Image analysis and glare sensitivity in human age-related cataracts

A new glare disability test and a diagnostic instrument, the Halometer, were proposed for measuring intraocular light scattering in the presence of human cataracts. The objectives of this work were to introduce new methods of computer-generated analysis of lens images and a glare disability test to validate the use of two new tests to measure the severity of cataract and to document and quantify changes in lens clarity at diagnosis in a group of patients with age-related cataract with minimal to advanced opacities.

The authors followed 28 patients (46 eyes) with an average age of 66.9 +/- 6 years. Tests included ophthalmoscopy, visual acuity, the halometer glare disability test, stereocinematographic slit-image and retro-illumination photography with subsequent interactive digital image analysis and three-dimensional (3-D) computer graphics of the areas of lens light scattering/absorbing.

The intra-reader reproducibility of measuring techniques for cataractous changes was good. The Halometer instrument measures the angular distance from the glare source from which a specific target can be recognised. The source and the target are in the same vertical and tangential planes and to measure the angular distribution of the glare light, it is necessary to measure the incident light angle between the source and the target, by measuring the distance between the source and the target. The clinical Halometry readings assessed the index of the forward scattered light that reaches the retina and produces a veiling luminance (glare). The glare sensitivity score was determined from the angle of the glare source using both red and green optotypes, so that the effects of light absorption were separated from those of light scatter.

The interactive and automated computerised system discriminated the photographic image features of the back light-scattering/absorb centres within different grey thresholds and documented objective lens findings such as optical density, areas of equidensities, geometric surfaces, opacity grading. Digital image analysis gave a topographic and 3-D assembling and visualisation for nuclear, cortical and posterior subcapsular opacities in human lenses revealed from the optical scanning tomographic study of the anterior eye segment. The results indicate on agreement between clinical findings and applied quantitative techniques of analysis. This system has the potential to be a useful objective clinical assessment of cataract.