tailieunhanh - Eyesight Associates of Middle - part 5

Phương pháp này rất hữu ích để xem sự phân bố của bệnh lý giác mạc, làm cho nó đặc biệt hữu ích trong việc đánh giá kính áp tròng (xem Chương 9). Một chùm tia rộng, cao là hướng vào khu vực limbal. Đèn chiếu sáng nên được một chút bù đắp cho kỹ thuật này và chỉ đạo từ một góc vừa phải. | 52 Chapter 4 Figure 4-8A. Schematic of sclerotic scatter. Reprinted with permission from Ophthalmic Photography SLACK Incorporated. OptT OphT cT Figure 4-8B. Example of sclerotic scatter. Photo by Val Sanders. Sclerotic Scatter This method is useful to view the distribution of corneal pathology making it especially useful in contact lens evaluation see Chapter 9 . A tall wide beam is directed onto the limbal area. The illuminator should be slightly offset for this technique and directed from a moderate angle. The illuminator is almost always left in a straight-ahead position. In a horizontal prism reflected microscope the illuminator is offset by simply rotating the slit scanning control ring. If your slit lamp has a vertical illumination source turn the slit centering knob near the bottom of the illumination arm. When the light is properly aligned with regard to the eye a ring of light will appear around the cornea. The light is absorbed and scattered through the cornea see Figures 4-8A and 4-8B highlighting pathology. Use 10X magnification with the microscope directed straight ahead. This technique is easiest if the patient is not dilated so that the iris provides a contrasting dark background. Observe general pattern of corneal opacities Retroillumination Retroillumination is used to evaluate the optical qualities of a structure. The light strikes the object of interest from a point behind the object and is then reflected back to the observer. Thus it is similar to a silhouette. Some professionals advocate setting the slit beam slightly off center via the slit scanning control ring or the slit centering knob for these techniques. The authors prefer to leave the slit beam in its usual position. Direct Retroillumination From the Iris This illumination method is used to view corneal pathology. A moderately wide slit beam is aimed toward the iris directly behind the corneal abnormality Figures 4-9A and 4-9B . Use a magnification of 16X to 25X and direct the light .