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Cornea:
Clinical Sciences

Comparison of Confocal Biomicroscopy and Noncontact Specular Microscopy for Evaluation of the Corneal Endothelium

Hara, Makiko MD; Morishige, Naoyuki MD, PhD; Chikama, Tai-ichiro MD, PhD; Nishida, Teruo MD, DSc

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Abstract

Purpose. To compare the clinical efficacy of confocal biomicroscopy with that of noncontact specular microscopy for the evaluation of the corneal endothelium.

Methods. The corneal endothelium was examined in 14 normal subjects (28 eyes) and in 6 patients (11 eyes) with Fuchs corneal endothelial dystrophy using a noncontact specular microscope (SP-2000P, Topcon, Japan) and a confocal biomicroscope (ConfoScan, Tomey, Japan). The images and the calculated densities of corneal endothelial cells obtained by the 2 techniques were compared.

Results. For normal subjects, the images of corneal endothelial cells obtained by the 2 techniques were almost identical, although the density of these cells determined by confocal biomicroscopy (2916 ± 334 cells/mm2) was slightly higher than that determined by noncontact specular microscopy (2765 ± 323 cells/mm2). In contrast, whereas clear images of corneal endothelial cells, allowing the determination of cell density, were obtained for all 11 eyes of the patient group by confocal biomicroscopy, clear images were obtained for only 4 of these 11 eyes (36.4%) by noncontact specular microscopy.

Conclusion. Both noncontact specular microscopy and confocal biomicroscopy revealed the shapes and number of endothelial cells in the normal cornea. However, for corneas with Fuchs dystrophy, clear images were obtained only by confocal biomicroscopy. Confocal biomicroscopy is thus an effective tool for evaluation of the diseased corneal endothelium.

The corneal endothelium plays an important role in maintenance of corneal transparency. The apical tight junctions present between the cells of the endothelium form a tight barrier. Furthermore, corneal endothelial cells exhibit water pumping activity, which contributes to regulation of the water content of the corneal stroma. 1 Another unusual characteristic of the corneal endothelium in humans is that the endothelial cells do not appear to proliferate. Damage to these cells caused by intraocular surgical maneuvers or postoperative inflammation, therefore, often results in stromal edema. In the clinical setting, it is thus important to evaluate the condition of the corneal endothelium to gain insight into the background pathology of corneal diseases and prognosis, especially before and after surgery, such as cataract extraction and refractive surgery.

The endothelium of both the normal and diseased cornea has for many years been evaluated with a specular microscope. 2 However, as a result of the optical principles involved, there are limitations to the use of this instrument. It is thus required that the cornea be transparent and that the endothelial surface be plain and smooth to obtain specular reflection 3; the images obtained with a specular microscope from individuals with corneal endothelial abnormalities, such as Fuchs dystrophy, contain many dark areas in which specular reflection was not achieved. Original versions of the specular microscope required contact with the corneal surface via a coupling gel. Although the images obtained with such a contact specular microscope are considered superior to those obtained by noncontact specular microscope, currently available models of noncontact instruments are more practical for most applications. 4 Combination of the noncontact specular microscope with computer-assisted morphometric analysis has contributed greatly to the examination of corneal endothelial cells in eye clinics.

The confocal biomicroscope has recently been introduced for examination of the cornea. 5–10 The principle of confocal optics is well documented. 11 In brief, light from the illumination source passes through a pinhole aperture and is focused at a spot within the specimen by an objective lens. Light reflected back from the specimen is then focused at the detector by passage through a pinhole aperture, whereas out-of-focus light is blocked. By changing the position of the focal plane, it is possible to obtain images at different depths of the specimen. Scanning of all the pinpoint images then provides sectional views of the specimen in a single plane. Confocal biomicroscopy thus allows examination of all cellular components of the cornea 12–14 layer by layer in a noninvasive manner. Confocal biomicroscopic images of corneal cells 15 and corneal nerves 16–18 have been obtained from both normal and diseased corneas. The images of the corneal endothelium obtained by confocal biomicroscopy appear almost identical to those obtained with a noncontact specular microscopy. However, no comparison between these two techniques with regard to clinical evaluation of the corneal endothelium has been reported.

We have now investigated the clinical efficacy of the confocal biomicroscope for evaluation of the corneal endothelium. We examined the same subjects by both noncontact specular microscopy and confocal biomicroscopy and compared both the quality of the images and the quantitative analysis of endothelial cell density between the 2 techniques.

© 2003 Lippincott Williams & Wilkins, Inc.

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