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The Acuityscope projects an image of a three bar resolution test target onto the patient's retina, where it is viewed and read by an observer. The test target consists of a series of three bar targets varying in size on a logarithmic scale. Individual targets are identified in the projected image by Bailey-Lovie log visual acuity equivalents. The projected image includes only those target sizes which are useful for estimating visual acuity. The Acuityscope is used for assessing the quality of retinal image formation, and is thus able to differentiate between poor visual acuity due to image degradation, (e.g. cataract or corneal disease) and poor visual acuity due to image handling defects (e.g. retinal or optic nerve disease). The use of the instrument is relevant to both clinical situations (e.g. pre-operative assessment of opacification of optical media) and experimental situations (e.g. clinical trials).

Intra-observer (within observers) and inter-observer (between observers) variability of the Oxford Clinical Cataract Classification and Grading System were studied. Twenty cataracts were examined and scored independently by four observers. On a separate occasion two of the observers repeated the assessments of the same cataracts in the absence of information from the initial observations. The chance corrected and weighted kappa statistics for observer agreement, both for inter-observer and intra-observer variability demonstrated satisfactory repeatability of the cataract grading system. The overall intra-observer mean weighted kappa was kappa w = +0.68 (range SE kappa = 0.012-0.052) and the overall inter-observer mean weighted kappa was kappa w = +0.55 (range SE kappa = 0.011-0.043).

A composite slit-lamp based system for the clinical classification and grading of cataract is described. Cataract features are classified morphologically, and individual features are graded by comparison with standard diagrams mounted adjacent to the slit-lamp. Attention has been paid to relevant aspects of measurement theory, with equal interval steps between the grades. The image degrading effect of the cataract is assessed using a 'resolution target projection ophthalmoscope'. The method may be used in conjunction with photographic and image analysing techniques.

The nuclear colour of in vivo human lenses has been investigated by means of a colour matching technique, using 'Munsell' colour samples. Observations covered an extended age range, and included all degrees of nuclear pigmentation. A positive correlation was noted between increasing nuclear pigmentation and age. The colour matching data generated was used as a basis for establishing a system of nuclear brunescence grading. The system of grading consists of a Grade 0 for absence of brunescence, and Grade 1 to Grade 5 for increasing brunescence. The 'Munsell' notation for samples representing these grades are: Grade 0 (5GY 6/1), Grade 1 (5Y 7/4), Grade 2 (2.5Y 7/8), Grade 3 (7.5YR 6/8), Grade 4 (5YR 4/6), and Grade 5 (2.5YR 2.5/2). Assessments of both inter- and intra-observer variability in the use of the derived scale have shown the new colour grading system to be reliable. The measure is simple to use during biomicroscopic slit-lamp examination of the lens, and has the potential for routine clinical application as well as for use in clinical trials where detailed documentation of lens morphology is required. The new colour scale may be used either as an isolated measure, or as part of a battery of lens measures in the Oxford Clinical Cataract Classification and Grading system.