1. Evaluating Post Laser Refractive Surgery Corneal Thickness Using Artemis-2 Very High Frequency Arc-Scanning Ultrasonography Versus Pentacam * † Sharon T. Wong, OD, PhD; * † Alethea E. Law, OD; * § Hugo F. Sutton, MD; * † Eric Pharand, OD; * § Allan Cheung BSc; *William Threlfall, MSc; *Francis Jean, OD. Institution: IRIS Ophthalmology Clinic Address: 8948-202 Street, Langley, British Columbia, Canada V1M 4A7. * These authors are affiliated with IRIS, The Visual Group, British Columbia, Canada. † These authors are affiliated with Pacific University College of Optometry, Oregon, USA. § These authors have financial interest in Artemis-2 technology.

2. Study Objectives (1) Retrospective comparison of imaging technologies for estimating pre/post laser refractive surgery corneal thickness using ultrasound vs light-based pachymetry. (2) Pre/post-op in vivo comparison of central vs peripheral epithelial thickness using Artemis- 2 ultrasonography. IRIS Ophthalmology Clinic

3. Equipment Artemis-2 ® (A-2) ultrasound (50 MHz at 8 meridians, Ultralink). Sonogage ® pachymeter (50 MHz, CorneoGagePlus, EyeScan). Pentacam ® topography (Oculus). IRIS Ophthalmology Clinic

4. Patient Selection Healthy laser refractive surgery candidates. >18 years old. No significant corneal pathology. Myopes with spherical equivalent: –1.00 to –10.00D No previous ocular surgery. IRIS Ophthalmology Clinic

5. Methods Sample population: Central and peripheral corneal thickness of myopic eyes (n=125) treated by laser refractive surgery were analyzed pre and post-operatively by paired 2-sample t-test. Myopes (spherical equivalent): Low (-1.00 to -4.00D) n=58 Moderate (-4.25 to -6.00D) n=32 High (-6.25 to -10.00D) n=35 IRIS Ophthalmology Clinic

6. Pre-Op Results: Ultrasound vs Pentacam Central corneal thickness: Pentacam 531.8 ± 3.2 μm A-2 530.2 ± 3.3 μm Sonogage 539.8 ± 3.3 μm No significant difference between Pentacam and A-2 on virgin eyes. Sonogage measurements overestimated corneal thickness. IRIS Ophthalmology Clinic

7. Post-Op Results: Ultrasound vs Pentacam Central corneal thickness Pentacam 476.9 ± 4.0 μm A-2 486.6 ± 3.8 μm A-2 corneal measurements were significantly thicker (mean 9.2  m) than Pentacam measurements (p<0.0001). IRIS Ophthalmology Clinic

8. Artemis-2 Results: Pre vs Post-Op Corneal Epithelium Post-op corneal epithelium was 22.6 μm thicker compared to pre-op values: Pre-op mean 38.5 μm Post-op mean 61.1 μm This post-op epithelial thickening was evenly distributed across the central and peripheral corneal zones. IRIS Ophthalmology Clinic

9. Artemis-2 Results: Epithelial Thickness vs Refraction However, moderate to high myopes showed significantly greater post-op epithelial thickening compared to low myopes (p<0.0001). Myopian Post-Op Thickening (µm) Low58+18.81 Moderate32+27.72 High35+24.07 IRIS Ophthalmology Clinic

10. Discussion After laser refractive surgery, A-2 ultrasound technology measures corneal thickness more accurately than light-based Pentacam technology. A-2 is currently the only ultrasound-based instrument available to measure in vivo corneal epithelial thickness. IRIS Ophthalmology Clinic

11. Discussion Sonogage overestimates corneal thickness. Pentacam underestimates post-op corneal thickness compared to ultrasound technology. This provides an increased safety margin when planning retreatment surgeries. IRIS Ophthalmology Clinic

12. References Reinstein et al. (2008). Epithelial thickness in the normal corneal: Three-dimensional display with very high frequency ultrasound. J Refract Surg 24(6): 571-581. Reinstein et al. (manuscript in preparation): Epithelial thickness profile changes induced by myopic LASIK as measured by Artemis very high-frequency digital ultrasound. IRIS Ophthalmology Clinic