Điều này có thể được thay đổi bằng cách di chuyển hình ảnh khe ra khỏi trung tâm, như là yêu cầu của một số kỹ thuật chiếu sáng (thảo luận trong chương 4). Trong khi ánh sáng trắng được sử dụng cho hầu hết các kỳ thi, có một số bộ lọc màu có thể được sử dụng, | 4 Chapter 1 Figure 1-3A. Magnification may be changed by flipping a lever. Photo by Mark Arrigoni. Figure rotating a knob. Reprinted with permission from Ophthalmic Photography SLACK Incorporated. Figure 1-4B. .or levers Reprinted with permission from Oph- thalmic Photography SLACK Incorporated. Photo by Steve Carlton. The Slit Lamp 5 Figure 1-5. The angle of the light source is indicated by a dial at the base of the arm. Photo by Val Sanders. and light are coordinated so that the structure to be viewed is magnified and illuminated. This can be altered by moving the slit image off center as is required by some illumination techniques discussed in Chapter 4 . While white light is used for most examinations there are several colored filters that can be utilized as well. The cobalt blue filter is used in conjunction with fluorescein dye. The dye pools in areas where the corneal epithelium is broken or absent. The blue light excites the fluorescein which then takes on a yellowish glow. The green filter obscures anything that is red hence the pseudonym red-free light thus blood vessels or hemorrhages appear black. This increases contrast revealing the path and pattern of inflamed blood vessels. Areas of the episclera where lymphocytes infection-fighting white blood cells have gathered in response to an inflammatory or immune response will appear as yellow spots under the red-free light. Fleischer ring seen in keratoconus see Chapter 5 can also be viewed satisfactorily with the red-free filter. Some instruments also have a diffuser which is a piece of frosted glass or plastic that flips in front of the illuminator. The diffuser scatters the light causing an even spread of light over the entire ocular surface. The filters are placed by flipping a lever Figure 1-6 . Patient positioning is achieved by an attached head rest unit that includes a moveable chin cup and a stationary forehead band. There may also be a strap that can be fastened behind the patient s head .
