• Repeatability and reproducibility of corneal thickness measurement [ Time Frame: 3 months ] [ Designated as safety issue: No ]
  

• Comparing central corneal thickness measurement among FD-OCT, ORA, and USP [ Time Frame: 3 months ] [ Designated as safety issue: No ]
  

Corneal thickness measurements are clinically important. Variation in corneal thickness affects the accuracy of applanation tonometry. A meta-analysis by Doughty and Zaman showed that a 10% change in central corneal thickness may result in an approximately 3.4-mmHg change in intraocular pressure.1 Accuracy of corneal thickness measurement is also important in considering eligibility for refractive surgery, and the amount of correction that can safely be performed. Underestimation of corneal thickness may lead to eligible patients being excluded for primary or enhancement refractive procedures. Overestimation may lead to over-ablation and inadvertent thinning of the stroma, thereby increasing the risk of iatrogenic keratectasia. Hence, studies assessing corneal thickness measurements by various instruments are of high clinical relevance.2-9 Fourier domain optical coherence tomography (FD-OCT, OptoVue, U.S.A), Confoscan 4 (CS-4, Nidek, USA) and ocular response analyzer (ORA, Reichert, USA) are non-invasive medical devices that have recently received FDA approval for measurement of the cornea thickness. However, the repeatability and reproducibility of these instruments remains unproven in the clinical settings. To our knowledge, this is the first study to describe agreement, repeatability and reproducibility in corneal pachymetric mapping between FD-OCT, ORA, CS-4 and conventional ultrasound (US), which has been the current reference corneal pachymetric mapping system for the majority of refractive surgeons.