Determination of corneal phase and group refractive indices in situ and dispersion ex vivo using a hybrid spectral-domain OCT and confocal scanning system.

SIGNIFICANCE: Precise determination of corneal refractive indices is essential for accurate refractive power calculations, personalized refractive surgery planning, and glaucoma management. However, current clinical methods fail to distinguish between the group refractive index ( n g ) for thickness quantification and the phase refractive index ( n p ) for optical power calculations, often relying on population-averaged constants that mask individual heterogeneity.

AIM: We aim to develop a multimodal measurement system integrating spectral-domain optical coherence tomography (SD-OCT) and confocal scanning for the precise extraction of the n g , n p , and dispersion coefficients of corneal tissues.

APPROACH: A dual-modality platform sharing an 860 nm source was constructed to jointly capture the optical path length (OPL) and confocal distance. A two-step progressive workflow was implemented: first, the n g and thickness were independently determined via the OPL method to serve as target ground truths for extracting tissue-specific dispersion through iterative optimization; second, these quantified priors were utilized to jointly decouple the in situ n g , n p , and thickness of intact corneas.

RESULTS: System validation using optical window plates yielded a relative error of only 0.01% to 0.09% for n g and 0.17% to 5.74% for dispersion coefficients. For biological tissues, we report the first direct experimental measurement of phase dispersion for human lenticules ( - 0.014468 ± 0.004060    μ m - 1 ) and porcine sections ( - 0.010223 ± 0.002811    μ m - 1 ), where the human data showed high consistency with the theoretical Cauchy model ( - 0.014186    μ m - 1 ). Utilizing these priors, the system successfully decoupled the in situ parameters of whole porcine eyes, yielding n g of 1.3845 ± 0.0006 and an n p of 1.3757 ± 0.0006 .

CONCLUSIONS: This technique successfully resolves the n g and n p decoupling challenge in corneal tissues, overcoming the limitations of relying on a single equivalent refractive index. By utilizing an empirically measured corneal dispersion coefficient as a mathematical constraint, the system enables the nondestructive decoupling of physical thickness, as well as phase and group refractive indices in situ. This breakthrough provides essential physical parameters to enhance clinical pachymetry precision and optimize personalized refractive surgery protocols.