Confocal corneal microscopy is a noninvasive technique for in vivo imaging of the living cornea; it compares to in vitro histochemical analysis of the 5 layers of the cornea. The basic principle of confocal microscopy is that a single point of tissue can be illuminated by a point source of light or laser and simultaneously imaged by a camera in the same plane (ie, confocal). Because this technique involves scanning a small region of tissue with thousands of spots of light, it produces a usable field of view at a cellular level and an image of very high resolution. A number of units are available for clinical use: (1) tandem scanning, (2) scanning-slit, and (3) laser scanning confocal microscopes. The major advantage of laser scanning confocal systems is the ability to serially produce extremely thin images of the cornea. The depth of focus is 7–9 μm in tandem scanning, 26 μm in slit scanning, and 5–7 μm in laser scanning.
Confocal microscopy is useful in identifying causative organisms in cases of infectious keratitis, such as Acanthamoeba keratitis, fungal keratitis, microsporidiosis, and herpetic eye disease. It is also helpful in evaluating corneal nerve morphology in diabetic neurotrophic keratitis and neuropathic pain occurring in ocular surface disease and after refractive surgery (Fig 2-9); it is similarly useful in evaluating the corneal endothelial layer. In addition, confocal microscopy may help differentiate some corneal dystrophies, for example, Reis-Bücklers corneal dystrophy from Thiel-Behnke corneal dystrophy, both of which involve the Bowman layer, as well as Fuchs and posterior polymorphous dystrophies, both of which involve the corneal endothelium (see Chapter 7, Figs 7-6A and 7-7A).
Alzubaidi R, Sharif MS, Qahwaji R, Ipson S, Brahma A. In vivo confocal microscopic corneal images in health and disease with an emphasis on extracting features and visual signatures for corneal diseases: a review study. Br J Ophthalmol. 2016;100(1):41–55.
Petroll WM, Cavanagh HD, Jester JV. Confocal microscopy. In: Mannis MJ, Holland EJ, eds. Cornea. Vol. 1. 4th ed. Philadelphia: Elsevier; 2017:180–191.
Villani E, Baudouin C, Efron N, et al. In vivo confocal microscopy of the ocular surface: from bench to bedside. Curr Eye Res. 2014;39(3):213–231.
Figure 2-9 Confocal microscopy of corneal nerves. A, Normal nerve architecture. B, Tortuous branching patterns.
(Courtesy of Mina Massaro-Giordano, MD.)
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.