of 20 hyperopic patients undergoing femtosecond LASIK were examined preoperatively and 6 months postoperatively. Corneal profile was measured using Pentacam HR device. Paired t test was used to compare preoperative and postoperative values. Spearman correlation analysis was performed to evaluate the relationship between the central corneal thickness changes and attempted spherical equivalent refraction (SER). Results: The mean uncorrected distance visual acuity significantly improved after surgery (P<0.001). Significant differences in central, midperipheral, ablative annular, and peripheral corneal thicknesses were observed from preoperatively to 6 months postoperatively (all P<0.001). There was no significant correlation between the changes in the central corneal thickness and attempted SER (P=0.23). Conclusions: The corneal thicknesses across the whole ablation zone including central corneal thickness, significantly decrease postoperatively compared with preoperatively.
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Quality of Life of Myopic Subjects With Different Methods of Visual Correction Using the NEI RQL-42 Questionnaire. Eye Contact Lens 2012; 38:116-21. [PMID: 22293405 DOI: 10.1097/icl.0b013e3182480e97] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Byun YS, Chung SH, Park YG, Joo CK. Posterior corneal curvature assessment after Epi-LASIK for myopia: comparison of Orbscan II and Pentacam imaging. KOREAN JOURNAL OF OPHTHALMOLOGY 2012; 26:6-9. [PMID: 22323878 PMCID: PMC3268172 DOI: 10.3341/kjo.2012.26.1.6] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2010] [Accepted: 12/20/2010] [Indexed: 11/23/2022] Open
Abstract
PURPOSE To compare the changes in posterior corneal curvature using scanning slit topography (Orbscan II) and Scheimpflug imaging (Pentacam) before and after Epi-laser in situ keratomileusis (LASIK) for myopia. METHODS In a prospective observational case-series study, 20 myopic patients having undergone Epi-LASIK were examined serially with two different devices, Orbscan II and Pentacam, preoperatively and one month postoperatively. Posterior central elevation (PCE) and posterior maximal elevation (PME) were compared between the two devices, and the changes in parameters after Epi-LASIK were analyzed using a difference map. RESULTS All parameters (preoperative and postoperative PCE and preoperative and postoperative PME) that were measured using the Orbscan II were significantly greater compared to those of the Pentacam (for all p < 0.001). PCE and PME were significantly increased one month postoperatively in the Orbscan II measurements (p < 0.05) but were not significantly increased in the Pentacam measurements. Also, ΔPCE and ΔPME, in the difference map obtained by each serial scanning, were significantly greater in the Orbscan II measurements than with the Pentacam (p = 0.012, p = 0.016). CONCLUSIONS The Pentacam measurements displayed significantly reduced values in all parameters related to posterior corneal elevation compared to those of the Orbscan II. The Pentacam showed no significant change in posterior corneal curvature after Epi-LASIK, based on the difference map.
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Affiliation(s)
- Yong-Soo Byun
- Department of Ophthalmology and Visual Science, Seoul St. Mary's Hospital, The Catholic University of Korea College of Medicine, Seoul, Korea
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Nishimura R, Negishi K, Dogru M, Saiki M, Arai H, Toda I, Yamaguchi T, Tsubota K. Effect of age on changes in anterior chamber depth and volume after laser in situ keratomileusis. J Cataract Refract Surg 2010; 35:1868-72. [PMID: 19878817 DOI: 10.1016/j.jcrs.2009.06.022] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2009] [Revised: 05/26/2009] [Accepted: 06/05/2009] [Indexed: 11/25/2022]
Abstract
PURPOSE To evaluate the effect of age on anterior chamber depth (ACD) and anterior chamber volume (ACV) after laser in situ keratomileusis (LASIK) for myopia. SETTING Department of Ophthalmology, Keio University School of Medicine, and a private clinic, Tokyo, Japan. METHODS In this retrospective study, patients who had uneventful LASIK for myopia or myopic astigmatism were divided into 2 groups: younger (younger than 40 years) and older (40 years and older). Central corneal thickness, central corneal true net power, ACV, and central ACD were measured using a rotating Scheimpflug camera preoperatively and 1 month postoperatively. These parameters were compared between the 2 groups. RESULTS The study evaluated 161 eyes of 83 patients (mean age 34.5 years +/- 8.3 [SD]). The decreases in central ACD and ACV after LASIK were statistically significant in the younger group (P<.0001 and P = .0050, respectively) but not in the older group. CONCLUSION Central ACD and the ACV decreased significantly after LASIK in younger patients (<40 years) but not in older patients, indicating that age influences changes in ACD and ACV after LASIK.
