The role of altered ciliary muscle morphology in refractive error and accommodative function

Abstract

The primary theme of this thesis was to investigate in vivo ciliary muscle morphology in refractive error, and how ciliary muscle parameters are linked with accommodative function in a young adult population. Anterior segment optical coherence tomography was utilised for all ciliary muscle image acquisition to examine morphological differences between eyes. High levels of inter-ocular ciliary muscle symmetry were shown in emmetropes and myopes. Whilst the myopic ciliary muscle was longer and thicker than in emmetropes for both eyes, ciliary muscle length and thickness were linked with axial length in both cohorts. In amblyopes and anisometropes, high levels of inter-eye ciliary muscle symmetry were observed. The ciliary muscle in amblyopic eyes appear to grow in accordance with the axial length of the non-amblyopic eye (P = 0.022, r2 = 0.438). The possibility of diurnal variation in accommodative axial elongation and accommodative error was explored in emmetropes and myopes. Daily stability in these accommodative functions were shown, and between groups there was no difference in accommodative axial elongation (P = 0.884) or accommodative error (P = 0.098). It was demonstrated that ciliary muscle morphology is not linked with accommodative function, disputing the theory that the thickened ciliary muscle has reduced contractility, which initiates hyperopic defocus in myopigenesis. In emmetropes, males had significantly longer ciliary muscle lengths (P = 0.031) and axial length (P = 0.001) compared with females. Novel parameters to analyse the ciliary muscle were investigated; both inner apical angle and ciliary muscle cross-sectional area measures were linked to axial length, as were the area and apical angle. Both measures are highly effective ciliary muscle analysis parameters which demonstrated high repeatability. The studies detailed demonstrated normal ciliary muscle growth with ocular development in myopia, and indicated that the ciliary muscle is not a crucial causative myopigenesis factor.