For indirect illumination, the microscope is focused on an area adjacent to the illuminated tissue. It is useful for observing corneal neovascularisation and non-opaque corneal lesions such as microcysts. For retro-illumination, light is reflected off the anterior surface of the iris or the retina as the cornea is focused. Opacities will be back lit and appear black due to absorption of the reflected light. The degree of light absorption will vary with the density of the lesion. A dense corneal opacity will appear black with retroillumination. This technique may be used for the detection, location and assessment of corneal opacities such as ulcers, the detection of fine epithelial and endothelial changes, keratic precipitates and small blood vessels. Pigment derived from the iris may become deposited on the rear surface of the cornea in a characteristic spindle or delta shape.
This is a difficult technique for the novice. Furthermore, it is of limited use during clinical evaluation because of the low magnification available on most slit-lamps and the small area of corneal endothelium that can be viewed at any one time. Assessment of the corneal endothelium when symptom...
Fluorescein is an orange dye that fluoresces green when illuminated with a cobalt filter. Areas of corneal or conjunctival epithelial damage will exhibit fluorescein dye uptake and will appear bright green. This positive fluorescein staining will help to identify the extent and distribution of ep...
Wratten 12 filters are yellow and absorb reflected blue light while transmitting green light. Fluorescein staining becomes more obvious.
