Risk Factor Analysis of Topographic Progression in Keratoconus

1
Risk Factor Analysis of Topographic Progression
in Keratoconus

• Seong Joon Ahn, MD1,2, Mee Kum Kim MD, PhD1,2,
• Won Ryang Wee, MD, PhD1,2

1Department of Ophthalmology, Seoul National
University College of Medicine, Seoul,
Korea 2Laboratory of corneal regenerative
medicine and ocular immunology, Seoul Artificial
Eye Center, Seoul National University Hospital
Clinical Research Institute, Seoul, Korea
The authors have no financial interest in the
subject matter of this poster.
2
Introduction

• Keratoconus is a progressive noninflammatory
  disease of the cornea characterized by central
  stromal thinning that causes apical protrusion,
  irregular astigmatism, and decreased
• vision.
• In previous studies on keratoconus progression,
  the criteria of progression had been diverse.
• From the clinical progression which needed
  penetrating keratoplasty
• To several topographic indices such as parameters
  of corneal apex, thinnest point, and central
  point

3
Table. The criteria for keratoconus progression
in previous studies
Author Year Number of patients Mean age Follow-up period (months) Indices used for progression Proportion of progressed case
Sahin et al.1 2008 79 31.6 24 Radius, semimeridian, elevation, pachymetry, tangential curvature, mean spheric curvature at apex and thinnest/center point, SimK max, SimK min NS
Kang et al.2 2010 68 22.3 17.5 SimK max, SimK min, Astigmatism, anterior/posterior elevation, corneal thinnest/central pachymetry, anterior/ posterior best fit sphere value NS
Suzuki et al.3 2009 34 24.1 72 Regular astigmatism, asymmetry, and higher-order irregularity component in the central 3 mm zone. NS
Hwang et al.4 2010 107 eyes 24.5 22.6/20.5 Sim Kmax, Sim Kmin, apical power, astigmatic index, irregularity index, anterior elevation NS
Weed et al.5 2007 364 eyes 19/24 1004 days Progression to corneal graft surgery 4
Reeves et al.6 2005 131 eyes 37.1 NS Progression to penetrating keratoplasty 45
Li et al.7 2007 369 32/39 4.0/3.8 years Central K (CK), I-S, and KISA values NS
McMahon et al.8 2006 1032 38.9 8 years Flat K 24.1 (gt or 3.0D)
Oshika et al.9 2002 64 28.3 1 year Spherical component, regular astigmatism, decentration component, and higher order irregularity NS
Follow-up periods and mean ages were denoted as
those in lens-wearing or keratoconus group /
those in control group.
4
Purpose

• We intended to develop the criterion for
  topographic progression of keratoconus.
• By including many topographic parameters which
  were reported previously
• Using the criterion, all patients were classified
  into progressed or non-progressed cases.
• Subsequently, we performed risk factor analysis
  to explore associated factors with topographic
  progression.

5
Methods

• Retrospective study
• The patients who visited Seoul National
  University Hospital from May 2005 to July 2009
• Inclusion criteria
• Patients who underwent follow-up examinations for
  more than 2 yrs.
• In patients who underwent surgical treatment, the
  preoperative follow-up examinations were
  performed for more than 2 years.
• Orbscan II topography were performed more than
  twice.
• Exclusion criteria
• Any surgical treatment before the first visit
• Corneal topography was performed using Orbscan II
  (Bausch Lomb, Claremont, CA).
• In total, 211 eyes of 128 patients were included.

6
Methods

• Previously used 8 topographic indices suggesting
  progression in earlier studies
• Increase in
• Simulated K (SimK), astigmatism
• Irregularity index of 3 mm and 5 mm
• Anterior and posterior elevation
• Inferior minus superior (I-S value) asymmetry
• Decrease in
• Thinnest-point pachymetry
• The criterion for topographic progression
• Patient showing 5 progressed parameters
  compared to baseline examination
• This criterion has the greatest value of kappa
  with gold standard (progression to keratoplasty)
• Logistic analysis was performed to evaluate the
  risk factors associated with
• topographic progression.
• Age, sex, the age of diagnosis, the use and
  duration of contact lens, follow-up period,
  severity at initial visit, atopic disease,
  slit-lamp findings.
• Using Statistical Package for the Social Sciences
  (SPSS) Ver. 12.0

