The thickness of the human cornea as determined by a specular method

The thickness of the human cornea was measured by a simple accurate method which entails measurement of the distance between the anterior and the posterior corneal reflections when the cornea is illuminated at an angle. As compared to methods measuring the width of the optical section, the advantage of this method is that the end-points of measurement are clearly defined, providing a better basis for an exact estimation of the corneal thickness. The optical principle of this specular method is presented in a general form. The influence of physiological variation in corneal curvature and index of refraction is analysed and shown to cause an insignificant error on the standard thickness estimate. Using this method, the corneal thickness was measured in a random population sample of 115 normal subjects, aged 10-90 years. The corneal thickness was found to approximate a normal distribution with a mean value (+/- SD) of 0.515 mm (+/- 0.033). A significant decrease in corneal thickness with age of 0.0045 mm per decade was found.