Risk Factor Analysis of Topographic Progression in Risk Factor Analysis of Topographic Progression in KeratoconusKeratoconus

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, Korea2Laboratory 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.

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

IntroductionIntroduction

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% (> or = 3.0D)

Oshika et al.9 2002 64 28.3 ≥1 year Spherical component, regular astigmatism, decentration

component, and higher order irregularity

NS

TableTable. The criteria for keratoconus progression in previous studies. The criteria for keratoconus progression in previous studies

* Follow-up periods and mean ages were denoted as those in lens-wearing or keratoconus group / those in control group.

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.

PurposePurpose

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.

MethodsMethods

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

MethodsMethods

Clinical characteristics Progression (n=94) No Progression (n=117) p value*

Sex (M:F) 58.5%:41.5% 59.0%:41.0% 0.946

Age of diagnosis 22.235.65† 24.657.87 0.049

Follow-up period (months) 43.112.4 40.7 14.0 0.214

History of atopic disease 12 (12.7%) 15 (12.8%) 0.991

Severity of keratoconus 7:54:33‡ 6:59:42 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

ResultsResultsTable. Comparision of clinical features and treatment methods between patients with and without progression

* P value was obtained by Chi-square test for nominal or interval variables and Student’s t test for continuous variables. † Mean standard deviation ‡ Mild (central K < 45D) : Moderate (45 central K 52D ) : Severe (central K > 52D)

IndexWith progression Without progression

P value for change*Baseline Follow-up Baseline Follow-up

SimK max 50.04.7 52.15.4 52.16.1 51.15.0 <0.001

Corneal astigmatism 3.92.6 5.12.8 5.23.4 4.22.6 <0.001

Irregularity at 3mm 5.52.7 6.22.5 6.32.9 5.12.7 <0.001

Irregularity at 5mm 6.23.2 6.52.6 7.13.2 6.02.8 <0.001

Thinnest-point pachymetry 44373 43678.3 43285 44491.1 <0.001

Anterior elevation 29.418.5 34.920.1 37.022.2 30.321.2 0.045

Posterior elevation 63.738.8 77.644.9 86.041.5 71.245.6 <0.001

Inferior minus superior

(I-S) index6.03.6 7.04.2 7.13.8 4.53.3 <0.001

ResultsResultsTable. Comparison of topographic parameters at baseline and follow-up examinations between patients with and without progression

*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 Student’s 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

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.

DiscussionDiscussion

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.

DiscussionDiscussion

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.

SummarySummary

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). "The Dundee University Scottish Keratoconus Study II: a prospective study of optical and surgical correction." Ophthalmic Physiol Opt 27(6): 561-567.

6. Reeves, S. W., S. Stinnett, et al. (2005). "Risk factors for progression to penetrating keratoplasty in patients with keratoconus." Am J Ophthalmol 140(4): 607-611.

7. Li, X., H. Yang, et al. (2007). "Longitudinal study of keratoconus progression." Exp Eye Res 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). "Progression of keratoconus assessed by fourier analysis of videokeratography data." Ophthalmology 109(2): 339-342.

ReferencesReferences