Optical properties of the human cornea : Shape and wave aberration measurements using the VU topographer and Scheimpflug photography

Abstract

In this study, the optical properties of the human cornea was investigated. Two major developments were made because current measurement techniques need improvement First, the VU topographer, which uses a color coded pattern, was validated with real eye data showing better performance compare to commercial ring topographers particularly in reconstructing the non-rotation symmetric features of the anterior corneal surface. For example, ring topographers underestimate astigmatism of the anterior corneal surface by 4%. This underestimation increases with complexity of the surface. The astigmatism underestimation was found to be 13% for a post radially-keratotomized cornea. Second, the aberration contribution of the posterior surface was revealed using Scheimpflug photography. Results show that the contribution of the posterior surface to corneal coma aberration is negligible. On the other hand, on average the posterior surface decreases corneal astigmatism by 31%. Also the contribution of the posterior surface to the spherical aberration of the cornea increase with age reaching up to 15% at age 65. Thus, measurement of the posterior surface is necessary to specify corneal astigmatism and spherical aberration accurately. The methods introduced in this study are useful for applications in laser refractive surgery, contact lens fitting and studies on wave aberration of the eye because it reveals the optical properties of the cornea more accurately.Heethaar, R.M. [Promotor]Heijde, G.L. van der [Copromotor]Berg, T.J.T.P. van den [Copromotor