However, attacks may lead to permanent axonal loss and thinning of the retinal nerve fiber layer. Compressive optic neuropathy
Tumors, infections, and inflammatory processes can cause lesions within the orbit and, less commonly, the optic canal. These lesions may compress the optic nerve, resulting optic disc swelling and progressive visual loss. Implicated orbital disorders include optic gliomas, meningiomas, hemangiomas, lymphangiomas, dermoid cysts, carcinoma, lymphoma, multiple myeloma, inflammatory orbital pseudotumor, and thyroid ophthalmopathy. Patients often have bulging out of the eye (proptosis) with mild color deficits and almost normal vision with disc swelling. Infiltrative optic neuropathy
The optic nerve can be infiltrated by a variety of processes, including tumors, inflammation, and infections. Tumors that can infiltrate the optic nerve can be primary (optic gliomas, capillary hemangiomas, and cavernous hemangiomas) or secondary (metastatic carcinoma, nasopharyngeal carcinoma, lymphoma, and leukemia). The most common inflammatory disorder that infiltrates the optic nerve is sarcoidosis. Opportunistic fungi, viruses, and bacteria may also infiltrate the optic nerve. The optic nerve may be elevated if the infiltration occurs in the proximal portion of the nerve. The appearance of the nerve on examination depends on the portion of the nerve that is affected. Traumatic optic neuropathy
The optic nerve can be damaged when exposed to direct or indirect injury. Direct optic nerve injuries are caused by trauma to the head or orbit that crosses normal tissue planes and disrupts the anatomy and function of the optic nerve; e.g., a bullet or forceps that physically injures the optic nerve.
Pentosuria is a condition where the sugar xylitol, a pentose, presents in the urine in unusually high concentrations. It was characterized as an inborn error of carbohydrate metabolism in 1908. It is associated with a deficiency of L-xylulose reductase, necessary for xylitol metabolism. L-Xylulose is a reducing sugar, so it may give false diagnosis of diabetes, as it is found in high concentrations in urine. However glucose metabolism is normal in people with pentosuria, and they are not diabetic. Patients of pentosuria have a low concentration of the sugar d-xyloketose. Using phenyl pentosazone crystals, phloroglucin reaction, and absorption spectrum, pentose can be traced back as the reducing substance in urine, with those that have pentosuria.Research has shown that pentosuria appears in 3 forms. The most widely studied is essential pentosuria, where  a couple of grams of L-xylusol are released into a persons system daily. L-xylulose reductase, contained in red blood cells, is composed of both a major and minor isozyme. For those diagnosed with essential pentosuria, the major isozyme appears to be the same as the minor one. Alimentary pentosuria can be acquired through fruits high in pentose. Finally, drug-induced pentosuria can be developed by those exposed to morphine, fevers, allergies, and some hormones.Those diagnosed with Pentosuria are predominantly of Jewish root. However, it is a harmless defect, and no cure is needed. References


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