New diagnostic methods for imaging the anterior segment of the eye to enable treatment modalities selection

New diagnostic instruments for imaging the anterior segment of the eye have been developed using the corneal topographer, wavefront sensor, and anterior segment optical coherence tomography (OCT). Data obtained from these instruments can be used to choose treatment modalities by providing information that is complementary to slit-lamp examination and visual acuity measurements. Zernike vector analysis was used to evaluate the corneal higher-order aberrations to quantify the effects of the corneal shape on the optical quality of the eye. The analyses showed the optical characteristics of the anterior and posterior surfaces of the cornea in patients with keratoconus or pellucid marginal corneal degeneration. The association between the deterioration of optical quality during rigid gas-permeable contact lens wear in patients with keratoconus and the residual coma due to posterior corneal shape was suggested by the findings made with this method. Zernike vector analyses also revealed the differences in the ocular higher-order aberrations between conventional Laser in situ keratomileusis (LASIK) and custom LASIK. Serial measurements of the ocular higher-order aberrations by a wavefront sensor enabled us to evaluate the effects of tear fluid dynamics on the optical quality of the eye. The findings clarified the characteristics of serial alterations of higher-order aberrations in normal eyes, dry eye with tear deficiency and dry eye with tear evaporation. The effects of internal lubricating agents on the soft contact lenses were also evaluated objectively. In addition, these results suggest that the effects of serial fluctuations in the ocular higher-order aberrations on refractive surgery should be considered. To observe the cornea at the cellular level with anterior segment OCT, a prototype machine of full-field OCT was developed. This made it possible to show epithelial edema in human donor corneas as well as the alterations in the epithelial layer and stromal layer associated with intraocular pressure elevation in ex vivo porcine eyes. An OCT-based corneal topographer was developed using a three-dimensional anterior segment OCT with the swept-source principle. Corneal topographic analyses of the anterior and posterior surfaces either in eyes with keratoconus or following keratoplasty was possible even in where it was difficult for conventional corneal topographers to analyze accurately. Also, OCT-based corneal topographer analyzed the host and donor cornea separately following Descemet stripping automated endothelial keratoplasty by recognizing the host-graft interface. The results from these new diagnostic methods for imaging the anterior segment of eye will be useful for the diagnosis of corneal disorders and the planning of treatment by evaluating the effects of corneal topographic abnormalities and tear fluid dynamics on visual function, by observing the abnormalities of the corneal tissue at the cellular level, and by showing corneal topography in diseased corneas more accurately and non-invasively.