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S. R. Uhlhorn, D. Borja, F. Manns, J.-M. Parel; Measurement of the Equatorial Profile of the Average Refractive Index of the Isolated Crystalline Lens Using Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5789. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To determine if there is a significant variation in the equatorial profile of the average refractive index of the human crystalline lens.
A Human crystalline lens was isolated from whole cadaver globes (age = 51 years, post-mortem time <4 days) and placed in a preservation media-filled chamber resting on a soft rubber ring. Cross-sectional images of the isolated lens was recorded with an optical coherence tomography system. From the recorded image, the average refractive index is calculated along each A-line in the image by measuring the optical thickness of the lens and the apparent location of the sample chamber window, which is determined by the refractive index of the lens. These 2 parameters are used to calculate the thickness and group refractive index of the lens as a function of lateral position at the light source wavelength (825nm). The average group refractive index is first converted to the phase refractive index at 825 nm and then to the phase refractive index at 589 nm using lens dispersion data from the literature. The measured index from each A-line is then analyzed as a function of lateral position to determine he equatorial profile of the average refractive index.
Over the central 3mm of the lens axis, the average refractive index is nearly constant (n = 1.415 +/- 0.001) for the 51 year old lens analyzed.
The nearly constant refractive index profile measured with the optical coherence tomography system is consistent with MRI measurements of the lens index gradient and the index plateau model for a presbyopic lens. This suggests that optical coherence tomography can be successfully used to accurately measure lens surface curvatures since the effect of the index gradient on the OCT imaging is nearly constant.Support: NIH R01 EY14225, F32 EY15362 (Kirschstein NRSA Fellowship, SRU), F31 EY15395 (Kirschstein NRSA Fellowship, DB); the Australian Federal Government CRC Scheme through the Vision Cooperative Research Centre; Dr Rakhi Jain, AMO, Santa Clara, CA; Florida Lions Eye Bank; NIH P30 EY14801 Center Grant; an unrestricted grant from Research to Prevent Blindness; Henri and Flore Lesieur Foundation (JMP).
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