Living histopathology - interrogation of ocular tissues by light: a celebration of the slit-lamp and a repertoire of clinical techniques

The evolution of the slit-lamp microscope has enabled ophthalmologists to examine the transparent tissues of the eye with histological detail. This paper considers the history and optics of the slit-lamp. Optical sectioning and retro-illumination are discussed; particularly, effective placement of the reflected light beam. A variety of less conventional slit-lamp examination techniques is described. These include remote dark-field retro-illumination, examination through refractive surfaces (particularly, meniscus retro-illumination to demonstrate tear cells and non-contact corneal endothelial specular microscopy), location of vitreous abnormalities by parallax, expanding radial cords of vitreous cells in lymphoma, mirror examination of the superior fornix and corneal epithelial folds in ocular hypotension. It concludes with brief discussions about haemoglobin video imaging, semi-quantification of aqueous outflow volume by aqueous column cross-section area, and autofocus for video-microscopy.