Mean Keratometry Measurement Post Penetrating Keratoplasty

Jacky Yeung MSc MD, Stephanie Baxter MD FRCS(C)

Department of Ophthalmology, Hotel Dieu Hospital, Queen’s University, Kingston

Authors have no financial interest

Achieving Surgical Success Post PKP

Goals of Penetrating Keratoplasty:

Anatomical Success and Visual Success Factors affecting visual success:

1) Irregular Astigmatism

- Treated with Selective Suture Removal (SSR) - guided by visual acuity (VA), refraction, manual keratometry, topography

2) Lens opacity post PKP

- Cataract formation, 1 in 4 PKP pts in 1 yr post-op1

1) Rathi et al. J Cataract Refract Surg. 1997 May;23(4):562-4

Dilemma: Post PKP Pt with Cataract

No longer able to use VA as a useful end-point to assist in SSR because of the cataract

Keratometry may not be stable enough for accurate IOL calculations to do cataract surgery

“What to do first: cataract surgery or SSR?”

Achieving Surgical Success Post PKP

Study Objective

To determine the extent that Selective Suture Removal (SSR) has on the mean corneal curvature (average K) post PKP

Experimental Methods

Design - Retrospective case series Approval by Queen’s Univ. Research Ethics Board

Patients PKP patients from 2004 to 2007 Inclusion : ≥18 yo, central round pk, 16 Interrupted

suture technique , ≥1 yr FU Exclusion : graft rejection, subsequent ocular sx, no

suture removal, incomplete data

Experimental Methods

Main outcome measure: Average manual keratometry readings at 4 time

points – 2-4, 5-7, 8-10 and 11-13 mo after SSR

Statistical analysis Paired samples t-test for comparing keratometry (K)

between time points Repeated measures ANOVA

Results - Demographics Mean age = 64.5 ± 18.8 yrs, M = 25, F = 27 Patient excluded - if no suture removal

N = 52 (2-4 mo), 41 (5-7 mo), 29 (8-10 mo), 21 (11-13 mo)

Reasons for PKP # %

PBK 23 44.23Failed PKP 11 21.15Keratoconus 5 9.62K scar 4 7.69K ectasia 2 3.85Fuchs 2 3.85Others 5 9.62 Total 52 100.00

Paired Student’s t-test comparisons Comparisons to the 2-4 month point (baseline, D±SE)

Comparisons of each measurement to its previous time point

Overall, no statistical difference in K change over time

Results

2-4 vs 5-7N=41

2-4 vs 8-10N= 29

2-4 vs 11-13N= 21

Mean Difference -0.270 ±0.162 -0.420±0.314 -0.419±0.302

P value 0.104 0.192 0.182

2-4 vs 5-7N=41

5-7 vs 8-10N=29

8-10 vs 11-13N= 20

Mean Difference -0.270±0.162 -0.162±0.262 -0.213±0.338

P value 0.104 0.543 0.538

Results Repeated measures ANOVA

SSR – at ANY time point after 2 to 4 mo., N=36

Descriptive Statistics

  Mean difference Std. DeviationK 2 to 4 43.77 0 2.13

K 5 to 7 44.16 -0.39 2.21

K 8 to 10 44.07 -0.30 1.85

K 11 to 13 44.61 -0.84 2.31

Tests of Within-Subjects Effects

P value 0.022

Overall, the difference in average K post PKP w/ SSR is < 0.4 to 0.8 D, with an average standard deviation of ~2D.

This suggest statistical, but minimal clinical significance.

Discussion

CE/PCIOL post-PKP Sequential / Staged procedure has

Better visual outcomes than Combined procedure2

Sequential procedure also safe3

Traditionally - approx. 1 year after PKP

Early cataract surgery post-PKP Potentially reduce visual rehab time Corneal wounds stability – stable by 3 mo5

Spherical equivalent – stable by 6 mo6

2) Shimmura et al. Cornea. 2003 22(3):234-8 3) Nagra et al. Cornea. 2004 23(4):377-9 4) Geggel H. Refract Corneal Surg. 1990 6(1):55-8 5) Hayashi et al. Am J Ophthalmol. 2006 141(2):241-247

Discussion Early cataract surgery post PKP

Current study:Avg. Ks measured at early time points post PKP

1) Appear to be stable 2) This may facilitate IOL power calculations that are clinically acceptable during early post-op PKP period

Study limitations:

Retrospective design, small sample size, applicability to other suture techniques, manual keratometry measurements used vs. automated (IOL master, topographic)

Conclusion

1. The average K post PKP does not seem to vary significantly with SSR

2. The average Ks can be used at any point 3 months post PKP for IOL power calculation in patients needing cataract surgery

3. If necessary, further SSR post cataract surgery should have little effect on the refractive outcome

4. Consider earlier cataract surgery for earlier visual recovery in post