Purpose To design a slit-lamp mountable spectrometer for the assessment of ophthalmic patients and to illustrate a potential clinical application by measuring the spectral characteristics of inflamed eyes of differing aetiologies.

Methods A slit lamp mountable instrument was designed and built, and methods for data analysis developed. Reflectance spectra were recorded from two patients with scleritis, three with non-scleritic red eyes and from two controls with non-inflamed eyes.

Results Measurements were reproducible and demonstrated statistically significant differences in the spectral characteristics between the three groups. Spectra from scleritic eyes revealed a relative increase in intensity of long wavelength red light, 650–740 nm, compared with non-scleritic red eyes. These longer wavelengths will be appreciated as dark red. There was no increase in relative intensity in the blue part of the spectrum in scleritic eyes.

Conclusions Reproducible measurements of the eye were made using an innovative, slit-lamp mountable spectrometer and its functionality demonstrated by differentiating the spectra from eyes with differing pathologies. While intending only to illustrate one potential application; for the cases examined, our results indicate that inflamed scleritic eyes exhibit a longer wavelength red light with no increase in shorter wavelength blue light. Thus our measurements would seem to confirm that the perceived redness of scleritis differs from other red eyes. However, it is a deeper darker red and not a bluish one as traditionally described.