Retinal nerve fiber layer and macular thickness measurements were made with the Spectralis SD-OCT (Heidelberg Engineering, Carlsbad, California) using our modified retinal thickness measurement protocol which permits high-density measurement in the macular region. Briefly, macular thickness is measured using 61 lines in the central 20 degree area (centered on the fovea). The retinal thickness is displayed as a color-coded thickness map, modified to reveal retinal thickness differences of 10–15 microns. This modification allows for improved visual detection of small differences in tissue thickness. The thickness maps are displayed with a grid demonstrating retinal thickness values in small 3×3 degree areas with the entire grid tilted to match the fovea-disc axis. Asymmetry analyses between the upper and lower halves of the macula are displayed as a gray scale plot. A black square represents a 30 micron difference at that location and a white square represents no difference between the two macular halves at that location.
Glaucoma is clearly the most studied optic neuropathy using OCT; approximately three quarters of the publications found on a query of “OCT” and “optic neuropathy” focus on glaucoma (personal observation, July 2012). However, recent studies have demonstrated the use of OCT in the management and prognosis of patients with optic neuritis and multiple sclerosis, and other aggressive inflammatory diseases of the central nervous system. In addition, recent publications show that OCT has been used for papilledema and disc edema, optic disc drusen, ischemic optic neuropathies, hereditary optic neuropathies, toxic optic neuropathies, and compressive optic neuropathies.
In a recent and thorough review of “glaucoma look-alikes” by Pasol, he GDC-0994 noted the importance of using the temporal quadrant of RNFL analysis, in differentiating non-glaucomatous optic neuropathies from glaucoma, as seen in our infectious and degenerative cases. As highlighted in our series, ischemic optic neuropathy and optic nerve head drusen have patterns similar to glaucoma, frequently affecting the superior-inferior quadrants as in glaucoma. In a recent prospective cross-sectional study, Suh and colleagues used a combination of optic disc rim area (measured by Heidelberg retinal tomography (HRT)) and RNFL thickness (measured by Cirrus time-domain OCT) to differentiate between glaucoma and non-arteritic ischemic optic neuropathy. In 2007, Chan and Miller examined the OCTs of patients with long-standing non-glaucomatous optic neuropathies and found a residual thickness of about 45 microns, confirming a thickness that could be attributed to the signal generated by the interface between the vitreous and inner retinal surface seen in earlier cadaveric studies.
Traditional descriptions of lymphatic eyelid drainage suggest that the lateral eyelids drain to the preauricular nodes, while the medial portions of the eyelids drain to the submandibular nodes. This understanding of the lymphatic drainage patterns of the eyelids derives from dye studies conducted several decades ago. Other knowledge to date has been extrapolated from investigations conducted postmortem or in animal models.
A sentinel lymph node is often the first site of malignant tumor spread before dissemination to more distant sites, and a SLNB is performed for histopathologic examination to determine the presence of microscopic metastasis. Unlike a lymph node dissection that traditionally involves removing a bulk of tissue with 10–15 lymph nodes, SLNB is less invasive and usually involves the biopsy of one or two lymph nodes.
Pre-operative imaging is an important feature of modern SLNB techniques. In advance of surgical excision, technetium-99m sulfur colloid is injected subcutaneously around the malignancy to identify the sentinel node to generate a lymphoscintography image (Fig. 1). (Intraoperative maneuvers including subcutaneous injection of isosulfan blue and technetium-99m with transcutaneous gamma probe further add to identification of the sentinel node.) With the increasing use of SLNB, the database for in vivo and in situ drainage pathways from the periocular region is increasing.