Cellular microstructure observed by scanning transmission electron microscopy (STEM) was analysed using Fourier methods. Fourier components of the density fluctuations in the sclera and the cornea of the human eye were quantified. The results show that the Fourier components responsible for the opacity of the sclera have sizes of the order of the wavelength of visible light. In the sclera, approximately 54% of the spectral energy of the density fluctuation falls in the range of 200-1100 nm (scattering range). In the cornea, approximately 24% of the total spectral energy falls in this range. The predominant Fourier components of the density fluctuations in the opaque sclera are approximately 300 nm in wavelength, whereas those of the transparent cornea are approximately 80 nm in wavelength. This method will be useful in quantitative analysis of microstructural changes accompanying biological phenomena such as normal development of transparency in the human lens, and abnormal loss of transparency during cataract formation.