Paraneoplastic causes of vision loss
Authors: Karanjia Rustum 
Published: December 2019

Paraneoplastic occular disorders are clinical syndromes resulting from nonmetastatic systemic effects of underlying cancers. While not fully elucidated the underlying mechanism is presumed to be a cross reaction of the immune reaction to the underlying cancer that attaches normal host tissue. This cross reaction can happen in a variety of occular tissues resulting in dysfunction of the retina, optic nerve and tear film and extraocular muscles. (1‐3). The lists of cancers and associated antibodies is constantly growing but, in many cases, the clinical phenotype is very similar. Cancer associated retinopathy (CAR) for example is associated with several antibodies including anti‐recoverin, anti‐alpha enolase, anti‐transducin, and anti‐carbonic anhydrase(2, 3). Each of these antibodies have been associated with a distinct cancer including skin, genital and small cell lung cancer (SCLC). CAR causes a slowly progressive asymmetric vision loss due to damage to retinal ganglion cells and bipolar cells which can result in optic nerve pallor. Melanoma associated retinopathy (MAR), similarly can present with nyctalopia, photopsia’s and loss of peripheral vision. The antibodies associated with MAR; anti‐transducin, anti‐rhodopsin and anti‐arrestin typically attack the on bipolar system. As with CAR the visual dysfunction can predate the discovery of the cancer. Conversely, autoimmune related retinopathy and optic neuropathy occurs without an underlying cancer and is associated with anti‐GAD and anti‐ anti‐collapsin‐responsive mediator protein‐5 (CRMP‐5) antibodies(2). In all three cases electroretinograms are key to making the diagnosis as the objective clinical examination can be normal. Electroretinograms are key to distinguishing retinal dysfunction which can cause an optic neuropathy from a paraneoplastic optic neuropathy (PON). The classical antibody in PON is. CRMP‐5 is associated with SCLC and thymoma and can produce optic disc edema with subsequent atrophy. The treatment and management of occular paraneoplastic disorders requires appropriate investigations to look for an underlying cancer. Knowing the specific antibody associated with the disorder can be helpful in this regard and in some cases a panel of antibody tests is appropriate in the right clinical context(4). Treatment of the underlying cancer can, in some cases, can lead to a resolution of the clinical symptoms. Symptom control can also be accomplished using immunosuppression with steroids or IVIG and in some cases plasmapheresis has been useful(4, 5).

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