Optimal pupil diameter for Scheimpflug slit image photography of the lens in man.

Densitometric analysis of Scheimpflug photography of the lens has been examined as a function of pupil diameter in normal volunteers. On the basis of both the length of the lens waveform and the integral area under the curve of the lens waveform, there is a critical pupil diameter above which the waveform is unchanged. Below this critical diameter the waveform becomes distorted by shortening and a change in shape. The critical pupil diameter is between 6 and 6.5 mm. This result is of importance either in longitudinal studies, where the pupil diameter may not be reproducible, or in studies where other drugs are used which may prevent full pupil dilatation.