that of water. Uses CLSM is widely used in various biological science disciplines, from cell biology and genetics to microbiology and developmental biology. It is also used in quantum optics and nano-crystal imaging and spectroscopy. Biology and medicine Clinically, CLSM is used in the evaluation of various eye diseases, and is particularly useful for imaging, qualitative analysis, and quantification of endothelial cells of the cornea. It is used for localizing and identifying the presence of filamentary fungal elements in the corneal stroma in cases of keratomycosis, enabling rapid diagnosis and thereby early institution of definitive therapy. Research into CLSM techniques for endoscopic procedures (endomicroscopy) is also showing promise. In the pharmaceutical industry, it was recommended to follow the manufacturing process of thin film pharmaceutical forms, to control the quality and uniformity of the drug distribution. Confocal microscopy is also used to study biofilms — complex porous structures that are the preferred habitat of microorganisms. Some of temporal and spatial function of biofilms can be understood only by studying their structure on micro- and meso-scales. The study of microscale is needed to detect the activity and organization of single microorganisms. Optics and crystallography CLSM is used as the data retrieval mechanism in some 3D optical data storage systems and has helped determine the age of the Magdalen papyrus. Audio preservation The IRENE system makes use of confocal microscopy for optical scanning and recovery of damaged historical audio. Variants and enhancements Improving axial resolution The point spread function of the pinhole is an ellipsoid, several times as long as it is wide. This limits the axial resolution of the microscope. One technique of overcoming this is 4Pi microscopy where incident and or emitted light are allowed to interfere from both above and below the sample to reduce the volume of the ellipsoid. An alternative technique is confocal theta microscopy. In this technique the cone of illuminating light and detected light are at an angle to each other (best results when they are perpendicular). The intersection of the two point spread functions gives a much smaller effective sample volume. From this evolved the single plane illumination microscope. Additionally deconvolution may be employed using an experimentally derived point spread function to remove the out of focus light, improving contrast in both the axial and lateral planes. Super resolution There are confocal variants that achieve resolution below the diffraction limit such as stimulated emission depletion