tailieunhanh - Optic Nerve Disorders - part 10

Dựa trên bằng chứng này một mình, giả thuyết thâm hụt võng mạc ở bệnh nhân này nên được coi là đáng ngờ. Thứ hai, cốt truyện 3D trong hình có thể được kiểm tra. Chú ý rằng cả hai đỉnh foveal và đĩa trầm cảm quang được di dời so với cốt truyện 3D t | 254 . Hood and K. Holopigian records. First compare the mfERG responses to the visual field. In this case her field depression extended at least to 25 Figure and clearly did not agree with the location of the depression of the mfERG circle in Figure . Based on this evidence alone the hypothetical retinal deficit in this patient should be considered suspicious. Second the 3D plot in Figure can be examined. Notice that both the foveal peak and the optic disc depression are displaced compared to the 3D plot from the control subject with normal fixation see Figure bottom . The patient appears to be fixating eccentrically and all the apparent abnormalities seen in the trace array in Figure are based on poor fixation. The left column of Figure illustrates the point. Here an individual with normal vision was asked to fixate down and to the left from the center. Notice how the pattern of the patient s mfERG resembles that of the results from the control in Figure and except that the patient was fixating up and to the left of the target. Figure illustrates an example in which the effects of a fixation error are subtler. These mfERGs are from a young woman with a very small central defect in her left visual field. Her acuity was good and her fixation appeared steady. It was initially thought that her problem was retinal because a few of the paracentral responses see responses in rectangle appeared reduced in amplitude. However an examination of the 3D plot indicated that she was fixating slightly off center this is easy to see when the 3D plot is compared to the plot from her unaffected right eye. In sum if care is not taken in the recording and interpretation of mfERGs then depressed responses caused by fixation errors can be misinterpreted as a retinal problem. Ruling Out Functional or Nonorganic Causes When diagnosing optic nerve disorders it is often important to rule out functional or non- os OD . I . Ar Ar Ar V