Transnational Science Fiction and Discourses on Cosmopolitan Conflicts
1.2. TOWARDS A CRITICAL COSMOPOLITAN TURN IN THE STUDY OF SCIENCE FICTION CINEMA
1.2.1. Critical Cosmopolitanism: The Methodological and Normative Dimensions This section explores the notion of cosmopolitanism and sketches the cosmopolitan approach
Studies using the new CTSP, PTI and pachymetric progression index (PPI) were in agreement with previous reports in the literature.15-17 Mandell and Polse pioneered this field using a modified Haag-Streit optical pachymeter, with an electronic recording system to document the variation in thickness over the horizontal meridian measured at different angles.15 In this study, the difference between the central and the peripheral measurements were much greater in keratoconus, which was most significant for their 35th position (which roughly corresponds to 3.5 mm from the apex) where they found a difference of greater than 85 microns as pathognomonic of keratoconus. The concept that the amount of corneal thinning is related to the severity of the disease in keratoconic eyes should be intuitive considering the definition of the ectatic diseases.
Pachymetric distribution or spatial profile was studied with the Orbscan IIz in 2004.
Data from 100 normal and 25 mild to moderate keratoconus cases were manually extracted using numeric pachymetric maps. A significant difference was found for all positions studied (Student Test, p>0.05).13 Colin Chan, MD (Australia) utilized Orbscan pachymetric data and evaluated cases with unexplained post-LASIK ectasia with no risk factors based on sagittal (axial) maps, central corneal thickness and with low scores on the Ectasia Risk Score System (ERSS).18,19 In three out of four eyes of two patients, the PTI graph revealed an abnormal profile and identified these patients at “risk” preoperatively (Luz and Ambrósio, 2008 – unpublished data).
A new thickness metrics: ART (Ambrósio Relational Thickness), utilizes the TP in relation to the pachymetric progression indices (PPI). ART may be calculated as the ratios between the TP and the maximal PPI meridian (ART Max= TP/PPI Max ) and the average (ART Ave = TP/PPI Ave). We have found ART Max and ART Ave among the best parameters for detecting ectasia. The performance of these novel indices for differentiating keratoconus from normal eyes was demonstrated as superior than CCT and TP.20 In addition, ART has been found to be more sensitive to detect mild ectatic changes in cases with subclinical keratoconus, such as those with very asymmetric presentations or cases that develop ectasia despite of no identifiable risk factors (anterior curvature and US CCT) (see CHAPTER 9).21
The CTSP and PTI graphs, along with the thickness map and pachymetric indices were combined with the “enhanced” best fit sphere (BFS) (See CHAPTER 8) in the Pentacam as the
“Belin/Ambrósio Enhanced Ectasia Display” (“ BAD”) (FIGURE 8). The goal of the BAD was to create an all elevation based screening tool for refractive surgeons. Clinical experience has demonstrated that the combination of the data in the BAD enhances the sensitivity of ectasia detection and is a useful screening tool for refractive surgeons. 11,22
Figure 8. The Belin/Ambrosio Display (BAD) showing both the elevation maps (anterior and posterior with standard and enhanced BFS) and complete pachymetric map, graphs, and indices.
REFERENCES
1. Ambrósio R Jr, Klyce SD, Wilson SE. Corneal topographic and pachymetric screening of keratorefractive patients. J Refract Surg. 2003;19:24-9.
2. Jonsson M, Behndig A. Pachymetric evaluation prior to laser in situ keratomileusis. J Cataract Refract Surg.
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3. Gromacki SJ, Barr JT. Central and peripheral corneal thickness in keratoconus and normal patient groups.
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4. Pflugfelder SC, Liu Z, Feuer W, Verm A. Corneal thickness indices discriminate between keratoconus and contact lens-induced corneal thinning. Ophthalmology. 2002;109:2336-41.
5. Gherghel D, Hosking SL, Mantry S, Banerjee S, Naroo SA, Shah S. Corneal pachymetry in normal and keratoconic eyes: Orbscan II versus ultrasound. J Cataract Refract Surg. 2004 Jun;30(6):1272-7.
6. Uçakhan OO, Ozkan M, Kanpolat A. Corneal thickness measurements in normal and keratoconic eyes:
Pentacam comprehensive eye scanner versus noncontact specular microscopy and ultrasound pachymetry. J Cataract Refract Surg. 2006 Jun;32(6):970-7.
