Specular reflection is used to visualize the integrity of the corneal and lens surfaces. If the surface is smooth, the reflection will be smooth and regular; if the surface is broken or rough, the reflection will likewise be irregular or appear to be textured. Its most common use is in evaluating the general appearance of the corneal endothelium. In this technique, position the illuminator about 30 degrees to one side and the microscope 30 degrees to the other side. The angle of the illuminator to the microscope must be equal and opposite (Figures 4-6A and 4-6B).
To visualize the endothelium, start with lower magnification (10X to 16X). Direct a relatively narrow beam onto the cornea so that the reflection of light off of the epithelium dazzles you. Then move the light a little to the side, and look adjacent to it, at the reflection from the endothe-lial surface. Now switch to the highest magnification available. Lowering the height of the slit beam may reduce glare. Widening the slit will increase the field but decrease contrast. The endothelium is best viewed using only one ocular, so you may want to close one eye. This technique is difficult to master, partly because the cells have such low contrast, and takes some experimentation and experience. Cell counts done strictly by slit lamp observation are not generally accepted. Contact specular microscopy is much more accurate. Observe: corneal epithelium and endothelium, endothelial mosaic, lens surfaces
Figure 4-7A. Schematic of proximal illumination. (Adapted with permission from Ophthalmic Photography, SLACK Incorporated.)
Figure 4-7B. Example of proximal illumination. (Photo by Val Sanders.)
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