Case 13-1. Focal Nerve Fiber Layer Defect
A 71 -year-old white man had primary open angle glaucoma and a focal nerve fiber layer defect in the left eye, Visual acuity in this eye was 20/20 and the intraocular pressure was 14 mm Hg, The pressure had decreased from 19 mm Hg measured one month earlier when the patient began using levobunolol 0.25% twice daily. Slit-lamp examination and gonioscopy revealed a normal anterior chamber and angle. Dilated fundus examination showed a narrow focal defect in the superotemporal nerve fiber layer (A, B; arrows) and a thinning of the neuroretinal rim temporally A distinct inferonasal step was noted on the Humphrey visual field (D) corresponding to the nerve fiber layer defect observed ophthalmoscopically
A circular OCT tomogram (E) taken at a diameter of 3,4 mm around the optic disc revealed a generally healthy nerve fiber layer with the exception of a focal area of thinning in the superotemporal nerve fiber layer (arrows), consistent with the defect observed clinically. The thinning was primarily evident at the superficial margin of the nerve fiber layer, and reached a minimum thickness of 90 \im in the image.
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