Evaluation of Long-Term Keratoconus Progression Using Scanning-Slit Topography
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Evaluation of Long-Term Keratoconus Progression Using Scanning-Slit TopographyFirst Author: 
David Galarreta, MDContributing Authors: Nestor Cortes, MD, Fernando Sanchez-Mannarelli, MD, Alejandro Portero, MD, Belen Carrasco, MD, Jesus Merayo-Lloves, MDHospital 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

Purpose Scanning-Slit Topography

  • To evaluate the long term changes and predictor factors of evolution in keratoconus using corneal elevation topography parameters measured by scanning-slit topography system

Methods Scanning-Slit Topography

  • 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.

Methods Scanning-Slit Topography

  • 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

Results Scanning-Slit Topography

  • 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 y1,94 (SD).

Results Scanning-Slit Topography

  • 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)

Results Scanning-Slit Topography

  • 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)

Results Scanning-Slit Topography

  • 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

Results Scanning-Slit Topography

  • 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)

Results Scanning-Slit Topography

  • 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)

Results Scanning-Slit Topography

  • 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)

Conclusions Scanning-Slit Topography

  • 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