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Affiliation(s)
- Ryo Nishimura
- Department of Ophthalmology, Keio University School of Medicine, Tokyo, Japan
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Tu KL, Aslanides IM. Orbscan II anterior elevation changes following corneal collagen cross-linking treatment for keratoconus. J Refract Surg 2009; 25:715-22. [PMID: 19714796 DOI: 10.3928/1081597x-20090707-06] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE To analyze anterior corneal elevation changes on Orbscan II following corneal collagen cross-linking (CXL) with riboflavin. METHODS This retrospective study included 8 patients (14 eyes) with keratoconus who underwent CXL, with a mean follow-up of 7 months (range: 5 to 10 months). Pre- and postoperative (at last clinic attendance) anterior elevation difference maps were examined for overall patterns of change. On preoperative maps, distances from maximum anterior elevation to pupil center and to topographic geometric center were compared between the two patterns identified. Pre- and postoperative topography, best spectacle-corrected visual acuity (BSCVA), and refraction were also compared between the two patterns. RESULTS Two patterns of anterior elevation change were visually identified: (1) paracentral steepening, no change, or flattening centrally; and (2) central steepening. The preoperative maps of eyes that manifested pattern 1 had shorter mean distances for maximum anterior elevation to pupil center (1.70 vs. 2.27 mm) and maximum anterior elevation to geometric center (1.45 vs. 1.99 mm) than those that resulted in pattern 2. Mean maximum topographic simulated keratometry decreased (P = .004) and mean irregularity indices at 3 mm (P =.03) and 5 mm (P =.04) were reduced postoperatively in pattern 1 eyes; all increased in pattern 2 eyes. Mean BSCVA improved postoperatively for both patterns. Mean preoperative myopia decreased in pattern 1 eyes by 0.44 diopters (D), whereas it increased for pattern 2 eyes by 1.83 D. CONCLUSIONS Corneal shape change influenced by anisotropy of collagen distribution is a factor in the outcome of CXL treatment for keratoconus.
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Affiliation(s)
- Kyaw Lin Tu
- Stepping Hill Hospital, Poplar Grove, Hazel Grove, Stockport, United Kingdom.
