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First of all, optic neuritis is usually unilateral especially in adults. Since it was your left eye which was diagnosed with optic neuritis, it is unlikely for the right eye to develop the same. Second thing to be noted is optic neuritis would not result in redness or acute pain in the eye. Multiple sclerosis per se does not affect the eyes or cause redness. Its main ocular involvement is in the form of optice neuritis.