7
Results
Table. Comparision of clinical features and
treatment methods between patients with and
without progression
Clinical characteristics Progression (n94) No Progression (n117) p value
Sex (MF) 58.541.5 59.041.0 0.946
Age of diagnosis 22.23?5.65 24.65?7.87 0.049
Follow-up period (months) 43.1?12.4 40.7 ? 14.0 0.214
History of atopic disease 12 (12.7) 15 (12.8) 0.991
Severity of keratoconus 75433 65942 0.764
Treatment
Glasses prescription 10 (10.6) 11 (9.4) 0.781
Contact lens use 76 (80.9) 98 (83.8) 0.487
Keratoplasty 21 (22.3) 16 (13.8) 0.098
Slit lamp findings
Central PEE 25 (26.6) 33 (28.2) 0.795
Corneal opacity 15 (15.6) 29 (24.8) 0.126
P value was obtained by Chi-square test for
nominal or interval variables and Students t
test for continuous variables. Mean ? standard
deviation Mild (central K lt 45D) Moderate
(45 ? central K ? 52D ) Severe (central K gt 52D)
8
Results
Table. Comparison of topographic parameters at
baseline and follow-up examinations between
patients with and without progression
Index With progression With progression Without progression Without progression P value for change
Index Baseline Follow-up Baseline Follow-up P value for change
SimK max 50.0?4.7 52.1?5.4 52.1?6.1 51.1?5.0 lt0.001
Corneal astigmatism 3.9?2.6 5.1?2.8 5.2?3.4 4.2?2.6 lt0.001
Irregularity at 3mm 5.5?2.7 6.2?2.5 6.3?2.9 5.1?2.7 lt0.001
Irregularity at 5mm 6.2?3.2 6.5?2.6 7.1?3.2 6.0?2.8 lt0.001
Thinnest-point pachymetry 443?73 436?78.3 432?85 444?91.1 lt0.001
Anterior elevation 29.4?18.5 34.9?20.1 37.0?22.2 30.3?21.2 0.045
Posterior elevation 63.7?38.8 77.6?44.9 86.0?41.5 71.2?45.6 lt0.001
Inferior minus superior (I-S) index 6.0?3.6 7.0?4.2 7.1?3.8 4.5?3.3 lt0.001

• The change of a topographic parameter was
  calculated by subtraction of the value at
  baseline from that at the last follow-up.
• The value was compared between patients with
  and without progression using Students t test.
• Logistic analysis for risk factors of
  topographic progression
• Age of onset was the only risk factor for the
  progression
• OR 0.948 (95 confidence interval 0.907 -
  0.991), p value 0.010

9
Discussion

• This study developed the criterion which
  determines
• whether keratoconic eye is topographically
  progressed or not.
• Despite its clinical usefulness, there has been
  no trial to develop the
• criterion.
• Keratoconic eye have diverse changes in several
  topographic indices. If some patients show
  progressive changes in only a few indices but
  these indices were used for the criterion for
  keratoconus progression, bias can come.
• We used various (8) parameters to evaluate
  topographic progression in
• keratoconus.
• Progression in equal to or more than 5 parameters
  indicates generalized progressive changes in
  corneal topography.
• We set gold standard as progression to
  keratoplasty and the most
• agreeable criterion with gold standard was
  chosen.
• Thus, patients with topographic progression under
  our criterion may
• have greater chance of keratoplasty.

10
Discussion

• Under the criterion of topographic progression,
• younger age was discovered to be a risk
  factor of topographic progression.
• Age is a well-known risk factor of keratoconus
  progression.3,6,8
• Our study confirmed it, using a new criterion for
  topographic progression.

11
Summary

• Our study developed the criterion for topographic
  progression of keratoconus and suggests that
• younger age is a risk factor for the
  progression.
• In clinical practice,
• Clinicians can envisage the course of keratoconus
  in
• individual patients with patients age
• The decision on the surgical treatment can be
  supported using the criterion.

12
References

• 1. Sahin, A., N. Yildirim, et al. (2008).
  "Two-year interval changes in Orbscan II
  topography in eyes with keratoconus." J Cataract
  Refract Surg 34(8) 1295-1299.
• 2. Kang, Y. S., Y. K. Park, et al. (2010). "The
  effect of the YK lens in keratoconus." Ophthalmic
  Physiol Opt 30(3) 267-273.
• 3. Shirayama-Suzuki, M., S. Amano, et al. (2009).
  "Longitudinal analysis of corneal topography in
  suspected keratoconus." Br J Ophthalmol 93(6)
  815-819.
• 4. Hwang, J. S., J. H. Lee, et al. (2010).
  "Effects of multicurve RGP contact lens use on
  topographic changes in keratoconus." Korean J
  Ophthalmol 24(4) 201-206.
• 5. Weed, K. H., C. J. Macewen, et al. (2007).
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  correction." Ophthalmic Physiol Opt 27(6)
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• 6. Reeves, S. W., S. Stinnett, et al. (2005).
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  keratoplasty in patients with keratoconus." Am J
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• 7. Li, X., H. Yang, et al. (2007). "Longitudinal
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  85(4) 502-507.
• 8. McMahon, T. T., T. B. Edrington, et al.
  (2006). "Longitudinal changes in corneal
  curvature in keratoconus." Cornea 25(3) 296-305.
• 9. Oshika, T., T. Tanabe, et al. (2002).
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  analysis of videokeratography data."
  Ophthalmology 109(2) 339-342.