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Short- and Long-term Comparison between Photorefractive Keratectomy and Laser In Situ Keratomileusis. Cornea 2009. [DOI: 10.1097/ico.0b013e3181ae9139] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Chang JH, Kim SW, Sun HJ, Kim EK. Anterior Segment Measurements Using Pentacam and Orbscan II 1 to 5 Years After Refractive Surgery. J Refract Surg 2009; 25:1091-7. [DOI: 10.3928/1081597x-20091117-08] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2008] [Accepted: 01/06/2009] [Indexed: 11/20/2022]
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Comparison of laser in situ keratomileusis and photorefractive keratectomy results: Long-term follow-up. J Cataract Refract Surg 2008; 34:1527-31. [PMID: 18721714 DOI: 10.1016/j.jcrs.2008.04.038] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2008] [Accepted: 04/28/2008] [Indexed: 11/23/2022]
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González L, Hernández-Matamoros JL, Navarro R. Multizone model for postsurgical corneas: analysis of standard and custom LASIK outcomes. JOURNAL OF BIOMEDICAL OPTICS 2008; 13:044035. [PMID: 19021362 DOI: 10.1117/1.2960621] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
A multizone model for postsurgical corneal topography is presented and applied to a comparative analysis of the outcome of standard and customized myopic LASIK. The different zones are segmented automatically by a clustering algorithm. The algorithm uses a set of three local descriptors, which correspond to normalized physical magnitudes computed for each point of the corneal topography map: Gauss curvature, root-mean-square (RMS) fit error to an ellipsoid surface model, and distance to the center of the topographic map. Both presurgical and post-LASIK corneal topographies of 31 eyes were analyzed using monozone and multizone models. The patients were classified into three groups according to the different LASIK treatments applied: Allegretto, Zyoptix, and PlanoScan. For post-LASIK corneas, the multizone model provided a lower fit error, an average of 1.2+/-0.4 microm versus 2.4+/-0.7 microm (monozone). The comparative analysis of the three different LASIK treatments showed no improvement of custom over standard treatments. The outcomes of Zyoptix and PlanoScan were basically equivalent and consistent with previous findings: The higher-order aberration (HOA) increased by a factor of two. The increase in HOA was higher, by a factor of three, after the Allegretto treatment. The multizone model shows a higher-fidelity representation and permits a deeper understanding of the postsurgical cornea.
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Affiliation(s)
- Luis González
- Clinica Oftalmológica Real Visión, Sta. Cruz de Marcenado 31, 28015 Madrid, Spain
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Matsuda J, Hieda O, Kinoshita S. Comparison of central corneal thickness measurements by Orbscan II and Pentacam after corneal refractive surgery. Jpn J Ophthalmol 2008; 52:245-249. [DOI: 10.1007/s10384-008-0550-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2007] [Accepted: 01/24/2008] [Indexed: 10/21/2022]
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Hashemi H, Mehravaran S. Corneal changes after laser refractive surgery for myopia: comparison of Orbscan II and Pentacam findings. J Cataract Refract Surg 2007; 33:841-7. [PMID: 17466859 DOI: 10.1016/j.jcrs.2007.01.019] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2006] [Accepted: 01/18/2007] [Indexed: 11/22/2022]
Abstract
PURPOSE To determine the agreement between scanning slit topography (Orbscan II, Bausch & Lomb) and Scheimpflug imaging (Pentacam, Oculus) in corneal elevation, corneal curvature, and anterior chamber depth (ACD) measurements before and after laser refractive surgery for myopia and to compare the postoperative changes seen with these devices. SETTING Noor Vision Correction Center, Tehran, Iran. METHODS In a prospective observational case-series study, 23 consecutive myopic patients having laser refractive surgery were examined with the Orbscan II and Pentacam preoperatively and 6 weeks postoperatively. Readings of ACD, anterior (A-) and posterior (P-) best-fit sphere (BFS) size, central elevation (CE), maximum elevation (ME), axial power in the 3.0 mm zone (AX3) and 5.0 mm zone (AX5), and tangential power in these zones (TG3 and TG5, respectively) were collected and used in the analyses. RESULTS Statistically significant interdevice differences were found preoperatively for all parameters except P-TG3 (P = .014) and in operated eyes for ACD, anterior parameters of A-AX3 and A-AX5, and all posterior corneal parameters. In posterior corneal measurements, Orbscan II demonstrated significant postoperative changes in all parameters except P-AX5 (P = .004) and P-TG5 (P = .034), although none of the differences was statistically significant with the Pentacam. The devices measured similar postoperative changes in anterior curvature parameters and in P-AX5 and P-TG5; all other changes were significantly different. CONCLUSIONS Compared to the Pentacam, the Orbscan II yielded larger posterior elevation values before and after surgery and significant postoperative changes in P-CE and P-ME. Further studies can determine which device gives more accurate images of the cornea and redefine screening criteria.
