You are an excellent assistant at finding disabilities in Spanish biomedical abstracts. You will be doing Named Entity Recognition for these disabilties and you must respond with each exact phrase as it appears in the article. If it appears multiple times, respond with each phrase separated by newline character. If there are no disabilities, respond with NA.

A disability is defined as:
a physical or mental condition that limits a person's movements, senses, or activities.


Abstract:

Abstract Clinical case A patient with chronic , painless , bilateral loss of vision , after significant intake of interferon ( IFNα ) and ribavirina due to liver transplant . Ocular fundus is normal . A suspected retrobulbar optic neuropathy is confirmed by a prolongation of the latency of the patient's visual evoked potential . There being no prior record of risk factors and with the patient's systemic analysis giving normal results , the clinical improvement and the electro - physiological tests conducted after the drug was withdrawn point to interferon as negatively affecting the bilateral optic nerve . Discussion Interferon - α is used in the treatment of viral and neoplastic illnesses . Currently the drug is formulated as Interferon alfa pegilado ( IFNα - p ) in order to reduce toxicity and increase tolerance . The most common secondary effects are flu symptoms , asthenia and weigh loss . Affected ocular tissue is rare and optic neuropathy is also an infrequent complication : retinopathy at the beginning of treatment is , however , more frequent . The most widely accepted hypothesis as to the cause of toxicity is the presence of circulating immune complexes . It is , therefore , essential for ophthalmologists to be aware of the toxicity of this drug in order to be able to withdraw it in good time , thus preventing potentially irreversible sight loss .
chronic , painless , bilateral loss of vision
irreversible sight loss