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Evaluation of Long-Term Keratoconus Progression Using Scanning-Slit Topography First Author: David Galarreta, MD Contributing Authors: Nestor Cortes, MD, Fernando Sanchez- Mannarelli, MD, Alejandro Portero, MD, Belen Carrasco, MD, Jesus Merayo-Lloves, MD Hospital Clinico Universitario Valladolid (Spain) IOBA. Universidad de Valladolid (Spain) The authors have no financial interest in the subject matter of this poster VI World Cornea Congress, Boston 7-9th April 2010
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Purpose To evaluate the long term changes and predictor factors of evolution in keratoconus using corneal elevation topography parameters measured by scanning-slit topography system
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Methods Retrospective study Ninety three eyes from 52 keratoconic patients were evaluated by scanning-slit topography system. Diagnosed by slit lamp findings and by corneal topography Minimum follow up of 3 years was required with topography examinations at least twice. Tenets of the Declaration of Helsinki were followed and local medical ethics comitee approved the study.
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Methods Age at onset and at analysis Sex Quantitative topographic parameters analyzed Keratoconus topographical pattern Minimum mean simulated keratometry (minSimK) Maximum mean simulated keratometry (maxSimK) Maximum keratometry reading (Kmax) Posterior and anterior best-fit sphere (BFS) Posterior/Anterior BFS ratio (P/A BFS) Thinnest and central pachymetry point
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Results Age 26,46 years 9,51 (SD) at onset (diagnosis). 39,12 years 10,4 (SD) at analysis. Sex: 53,84% male Follow up: 3,91 y1,94 (SD). Topographical patternsCasesPercentage Asymmetric bow tie with skewed radial axis (ABT/SRAX) 2425,8% Asimetric bow tie inferior77,5% Asimetric bow tie superior66,5% Central nipple99,7% Central oval11,1% Inferior steepening3335,5% Irregular11,1% Pellucid like88,6% Simmetric bow tie22,2% Simmetric bow tie with skewed radial axis22,2% Total93100%
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Results Whole keratoconus group (n=93) MaxSimK: 49,63D to 50,40D (p=0,006) MinSimK: 44,94D to 45,94D (p<0,001) ABT/SRAX pattern group (n=24) Posterior BFS: 54,06D to 54,62D (p=0,042) MaxSimK:48,55D to 49,47D (p=0,01) MinSimK: 43,67 to 45D (p=0,01) Kmax: 51,66D to 52,46D (p=0,03) Inferior steeping pattern group (n=33) Anterior BFS: 43,87D to 44,42D (p=0,004) Posterior BFS: 54,59D to 55,41D (p=0,006) MinSimK: 45,12D to 46,14D (p=0,017) Kmax: 53,24D to 54,99D (p=0,006) No changes detected in other patterns (low n bias)
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Results Age at onset (percentile 50th= 31,26 years) Younger patients (<31,26 years) MaxSimK: 50,05D to 51,23D (p=0,022) MinSimK: 44,83D to 46,48D (p<0,001) Posterior BFS: 54,86D to 55,70D (p=0,002) Kmax: 53,52D to 55,45D (p<0,001) No changes detected in older patients (p>0,05)
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Results Kmax groups <47D MaxSimK: 45,16D to 46,35D (p=0,04) 47D-50D Posterior BFS: 54,23D to 55,01D (p=0,011) MinSimK: 43,78D to 44,78D (p=0,028) 50D-53D MaxSimK: 51,15D to 52,22D (p=0,025) MinSimK: 46 to 47,56D (p=0,012) >53D: Showed no pregression Nor difference in age at onset nor at follow up
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Results Thinnest pachymetry (p50th=432 microns) Thinner pachymetry (<432 microns) MaxSimK: 51,37D to 52,06D (p=0,02) MinSimK: 46,6D to 47,9D (p<0,001) Thicker pachymetry (>433 microns) Anterior BFS: 43,4D to 43,87D (p<0,001) Posterior BFS: 52,82D to 53,66D (p<0,001) Central pachymetry: 501 microns to 493 microns (p=0,016) Thinnest pachymetry: 480,6 microns to 470,7 microns (p=0,019) MaxSimK 47,88D to 48,78D (p=0,021)
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Results Posterior BFS (p50th=54,5D) <54,5D Posterior BFS: 52,22D to 52,74D (p=0,013) Central Pachymetry: 481 microns to 476 microns (p=0,04) MaxSimK: 46,9D to 47,83D (p=0,027) MinSimK: 43D to 43,69D (p=0,038) >54,5D MinSimK 46,96D to 48,28D (p<0,001)
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Results Posterior/Anterior BFS (p50th=1,24) <1,24 Posterior BFS: 52,89D to 53,37D (p=0,002) Central Pachymetry: 481 microns to 473 microns (p=0,022) Thinnest pachymetry: 460 microns to 451 microns (p=0,021) MaxSimK: 48D to 48,8D (p=0,04) Posterior/anterior BFS: 1,20 to 1,21 (p=0,03) >1,24 MinSimK 46,1D to 47,39D (p<0,001)
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Conclusions Younger age at onset increased the probability of progression of topographical parameters in keratoconus. Topographical patterns of keratoconus (Asymmetric bow tie with skewed radial axis and inferior steepeninig) provide information about a higher risk of progression. Very high K readings, thinner corneas, high power in posterior BFS,and high posterior/anterior BFS showed less progression of keratoconus topographical parameters. These variables normally correlates with an advanced keratoconus. Low K readings, thicker corneas, low power in posterior BFS, and low posterior/anterior BFS can potentially showed a wide margin for advance in keratoconus
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