Figure 1.  .

Optical system for combined fluorescence and tear film thickness measurements. Tungsten filament sources are used. The long pass filter of the spectral interferometer passes wavelengths above 630 nm, whereas the excitation filter for fluorescence passes wavelengths from 455 to 495 nm. The spectrophotometer covers the wavelength range 450 to 1050 nm and so records spectral oscillations (for tear thickness) at longer wavelengths, fluorescence in a middle spectral range (approximately 500–600 nm) and excitation light scattered from the cornea at shorter wavelengths (455–495 nm). Details of the eye alignment system are given by Nichols et al.²⁶