Brief Answer: It can be nerve palsy or phoria. Detailed Answer: Hello Welcome to health care magic. I am Dr Dadapeer, an ophthalmologist and I answer health problems related to eye. It seems from the history that you had a sudden onset of double vision which was diagnosed as decompensating phoria and was given prism glasses. Phoria is latent squint where the person will experience intermittent squint and intermittent phoria and it is seen after excess of near work or work in one eye. If you are having these above mentioned complaints then the diagnosis of latent squint is confirmed and treatment is by prism glasses and correction of refractive error if any. However if you have sudden onset of diplopia I need to rule out nerve palsy or paresis as cause. This will be present typically when you open both the eyes and there will be limitation of eye movement. Diplopia is increased on seeing towards the limited or restricted eye movement. Most of the times this will resole over 3-6 months and need treatment of underlying systemic problems. The common diseases to be ruled out are diabetes, hypertension.... Hence I advice you to answer few following questions so that I can answer you more accurately. Whether you have diplopia only on opening both eyes or on opening one eye also Whether there is any inability in eye movements Whether diplopia increases in any direction Do answer the above questions so that I can answer you more accurately. Thank you

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