7. Oh KT, Weil LJ, Oh DM, Mathers WD. Corneal thickness in Fuchs’ dystrophy with and without epithelial oedema. Eye. 1998;12 ( Pt 2):282-4.
8. Shah S, Chatterjee A, Mathai M, Kelly SP, Kwartz J, Henson D, McLeod D. Relationship between corneal thickness and measured intraocular pressure in a general ophthalmology clinic. Ophthalmology. 1999 Nov;106(11):2154-60.
9. Copt RP, Thomas R, Mermoud A. Corneal thickness in ocular hypertension, primary open-angle glaucoma, and normal tension glaucoma. Arch Ophthalmol. 1999 Jan;117(1):14-6.
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11. Ambrósio R Jr, Belin MW. Imaging of the cornea: topography vs tomography. J Refract Surg. 2010;26:847-9.
12. Maurice DM: The cornea and sclera. In Davison H, editors: The eye, 3 ed, Vol IB, Vegetative physiology and biochemistry, Orlando, 1984, Academic Press.
13. Luz A, Ursulio M, Castañeda D, Ambrósio R Jr. Corneal thickness progression from the thinnest point to the limbus: study based on a normal and a keratoconus population to create reference values. Arq Bras Oftalmol.
2006 Jul-Aug;69(4):579-83.
14. Ambrósio R Jr, Alonso RS, Luz A, Coca Velarde LG. Corneal-thickness spatial profile and corneal-volume distribution: tomographic indices to detect keratoconus. J Cataract Refract Surg. 2006 Nov;32(11):1851-9.
15. Mandell RB, Polse KA. Keratoconus: spatial variation of corneal thickness as a diagnostic test. Arch Ophthalmol.
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17. Avitabile T, Franco L, Ortisi E, Castiglione F, Pulvirenti M, Torrisi B, Castiglione F, Reibaldi A. Keratoconus staging: a computer-assisted ultrabiomicroscopic method compared with videokeratographic analysis. Cornea.
2004;23:655-60.
18. Randleman JB, Trattler WB, Stulting RD. Validation of the Ectasia Risk Score System for preoperative laser in situ keratomileusis screening. Am J Ophthalmol. 2008 May;145(5):813-8.
19. Randleman JB, Woodward M, Lynn MJ, Stulting RD. Risk assessment for ectasia after corneal refractive surgery.
Ophthalmology. 2008 Jan;115(1):37-50.
20. Ambrósio Jr R, Caiado ALC, Guerra FP, Louzada R, Roy AS, Luz A, Dupps WJ, Belin MW. Novel Pachymetric Parameters Based on Corneal Tomography for Diagnosing Keratoconus. J Refract Surg. 2011; in press 21. Ambrósio R Jr, Dawson DG, Salomão M, Guerra FP, Caiado AL, Belin MW. Corneal ectasia after LASIK despite
low preoperative risk: tomographic and biomechanical findings in the unoperated, stable, fellow eye. J Refract Surg. 2010;26:906-11.
22. Belin MW, Ambrosio R. Corneal Ectasia Risk Score System – “Statistical Validity and Clinical Relevance” J Refract Surg 2010; 26(4): 238 – 240.
The early detection of ectatic disease is of utmost importance to the refractive surgeon. Measurements such as aberrometry and curvature can be used in evaluating a patient for ectatic disease, but these are derivatives of elevation. With subclinical disease, anterior curvature alone may not provide enough information to detect an early corneal abnormality.1,2 The goal of the Belin / Ambrósio Enhanced Ectasia Display is to combine elevation and pachymetric derived corneal evaluation in an all inclusive display. This gives the computation of a complete pachymetric map.3-7 This chapter will concentrate on the use of the enhanced elevation map which makes up half of the Keratoconus / Ectasia detection display (Belin / Ambrósio Enhanced Ectasia Display III) available on the Oculus Pentacam (OCULUS Optikgeräte GmbH, Wetzlar, Germany). The other half, the pachymetric graphs and and the subtracted reference shapes commonly used (best-fit-sphere (BFS)), best-fit-ellipse, and the best-fit-toric ellipsoid) were first introduced by Belin in 1990 on the PAR CTS.8
Belin / Ambrósio Enhanced Ectasia Display III
Michael W. Belin, MD, FACS Renato Ambrósio Jr., MD, PhD Stephen S. Khachikian, MD