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To compare changes in human corneal thickness after the instillation of proparacaine with those after oxybuprocaine instillation with time over a period of 10 minutes.Eighteen healthy young participants were recruited. Proparacaine was used in the right eye and oxybuprocaine in the left. Right and left baseline corneal thicknesses were measured every 30 seconds for 10 minutes using a noncontact specular microscope by 1 observer. Baseline corneal thickness was defined as the average of all values taken over 10 minutes. Changes in corneal thickness were measured every 20 seconds for 10 minutes after the administration of 1 drop of 0.5% proparacaine onto the right cornea and 1 drop of 0.4% oxybuprocaine onto the left cornea.Mean baseline right cornea thickness was 531 ± 45 μm, and that of the left cornea was 531 ± 42 μm. The corneal thickness after proparacaine increased by 8.6 μm (∼4.5-12.6 μm, 95% CI) and then returned to baseline within 80 seconds. Corneal thickness after applying oxybuprocaine increased by 7.7 μm (3.6-11.2 μm, 95% CI) and then returned to baseline within 80 seconds. There was a second transient increase about 5 minutes later after proparacaine instillation but no additional transient increase after oxybuprocaine instillation.Oxybuprocaine is similar to proparacaine in terms of the severity of its effect on corneal thickness. Corneal thickness instability may occur for 5 minutes after proparacaine administration. Changes in corneal thickness after topical anesthetic instillation should be considered when performing measurements for refractive surgery or central corneal thickness in glaucoma patients.