Theoretical Background to Correct Intraocular Pressure After LASIK

Abstract

Abstract: : Purpose: To elucidate the reason why differences in corneal curvature can be ignored to correct intraocular pressure (IOP) after laser in situ keratomileusisL(ASIK) for myopia Methods: Equations were theoretically drawn to clarify relationships among parameters such as original corneal curvature R₀, central deflection of corneal sphere (δ), corneal thickness t, and changes in the IOP (Δ IOP). Results: After the LASIK for myopia, anterior corneal surface and posterior corneal surface are not parallel, thus, Imbert-Fick law cannot be applied. An equation for central deflection: δ=A(µ)*R₀ P/t²*√(1-ν²)/E was useful to know relationship between the R_0, δ and Δ IOP. Where A(µ) is a function of the corneal radius and thickness, t; corneal thickness, ν; Poisson's ratio, E; Young modulus.As the cornea becomes flatter, the δ becomes smaller. In spite of this, theoretically calculated Δ IOP was nearly constant at different setting of the R₀. Conclusions: An effect of differences in corneal curvature R₀ on Δ IOP was theoretically drawn. Following the theory, effect of the differences in corneal curvature on the Δ IOP was minimal. On the otherhand, ablated thickness of the central cornea was an important parameter to correct post LASIK IOP.  

Keywords: intraocular pressure • refractive surgery • myopia