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Affiliation(s)
- Hassan Hashemi
- Farabi Eye Hospital, Department of Ophthalmology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran
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Nishimura R, Negishi K, Saiki M, Arai H, Shimizu S, Toda I, Tsubota K. No forward shifting of posterior corneal surface in eyes undergoing LASIK. Ophthalmology 2007; 114:1104-10. [PMID: 17239440 DOI: 10.1016/j.ophtha.2006.09.014] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2006] [Revised: 09/07/2006] [Accepted: 09/07/2006] [Indexed: 11/29/2022] Open
Abstract
PURPOSE To evaluate structural changes in the cornea and anterior chamber (AC) after LASIK for myopia. DESIGN Retrospective nonrandomized study. PARTICIPANTS One hundred sixty-one eyes of 83 patients (mean age, 34.5+/-8.3 years) who underwent uneventful LASIK for myopia and myopic astigmatism. The preoperative refractive error (spherical equivalent) and corneal thickness were -6.02+/-2.10 diopters (D) and 549.9+/-29.3 mum, respectively. METHODS The AC volume (ACV), AC depth (ACD), corneal thickness, central corneal true net power, and posterior corneal tangential curvature were measured using a rotating Scheimpflug camera before and 1 week and 1 month after surgery. In 84 eyes of 42 cases, anterior and posterior corneal elevations and corneal thicknesses also were measured by scanning-slit topography before and 1 month after surgery. MAIN OUTCOME MEASURES Time course of the ACV, ACD (central, midperiphery, periphery), corneal thickness, central corneal true net power, posterior corneal tangential curvature using the Scheimpflug camera, and amount of forward shifting of the posterior corneal surface at the center of the difference map using scanning-slit topography. RESULTS Preoperative and 1-month postoperative mean ACVs were 198.1 mm3 and 196.4 mm3, respectively, and preoperative and postoperative mean ACDs (center, midperiphery, periphery) were 3.24, 2.65, and 1.89 mm, and 3.21, 2.63, and 1.87 mm, respectively. The corneal thickness within the optical zone, subjective refraction, and central corneal true net power significantly changed by tissue subtraction after LASIK (P<0.0001). There were no significant differences in the ACV, ACDs (center, midperiphery, periphery), peripheral corneal thickness, and posterior corneal tangential curvature from preoperatively to 1 month after LASIK. However, using scanning-slit topography, the posterior corneal surface displayed a mean forward shift of 29.0+/-19.0 microm 1 month after surgery. CONCLUSION The posterior corneal curvature, peripheral corneal thickness, ACDs, and ACV were consistent. These observations indicated that neither forward shifting of the central posterior corneal surface (bulging) nor backward shifting of the peripheral posterior corneal surface due to corneal swelling after ablation occurred after LASIK.
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Affiliation(s)
- Ryo Nishimura
- Department of Ophthalmology, Keio University School of Medicine, Tokyo, Japan
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Maldonado MJ, Nieto JC, Díez-Cuenca M, Piñero DP. Repeatability and Reproducibility of Posterior Corneal Curvature Measurements by Combined Scanning-Slit and Placido-Disc Topography after LASIK. Ophthalmology 2006; 113:1918-26. [PMID: 16935339 DOI: 10.1016/j.ophtha.2006.05.053] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2005] [Revised: 05/20/2006] [Accepted: 05/20/2006] [Indexed: 10/24/2022] Open
Abstract
OBJECTIVE To assess the repeatability and reproducibility of posterior corneal curvature (PCC) measurements made by combined scanning-slit/Placido-disc topography (Orbscan II) after LASIK. DESIGN Experimental instrument validation study. PARTICIPANTS We recruited 22 consecutive postmyopic LASIK patients for the repeatability study and another 50 consecutive postmyopic LASIK patients for the reproducibility study. METHODS To analyze intrasession repeatability, 1 examiner measured 22 postmyopic LASIK eyes 10 times successively in the shortest time possible. To study intersession reproducibility, the same operator obtained measurements from another 50 eyes with