1. Naomi R. Goldberg, MD PhD Kenneth J. Wolf, MD Eric J. Wolf, MD FACS The authors have no financial interest in the subject matter of this poster. Comparison of central corneal thickness measurements from contact ultrasound pachymetry and non-contact specular microscopy

2. Purpose: To assess the relationship of central corneal thickness (CCT) measurements taken from the non-contact Tomey EM3000 Specular Microscope system to those measured by ultrasound (US), the current standard for pachymetry.

3. Background: Central corneal thickness measurements are important factors in multiple ophthalmic evaluations. Intraocular pressure measurements made by applanation tonomety are overestimated in thicker corneas and underestimated in thinner corneas. Preoperative central corneal thickness is used to determine the residual stromal bed following laser vision correction to insure a stromal bed that is sufficient to prevent postoperative ectasia.

4. Methods: One specular microscope scan, followed by three ultrasonic measurements of seventy-six eyes from thirty- eight patients were recorded. Corneas were anesthetised with topical proparacaine before performing the contact pachymetry. Ultrasonic measurements were performed using the Accutome AccuPach V and specular microscopy measurements were made using the Tomey EM3000 Specular Microscope. All patients had not used contact lenses for at least 24 hours prior to evaluation.

5. Instruments: Tomey EM 3000 Accutome AccuPach V

6. Results:

7. Correlation between individual measurements of CCT from Ultrasound Pachymetry and Specular Microscopy

8. Distribution of difference between CCT measured by ultrasound (US) pachymeter and Tomey Specular Miscroscope vs. their average

9. Sub-group analysis, using mean Ultrasound CCT as cutoff

10. Conclusions: There exists a strong correlation between corneal thickness measurements made using contact ultrasound pachymetry and non-contact specular microscopy. The correlation is stronger with thinner corneas and weaker with thicker corneas. Non-contact modalities for determining central corneal thickness may be appropriate for pachymetry for glaucoma evaluations and possibly for laser vision correction evaluations, though the latter requires a more exact measurement and may benefit from multiple measurements.