stable refraction in 2 consecutive visits at the same time of the day between 6 and 9 months after myopic LASIK. We explored any association between residual stromal bed thickness and measurement variability. MAIN OUTCOME MEASURES Orbscan II scanning-slit PCC data, precision, within-subject coefficient of variation (CV(w)), limits of agreement (LoA), and intraclass correlation coefficient (ICC). RESULTS For intrasession repeatability, precision was 0.067 mm (best-fit sphere [BFS]), 0.110 diopters (D; power within 5 mm), 0.158 D (power within 3 mm), and 0.46 (eccentricity). Repeatability was high for PCC BFS and power measurements within 3-mm and 5-mm zones (CV(w) ranged from 0.5%-1.2%) but poor for eccentricity data (CV(w), 31.6%). Correspondingly, ICCs ranged from 0.89 to 0.98 for PCC BFS and power, and the ICC was 0.20 for PCC eccentricity values. For intersession reproducibility, on average, no difference in PCC measurements could be found, indicating that when there is variability, it is due to random factors. The width of the 95% LoA between sessions was clinically acceptable for BFS (0.25 mm) and power (0.4 D [within 5 mm] and 0.6 D [within 3 mm]). Similarly, ICCs indicated good intersession reliability for BFS and power (0.98, 0.96, and 0.85 for BFS, power within 5 mm, and power within 3 mm, respectively) but poor reliability for eccentricity (0.59). Repeatability and reproducibility were unrelated to stromal bed thickness. CONCLUSIONS Orbscan II provides reliable post-LASIK PCC data for symmetrical parameters (BFS and power), independent of the residual stromal bed thickness, but is unreliable for measurements that are radially asymmetrical (eccentricity). Orbscan II is useful for monitoring the PCC after LASIK once the early postoperative period is over.
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Affiliation(s)
- Miguel J Maldonado
- Department of Ophthalmology, University Clinic, University of Navarra, Pamplona, Spain
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Fam HB, Lim KL. Corneal elevation indices in normal and keratoconic eyes. J Cataract Refract Surg 2006; 32:1281-7. [PMID: 16863962 DOI: 10.1016/j.jcrs.2006.02.060] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2006] [Accepted: 03/06/2006] [Indexed: 11/29/2022]
Abstract
PURPOSE To determine an index that distinguishes keratoconus and keratoconus-suspect eyes from normal eyes with Orbscan (Bausch & Lomb) corneal elevation maps. SETTING Department of Ophthalmology, Tan Tock Seng Hospital, Singapore, and iLaser Centre, Island Hospital, Penang, Malaysia. METHODS In this initial phase of this multicenter nonrandomized retrospective study, 1 eye of 166 normal subjects, 15 keratoconus patients, and 11 keratoconus suspects was examined at 1 clinic. The anterior best-fit sphere (BFS), posterior BFS, anterior elevation, posterior elevation, and maximum and minimum keratometries were analyzed. Two indices with the highest sensitivity and specificity classifying these conditions were identified using receiver operating characteristic curves. These 2 indices were evaluated in a subsequent validation study using 1 eye of 221 normal subjects, 43 keratoconus patients, and 23 keratoconus suspects from another clinic. RESULTS The anterior elevation and anterior elevation ratio (anterior elevation ratio = anterior elevation/anterior BFS) best classified the different groups. An anterior elevation ratio of 0.5122 mm or less had 99% sensitivity and 95.2% specificity while a ratio 16.5 mum or less had 80.1% sensitivity and 80.8% specificity in discriminating normal eyes from keratoconus and keratoconus suspects. The results were similar in the validation study. In addition, these anterior elevation and anterior elevation ratio cutoff values had high sensitivity and specificity in identifying keratoconus suspects from normal eyes in the validation study. CONCLUSION Anterior corneal elevation parameters are clinically relevant measures for detecting keratoconus and suspected keratoconus eyes.
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Affiliation(s)
- Han-Bor Fam
- From The Eye Institute, Tan Tock Seng Hospital, Singapore
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